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  • 1
    Digitale Medien
    Digitale Medien
    A New General Synthesis of 2,2-Dialkyl-2,3-dihydro-4H-pyran-4-ones and Their Application for the in situ Preparation of Electron-Rich Dienes in Carbonyl-Alkyne Exchange Reactions with AcetylenesPresented in part at the autumn meeting of the Swiss Chemical Society in Bern on October 20, 1989. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 27-46 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones of type II and III have been prepared by acid-catalyzed cyclization of the corresponding substituted acetylenic ketones I in good to excellent yields (Scheme 1). These 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones II and III have been used for the in situ preparation of highly reactive dienes of type IV-VI (Scheme 2) in carbonyl-alkyne exchange reactions with electron-poor alkynes VII to yield the highly substituted aromatic compounds VIII and IX. These reactions proceed in good yields and with excellent degree of regioselectivity. Aryl-substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones III (R1 = Ar) subsequently yield highly substituted biaryls. Reaction mechanisms are presented for the formation of the 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones as well as for the carbonyl-alkyne exchange reactions with electron-poor acetylenes.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740106
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  • 2
    Digitale Medien
    Digitale Medien
    Structural and Luminescence Study of the 3:2 Complex between Europium Nitrate and the B Isomer of Dicyclohexyl-18-crown-6Part 40 of the series ‘Complexes of Lanthanoid Salts with Macrocyclic Ligands’; Part 39 [1]. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 65-78 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal and molecular structure of bis[dinitrato-(2,4,8,15,18,21-hexaoxatricyclo[20.4.0.09,14]hexacosane)europium(III)]pentakis(nitrato)europiate(III) [Eu(NO3)2LB]2([Eu(NO3)5]), has been determined at 170 K from single-crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P21/n (ITC No. 14): a = 16.338(3) Å, b = 15.704(3) Å, c = 24.474(4) Å, β = 97.73(1)°, Z = 4. The structure was refined to a final R value of 0.058 (Rw = 0.060). The asymmetric unit contains three independent ions lying on general positions: [Eu(NO3)5]2- and two distinct [Eu(NO3)2LB]+ cations with the macrocyclic ligand in the cis-anti-cis conformation (B-isomer). The EuIIIions are 10-coordinate with the following mean bond lengths: Eu-O(nitrate) = 2.48(2) Å in the anion and 2.45(2) Å in the two cations, Eu-O(ether) = 2.56(8) and 2.55(5) Å. Small but significant differences are observed between the two complex cations, especially with respect to the positions of the cyclohexyl substituent. A conformational analysis performed on the six O-atoms of the complex cations confirms the predictions of a simple model. The metal ion sites of the complex have been probed by high-resolution excitation and emission spectra at 296 and 77 K. The 5D0←7F0 excitation spectrum displays two main bands along with several other minor components. A detailed analysis of the corresponding and selectively excited emission spectra leads to the observation of three types of spectra corresponding to the three crystallographically different EuIII ions. Moreover, three minor sites are identified, one anionic and two cationic, with a population equal to ca. 10% of the population of the main sites. We interpret this finding as reflecting the presence of molecules with slightly different conformations.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740109
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  • 3
    Digitale Medien
    Digitale Medien
    Asymmetric Diels-Alder Cycloadditions with C2-Symmetrical Chiral Carbamoylnitroso Dienophiles (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 103-109 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The C2-symmetrical chiral pyrrolidines 2 and 3 are of opposite helicity. The corresponding N-acylnitroso dienophiles 6 and 7 react in good yield with cyclohexadiene, leading thereby with excellent diastereoisomeric excess to the expected Diels-Alder cycloadducts (see Scheme). The [2.2.2] bicyclic moieties of the major diastereoisomers 9 and 11 proved to be of opposite configuration, as expected. Their configuration is best explained by assuming the acylnitroso dienophile to be in the s-cis conformation in the transition state, the approach of the diene being endo (see Fig.).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740112
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  • 4
    Digitale Medien
    Digitale Medien
    2,3- and 4,5-Secodopa, the Biosynthetic Intermediates Generated from L-Dopa by an Enzyme System Extracted from the Fly Agaric, Amanita muscaria L., and Their Spontaneous Conversion to Muscaflavin and Betalamic Acid, Respectively, and Betalains (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 124-140 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An enzyme is extracted from the red peel of Amanita muscaria which cleaves the C(2)-C(3) and the C(4)-C(5) bond of the aromatic ring of L-dopa (1) to form a mixture of 4,5-secodopa (= salt of 6-amino-2-hydroxy-4-(2′-oxoethylidene)hept-2-enedioic acid; 2) and 2,3-secodopa ( = salt of 7-amino-5-formyl-2-hydroxyocta-2,4-dienedioic acid; 3), two hitherto hypothetical biosynthetic intermediates (see Scheme). Though isolation of these products has not been possible, structural evidence is inferred from reaction products, kinetics, and spectroscopical characteristics in comparison with known compounds. Secodopas 2 and 3 are characterized in dilute solution by HPLC and UV/VIS spectroscopy (anions; λmax 424 and 414 nm, resp., ∊420 = 25500; on acidification, shift to 380 and 372 nm, resp.). They cyclize without enzyme catalysis, optimally at pH 4.5-5; 3 produces muscaflavin (5) and 2 betalamic acid (4). The products arc identified by direct comparison with authentic samples in HPLC, by 1H-NMR of 5, and by condensation of 4 with L-proline to form the well known betalain indicaxanthin (7). The enzymatic conversion of L-dopa (1) via 2 to betalamic acid (4; (S)) and its condensation with L-proline leads to pure natural indicaxanthin (7; (2S,115)); correspondingly, the enzymatic conversion of D-dopa to (R)-betalamic acid and its condensation with L-proline produces isoindicaxanthin ((2S,11R)) which is unknown in nature. Particularly relevant is the fact that the same enzyme cleaves pyrocatechol to produce a solution of the enolate form of the known 2-hydroxy-6-oxohexa-2,4-dienoate (secopyrocatechol; 9; see Fig. 5). Dissociation constants of the corresponding enolic functions in the cleavage products are determined by spectrometric titration and compared to those of known systems.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740115
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  • 5
    Digitale Medien
    Digitale Medien
    Photochemical Reactions of Tetrahydroquinoxalin-2(1H)-ones and Related Compound (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 225-231 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Photochemical behaviors of the pyrazinone derivatives 5,6,7,8-tetrahydroquinoxalin-2(1H)-ones 1a-c and 1,5,6,7,8,9-hexahydro-2H-cyclohepta[b]pyrazin-2-one 1d were investigated. Dye-sensitized photo-oxygenation of 1a-c gave the 1:1 adducts 5a-c of the corresponding 3,8a-epidioxy-3,5,6,7,8,8a-hexahydroquinoxalin-2(1H)-one 4 and H2O, whereas 1d gave 3,9a-epidioxy-1,3,5,6,7,8,9,9a-octahydro-2H-cyclohepta[b]pyrazin-2-one 4d (Scheme 2). The different kind of products was interpreted as being the result of the ring strain and steric hindrance of endoperoxides produced from 1a-d with singlet oxygen. Irradiation of 1a-b in the presence of alkenes gave tricyclic azetidine derivatives 9 by [2 + 2] cycloaddition of the C=N bond of 1 to the alkene.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740122
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  • 6
    Digitale Medien
    Digitale Medien
    Analogues of Sialic Acids as Potential Sialidase Inhibitors. Synthesis of C6 and C7 Analogues of N-Acetyl-6-amino-2,6-dideoxyneuraminic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 343-369 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The piperidines 12-18, piperidmose analogues of Neu5Ac (1) with a shortened side chain, were synthesized from N-acetyl-D-glucosamine via the azidoalkene 32 and tested as inhibitors of Vibrio cholerae sialidase. Deoxygenation at C(4) of the uronate 22, obtained from the known D-GlcNAc derivative 20, was effected by β-elimination (→ 23), exchange of the AcO at C(3) with a (t-Bu)Me2SiO group and hydrogenation (→ 26; Scheme 1). Chain extension of 26 by reaction with Me3SiCH2MgCl gave the D-ido-dihydroxysilane 28, which was transformed into the unsaturated L-xylo-mesylate 29 and further into the L-lyxo-alcohol 30, the mesylate 31, and the L-xylo-azide 32. The derivatives 29-31 prefer a sickle zig-zag and 32 mainly an extended zig-zag conformation (Fig. 2). The piperidinecarboxylate 15 was obtained from 32 by ozonolysis (→ 33), intramolecular reductive animation (→ 34), and deprotection, while reductive animation of 34 with glycolaldehyde (→ 35) and deprotection gave 16 (Scheme 2). An intramolecular azide-olefin cycloaddition of 32 yielded exclusively the fused dihydrotriazole 36, while the lactone 39 did not cyclize (Scheme 3). Treatment of 36 with AcOH (→ 37) followed by hydrolysis (→ 38) and deprotection led to the amino acid 18. To prepare the (hydroxymethyl)piperidinecarboxylates 12 and 17, 32 was first dihydroxylated (Scheme 4). The L-gluco-diol 40 was obtained as the major product, in agreement with Kishi's rule. Silylation of 40 (→ 42), oxidation with periodinane (→ 44), and reductive animation gave the L-gluco-piperidine 45. It was, on the one hand, deprotected to the amino acid 12 and, on the other hand, N-phenylated (→ 46) and deprotected to 17. While 45 and 12 adopt a 2C5 conformation, the analogous N-Ph derivatives 46 and 17 adopt a 5C2 and a B3,6 conformation, respectively, on account of the allylic 1,3-strain. The conformational effects of this 1,3-strain are also evident in the carbamate 47, obtained from 45 (Scheme 5), and in the C(2)-epimerized bicyclic ether 48, which was formed upon treatment of 47 with (diethylamino)sulfur trifluoride (DAST). Fluorination of 40 with DAST (→ 49) followed by treatment with AcOH led to the D-ido-fluorohydrin 50. Oxidation of 50 (→ 51) followed by a Staudinger reaction and reduction with NaBH3CN afforded the (fluoromethyl)piperidine 52, while reductive amination of 51 with H2/Pd led to the methylpiperidine 55, which was similarly obtained from the keto tosylate 54 and from the dihydrotriazole 36. Deprotection of 52 and 55 gave the amino acids 13 and 14, respectively. The aniline 17 does not inhibit V. cholerae sialidase; the piperidines 12-16 and 18 are weak inhibitors, evidencing the importance of an intact 1,2,3-trihydroxypropyl side chain.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740214
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  • 7
    Digitale Medien
    Digitale Medien
    Synthese von Monomorin I, einem Spurpheromon der Pharao-Ameise (Monomorium pharaonis) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 438-444 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of Monomorin I, a Trail Pheromone of the Pharao Ant (Monomorium pharaonis)Katalytic hydrogenation of the 4-nitroalkanone 5 yielded the cis-pyrrolidine ester 6 (Scheme). The preparation of 5 was accomplished by ethanolysis of the nitrocyclohexanone derivative 4. Iodination at C(α) of 6, followed by cyclization, gave a nearly 5:6 mixture of the two C(5)-epimers 10/9 of octahydroindolizine. Epimerisation of the undesired 10 to 9 and subsequent transformation of the latter gave racemic monomorine I (1; 34% yield from 5).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740221
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  • 8
    Digitale Medien
    Digitale Medien
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740301
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  • 9
    Digitale Medien
    Digitale Medien
    Structure cristalline d'une thiazolorifamycine: rifamycine P (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 326-330 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Crystal Structure of a Thiazolorifamycine: Rifamycine PThe crystal structure of a natural thiazolorifamycin, rifamycin P, as an adduct with EtOH and H2O, has been determined by X-ray crystallography by a combination of direct methods and Patterson techniques. Block-diagonal least-squares refinement using 5996 independent reflections and 1475 parameters led to an R factor of 0.092 (two independent molecules of rifamycin P). The middle part of the ansa chain, essential for activity against the bacterial DNA-dependent RNA polymerase (DDRP) resembles that of active rifamycins. The four OH groups lie on the same side of the molecule and are almost in the same plane. Interatomic distances between the O-atoms agree well with a spatial model derived from X-ray studies, performed on semisynthetic active rifamycins.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740211
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  • 10
    Digitale Medien
    Digitale Medien
    Synthesis of 4-{{[(Isopropyloxy)methylphosphoryloxy]imino}methyl}-1-methylpyridinium Iodide and Its Characterisation (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 331-335 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oximes are used in the therapy of organophosphate poisoning. They form an interaction product with the organophosphate which is claimed to be more toxic than the organophosphate itself. We have synthesized one of these compounds which would be formed by the reaction of pyridine-4-carbaldehyde oxime methiodide with sarin (GB). Thus, reaction of oxime 1 with sarin chloridate (2), yielded 4-{{[(isopropyloxy)methylphosphoryloxy]-imino}methyl}-1-methylpyridinium iodide (4) which was characterized by NMR spectroscopy and X-ray crystallography.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740212
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  • 11
    Digitale Medien
    Digitale Medien
    Transformations in the Isoxazole Series: Synthesis of Substituted 2-AminothiazolesDedicated to Prof. Dr. Oskar Jeger (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 531-542 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Substitued N-(isoxazol-4-yl)thioureas 1 undergo a transformation in the presence of hexacarbonylmolybdenum and acid to yield functionalized thiazoles 3 in a one-pot reaction. In a few cases, 1,4,5-trisubstituted dihydroimidazolethiones 4 are also isolated as side products. Mechanistic considerations are outlined and scope and limitations of this new methodology discussed.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740309
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  • 12
    Digitale Medien
    Digitale Medien
    Biosynthesis of the Spermine Alkaloid Aphelandrine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 565-571 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Aphelandrine (1) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL) NEES from labelled putrescine (4), spermidine (5), and cinnamic acid (3). Whether spermine (6) and the (p-hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5. Methionine (7) is the source of the 3-aminopropyl unit of 5 and 6.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740313
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  • 13
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes. Part 3. Synthesis of SpirocyclopropanesPresented at the ‘XVIth International Carbohydrate Symposium’, Yokohama, Japan, 12th-17th August 1990, Abstr. PL-05. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 585-593 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Thermolysis of the glycosylidene-derived O-benzylated diazirine 1 in the presence of N-phenylmaleimide (2), acrylonitrile (3), dimethyl fumarate (4), or dimethyl maleate (5) led in good yields to mixtures of the spirocyclopropanes 6/7, 8-11, 12/13, and 12/13/16/17. The diastereoselectivity depends upon the alkene. The cycloaddition of 1 to 5 is not diastereospecific, in keeping with previous results. Deprotection of 12, 13, 16, and 17 yielded the tetrols 14,15, 18, and 19, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740316
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  • 14
    Digitale Medien
    Digitale Medien
    Lithium-Salt Effects in Peptide Synthesis. Part II. Improvement of Degree of Resin Swelling and of Efficiency of Coupling in Solid-Phase Synthesis (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 628-643 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The course of solid-phase peptide-coupling reactions as well as the swelling properties of a peptide-resin are influenced by the addition of inorganic salts (LiCl, LiBr, LiClO4, KSCN). Used as additives, these salts can (i) improve coupling yields (e.g., for Fmoc-(Ala)5-Phe-resin → Fmoc-(AIa)6-Phe-resin in DMF/CH2Cl2 1:1 from 89.4 to 97.1% (for polyethylene oxide) on polystyrene (= PEO-PS) resin) or from 77.5 to 93.8% (for poly-(N,N′-dimethylacrylamide) on ‘Kieselgur’ (=PDMAA-KG) resin) without and with 0.4M LiCl, respectively), (ii) increase resin swelling (e.g. for Fmoc-(Ala)5-Phe-(polystyrene resin) from 2.42- to 5.73-fold in 1-methylpyrrolidin-2-one (=NMP) without and with LiCl, (respectively), and (iii) change coupling rates. Example;; of coupling reactions and swelling behaviour (degree and rate) in different solvents (DMF, DMF/CH2Cl2 1:1, THF, NMP, N,N-dimethylpropyleneurea (= DMPU) with and without salts) using different resins (polystyrene (PS); PEO-PS, and PDMAA-KG) and an improved analysis of alanine oligomers up to Ala12-Phe by HPLC and FAB-MS are reported.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740320
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  • 15
    Digitale Medien
    Digitale Medien
    On the Methyl-Transfer Reaction in Crystalline Methyl 2-(Methylthio)benzenesulfonate: a Thermally Induced Non-Topochemical Solid-State Reaction (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 662-669 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rearrangement of methyl 2-(methylthio)benzenesulfonate (1) to the zwitterionic 2-(dimethyl-sulfonium)benzenesulfonate (2) is known to proceed in solution by intermolecular Me transfers. The same rearrangement has been observed to occur in crystalline 1, but the crystal structure shows that the molecular packing is not conducive to intermolecular Me transfer. The reaction has been carried out with mixed crystals composed of 1 and deuteriomethylated (D6)-l. By fast-atom-bombardment mass spectroscopy, it has been shown that the product consists of a 1:2:1 mixture of the non-, tri-, and hexadeuterated species, the mixture expected, if the solid-state reaction proceeds by intermolecular Me transfers. From this result, together with the slower rates of conversion in the single crystal compared with the melt, it can be concluded that the reaction must occur not topochemically but rather at defects such as microcavities, surfaces, and other irregularities in the ordered crystal arrangement.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740323
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  • 16
    Digitale Medien
    Digitale Medien
    Syntheses and Crystal Structures of 4,5-Dihydro-2-(2′-hydroxyphenyl)oxazole-Containing Metal Complexes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 717-726 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the complexes 3 of various metals ligated to chiral 4,5-dihydro-2-(2′-oxidophenyl-ϰO)oxazoles-ϰN is described (Scheme). Three of them, i.e. 3a, 3e, and 3f containing CuII, ZnII and NiII, respectively, were analyzed by X-ray diffraction studies. A series of CuII complexes (6a-d) with differently substituted dihydrooxazoles have been synthesized.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740405
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  • 17
    Digitale Medien
    Digitale Medien
    1-(2′-Deoxy-β-D-xylofuranosyl)thymine Building Blocks for Solid-Phase Synthesis and Properties of Oligo(2′-Deoxyxylonucleotides) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 748-760 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1-(2′-Deoxy-β-D-threo-pentofuranosyl)thymine (= 1-(2′-deoxy-β-D-xylofuranosyl)thymine; xTd; 2) was converted into its phosphonate 3b as well as its 2-cyanoethyl phosphoramidite 3c. Both compounds were used for solid-phase synthesis of d[(xT)12-T] (5), representing the first DNA fragment build up from 3′-5′-linked 2′-deoxy--β-D-xylonucleosides. Moreover, xTd was introduced into the innermost part of the self-complementary dodecamer d(G-T-A-G-A-A-xT-xT-C-T-A-C)2 (9). The CD spectrum of d[(xT)12-T] (5) exhibits reversed Cotton effects compared to d(T12) (6; see Fig. 1), implying a left-handed single strand. With d(A12) (7) it could be hybridized to form a propably Left-handed double strand d(A12) · d[(xT)12-T] (7·5) which was confirmed by melting experiments in combination with temperature-dependent CD spectroscopy. While 5 was hydrolyzed by snake-venom phosphodiesterase, it was resistant towards calf-spleen phosphodiesterase. The modified, self-complementary duplex 9 was hydrolyzed completely by snake-venom phosphodiesterase, at a twelvefold slower rate compared to unmodified 8; calf-spleen phosphodiesterase hydrolyzed 9 only partially.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740408
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  • 18
    Digitale Medien
    Digitale Medien
    Conformational Analysis of Marine Polyhalogenated β-Chamigrenes Through Temperature-Dependent NMR SpectraPresented in part by G.G. at both CISCI 90, S. Benedetto del Tronto, 30 September-5 October 1990, and the Congresso Nazionale di Risonanze Magnetiche, Pisa, 22-24 October 1990. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 774-786 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Temperature-dependent 1H- and 13C-NMR spectra reveal that polyhalogenated marine β-chamigrenes or synthetic derivatives thereof which are trans-diequatorially, substituted at C(8) and C(9), such as rogiolol ((-)-2), obtusol ((+)-3), and their acetates (+)-1 and (-)-4, undergo slow ring-A chair-chair inversion. Conformational equilibria and kinetics are investigated with the aid of synthetic model compounds and molecular-mechanics calculations. Thus, steric repulsions between Brax-C(2) and Heq-C(7) are seen to disfavour thermodynamically conformers 1b, 2b, 3b, and 4b, which can only be detected through cross-saturation transfer, while additional steric repulsions between Meax-C(1) and OHax-C(3) make conformer 8b of obtusol epimer so scarcely populated that it can not be detected. In agreement, with (+)-9 and (+)-10, which have a trigonal C(2), two conformers can be directly observed by NMR. The kinetic barriers, which are seen to arise mainly from steric repulsions between Hax-C(14) and the axial H or halogen atoms at C(8) and C(10), are calculated and discussed with respect to well documented exocycliemethylidene-substituted cyclohexane(ene) systems. This helps to rationalize why in rogiolol acetate ((+)-1) ring B is unusually inert towards Zn/Et2O/AcOH which causes bromohydrine-group elimination from ring A.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740411
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  • 19
    Digitale Medien
    Digitale Medien
    Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol), ein neues Carotinoid aus Paprika (Capsicum annuum) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 819-824 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3.6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,5′-diol), a Novel Carotenoid from Red Paprika (Capsicum annuum)From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740416
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  • 20
    Digitale Medien
    Digitale Medien
    Studies Directed Towards the Biosynthesis of the C7N Unit of Rifamycin B: A New Synthesis of Quinic Acid from Shikimic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 807-818 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of quinic acid (4) via epoxide 13, starting from shikimic acid (5), is described (Scheme 1). Treatment of 13 with thiophenol yielded not only 17, but also the γ-lactones 18 and 19 as result of migration of silyl groups within a cis- and trans-diol system. The conversion provides a direct stereoselective epoxidation of a shikimic-acid derivative as well as an alternative pathway for the preparation of 4. A shorter approach via the disilylated epoxide 22 was unsuccessful because the γ-lactone 25 was obtained in place of the desired α-hydroxy ester 24 (Scheme 2).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740415
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  • 21
    Digitale Medien
    Digitale Medien
    Nucleotides. Part XXXVIPart XXXV:[1]. Syntheses and biological characterization of phosphorothioate analogues of (3′-5′)adenylate trimer (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 892-898 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The four protected diastereoisomcrs 7a/7b and 8a/8b P-thioadenylyl-(3′-5′)-P-thioadenylyI-(3′-5′)-adenosine were synthesized, separated, and deblocked to the free oligonucleotides (Scheme). Biochemical characterization of these (3′-5′)phosphorothioate analogues of adenyiate trimer indicate that these compounds, and the corresponding 5′-monophosphates, neither bind to nor activate RNase L, and are considered to be valuable control compounds in screening experiments.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740420
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  • 22
    Digitale Medien
    Digitale Medien
    Double-Diamond Inclusion Compounds of 2,6-Dimethylydeneadamantane-1,3,5,7-tetracarboxylic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 825-877 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structures of four inclusion compounds of 2,6-dimethylideneadamantane-1,3,5,7-tetracarboxylic acid (4) are described, which involve the following guest species: (a) a mixture of 4-methylpent-3-en-2-one, 2,6-dimethylhepta-2,5-dien-4-one, and mesitylene (condensation products of acetone); (b) mesitylene; (c) a mixture of 4-methylpent-3-en-2-one and mesitylene; (d) (tert-butyl)benzene. In all four cases, the host architectures consist of two interpenetrating super-diamond networks built up by the tetra-acid molecules via pairwise H-bonds between the tetrahedrally directed COOH groups. In the first three cases (tetragonal crystal symmetry), the two diamond-like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically. This asymmetry is brought about by the increased steric bulk of the (tert-butyl)benzene guest molecules. Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond-like host lattice by offering still bulkier guest molecules have as yet not been met with success. The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane-1,3,5,7-tetracarboxylic acid, which represents a fivefold diamond-like self-inclusion compound. Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained. On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4-H2O), which was also subjected to X-ray analysis. The (triclinic) crystal structure of 4·H2O involves an interesting dichotomy inasmuch its pattern of H-bonding may be rationalized either in terms of a double, cross-linked super-zincblende (sphalerite) architecture, or as a system of porous, puckered 4-connected sheets, which interpenetrate each other pairwise and are cross-linked by the H2O molecules. Various structure and (space group) symmetry characteristics of the supramolecular solid-state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740417
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  • 23
    Digitale Medien
    Digitale Medien
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740501
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  • 24
    Digitale Medien
    Digitale Medien
    Novel Antifungal Tetracyclic Compounds from Bauhinia rufescens LAM.Presented in part at the Meeting of the Swiss Chemical Society, Bern, 19th October 1990. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 791-799 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As the root bark CH2Cl2 extract of Bauhinia rufescens showed antifungal activity in a bioassay with the plant pathogenic fungus Cladosporium cucumerinum, a phytochemical investigation was undertaken on material collected in Niger. Activity-guided fractionation of this extract, using different preparative chromatographic methods, allowed the isolation of the four new antifungal tetracyclic compounds 1-4. Their structures were established by 1H- and 13C-NMR data, and single-crystal X-ray analyses were used to confirm the structures of 1 and 3. The isolated compounds seem to be biogenetically related to a stilbene.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740413
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  • 25
    Digitale Medien
    Digitale Medien
    Versatile Stereoselective Synthesis of Completely Protected Trifunctional α-Methylated α-Amino Acids Starting from Alanine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 800-806 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new route to completely protected α-methylated α-amino acids starting from alanine is described (see Scheme). These derivatives, which are obtained via base-catalyzed opening of the oxazolidinones (2S,4R)- and (2R,4S)-2, can be directly employed in peptide synthesis. The synthesis of both enantiomers of Z-protected α-methylaspartic acid β-(tert-butyl)ester (O4-(tert-butyl) hydrogen 2-methylaspartates (R) or (S)-4a), α-methyl-glutamic acid γ-(tert-butyl) ester (O5-(tert-butyl) hydrogen 2-methylglutamate (R)- or (S)-4b), and of Nε-bis-Boc-protected α-methyllysine (N6,N6-bis[(tert-butyloxy)carbonyl]-2-methyllysine (R)- or (S)-4c) is described in full detail.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740414
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  • 26
    Digitale Medien
    Digitale Medien
    Nucleotides. Part XXXVPart XXXV:[1]. Synthesis of 3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenyIyl-(2′-ω)-9-(ω-hydroxyalkyl)adenines (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 887-891 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Via the phosphotriester approach, new structural analogs of (2′-5′)oligoadenyiates, namely 3′-deoxyadenylyl-(2′-5′)-3′-dcoxyadenylyl-(2′-ω)-9-(ω-hydroxyalkyl)adenines 18-21, have been synthesized (see Scheme) which should preserve biological activity and show higher stability towards phosphodiesterases. The newly synthesized oligonucleotides 18-21 have been characterized by 1H-NMR spectra, TLC, and HPLC analysis.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740419
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  • 27
    Digitale Medien
    Digitale Medien
    Mitteilungen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 905-906 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740423
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  • 28
    Digitale Medien
    Digitale Medien
    [5-Leucin]enkephalin-Related Glycoconjugates: Structurally Novel Agents Effective against HIV-1 (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 951-955 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of [Leu5]enkephalin-related glycoconjugates with an ester-, ether-, or amide-type linkage were synthesized and evaluated for antiviral activity against HIV-1 in a cell-culture system using peripheral blood lymphocytes. All tested glycoconjugates exhibited a certain antiviral activity which was significantly higher than the activity of the parent peptide compound itself. These results indicate that synthetic glycoconjugates of opioid peptides are good candidates for the development of anti-HIV agents.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740505
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  • 29
    Digitale Medien
    Digitale Medien
    Synthesis, Isolation, and Full Spectroscopic Characterization of Eleven (Z)-Isomers of (3R,3′R)-Zeaxanthin (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 969-982 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Developmental efforts to improve the yield of the chemical synthesis of (3R,3′R)-zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 1H-NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)-isomers of zeaxanthin: (7Z)-, (9Z), (13Z)-, (15Z)-, (7Z,7′Z)-, (9Z,9′Z)- (7Z,9Z,7Z)-, (7Z,11Z,7′Z)-, (9Z,13Z,9′Z)-, (7Z,9Z,7′Z,9′Z)-, and (7Z,9Z,11Z,7′Z,9′Z)-zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)-, (7Z,7′Z)-, (9Z,9′Z)-, (7Z,9Z,7′Z)-, and (7Z,9Z,7′Z-9Z)-isomers.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740507
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  • 30
    Digitale Medien
    Digitale Medien
    Ringerweiterung von 1,2-Thiazol-3(2H)-on-1,1-dioxiden und 3-Amino-2H-azirinen zu 4H-1,2,5-Thiadiazocin-6-on-1,1-dioxiden (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1002-1010 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ring Enlargement of 1,2-Thiazol-3(2H)-one-1,1-dioxides and 3-Amino-2H-azirines to 4H-1,2,5-Thiadiazocin-6-one-1,1-dioxidesReaction of 3-amino-2H-azirines 2 with the 1,1-dioxides 4 and 7 of 1,2-thiazol-3(2H)-ones and 1,2-thiazoli-din-3-ones, respectively, in i-PrOH at room temperature leads to 4H-1,2,5-thiadiazocin-6(5H)-one-1,1-dioxides 5 (Scheme 2, Table) and the corresponding 7,8-dihydro derivatives 8 (Scheme 4), respectively. The structure of some of the new 8-membered heterocycles as well as the structure of the minor by-product 6 (Scheme 3) have been established by X-ray crystallography (Chapt. 4). The proposed reaction mechanism for the ring expansion to 5 and 8 (Scheme 2) is in accordance with previously published results of reactions of 2 and NH-acidic heterocycles and is further supported by the results of the reaction of 4a and the (1-15N)-labelled aminoazirine 2a*.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740511
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  • 31
    Digitale Medien
    Digitale Medien
    Zur Oxidation von 1,2-Thiazolen: Ein einfacher Zugang zu 1,2-Thiazol-3(2H)-on-1,1-dioxidenHerrn Prof. Dr. Siegfried Hauptmann zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1059-1070 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxidation of 1,2-Thiazoles; A Convenient Approach to 1,2-Thiazol-3(2H)-one 1,1-DioxidesThe 1,2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate (7 → 9, Scheme 1) are easily transformed to 1,2-thiazol-3(2H)-one 1,1-dioxidcs 10 on treatment with H2O2 in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2-thiazolidin-3-one 1,1-dioxides 16 (Scheme 3). Cycloalka[c]-1,2-thiazoles 18 are prepared from 2-[(thiocyanato)methyliden]cycloalkan-1-ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H2O2 in AcOH yields the tricyclic oxaziridine 19.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740515
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  • 32
    Digitale Medien
    Digitale Medien
    Zur Synthese von Derivaten des Pyrido[1,2-a]azepinsProf. Horst Prinzbach zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1095-1101 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On the Synthesis of Derivatives of Pyrido[1,2-a]lazepineThe conjugated pyridinium ylides of type 4 undergo 8π -electrocyclisation affording the heterobicyclic allenes 5 which, in the presence of H2O and H2O2, are subsequently transformed into the substituted pyrido[1,2-a]-azepinones 6, a novel heterocyclic system. The chemical behaviour of 6a,b is dominated by cleavage of the lactam bond and subsequent reaction to pyridinc and isoquinoline derivatives, respectively; e.g. reaction of 6a, b with 4,5-dihydro-4-methyl-3H-1,2,4-triazole-3,5-dione affords the cycloadducts 11 and 12 almost quantitatively. The successful transformation of 6b into 15 is described, the latter being the first representative of the presently unknown, potentially antiaromatic pyrido[1,2-a]azepine (1).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740519
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  • 33
    Digitale Medien
    Digitale Medien
    Mitteilungen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1156-1156 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740525
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  • 34
    Digitale Medien
    Digitale Medien
    Regioselectivity, Stereoselectivity, and Isotopically Sensitive Branching in the Fe(I)-Mediated Dehydrogenation of Octane-1,8-diol in the Gas PhaseDedicated to Prof. Jürgen Sauer on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1127-1134 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Regio- and stereospecific labeling experiments are conducted to unravel the mechanistic features of the Fe+-induced dehydrogenation of octane-1,8-diol in the gas phase. With regard to the regioselectivity, ca. 20% of molecular hydrogen originates from the C(3)/C(4) or the equivalent C(5)/C(6) positions. The remaining 80% are, provided by the C(4)/C(5) methylene units. The steps, preceding the reductive elimination of hydrogen, are irreversible, and the overall reaction follows a 1,2-elimination mode. The loss of HD from C(3)/C(4) is associated with a kinetic isotope effect KH2/KHD = 1.68. Formation of D2 from the positions C(4)/C(5) has an isotope effect of KH2/KD2 = 4.7; this figure is slightly dependent on the configuration at C(4)/C(5). Most interesting is the finding that the configuration at C(4)/C(5) in [4,5-D2]octane-1,8-diol, i.e. 5c vs. 5d, plays a pivotal role in the dehydrogenation of the central C(4)/C(5) part. This unexpected and unprecedented result is explained in terms of conformational analysis. A staggered-like conformation serves as a precursor to generate a trans-fused bicyclic intermediate 6. It is this very intermediate from which most of the molecular hydrogen is eliminated. Of minor importance is the as-fused chelate 7, which is formed from an eclipsed-like conformation of the octane-1,8-diol/Fe+ complex. The contribution of 6 and 7 to the product formation is controlled by the relative configuration at the labeled positions C(4)/C(5). For the D,L-form 5c, we estimate a ratio of ca. 9:1 for the contribution of 6 vs. 7; due to an isotope effect, this ratio drops to 1:85:1 for the meso-form 5d. This finding constitutes the first example for the existence of isotopically sensitive branching (‘metabolic switching’) in gas-phase organometallic chemistry.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740522
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  • 35
    Digitale Medien
    Digitale Medien
    Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1163-1170 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structures of the LaIII, EuIII, and TbIII complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La3+ ⊂ 1]3 Cl- ( = 3-La), [Tb3+ ⊂ 1]3 Cl- ( = 3-Tb), and [Eu3+ ⊂ 2]3 C1- ( = 3-Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl- ions or H2O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the EuIII and TbIII cryptates, which indicated residual coordination of H2O molecules.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740603
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  • 36
    Digitale Medien
    Digitale Medien
    Biphenyltetrols and Dibenzofuranones from Oxidative Coupling of Resorcinols with 4-Alkylpyrocatechols: New Ciues to the Mechanism of Insect Cuticle Sclerotization (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1205-1212 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxidation of 4-alkylpyrocatechols 2 by means of an insect diphenoloxidase (laccase) or K3 [Fe(CN)6] yields, in the presence of resorcinols 1 (R2 = H), complex mixtures of products from which biphenyltetrols 3 (R3 = H) and dibenzofuranones 5 and 6 were isolated. It is suggested that similar homo-coupling products are formed from pyrocatechols 2b and 2c in insects during cuticle sclerotization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740607
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  • 37
    Digitale Medien
    Digitale Medien
    Quantitative Formation in Water of [Ru(CO)(H2O)5]2+ from Hexaaquaruthenium(II) and Carbon Monoxide (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1236-1238 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: High-pressure 17O- and 13C-NMR show that [Ru(H2O)6]2+ reacts quantitatively with carbon monoxide (50 bar) in water to form [Ru(CO)(H2O)5]2+.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740611
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  • 38
    Digitale Medien
    Digitale Medien
    Synthese von ‘Push-Pull’-Oligoacetylenen24. Miteilung über Aminoacryl-Derivate. 23. Mitteilung: [1]Kurzmitteilung: [2] (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1264-1272 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of ‘Push-Pull’-OligoAcetylenes‘Push-pull’ triacetylenes 11a, b, c, as well as ‘push-pull’ tetraacetylene 13b have been prepared by reaction of the corresponding trichloroene(oligoinyl)amines 9 and 10 with 2 mol-equiv. of BuLi followed by acylation. The sequences (Schemes 3 and 4) are very simple and straightforward, they could in principle be applied to the synthesis of ‘push-pull’ pentaAcetylenes 15 and hexaacetylenes 17 (Scheme 5). Main limitations are the moderate yields as well as the low thermal stability of push-pull oligoacetylenes.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740614
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  • 39
    Digitale Medien
    Digitale Medien
    Metabolic products of microorganisms. Part 262Part 261: [1].. The absolute configuration of sphydrofuran, a widespread metabolite from streptomycetes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1281-1286 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Sphydrofuran (1) was isolated from the culture filtrate of Streptomyces sp. (strain Gö 28 and Tü 3616) by chemical screening methods. Metabolite 1 is an anomeric and ring-chain tautomeric mixture and could easily be transformed into the stable furan derivative 2 under acidic conditions. The constitution and relative configuration of 1 was established by X-ray crystallography of its 8-O-methyl derivative 3a. The absolute configuration at C(4) of 1 and thus of the whole molecule (3R,4S,5S) could be determined starting from 2 using the Helmchen method.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740617
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  • 40
    Digitale Medien
    Digitale Medien
    Structure and reactivity of xanthocorrinoids. Part VPart IV, [1].. Formation of trans-diol derivatives of 5,6-dihydrocobyrinic acid from xanthocorrinoids under acidic conditions (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1287-1295 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On treatment with H2SO4/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam (3) takes place quantitatively at C(6), yielding the corresponding trans-diol 4. The corresponding lactone 7, whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740618
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  • 41
    Digitale Medien
    Digitale Medien
    Alternative Strategies for the Fmoc Solid-Phase Synthesis of O4-Phospho-L-tyrosine-Containing Peptides (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1314-1328 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A number of biologically relevant O4-phospho-L-tyrosine-containing peptides have been synthesized by either the global phosphorylation of the side-chain-unprotected L-tyrosine moiety in presynthesized resin-bound peptides or alternatively by the incorporation of suitably protected O4-phospho-L-tyrosine building blocks in the continuous-flow method of Fmoc solid-phase peptide synthesis. Different phosphate-protecting groups have been applied.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740621
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  • 42
    Digitale Medien
    Digitale Medien
    Stereoselektive Synthese von Pyrrolizidin-Alkaloiden aus NitroalkanonenHerrn Professor Dr. C. H. Eugster zurn 70. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1352-1361 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereoselective Synthesis von Pyrrolizidin Alkaloids from NitroalkanonesReduction of 5-nitropentadecane-2,8-dione (11), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec-1-en-3-one, gave, depending on the conditions, two epimeric 3-heptyl-2,3,5,6,7,7a-hexahydro-5-methyl-1H-pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα-hydro epimer 1b with cis-orieted H-atoms at C(3), C(5), and C(7a). NaBH3CN/NH4OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ-hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N-atom of the pyrrolizidine ring stems from NH4OAc exclusively as shown by reduction of 11 with NaBH3CN/(15N)H4OAc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740624
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  • 43
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes. Part 4. Synthesis of Spirocyclopropanes from Acetamidoglycosylidene-Derived Diazirines (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1362-1372 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the first glycosylidene-derived 2-acetamido-2-deoxydiazirine 4 from N-acetylglucosamine 6 is described. Thus, 6 was transformed into the 3-O-mesylglucopyranoside 9 by glycosidation with allyl alcohol, benzylidenation, and mesylation (Scheme 2). Solvolysis of 9 gave the allopyranoside 10 which, upon benzylation and glycoside cleavage, yielded the hemiacetals 12. Using our established method (via the lactone oxime 14 and the diaziridines 16), 12 gave the diazirine 4. Thermolysis of this diazirine in the presence of i-PrOH gave the dihydro-1,3-oxazole 5 (Scheme 1); in the presence of acrylonitrile, the four diastereoisomeric spirocyclopropanes 17-20 and the acetamidoallal 21 were obtained and separated by prep. HPLC (Scheme 3). Assignment of the configuration of 17-20 is based on NOE measurements and on the effect of diamagnetic anisotropy of the CN group. The ratio of the four cyclopropanes, which is in keeping with earlier results, is rationalized.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740625
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  • 44
    Digitale Medien
    Digitale Medien
    Mammalian alkaloids: Synthesis and O-methylation of (S)- and (R)-3′-hydroxycoclaurine and their N-methylated analogues with S-adenosyl-L-[methyl-14C]methionine in presence of mammalian catechol O-methyltransferase (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1399-1411 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: O-Methylation of the optically active 3′-hydroxycoclaurines 3a and 3b and of the N-methylated analogs 5a,b with S-adenosyl-L-[methyl-14C]methionine in presence of mammalian COMT was investigated in vitro. The N-unsubstituted (1S)- and (1R )-isomers 3a and 3b, respectively, afforded almost equal amounts of the corresponding N-norreticuline 4 and N-nororientaline 19, besides two unknown by-products (see Fig. and Table 1). The N-methylated (1S)-isoquinoline 5a, on the other hand, afforded largely (S)-orientaline ((S)-19), while an almost equal mixture of (R)-reticuline (6b) and (R)-orientaline ((R)-19) was obtained from the (1R)-enantiomer 5b. The isoquinolines 3a,b and 5a,b were prepared by a Bischler-Napieralski cyclization yielding O-benzyl-protected isoquinoline 10 (Scheme 1). The optical resolution of 10 was accomplished with 2′-bromotartranilic acid. The N-methylated isoquinolines were prepared by N-formylation of 10a,b and reduction of the formamides 13a,b with diborane (→ 14a,b). Deblocking of the benzyl-ether moieties of 10a,b and 14a,b was accomplished by catalytic hydrogenation in presence of HCl, affording directly 3a,b·HCl and 5a,b·HCl, respectively.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740704
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  • 45
    Digitale Medien
    Digitale Medien
    A Novel, Degraded Polyketidic Lactone, Leptosphaerolide, and Its Likely Diketone Precursor, Leptosphaerodione. Isolation from Cultures of the Marine Ascomycete Leptosphaeria oraemaris (LINDER)Presented in part by A. G. at the ‘Giornate di chimica delle Sostanze Naturali’ meeting, Maratea (Potenza), on June 3, 1991. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1445-1450 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Acetone extraction of cultures of the marine ascomycete Leptosphaeria oraemaris (LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide ( = (+)-7-[(1E)-l,3-dimethylpent-1-enyl]-10-hydroxy-3-methoxybenzo[1,2-b:5,4-c′]dipyran-2(9H)-one; (4+)-8) besides the o-dihydroquinone 3-[(1E)-1,3-dimethylpent-1-euyl]-8,10-dihydroxy-7-methoxy-8-(2-oxopropyl)-1H-naphtho[2,3-c]pyran-9(8H)-one (1) as a 10:9 mixture of epimers. retro-Aldol reaction of 1 gave leptosphaerodione ( = (-)-3-[(1E)-1,3-dimethylpent-1-enyl]-10-hydroxy-7-methoxy-1H-naphtho[2,3-c]pyran-8,9(8H)-dione; (-)-6) which was also present in small amounts in the extracts and which gave 1 on reaction with acetone. It is thus likely that 1 is an artefact of the extraction by acetone. Biogenetically (+)-8 might derive from (-)-6 via an unusual oxidation with loss of CO2.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740707
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  • 46
    Digitale Medien
    Digitale Medien
    1,2-Stereoinduction in Radical Reactions: Stereoselective Synthesis of 2-Alkyl-3-hydroxybutanoates (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1600-1607 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Radical addition to 2-cyclohexyl-5-methylidene-6-methyl-1,3-dioxan-4-one (2) affords stereoselectively 5,6-trans-products trans-3. The size of the radical has no influence on the selectivity. These trans-acetals are converted into threo-3-hydroxy-butanoates 4. Methyl 2-methylidene-3-[(tert-butyl)diphenylsilyloxy]butanoate (5), treated under the same conditions, leads mainly to the erythro-isomer of 4 after deprotection. An influence of the steric bulkyness of the radical is observed. The stereochemical course of the reactions is discussed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740722
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  • 47
    Digitale Medien
    Digitale Medien
    Gas-Phase Chemistry of Ti+ to Zn+ with Butyl Isothiocyanate (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1609-1621 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using a complete set of 2H-labeled isotopomers, the gas-phase reactions of Ti+ to Zn+ with butyl isothio-cyanate are studied. The main product for most of the metal ions is MHNCS+ formed by an ion/dipole mechanism. Exceptions are Cr+, which yields significant amounts of H2 and H2S loss, Mn+, which is the only ion that does not form MHNCS+ at all but produces mainly C2H4 and C3H6, and Zn+, which predominantly reacts by charge transfer.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740802
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  • 48
    Digitale Medien
    Digitale Medien
    1,3-Oxathiolan-Synthese: Spirocyclische 1,3-Oxathiolane aus der Lewis-Säure-katalysierten Umsetzung von cyclischen Trithiocarbonaten und OxiranenHerrn Professor Dr. C. H. Eugster zum 70. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1500-1510 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,3-Oxathiolanc Synthesis: Spirocyclic 1,3-Oxathiolanes from the Lewis-Acid-Catalyzed Reaction of Cyclic Trithiocarbonates and OxiranesThe cyclic trithiocarbonates 1.3-dithiolane-2-thione (4) and 1,3-dithiole-2-thione (9) in 1,2-dichloroethane and MeCN, respectively, react with alkyl- and phenyl-substituted oxiranes 2 in the presence of Lewis acids to give 1-oxa-4,6,9-trithiaspiro[4.4]nonanes 5 and 6 (Scheme 2) and 1-oxa-4,6,9-trithiaspiro[4.4]non-7-enes 10 and 11 (Scheme 3), respectively. The reactions proceed regioselectively yielding 2-alkyl (5, 10) and 3-phenyl derivatives (6, 11) as the main products. From the reaction of 4 and 2-phenyloxirane (2e) with TiCl4, 2-phenyl-1,4,6,9-tetrathia-spiro[4.4]nonane (7) is isolated as a minor product. The molecular structures of 5a, 6e, and 7 are established by X-ray crystallography.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740714
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  • 49
    Digitale Medien
    Digitale Medien
    2D-NMR ConformationaL Studies of ChiraL Functionalized Ferrocenylphosphine Ligands for the Gold(I)-Catalyzed Aldol Reaction (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1533-1543 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformations in solution of six selected chiral 1,1′-bis (diphenylphosphino)ferrocenyl ligands bearing functionalized side chains, the diastercoisomers 4 and 5 and 6-9, have been elucidated by 2D-NMR methods (COSY, TOCSY, NOESY, and 1H,31P and 1H,13C correlations). The possible relationship between the preferred conformation and the stereoselectivity observed in the gold(I)-catalyzed asymmetric aldol condensation in the presence of these ligands is discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740717
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  • 50
    Digitale Medien
    Digitale Medien
    Crystal Structure and ESR Study of a Bimetallic Copper/Iron Crown Ether Inclusion Complex (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1591-1599 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bimetallic inclusion complexes have been synthesized by a secondary coordination interaction between the guest complex [Fe(η5-C5H5)(CO)2(NH3)][PF6] and copper(II) complex 1a or nickel(II) complex lb containing crown-ether hosts. The X-ray crystal-structure analysis established that the Cu,Fe inclusion complex 2 crystallize as a centrosymmetric dimer with a Cu—Cu separation of 3.73 Å and a novel out-of-plane Cu—N interaction. The magnetic parameters for 2 were obtained by ESR and ENDOR spectroscopy. ESR susceptibility measurements down to 6 K exclude the presence of any antiferromagnetic coupling interaction between the CuIIcenters of the dimer.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740721
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  • 51
    Digitale Medien
    Digitale Medien
    Synthesis of Aristotelia-type alkaloids. Part VIIIPart VII: [1].. Synthesis of (±)-aristolasicone (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1636-1642 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The revised structure of the indole alkaloid aristolasicone (2) was confirmed through a convergent total synthesis of the racemic form of this metabolite. The key step involves a one-pot condensation/cyclization reaction between 1-(4-methoxyphenylsulfonyl)-1H-indole-2-acetaldehyde (9) and (±)-trans-5-(2,6-difluorobenzyloxy)-p-menth-l-en-8-amine ((±)-7). The resulting allohobartine derivative (±)-13, obtained in 84% yield, was deprotected and oxidized to (±)-alloscrratenone ((±)-15) which cyclized smoothly to the target molecule (±)-2 upon exposure to BF3 · Et2O.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740804
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  • 52
    Digitale Medien
    Digitale Medien
    From 1-(Silyloxy)Butadiene to 4-Amino-4-Deoxy-DL-Erythrose and to 1-Amino-1-Deoxy-DL-Erythritol Derivatives via Hetero-Diels-Alder Reactions with Acylnitroso Dienophiles (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1653-1670 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Acylnitroso dienophiles 4 reacted instantly with 1-(silyloxy)butadiene 5α and led in good yield to the regioisomeric cycloadducts 6 (major) and 7 (minor; Scheme 2, Table 1). cis-Hydroxylation of these primary cycloadducts with OsO4 (catalyst) occurred stereospecifically and in high yield (→8 and 9, resp.; Scheme 2). It was followed by reductive ring cleavage to give either 1-amino-1-deoxy-DL-erythritol or 4-amino-4-deoxy-DL-erythrose derivatives 10 and 14, respectively, depending on the nature of the reducing agent (Schemes 3 and 4).
    Zusätzliches Material: 7 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740806
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  • 53
    Digitale Medien
    Digitale Medien
    Cuprous complexes and dioxygen. Part 11Part 10: [1].. Concomitant one- and two-electron reduction of O2 by the Cuaq+ ion (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1679-1688 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The autoxidation of CuI in aqueous MeCN has been studied using a Clark oxygen electrode in the presence and absence of Cu11. The reaction is inhibited by Cu11 in the pH range of 0.5 to 5.0, reaching a lower limiting value at the highest concentrations. The reaction order changes from 1 to 2 with respect to CuI under the influence of Cu2+ ion. Detailed kinetics analysis of a total of 275 measurements has shown that an unstable primary adduct CuO+2 decomoses to give .O2- or HO2., depnding on pH, and also reacts directly with a second Cu+ ion, avoiding one-electrton reduction of O2 by this path. Reaction of HO2. is faster with CuI than with Cu11 by a factor of 20, and single-electron transfer within CuO+2 to Cu2+ and .O2- predominates over reaction with a second copper ion for [CuItot] 〈 2. 10-3M in the absence of Cu2+. The most likely value for the reaction of .O2- with CuI is 5.3 · 108 M-1S-1, but even this high rate constant is at the limit of significance. All secondary reactions followinfg the initial formation of CuO+2 are shown to be very fast, a fact that should be properly considered in the discussion of mechanisms of copper-catalyzed oxidations and oxygenations.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740808
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  • 54
    Digitale Medien
    Digitale Medien
    A Molecular-Mechanics Analysis of Complexes of the Sexidentate Macrocycles cis- and trans-6,13-Dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1834-1842 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular-mechanics calculations of the sexidentate coordinated complexes of the pendant arm macrocyclic hexaamines trans- (L1) and cis-6,13-dimethyl-3,4,8,11-tetraazacyclotetradecane-6,13-diamine (L2) reveal that the trans-isomer shows a preference toward small metal ions, whereas the L2 may coordinate a wider range of metal ions without significant intramolecular strain. Conformational disorder in previously reported crystal structures of complexes of L1 is interpreted, and predictions for some, as yet, unknown complexes of L2 are made.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740826
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  • 55
    Digitale Medien
    Digitale Medien
    3-Deazaguanine N7- and N9-(2′-Deoxy-β-D-ribofuranosides): Building Blocks for Solid-Phase Synthesis and Incorporation into Oligodeoxyribonucleotides (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1790-1800 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oligonucleotides continuing 3-deaza-2′-deoxyguanosine (I) or its N7-regioisomer 2 were prepared by solid-phase synthesis using P111 chemistry. Protection of 1 or 2 with N,N V-dimethylformamide diethyl acetal followed by 4,4′-dimethoxytritylation afforded imidazo[4,5-c]pyridines 10b and 11b, respectively. The latter were converted into the 3′-phosphonates 10c or lie, respectively; the cyanoethyl N,N-diisopropylphosphoramidite 10d was also prepared. The oligonucleotide building blocks were employed in automated solid-phase synthesis. 1 he self-complementary oligomers 13, 15, and 17 were prepared and characterized by enzymatic hydrolysis with snake-venom phosphodiesterase followed by alkaline phosphatase. There CD spectra exhibited the general structure of a B-DNA.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740821
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  • 56
    Digitale Medien
    Digitale Medien
    Steric Effects on Reaction Rates. Part XII. Force-Field Calculations for the Solvolysis of Cyclobutyl and Tricyclyl Derivatives (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1808-1816 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Force-field parameters have been developed for the molecular-mechanics calculation of tertiary carbenium ions with tricyclane structure, for tertiary cyclobutyl and cubyl cations. The cyclobutyl parameters are also applicable to tertiary 7-norbornyl cations. Satisfactory plots are obtained for correlation of the rates of solvolysis with the differences in steric energies between carbenium ions and the corresponding bromides.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740823
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  • 57
    Digitale Medien
    Digitale Medien
    Nitrostyrene Derivatives of Adenosine 5′-Glutarates Modified with an Alkyl Spacer and their inhibitory activity on epidermal growth factor receptor protein tyrosine kinase (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 59-69 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: β-Nitrostyrene derivatives of adenosine 5′-glutarates are potent and selective bisubstrate-type inhibitors of the epidermal growth factor receptor protein tyrosine kinase (EGF-R PTK). In an attempt to improve the inhibitory activity, this type of compounds was modified with alkyl spacers of varying length between the nitrostyrene and the glutaryl units. The spacers consisted of 1, 3, 4, and 5 atoms to give compounds of the benzyl, oxyethyl, oxypropyl, and oxybutyl series, respectively (Schemes 1 and 2). Adenosine 5′-esters were prepared in the benzyl and oxypropyl series only. Compared to the compounds in the parent series without spacer (IC50 = 0.7-12 μM), most of the modified compounds inhibited the EGF-R PTK only marginally or were inactive (IC50 ≥ 100 μM). The only exceptions were the free acids 19 and 20 with IC50 values of ca. 5 μM. It is noteworthy that esterification of these two hydrogen glutarates with either MeOH or adenosine yielded inactive compounds, which is in contrast to the corresponding substances without spacers.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770109
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  • 58
    Digitale Medien
    Digitale Medien
    Synthese und Eigenschaften der Furo- und Thieno-Analogen von PQQ-TriesterTeil einer Präsentation am ‘2nd International Symposium on PQQ and Quinoproteins’, 19.-22. Nov. 1991, Yamaguchi, Japan. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 100-110 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis and Characterization of the Furo and Thieno Analogues of the Triester of PQQWe report here the synthesis and properties of the furo and thieno analogues of 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9- tricarboxylic acid ( = PQQ), i.e. the furo- and thieno[2,3-f]quinoline-4,5-quinone (FQQ and TQQ, resp.) derivatives B and C, obtained as triesters. The triester of PQQ derivative A is much more stable than the triesters of B or C, and only the triester of A shows strong activity in nonenzymatic catalytic oxidations.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770113
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  • 59
    Digitale Medien
    Digitale Medien
    Imidazole-Analogues of 6-Epicastanospermine and of 3,7a-Diepialexine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 934-940 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chiral bicyclic imidazol derivatives 7 and 8 were obtained from D-glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and 8 are analogues of 6-epica-stanospermine (4) and of 3,7a-diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti-HIV activity proved to be only marginal.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740503
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  • 60
    Digitale Medien
    Digitale Medien
    Ionization Behavior and Ionization-Dependent Conformation of Raclopride, a Dopamine D2 Receptor Antagonist (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 956-968 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Raclopride, an antipsychotic 6-methoxysalicylamide (= 2-hydroxy-6-methoxybenzamide) derivative, was shown by titrimetry and UV-pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate-ammonium ionic bond. These findings indicate that raciopride and other halogenated 6-melhoxysalicylamides with a highly acidic phenolic group may not resemble other ortho-methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D2 receptor.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740506
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  • 61
    Digitale Medien
    Digitale Medien
    Computational Approach to the Receptor-Bound Conformation of Cyclosporin A (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 171-181 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conversion of the conformation of cyclosporin A (CsA) observed in CHCl3 to the receptor-bound state is investigated by two molecular-mechanics methods, template forcing and dynamic forcing. The conformations of CsA in CHCl3 and complexed with LiCl in THF as determined by NMR are used as starting structures. The transition starting from the CsA/CHCl3-derived conformation is hindered by steric interactions of two side chains (MeBmt1 and Val5). While starting with the CsA/LiCl-derived conformation, the conversion is facile. It is illustrated that these calculations, which are of artificial character, using only the starting and final structures of the observed conformational transition during the receptor-binding event, allow an insight into the interactions between the substrates and receptor in terms of an induced fit.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770120
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  • 62
    Digitale Medien
    Digitale Medien
    Electrochemical Study of Phase-Transfer Catalysis Reactions: The Williamson ether synthesis (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 231-242 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The transfer properties of the ionic species involved in the Williamson ether synthesis by phase-transfer catalysis were investigated using electrochemical techniques developed for the study of polarised liquid/liquid interfaces. This approach allows the measurement of the apparent partition coefficients of the transferring species. From these data, it is proposed that the role of the phase-transfer catalyst salt in the reaction mechanism is to establish a Galvani distribution potential difference between the two phases which in turn acts as the driving force for transferring the reactive aqueous ions to the organic phase.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770125
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  • 63
    Digitale Medien
    Digitale Medien
    Synthesis of (R)- and (S)-5-(Hydroxymethyl)-3-isopropyloxazolidin-2-one, intermediates in the preparation of optically active β-blockers (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 252-256 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The (R)- and (S)-5-(hydroxymethyl)-3-isopropyloxazolidin-2-ones, ((R)- and (S)-2, resp.), pivotal intermediates in the preparation of optically active β-blockers, were synthesized using (R,E)-2-hydroxypent-3-enenitrile (1) as the chiral starting material. In the synthesis of (R)-2, a known cyclization/inversion step was applied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770127
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  • 64
    Digitale Medien
    Digitale Medien
    Calorimetric Measurements of the Complexation of Cyclosporin A, Ascomycin, Fujimycin, and Rapamycin with Lithium Chloride and with an Immunophilin (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 291-305 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Solutions (2 ml) of small linear and cyclic peptides (4-11), of a peptolide containing nine amino acids and a lactate moiety (12), of the cyclic undecapeptide cyclosporin A (CS, 1), and of the macrolides ascomycin, fujimycin, and rapamycin (13-15) in THF were added to excess LiCl, LiBr, or LiClO4 (up to 3000 equiv. in 40 ml THF) in a calorimeter (calorimetric titration). The enthalpies of interaction measured are in the range of ΔH = -8 to -37 kcal/mol. A similar experiment was carried out with one of the binding proteins of cyclosporin, the human cyclophilin A, to give the thermodynamic parameters for the complexation ΔH = -16, ΔG° = -10 kcal/mol, and ΔS° = -20 cal/mol·deg. at 25° which corresponds to an equilibrium constant K = 2·107 l/mol, in good agreement with the result of independent measurements using different methods. NMR Measurements of the macrolides in (D8)THF containing LiCl show strong down-field shifts of signals of the H-atoms next to C=O and C-OH groups in these molecules.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770129
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  • 65
    Digitale Medien
    Digitale Medien
    NMR of Terminal Oxygen. Part 13Part 12: [1].. 17O-NMR spectra of C-nitroso compounds, thionitrites and NO+ Ion: Resonance effects in O=N - X compounds and correlation with CD spectra (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 306-316 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 17O-NMR signals of four true C-nitroso compounds 1-4 appear at particularly low field (1550-1265 ppm), whereas the dimers (azodioxy type) resonate at ca. 400 ppm and the ‘isonitroso compounds’ ( = quinone-oximes; 5 and 6) at ca. 250 ppm. S-Nitroso compounds ( = thionitrites; 8 and 9) show shift values of ca. 1300 ppm, not far from C - NO; the NO+ ion is much stronger shielded (474 ppm). The results, together with those for higher-shielded nitroso compounds X - NO (X = RO, R2N, Cl, O-) are discussed in terms of (a) resonance stabilization through n-donation from X(π-bond order, approximated by the known barriers of rotation around the X - N bond) and of (b) electronic excitation energies ΔE. The latter are approximated by long-wave (symmetry-forbidden) UV/VIS absorptions and confirmed, where available, by the maxima of the curves of circular dichroism (CD); the CD curve of thionitrite 9 has been measured. It is found that the δ(17O) values of X - NO depend both on bond order and on ΔE, which could not be separated. The higher shielding of NO+ compared with X - N=O is explained on the basis of anisotropy effects, which differ between sp and sp2 systems.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770130
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  • 66
    Digitale Medien
    Digitale Medien
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770101
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  • 67
    Digitale Medien
    Digitale Medien
    Enantioselective synthesis of (-)-conduramine C1 and aminobromocyclitol derivatives‘Naked Sugars’ as Synthetic Intermediates, Part XXV. Part XXIV, see [1a]; Part XXIII, see [1b]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1-9 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (1S,2R,6R,7R)-4-Phenyl-3,10-dioxa-5-azatricyclo[5.2.1.02,6]dec-4-en-9-one ((+)-5) obtained in 6 steps from the Diels-Alder adduct of furan to 1-cyanovinyl (1S)-camphanate ((+)-3) was reduced to the corresponding endo-alcohol (-)-6 the treatment of which with HBr/AcOH provided (-)-(3aS,4S,6R,7S,7aR)-4β-bromo-3aβ,4,5,6,7,7aβ-hexahydro-2-phenyl-1,3-benzoxazole-6β,7α-diyl diacetate ((-)-17). Elimination of HBr with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and acidic hydrolysis furnished (-)-(1R,2S,3R,4R)-4-aminocyclohex-5-ene-1,2,3-triol ( = (-)-conduramine C1;(-)-1).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770103
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  • 68
    Digitale Medien
    Digitale Medien
    Nucleotides Part XLPart XXXIX: [1].. Synthesis and Characterization of Modified 2′-5′ Adenylate Trimers-Potential Antiviral Agents (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 10-22 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 2′-5′ Adenylate trimers 41-44 carrying the (tert-butyl)dimethylsilyl (tbds) group at the 3′-OH position of various sugar moieties were synthesized via the phosphoramidite method. The use of the (tert-butyloxy)carbonyl (boc) and 2-(4-nitrophenyl)ethylsulfonyl (npes) groups for 2′-OH protection in neighbourhood to the 3′-O-tbds residue was compared during the synthesis of the target trimers. For other functional positions, the use of the 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) blocking groups were favoured.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770104
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  • 69
    Digitale Medien
    Digitale Medien
    Metal complexes of macrocyclic ligands. Part XXXVIIPart XXXVI: [1].. Synthesis of Heteroditopic Bis-macrocycles and Their Potential for Preparing Heterobinuclear Metal Complexes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 23-35 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new and generally applicable synthetic path for the preparation of heteroditopic bis-macrocycles using tri-N-protected tetraazacycloalkanes as building blocks and bromoacetyl bromide as bridging reagent is described. In the first step, bromoacetyl bromide is used as acylating agent for one of the macrocycles, whereas in the second step it is used as alkylating agent for the second macrocycle, thus giving protected bis-macrocyclic amides (e.g. 6). After reduction of the amide moiety and deprotection, bis-azamacrocycles with an ethylene bridge are obtained (e.g. 8). The corresponding homoditopic bis-macrocycles 16 and 17 are also prepared for comparison purpose. Spectrophotometric studies indicate that bis-macrocycle 8, which consists of a 12- and a 14-membered ring, binds two metal ions with equal affinity, whereas compound 13, in which an unsubstituted (cyclam) and a trimethyl-substituted tetraazacyclotetradecane unit (Me3cyclam) are bridged, shows selective metal-ion binding. The first metal ion is always incorporated into the cyclam unit, whereas the second one binds to the Me3cyclam macrocycle. Thus, by sequential addition of two different metal ions, heterobinuclear complexes can easily be prepared. The electrochemistry of the binuclear Ni2+ complexes, studied by CV and DPV, as well as the EPR spectra of the binuclear Cu2+ complexes clearly indicate metal-metal interactions.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770105
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  • 70
    Digitale Medien
    Digitale Medien
    Thermoconversion of Caryophyllene- to Farnesene-Type Sesquiterpenes. Short access to the enantiomers of (6RS,7RS)- and (6RS,7SR)-6,7-epoxy-6,7-dihydro-β-farnesenes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 36-40 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Flash-vacuum thermolysis of the four diastereoisomeric 5,6-epoxy-5,6-dihydro-caryophyllenes 1-4 at 500-550°/0.1-0.7 Torr leads to the hitherto unreported enantiomers of (6RS,7RS)- and (6RS,7SR)-6,7-epoxy-6,7-dihydro-β-farnesenes ((±)-5 and (±)-6, resp.). In particular, (+)-5 is formed in 45% yield (ca. 90% ee) and is, thus, an attractive chiral building block for natural-product synthesis.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770106
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  • 71
    Digitale Medien
    Digitale Medien
    Oceanapins A-F, Unique Branched Ceramides Isolated from the Haplosclerid Sponge Oceanapia cf. tenuis of the Coral SeaDedicated to the memory of Margherita Ratti (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 51-58 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of ceramides, called oceanapins A-F (2-7), which are unique for branching at both the sphingosine and fatty-acid chains, have been isolated as pure compounds from the haplosclerid sponge Oceanapia cf. tenuis of the Coral Sea. Following acid hydrolysis, both the fatty-acid and the sphingosine portions were obtained separately, which allowed their unequivocal structural definition. The absolute configuration was secured via protection of C(1′)-OH and Mosher's esterification at C(3′)-OH of the oceanapins.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770108
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  • 72
    Digitale Medien
    Digitale Medien
    Single-Crystal Structure of the Solvent-Separated Radical Ion Pair [9,10-diphenylanthracene.⊖][Na⊕(THF)6] and its implication for cation solvationDedicated to Peter Weyerstahl on the occasion of his 60th birthdayPart 26 of ‘Structures of Charge-Perturbed or Sterically Overcrowded Molecules’; Part 25: [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 41-50 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The one-electron transfer to large π-delocalized hydrocarbons provides an interesting possibility to crystallize solvent-separated ion-pair salts containing optimally solvated cations. Accordingly, the reduction of 9,10-diphenylanthracene in aprotic THF solution at a sodium metal mirror allows to grow dark-blue prismatic crystals of its radical anion and sixfold THF-solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AM1 hypersurface calculations based on the structural data, the phenyl twist angles obviously must be determined by lattice packing, and the negative charge is delocalized predominantly within the anthracene π system. The counter cation [Na⊕(THF)6], reported ordered for the first time, shows nearly octahedral coordination within a rather densily packed solvent shell. Due to the strong repulsions between the solvent molecules, its isodesmically calculated solvation enthalpy is smaller than that of the analogous dimethoxyethane complex [Na⊕(DME)3].
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770107
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  • 73
    Digitale Medien
    Digitale Medien
    Radical Cations of Tetrazinodi(heteroarenes): An ESR and ENDOR Study (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 86-91 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 14N- and 1H-Coupling constants, determined by ESR, ENDOR, and general-TRIPLE-resonance spectroscopy, are reported for the radical cations of tetrazinodi(heteroarenes) 1-8. The results comply with the expectation that donor properties of these compounds are mainly due to the electron-rich dihydrotetrazine ring.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770111
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  • 74
    Digitale Medien
    Digitale Medien
    Antiparallel β-Sheet Conformation in Cyclopeptides Containing a Pseudo-amino Acid with a biphenyl moiety (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 70-85 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The biphenyl-containing pseudo-amino acids 2′-(aminomethyl)biphenyl-2-carboxylic acid (Abc; 1) and 2′-(aminomethyl)biphenyl-2-acetic acid (Aba; 2) are used as rigid spacers in the backbone of the cyclic peptides cyclo (-Abc-Ala-Phe-Gly-)2 (5), cyclo(-Abc-Ala-Val-Gly-)2 (6), cyclo(-Aba-Gly-Phe-Ala-)2 (7), and cyclo(-Aba-Ala-Phe-Gly-)2(8). Three different interconverting diastereoisomers are found in solutions of each of these cyclopeptides due to the atropisomerism of the biphenyl units. NMR Techniques and molecular-dynamics calculations allow to conclude that the major diastereoisomer of 5 (and 6) in (D6)DMSO adopts a β-sheet conformation. It is proposed that the pseudo-amino acid 1 of (R)-chirality forms, with attached L-amino acids, a H-bonding pattern comparable to a β-turn (see D in Fig. 4 and F).
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770110
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  • 75
    Digitale Medien
    Digitale Medien
    Vitamin-B12-katalysierte C,C-Bindungsverknüpfung: Synthese von Jasmonaten via sequentielle Radikal-Reaktion (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 92-99 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Vitamin-B12-Catalyzed C, C-Bond Formation: Synthesis of Jasmonates via Sequential Radical ReactionThe Cbl-catalyzed electroreduction of 3-(2′-bromo-1′-ethoxyethoxy)cyclopenten (1a) in presence of 1-cyanovinyl-acetate (8) gave, in a sequential radical reaction (5-exo-trig-cyclization of 1a followed by addition to 8), 1-cyano-2-(2′-ethoxy-hexahydro-2′H-cyclopenta[b] furan-4′-yl)ethyl acetate (10a). This intermediate was transformed to methyl jasmonate (7; four steps) and epituberolide (9; three steps) in 20 and 31% yield, respectively, from cyclopent-2-en-l-ol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770112
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  • 76
    Digitale Medien
    Digitale Medien
    Die Synthese von Azaisomeren des Triesters von PQQ: 3H-Pyrrolo[3,2-f]-, 1H-Pyrrolo[3,2-h]- und 7H-Pyrrolo[2,3-h]chinolinchinon-Derivate (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 111-120 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Synthesis of Azaisomers of the Triester of PQQ: 3H-Pyrrolo[3,2-f]-, 1H-Pyrrolo[3,2-h]-, and 7H-Pyrrolo[2,3-h]quinolinequinone DerivativesWe describe here the synthesis of the title compounds 3-5, starting from highly substituted aminoindoles. The annelated pyridine rings were built up in each case with dimethyl 4-oxoglutaconate according to Corey's procedure. All three o-quinone derivatives 3-5 are stable compounds, comparable to PQQ-triester. The azaisomers vary in biological activity from practically inactive to strong inhibition of the α-amidating enzyme or the ornithin decarboxylase.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770114
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  • 77
    Digitale Medien
    Digitale Medien
    A Novel Approach to 2,2-Disubstituted 1,2-Dihydro-4-phenylquinolines (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 608-614 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of 2-(1-phenylvinyl)aniline and 4-chloro-2-(1-phenylvinyl)aniline with acetophenone derivatives, 1-(naphthalen-1-yl)ethanone and 1-(furan-2-yl)ethanone in toluene at 110-115° with toluene-4-sulfonic acid as a catalyst leads in good-to-excellent yields to the 2,2-disubstituted 1,2-dihydro-4-phenyl-quinolines 1-18 (Scheme 1, Table). The structure of the new racemic 1,2-dihydroquinolines 1-18 is determined by NMR spectroscopy. A reaction mechanism proceeding via a 6π-electrocyclic rearrangement of 2-(1-phenylvinyl)anils 19 as the key step is proposed for the formation of these compounds (Scheme 1). The scope and limitations of the novel methods are discussed (Scheme 2).
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770303
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  • 78
    Digitale Medien
    Digitale Medien
    Facile Synthesis of 2′-Deoxyisoguanosine and Related 2′,3′-Dideoxyribonucleosides (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 622-630 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 2′-deoxyisoguanosine (1) was synthesized by a two-step procedure from 2′-deoxyguanosine (5). Amination of silylated 2′-deoxyguanosine yielded 2-amino-2′-deoxyadenosine (6) which was subjected to selective deamination of the 2-NH2 group resulting in compound 1. Also 2′,3′-dideoxyisoguanosine (2) was prepared employing the photo-substitution of the 2-substituent of 2-chloro-2′,3′-dideoxyadenosine (4). The latter was synthesized by Barton deoxygenation from 2-chloro-2′-deoxyadenosine (3) or via glycosylation of 2,6-dichloropurine (12) with the lactol 13. Compound 1 was less stable at the N-glycosylic bond than 2′-deoxyguanosine (5). The dideoxynucleoside 2 was deaminated by adenosine deaminase affording 2′,3′-dideoxyxanthosine (17).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770305
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  • 79
    Digitale Medien
    Digitale Medien
    Derivatives of (2R)-N-Glyoxylbornane-10,2-sultam and Their Use as auxiliaries in the diastereoselective spirocyclization of 2-substituted tryptamines7th Communication on ‘Indoles, Indolenines, and Indolines’; 6th communication: [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 615-621 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A crude hydrate 6 and a crystalline hemiacetal 7 of glyoxylamide 4 were prepared from crotonamide 5 (Scheme 2). Particularly hemiacetal 7, but also 6 and the ‘dimer’ 8 (obtained from 7) may serve as homochiral auxiliaries. The structure of 8 was determined by X-ray analysis. By arenesulfonyl halides, tryptimines 12-14 of 4 were diastereoselectively transformed into spirotricycles 15-17 and 19.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770304
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  • 80
    Digitale Medien
    Digitale Medien
    Synthesis and Conformational Analysis of 2′-Deoxy-2′-(3-methoxybenzamido)adenosine, a rational-designed inhibitor of trypanosomal glyceraldehyde phosphate dehydrogenase (GAPDH) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 631-644 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of 2′-benzamido-2′-deoxyadenosine analogues were synthesized in an effort to find new lead structures for the treatment of sleeping sickness. The 2′-deoxy-2′-(3-methoxybenzamido)adenosine (1h) was proved to be a selective inhibitor of the parasite glyceraldehyde 3-phosphate dehydrogenase which confirms the modeling studies. The solution-state conformation of 2′-(thiophene-2-carboxamido) analogue 1d demonstrates a 2′-endo conformation, an orientation of the thiophene ring under the ribose moiety, and the base part occupying a ‘syn’/‘anti’ equilibrium.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770306
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  • 81
    Digitale Medien
    Digitale Medien
    Enantioselective Formation of Bicyclic Lactones by Rhodium-Catalyzed Intramolecular CH-insertion reactions (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 645-654 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The decomposition of cyclohexyl diazoacetate (5a) in the presence of the chiral [Rh2{(2S)-mepy}4] catalyst leads to a 3:1 cis/trans mixture of bicyclic lactone 6a with an enantiomeric excess of 95-97% (cis) and 90% (trans). The conformationally rigid tert-butyl derivatives 5b and 5c afford, in the presence of the same catalyst, 6b and 6c, respectively, via insertion into the equatorial C—H bonds exclusively, with ee's of ca. 95%. A remarkable degree of induction (92-95%) results in the lactone 6g upon decomposition of 1-isopropyl-2-methylpropyl diazoacetate (5g). The diazoacetates derived from 1-methylcyclohexanol, cyclopentanol and 1-methylcyclopentanol (5d-f) afford under similar conditions insertion products with higher diastereoselectivity, but significantly lower enantioselectivity. Other dirhodium catalysts are less efficient.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770307
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  • 82
    Digitale Medien
    Digitale Medien
    A Concise Synthesis of (E)- and (Z)-Neomanoalides (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 661-667 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The first synthesis of (Z)-neomanoalide (4) and an improved synthesis of its (E)-isomer 3 was accomplished in a concise, regiocontrolled manner by exploiting 2-[(tert-butyl)dimethylsiloxy]-4{[(tert-butyl)dimethylsiloxy]-methyl}furan (6) as the key reagent. Lithiation of 6 and subsequent reaction with the (2Z)- or (2E)-isomer of (6E)-3-{[(tert-butyl)dimethylsiloxy]methyl}-7-methyl-9-(2′,6′,6′-trimethylcyclohex-1′-enyl)nona-2,6-dienyl bromide (5), followed by hydrolysis, afforded the corresponding neomanoalide.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770309
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  • 83
    Digitale Medien
    Digitale Medien
    Stable Quinone Methides: Regioselective para-Oxidation of a 2,4-bis[(alkylthio)methyl]phenol and addition reactions to quinonemethides (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 655-660 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 2,4-bis-functionalized phenol 1 is dehydrogenated regioselectivity with potassium ferricyanide, affording the corresponding p-quinonemethide 2. Hydrolysis of 2 affords a mixture of dithioacetal 5a and benzaldehyde 6; 1,6-addition of thiols to 2 gives the dithioacetals 5 of benzaldehyde 6; reaction of 2 with 2,2′-azobis(isobutyronitrile) (= 2,2′-dimethyl-2,2′-azobis(propanenitrile)) leads to 9a, 9b, and 10, addition products of the 1-cyano-1-methylethyl radical. The structures of all products are confirmed mainly by 1H- and 13C-NMR spectroscopy, and the mode of their formation is discussed.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770308
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  • 84
    Digitale Medien
    Digitale Medien
    Oligosaccharides Related to Tumor-Associate Antigens. Part 2Part 1: [1].. Conformational analysis of the trisaccharide α-L-Fucp-(1→2)-β-D-Galp-(1→3)-β-D-GalpNAc, epitope structure recognized by the MBr1 antibody (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 668-678 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational space of the trisaccharide α-L-Fuc-(1→2)-β- D-Gal-(1→3)-β -D-GalNAc-1-OPr (2) and of its component disaccharide moieties α -L-Fuc-(1→2)-β -D-Gal-1-OMe (3) and β -D-Gal-(1→3)-β- D-GalNAc-1-OPr (4) was investigated with the aid of molecular-mechanics energy minimizations and molecular-dynamics simulations. These calculations suggested the occurrence of two conformations for each compound characterized by different φ and Ψ glycosidic angles. However, 1H-NMR investigation of D2O solutions of 2-4 indicated a sure preference for one of the two conformers with a contribution of the other one ranging from negligible to low.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770310
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  • 85
    Digitale Medien
    Digitale Medien
    Synthesis of a New Bivalent Hirudin Analog (hirufos), which includes a stable 4′-phosphono-L-phenylalanine mimic of (L-tyrosine O4-sulfate)-63 (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 679-684 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis on solid phase of a new derivative of the anticoagulant protein hirudin is described (see Scheme and Fig.1, I). The henicosapeptide is a bivalent conjugate of the C-terminus of hirudin and of the active-site-binding tetrapeptide D-Phe-Pro-Arg-Pro linked via a tetraglycine spacer. The peptide, for which the name hirufos was coined, incorporates a stable phosphono derivative of L-phenylalanine which, combined with the other structural modifications, leads to a potent anticoagulant agent. Synthesis was readily achieved by the (9H-fluoren-9-yl)-methoxycarbonyl (Fmoc) strategy followed by acidolytic cleavage from the resin and deprotection, including the liberation of the crucial phosphonic group on L-phenylalanine.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770311
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  • 86
    Digitale Medien
    Digitale Medien
    Organic Reactions in the Solid State: The reactivity of guest molecules in tri-o-thymotide clathrates (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 691-708 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tri-o-thymotide (TOT) clathrates are enantiomorphous and enantioselective (chiral cages). It was shown that an external molecular reactant can diffuse into the TOT host crystal lattice and reacts with the included molecule (guest) in characteristic ways, differing from those occurring in liquid solutions. Several aspects of the action of hydrogen halides (HCl, HBr) on the chemical behavior of included oxiranes were investigated for solid-gas and solid-liquid (aqueous) systems. Under well established experimental conditions, these reactions gave regiospecifically one target product and were asymmetric. The included substrate underwent first an acid-catalyzed allylic isomerization that is cage-specific and mostly quantitative. In sheer contrast, strong basic conditions were required to promote, in reduced yield, the analogous transformation in solution. The regiospecificity and enantioselectivity of several intra-crystalline conversions allowed the accurate determination of the absolute configuration of several guest molecules. Kinetic measurements were achieved that disclosed some striking features of this new type of heterogeneous reactions. Tentative models for the cage stereoselective mechanisms are briefly discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770313
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  • 87
    Digitale Medien
    Digitale Medien
    1:1 Metal Complexes of Bivalent Cobalt, Nickel, Copper, Zink, and Cadmium with the Tripodal Ligand tris[2-(dimethylamino)ethyl]amine: Their stabilities and the X-ray crystal structure of its copper(II) complex sulfate (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 685-690 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complex formation by Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ with tris[2-(dimethylamino)ethyl]amine (N(CH2CH2NMe2)3, Me6tren) was investigated at 25° and at an ionic strength of 1, using VIS spectroscopy and potentiometric measurements. The stability constants of these complexes are compared with those of tris(2-aminoethyl)amine (N(CH2CH2NH2)3, tren), obtained under the same conditions. The values of the constants for Me6tren are much lower than those for tren, due to the bulky Me substituents. The values of the constants can be correlated with the ability of the individual metal ions to adopt coordination number 5. This appears to be easier for Cu2+ and Co2+ than for Cd2+ and Zn2+ and is very difficult for Ni2+. The 1:1 complexes [ML(H2O)]2+ are monoprotonic acids whose pKs values are similar or lower than those of the corresponding aquametal ions. The X-ray crystal structure of the copper(II) complex [Cu(SO4)(Me6tren)] · 8H2O reveals pentacoordination at the central ion. The UV/VIS spectra of the aqueous solutions of the Co2+, Ni2+, and Cu2+ 1:1 complexes confirm that the same coordination number is present also in these complexes.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770312
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  • 88
    Digitale Medien
    Digitale Medien
    The Revised Structure of the Norditerpenoid Alkaloid Peregrine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1768-1772 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structure of peregrine (1), a norditerpenoid alkaloid isolated from Delphinium peregrinum var. elongatum BOISS., was revised on the basis of the 1H-COSY, HMQC, HMBC, and ROESY NMR spectra and of the X-ray analysis of its parent alcohol 2. Some of the 13C-NMR resonances of 1 and the related alkaloids peregrine alcohol (2), 14-O-acetylperegrine (3), bicoloridine (4), bicoloridine alcohol (5), 6-O-acetylbicolorine (6), bicolorine (7), and 14-O-acetylbicolorine (8), were also reassigned.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770708
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  • 89
    Digitale Medien
    Digitale Medien
    Nucleotides. Part XLIVPart XLIII: [1].. Synthesis, characterization, and biological activity of monomeric and trimeric cordycepin-cholesterol conjugates and inhibition of HIV-1 replication (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1757-1767 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The antivirally active 3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenosine (cordycepin trimer core) was modified at the 2′- or 5′-terminus, by attachment of cholesterol via a carbonate bond (→ 15) or a succinate linker (→ 16 and 27) to improve cell permeability. The corresponding monomeric conjugates 4, 7, and 21 of cordycepin were prepared as model substances to study the applicability of the anticipated protecting groups - the monomethoxytrityl (MeOTr), the (tert-butyl)dimethylsilyl (tbds), and the β -eliminating 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) groups - for the final deblocking steps without harming the ester bonds of the conjugate trimers. The syntheses were performed in solution using phosphoramidite chemistry. The fully protected trimer conjugates 13, 14, and 26 as well as all intermediates were characterized by elemental analyses, UV and 1H-NMR spectra. The deblocked conjugates 15, 16, and 27 were pure according to HPLC and showed the correct compositions by mass spectra. Comparative biological studies indicated that cordycepincholesterol conjugate trimers 16 and 27 were 333- and 1000-fold, respectively, more potent inhibitors of HIV-1-induced syncytia formation than cordycepin trimer core.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770707
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  • 90
    Digitale Medien
    Digitale Medien
    Metal-Ion-Coordinating Properties of a Viral Inhibitor, a pyrophosphate analogue, and a herbicide metabolite, a glycinate analogue: The solution properties of the potentially five-membered chelates derived from phosphonoformic acid and (aminomethyl)phosphonic acid (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1738-1756 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The pyrophosphoric-acid-analogue phosphonoformic acid (pfa) and the amino-acid-analogue (aminomethyl)phosphonic acid (ampa) both form, in the deprotonated state, i.e., as -OOC-PO32- and H2N—CH2—PO32-, respectively, five-membered chelate rings with metal ions. pfa inhibits both phosphate transport and virus replication, while ampa is a metabolic product of the common herbicide glyphosate ( = N-(phosphonomethyl)glycine). The acidity constants of H2pfa- and H2ampa± as well as the stability constants of the [M(Hpfa)], [M(pfa)]-, [M(Hampa)]+, and [M(ampa)] complexes, where M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Cu(2,2′-bipyridyl)2+, Cu(1,10-phenanthroline)2+, Zn2+, or Cd2+, have been determined by potentiometric pH titrations in aqueous solution at 25° and I = 0.1M (NaNO3). The structures of isomeric complexes and the connected intramolecular equilibria are deduced and evaluated based on the equilibrium constants measured and those calculated via the pKa values of the above mentioned ligands and previously established log K vs. pKa straight-line plots (H. Sigel et al., Helv. Chim. Acta 1992, 75, 2634) for a simple phosphonate-M2+ coordination. pfa forms stronger complexes than ampa with all the above mentioned metal ions, with the single exception of [Cu(ampa)] which is slightly more stable than [Cu(pfa)]-. In neutral solutions, more precisely at pH of ca. 6, pfa complexes of alkaline-earth-metal ions retain one phosphonate-bound proton, [M(Hpfa)], while those of the transition-metal ions chelate with the trianionic ligand, pfa3-. In accord with increasing ligand-basicity, the stability-constant order for all metal-ion complexes is oxalate 〉 pfa 〉 pyrophosphate but, owing to proton competition in pyrophosphate, in neutral solutions metal-ion complexation of pfa3- competes with P2O74-. With ampa alkaline-earth-metal ions interact only with the phosphonate group of even the dianionic ligand (though Mg2+ appears to form a low fraction of a [Mg(ampa)] chelate) while transition-metal ions form chelates which are comparable in stability to those of glycinate.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770706
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  • 91
    Digitale Medien
    Digitale Medien
    X-Ray Crystal Structure of the 2-Phenyladamant-2-yl Cation (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1773-1780 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structure of the Sb2F11 salt of the 2-phenyladamant-2-yl cation, 1 · Sb2F11, was determined at 183 K (P21/c, R1 = 0.0652, σ(C—C) = 0.02 Å), because earlier published results indicated a charge delocalization from the cationic C(2) into the σ framework (C—C hyperconjugation) and a bending of the C(2) bridge. In the structure of 1, a displacement of the C(2) bridge by 7.8(12)° from the symmetrical position and C—C bond-length deviations from expectation values were found which are in agreement with preferential C—C hyperconjugation on one face of C(2). The interactions of 1 with two Sb2F11 counterions nearest to C(2) also indicate different behaviour of the two faces of C(2). The benzylic resonance in 1 is confirmed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770709
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  • 92
    Digitale Medien
    Digitale Medien
    Facile Preparation of (±)-12-Epiprostaglandins from 7-Oxabicyclo[2.2.1]hept-5-en-2-one via an all-cis-formyllactone related to Corey lactoneA preliminary communication of one part of this work was published [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1781-1790 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The bicyclic monoselenoacetal 7, easily obtained from (±)-7-oxabicyclo[2.2.1]hept-5-en-2-one (6) via a radical addition-acyl migration sequence, was converted to racemic 12-epiprostaglandins 3 and 4. The key intermediate was the all-cis-formyllactone 2b related to Corey lactone (see 12; Scheme 1). The presence of a (tert-butyl)-dimethylsilyl protective group for the 11-OH substituent (prostaglandin numbering) was found to be crucial in avoidingβ -elimination and epimerization during the Wittig-Horner reaction (Scheme 2). Epimerization at C(12) at the formyllactone stage (see 2b) was also possible and gave the known precursor 1b of naturally occurring prostaglandins and analogs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770710
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  • 93
    Digitale Medien
    Digitale Medien
    Stability of Charge-Transfer Complexes of CS2 with PH3 and its derivatives: Ab initio MRSDCI/CASSCF StudyDedicated to Prof. Jan Linderberg, an excellent theoretician and marvelous friend, on the occasion of his 60th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1810-1816 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: While trialkylamines and dialkyl(phenyl)amines do not react with CS2 in the sense of an addition reaction, the analogous phosphines react smoothly. Attempts to interpret the reaction course on the basis of semiempirical, HF, MP2, and MP4 calculations of energy changes failed completely. To understand why Me3P or Me2PhP react so vigorously (liquid phase, 300 K) with CS2, CASSCF and MRSDCI calculations must be carried out.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770712
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  • 94
    Digitale Medien
    Digitale Medien
    Synthesis and Complexation Properties of a New Class of Receptors based on a cone-configurated tetra-p-(tert-butyl)calix[4]arene and bipyridyl subunits (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1817-1825 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 0The bipyridyl-armed tetra-p-(tert-butyl)calix[4]arenes 1-5 were synthesized from tetra-p-(tert-butyl)-calix[4]arene A and 6-(bromomethyl)-6′-methyl-2,2′-bipyridine (B) by direct base-strength-driven regioselective O-alkylation or by stepwise procedures. Preliminary complexation studies of the ligands 1-3 with CuI affording the complexes 6-8 are described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770713
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  • 95
    Digitale Medien
    Digitale Medien
    A Kinetic Analysis of the Reaction Catalysed by (Hydroxymethyl)bilane SynthaseAbbreviations used: FPLC, fast-protein liquid chromatography; HMBS, (hydroxymethyl)bilane synthase; MAD, multiwavelength anomalous diffraction: PBG, porphobilinogen: SeMet, selenomethionine. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1791-1809 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (Hydroxymethyl)bilane synthase (HMBS) catalyses the conversion of porphobilinogen (2) into the (hydroxymethyl)bilane derivative 3, a linear tetrapyrrolic intermediate in the biosynthesis of haem, chlorophyll, and related pigments. The conversion involves the sequential formation of four intermediate covalent enzyme-substrate complexes, before the product is released. We analysed the pre-steady-state kinetics of the formation of the complexes, taking advantage of their remarkable chemical stability allowing chromatographic separation. The experimental approach involved the generation of the complexes while HMBS was immobilised on an anion-exchange column. A solution being 0.2 Km in substrate was pumped through the column during a time interval which was varied to sample the pre-steady-state period. Then, the enzyme and enzyme-substrate complexes were eluted and their proportions evaluated. A computer simulation of the pre-steady-state time course, in combination with a χ2 fitting to the experimental data, allowed the specificity constants kcat/Km for the individual steps of the process to be derived. By repeating the analysis with variants of HMBS in which specific amino acids were replaced by others, we demonstrated that it is possible to trace the consequences of amino-acid replacements down to the individual steps of the reaction sequence. Since the positions of the amino acids concerned in the three-dimensional structure were known, detailed structure-function relationships become evident in this way.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770711
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  • 96
    Digitale Medien
    Digitale Medien
    Preparation and Structure of Oligolides from (R)-3-Hydroxypentanoic Acid and comparison with the hydroxybutanoic-acid derivatives: A small change with large consequencesPart of the projected Ph.D. theses of T.H., F.N.M.K., and U.D.L., ETH-Zürich. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2007-2034 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cyclic oligomers of (R)-3-hydroxyvaleric acid (3-HV) are prepared from the monomer by three different methods, giving various ratios of the oligomers. The macrocycles containing three to twelve 3-HV units (12- to 48-membered rings) are isolated in pure form by chromatography. The triolide 3 can be separated by distillation and isolated on large scale. Biopol, the copolymer of (R)-3-hydroxybutanoic acid (3-HB) and (R)-3-hydroxyvaleric acid (3-HV), is degraded to mixtures of Me- and Et-substituted triolides (‘mixolides’) with high crystallization tendency. The X-ray crystal structures of the tetrolide 4, pentolide 5, hexolide 6, heptolide 7, and of two ‘mixolides’ (with inclusions of solvent) have been determined (Figs. 3-7, 10, and 11) and are compared with those of the corresponding 3-HB derivatives reported previously. From the structural data, a 31 and a 21 helix of 3-HV can be modelled, and the latter one compared with helix structures of P9(3-HB) and P(3-HV) derived from stretch-fibre X-ray scattering. Crystals of a water-containing NaSCN complex of the triethyl triolide 3 were obtained in good quality for X-ray analysis. The structure (Figs. 12, 13, and Table 6) contains an interesting array of C=O and H2O O-atoms around the Na+ ions along a channel-type tube (a-axis of the crystal) which may be relevant to the role of P(3-HB) and P(3-HV) as components of cellular ion channels.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770727
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  • 97
    Digitale Medien
    Digitale Medien
    Synthesis of Tri-, Penta-, and Heptapeptides Containing and (R)-2-alkyl-2-amino-3-(methylamino)-propionic acid residue in the central positionThis project was supported by the Swiss National Science Foundation, project No. 20-30770.91 (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2035-2050 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: By conventional peptide-coupling methods (C to N direction; mixed anhydride, bis(2)-oxooxazolidin-3-yl)phosphinoyl chloride (Bop-Cl), or dicyclohexylcarbodiimide (DCC), 2-amino-2-methyl-3-(methylamino)-propionic acid and 2-amino-2-ethyl-3-(methylamino)propionic acid ( = 2-amino-2-[(methylamino)methyl]butanoic acid) are incorporated in the central position of tri-, penta-, and heptapeptides (see 3-7, 21, and 22). The fragment coupling of the β -amino group of the diamino-acid moiety in a tetrapeptide led to partial epimerization, and thus, two epimeric heptapeptide derivatives were actually obtained (7 and epi-7). The final deprotection to the free heptapeptide (involving a Me3SiI cleavage of BocNH and MeOCONH, a saponification with NaOH, and HPLC purification) gave both the desired product (isopeptide 21), with the β -amino group inside the peptide backbone, and a product (peptide 22) of transpeptidation, with the α-amino group of the diamino acid incorporated and a (methylamino)methyl group as the side chain. Peptide 22 is completely converted to the isopeptide 21 by prolonged treatment with base. The heptapeptide 21 was analyzed by elaborate 2QF-COSY and NOESY NMR measurements in H2O/CD3OD at -5° (Table, Fig.); there is no indication for β -sheet or helical structures, a fact which was also confirmed by CD measurements.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770728
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  • 98
    Digitale Medien
    Digitale Medien
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770801
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  • 99
    Digitale Medien
    Digitale Medien
    Mitteilungen - Communications (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2070-2070 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770731
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  • 100
    Digitale Medien
    Digitale Medien
    Preparation and Transmetallation of a Triphenylstannyl β-D-Glucopyranoside: A highly stereoselective route to β-D-C-glycosides via glycosyl dianions (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2060-2069 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The triphenylstannyl β-D-glucopyranoside 4 was synthesized in one step from the 1,2-anhydro-α-D-glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD3OD gave (1S)-1,5-anhydro-3,4,6-tri-O-benzyl-[1-2H]-D- glucitol (8) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β-D-configurated products 11, 12, and 13 in good yields. Preparation of C-acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14. Treatment of 7 with MeI led to 15 (30%) along with 40% of 18, C-alkylation being accompanied by halogen-metal exchange. Prior addition of lithium 2-thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15. No α-D-anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19940770730
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