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  • General Chemistry  (12,278)
  • Cell & Developmental Biology  (5,633)
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  • 1
    ISSN: 1434-193X
    Keywords: Nitrosobenzenes ; ortho-Nitrosoanilines ; 2-Nitroso-1,3-phenylenediamines ; Nucleophilic aromatic substitution ; Oxidative nucleophilic substitution of hydrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of primary amines bearing tertiary alkyl groups (e.g. R-NH2; R = tBu, 1-adamantyl) with nitrosobenzenes has been found to proceed by oxidative nucleophilic aromatic substitution of hydrogen, thereby affording N-(tert-alkyl)-ortho- and -para-nitrosoanilines. The replacement of hydrogen proceeds more rapidly than the replacement of ortho- or para-nitro or -bromo substituents. With p-nitronitrosobenzene, both ortho-hydrogen atoms are substituted to afford N,N′-di(tert-alkyl)-4-nitro-2-nitroso-1,3-phenylenediamines 8a,b. The addition of oxidizing agents (e.g. MnO2) increases the yield of products. 1H-, 13C-, 14N- and 15N-NMR studies have confirmed the structures of the compounds under investigation. In ortho-nitrosoanilines, the rotamer with the nitroso group syn to the amino group is favored.
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  • 2
    ISSN: 1434-193X
    Keywords: Nucleophilic addition ; Solvent effect ; Reversal of diastereoselectivity ; Temperature effect ; Imines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Commonly observed, but rarely explored, is the possibility of modifying the diastereomeric excess (de%) by means of temperature. A complete reversal in the diastereofacial selectivity could be obtained whenever the diastereoisomers concerned are differentially favored by enthalpy and entropy. The enthalpic or entropic dominance of a diastereoisomer depends greatly on the reaction solvent used.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 91-96 
    ISSN: 1434-193X
    Keywords: Alkenes ; Electrophilic additions ; β-Sultones ; sec-Alkyl chlorosulfate ; 2-Chloro-1-alkanesulfonic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -An exploratory study has been made on the reaction of a number of non-branched alkenes in [D]chloroform as an aprotic solvent, using chlorosulfuric acid as reagent both in the presence and the absence of [D8]1,4-dioxane as complexing agent. Reaction of cyclopentene (1a) with 1.1 mol-equiv. of chlorosulfuric acid in [D]chloroform in the presence of 2.2 mol-equiv. of [D8]1,4-dioxane at 0 °C yielded quantitatively 1,2-cyclopentanesultone (2a). Under similar reaction conditions, the linear alkenes 1b-g afforded the corresponding β-sultones 2b-g. The ClSO3H-dioxane complex acted as a sulfonating reagent with the alkenes to yield the corresponding β-sultones in a syn cycloaddition of SO3 to the Carbon-Carbon double bond. In the absence of [D8]1,4-dioxane the reaction of the linear alkenes 1a-1k in [D]chloroform with chlorosulfuric acid at -40 °C led to the formation of the sec-alkyl chlorosulfates 5a-i, which were formed after initial protonation of the alkene by the strongly acidic ClSO3H. Cyclopentyl chlorosulfate (5a) in [D]chloroform at 0 °C was quantitatively converted into 1,2-cyclopentanesultone (2a). The sec-alkyl chlorosulfates 5b-i at 0 °C gave rise to a mixture of the internal trans- and cis-β-sultones 2b-m. Reaction of 1-octene (1g) with both acetyl sulfate (6a) and trifluoroacetyl sulfate (6b) as reagent in [D]chloroform at -20 °C directly afforded the products 1,2-octanesultone (2g), and the (E) and (Z) isomer of 2-octene-1-sulfonic acid (4g).
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  • 4
    ISSN: 1434-193X
    Keywords: Fluorine ; Pheromones ; Sulfoxides ; Sulcatol ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The pheromone (R)-(-)-sulcatol (10a) and three of its enantiomeric mono-, di-, and trifluoro analogues 10b-d have been synthesized, in six steps and with good overall yields, starting from chiral (R)-2-methyl-5-[(4-methylphenyl)sulfinyl]pent-2-ene (1) and commercially available fluorinated or non-fluorinated acetates.Supporting information for this article is available on the WWW under http://www.wileY-Vch.de/contents/jc_2046/1999/98375_s.pdf or from the author.
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  • 5
    ISSN: 1434-193X
    Keywords: Alkylation ; Oxazolines ; anti-α-Alkyl α-hydroxy β-amino acids ; Lithium dianion ; Penicillin G acylase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -As part of an ongoing project concerning the synthesis of enantiomerically pure α-hydroxy β-amino acids, we have now developed a general strategy allowing the synthesis of anti-α-alkyl α-hydroxy β-amino acids. Our procedure involves the intermediate formation of trans-oxazolines, which are alkylated at C-5 with good to high diastereoselectivity and then hydrolysed under mildly acidic conditions, affording in quantitative yield the corresponding hydroxy amides. The starting (R)-3-amino-3-phenylpropanoic acid and (S)-3-aminobutanoic acid were obtained in enantiomerically pure form by selective enzymatic hydrolysis of the corresponding phenylacetylamides with penicillin G acylase.
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  • 6
    ISSN: 1434-193X
    Keywords: 1,3-Indandione ; Ninhydrin ; Chromium complexes ; Acetals ; Oxidation ; Hetero Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The syntheses and characterization of the tricarbonylchromium complexes of 1,3-indandione and ninhydrin are described. As the direct complexation proved unsuccessful, the acetal route was tried. Although some complexes were obtained, complex deacetalization did not work in the case of ninhydrin. Finally, the oxidation of tricarbonyl(η6-1,3-indandione)chromium(0) with dimethyldioxirane gave the ninhydrin complex in 75% yield in equilibrium with the indantrione complex. The latter reacts in hetero Diels-Alder reactions with dienes with diastereoselective formation of spiro anellated pyran derivatives.
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  • 7
    ISSN: 1434-193X
    Keywords: Fluorinated dideoxynucleosides ; Through-space interactions ; Hydrogen bonds ; Long-range coupling constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A collection of 5′-O-benzyl-2′,3′-dideoxy-4′-(fluoromethyl)nucleosides carrying both purinic and pyrimidinic nucleobases (uracil, 5-Br-uracil, 5-O2N-uracil, 6-Cl-purine and inosine) were synthesized in both the α and the β form. Through-space-transmitted 6JCF NMR coupling constants between F and C-6 (pyrimidinic base) or C-8 (purinic base) were observed for all of the α anomers of the compounds examined, whilst the corresponding 7JHF coupling constants were resolved only for the 5-substituted uracil derivatives. The absolute values of all the through-space couplings were found to decrease monotonically with increasing solvent polarity (CDCl3, MeOD, [D6]acetone, [D6]DMSO). This trend suggests that the through-space interaction is mediated by an intramolecular (sp3)C-F…H-C(sp2) hydrogen bond. The possibility of any relevant solvent-induced conformational change influencing the F/base mutual spatial relationship in the molecules investigated was ruled out by heteronuclear steady-state 1H{19F}-NOE experiments. A linear correlation was observed between 6JCF and 7JHF coupling constants and the Kamlet-Taft's hydrogen bond basicity parameter β. The crystal structures of the α and β anomers of the 5-nitrouracil nucleoside show evidence that the H-6 of the nucleobase forms hydrogen-bond-like interactions involving the O-benzyl oxygen atom in the β anomer, and that in the case of the α anomer this is replaced by the F atom of the fluoromethyl group.
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  • 8
    ISSN: 1434-193X
    Keywords: Diterpene ; Dolabellane ; Sigmosceptrella quadrilobata ; Sponge ; Antitumor agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new diterpene with the dolabellane skeleton 1 has been isolated from the sponge of the Indian Ocean, Sigmosceptrellaquadrilobata. Its structure elucidation, including absolute stereochemistry, was performed with the aid of MS, NMR, and CD data and by molecular modeling. Compound 1 is moderately cytotoxic against four tumor cell lines.
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  • 9
    ISSN: 1434-193X
    Keywords: Cyclopropanes ; Rearrangements ; Cyanohydrins ; Schiff bases ; Small ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The direct cyclization of 2-amino-4-chloro-3,3-dimethylbutanenitrile with potassium tert-butoxide in THF afforded 1-amino-2,2-dimethylcyclopropane-1-carbonitrile and a dimerization product. Various new cis- and trans-1-(tert-butylamino)-2-benzyl-2-methylcyclopropane-carbonitriles and© the corresponding cyclopropanecarboxamides have been synthesized, with focus on the isolation of the pure stereoisomeric cyclopropanecarboxamides. The relative configuration of the stereoisomers was established by X-ray crystallographic analysis of one of the model compounds. A new route to the latter functionalized cyclopropanes was developed by reaction of 1-methoxycyclopropylamines with potassium cyanide. Some remarkable rearrangements of 1-aminocyclopropane-1-carbonitriles into azetidine and oxazine derivatives via Favorskii-derived intermediates are reported. Various aspects of the chemistry of geminally functionalized cyclopropanes are discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 129-134 
    ISSN: 1434-193X
    Keywords: Tetrahydro-2-vinylquinoxaline ; Cyclization ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Reaction of (Z)-1,2-bis(methoxycarbonyloxy)but-2-ene (2) with various N,N-bis(arylsulfonyl)-o-phenylenediamines 1 was catalyzed by a palladium complex associated with chiral ligands to give optically active 1,4-bis(arylsulfonyl)-1,2,3,4-tetrahydro-2-vinylquinoxalines 3 with up to 62% ee. The use of (S)-MeOBIPHEP as the chiral ligand and N,N-bis(p-tolylsulfonyl)-o-phenylenediamine (1i) as the nucleophile led to the highest ee at 25 °C, regardless of the solvent used. The enantioselectivity of the cyclization is strongly affected by the nature of the substituents at the nitrogen atom.
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  • 11
    ISSN: 1434-193X
    Keywords: Nitrosobenzene ; 4-Methoxy-N-methyleneaniline ; 1,3,5-Tris(4-methoxyphenyl)-1,3,5-triazinane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A 1:1 adduct produced in the reaction of nitrosobenzene (2) with 1,3,5-tris(4-methoxyphenyl)-1,3,5-triazinane (3) has been shown by X-ray diffraction structure analysis to be the N′-(4-methoxyphenyl)-N-phenyl-N-oxyformamidinium species 5.
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  • 12
    ISSN: 1434-193X
    Keywords: Morphine alkaloids ; 6,14-Ethenomorphinans ; Chromium(II) complex reagents ; Organochromium(III) complex intermediates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A synthetic method for the selective transformations of a selected morphine alkaloid in neutral aqueous medium is introduced. Full diastereoselectivity was achieved by the transformation of nepenthone (1) with [Cr(ida)(H2O)3] into 2a (20R) showing a complementary method as compared to the reactions with classical reagents to result in 2b (20S). A new unexpected morphine derivative 3 was prepared by a ligand-induced modification of the reaction which involves an unprecedented rearrangement.
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  • 13
    ISSN: 1434-193X
    Keywords: Palladium catalysis ; Homogeneous catalysis ; Anilines ; Alkylation ; Oxazolidinones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Palladium-catalyzed reaction of acidic anilines with (Z)-2-butene-1,4-diyl dicarbonate affords N-aryl-4-vinyloxazolidin-2-ones. The success of the reaction depends on the acidity of the aniline and requires in situ conversion of the dicarbonate into carbamate carbonate by nucleophilic attack of the aniline conjugate base followed by palladium-catalyzed intramolecular cyclization.
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  • 14
    ISSN: 1434-193X
    Keywords: Density functional calculations ; Vinylcyclopropane-cyclopentene rearrangement ; [1,3]-Sigmatropic shift ; Biradical-like transition structure ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane-cyclopentene rearrangement was calculated by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the two radical substructures. Thus, the transition structures may be considered, in good approximation, as structures consisting of two weakly interacting radicals.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98349_s.pdf or from the author.
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  • 15
    ISSN: 1434-193X
    Keywords: O-Alkylation ; Ambident nucleophile ; Thiazolethione ; Thiohydroxamic acid ; Phase-transfer reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -O-Alkylation of cyclic thiohydroxamic acids 1 and 3-5 has been studied with a view to developing an efficient method for the synthesis of N-(alkoxy)pyridine-2(1H)-thiones and N-(alkoxy)thiazole-2(3H)-thiones. Four issues have been addressed and the following conclusions can be drawn: (i) Thiones 1 and 5 exist as O-H acids in the solid state. (ii) According to NMR investigations (1H, 13C), the thione structures should be largely retained in CDCl3, [D6]DMSO, and CD3OD solutions of acids 1, 3-5, as is also the case for pyridinethione salts 2a-h. (iii) O-Alkylation of pyridinethione salts occurs in competition with S-alkylation. Selective O-alkylation is however possible, if thiohydroxamate salts with large countercations, such as M = NBu4, are treated with hard alkylating reagents in polar aprotic media. (iv) As tetrabutylammonium thiohydroxamates, such as 2f, are highly useful in the synthesis of cyclic thiohydroxamic acid O-esters, we have developed an efficient protocol for the preparation of N-(alkoxy)pyridine-2(1H)-thiones directly from acid 1 using phase-transfer conditions (alkyl halide or sulfonic acid ester, CH3CN, K2CO3, Bu4NHSO4). This method has proved particularly successful for the synthesis of N-(alkoxy)thiazole-2(3H)-thiones 11, 20-28, which were obtained in yields of up to 87%.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1-13 
    ISSN: 1434-193X
    Keywords: Dynemicin ; Enediynes ; Antitumor agents ; Antibiotics ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Dynemicin A is a member of the family of enediyne natural products. It is unique in that it combines a ten-membered enediyne with an anthraquinone substructure. These features stimulated the development of synthetic approaches to the natural product itself and of analogs thereof. This review summarizes the total syntheses of dynemicin A. In addition, an overview of the known analogs is presented. The analogs can be classified according to the designed trigger mechanism. Most of the analogs contain a removable carbamate on the nitrogen atom. Others are quite similar to the natural lead in that they contain a quinone substructure, which upon reduction causes opening of the oxirane ring. In addition, there are analogs that contain an aromatic sector, the enediyne, and the oxirane ring but lack the nitrogen heterocycle. In these compounds the aryl ring assumes a different conformation from that in dynemicin A. Many of the simplified analogs proved to be quite active in vitro as well in vivo against murine tumor models. A highlight is compound 30 which is much more active than dynemicin A itself. However, looking at all analogs there is no clear-cut correlation between the DNA-cleaving ability at neutral pH and the in vitro results. From this one might conclude that there are possibly two mechanisms for antitumor activity. One involves diradical formation whereas the other might be due to a ligand-receptor interaction.
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  • 17
    ISSN: 1434-193X
    Keywords: Enantiomerically pure (2-bromophenyl)acetaldehyde acetals ; Halogen-metal exchange ; Diastereoselective addition to imines ; Asymmetric synthesis ; Tetrahydroisoquinolines ; NMDA antagonists ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A novel asymmetric synthesis of 1-aryl-1,2,3,4-tetrahydroisoquinolines has been developed. The key step in this synthesis is the diastereoselective addition of homochiral (2-lithiophenyl)acetaldehyde acetals to the sulfonylimine 25 and to the arylimines 28 and 31. The best diastereoselectivity is obtained by addition of the bis(2-methoxypropan-2-yl)-substituted 1,3-dioxolane 6e to benzylidene-p-anisidine (31) with an HPLC-determined diastereomeric ratio 32c/33c = 92.1:7.9. The N-tosyl and the N-(4-methoxyphenyl) groups of the addition products 26d, 27d, 32c, and 33c are cleaved with sodium in liquid ammonia and ammonium cerium(IV) nitrate, respectively, to yield the primary amines 35 and 36. The acid-catalysed cyclization of the sulfonamides 26d and 27d and the carbamates 37 and 38, prepared from 35 and 36, leads to the enantiomerically pure dihydroisoquinolines 40 and 41, respectively. During the cyclization of the sulfonamides 26d, 27d and the carbamates 37, 38 the chiral auxiliary - the diol 39 - is cleaved unchanged and can be recovered in good yields.
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  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 527-538 
    ISSN: 1434-193X
    Keywords: Tris(pentafluorophenyl)borane ; Diarylborinic acid ; Arylboronic acid ; Chiral arylboron catalyst ; Lewis acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Arylboron compounds, ArnB(OH)3-n (n = 1-3), bearing electron-withdrawing aromatic groups such as triarylboranes, diarylborinic acids, and arylboronic acids represent a new class of air-stable and water-tolerant Lewis acid or Brønsted acid catalysts in organic synthesis. In particular, while tris(pentafluorophenyl)borane has primarily been used as a co-catalyst in metallocene-mediated olefin polymerization, its potential as a Lewis acid catalyst for organic transformation is now much more extensive. Diarylborinic acids and arylboronic acids have shown themselves to be powerful tools in the design of chiral boron catalysts. This article provides a comprehensive summary of the organic transformations catalyzed by arylboron compounds as acids.
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  • 19
    ISSN: 1434-193X
    Keywords: Structure elucidation ; Constitutional analysis ; Natural products ; HMBC ; Computational chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The computer program COCON is introduced as a tool for the comprehensive structure elucidation of unknown organic compounds. In particular, structural proposals made on the basis of the molecular formula and of 2D-NMR experiments can be analyzed for the existence of alternative constitutions being in agreement with the same data set. The computational speed grounds on the evaluation of ambiguous long-range connectivity information during the process of structure generation. The data set experimentally obtained for the marine natural product oroidin (1) was selected, because proton-poor compounds usually cause uncertainties in NMR-based structure determinations. The calculation results encourage to move from the experience-based analysis of NMR chemical shifts or of MS fragmentations to the automated evaluation of routinely available connectivity information.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98241_s.pdf or from the author.
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  • 20
    ISSN: 1434-193X
    Keywords: Structure elucidation ; Computational method ; Natural products ; HMBC ; Constitutional analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the new computer program COCON (Constitutions from Connectivities) to the 2D-NMR data sets of three different complex natural products is described. The investigated compounds are proton-poor and therefore underdetermined systems. For such molecules the number of possible constitutions and the computational speed of COCON are of interest. Our investigation is focused on how methods of 13C-NMR chemical shift prediction can assist chemists with regard to refining the selection among the constitutions proposed by COCON.
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  • 21
    ISSN: 1434-193X
    Keywords: S Heterocycles ; Cyclic oligosulfides ; Pentathiepanes ; Conformational analysis ; Sulfuration ; Ring inversion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Acenaphtho[1,2-a]acenaphthylene (1) was sulfurated with elemental sulfur to give a pentathiepane derivative (2). A dynamic NMR spectrum analysis revealed that the two naphthalene rings of 2 are chemically nonequivalent up to 100 °C. The pentathiepane ring of 2 was shown to adopt a chair conformation both in solution and crystals. In accordance with the NMR spectrum analysis, the sulfuration of 5-phenylacenaphtho[1,2-a]acenaphthylene (12) gave a pair of conformers (16a and 16b), which were isolated in pure form. The Friedel-Crafts acetylation of 2, followed by dithioacetalization with 1,2-ethanedithiol, also gave a pair of isolable conformers (18a and 18b). These two pairs of conformers isomerized, as a result of the ring inversion, to each other in solution at room temperature in the first-order kinetics. The activation parameters for this process, Ea, ΔH#, and ΔS#, were determined. Based on the experimental observations, a probable mechanism for the inversion process is proposed.
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  • 22
    ISSN: 1434-193X
    Keywords: 1β-Methylcarbapenems ; Palladium ; Ruthenium ; Catalysis ; Cyclizations ; Stereoselective hydrogenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -An efficient diastereoselective multi-step synthesis of bicyclic 1β-methylcarbapenem antibiotic precursors has been developed, starting from the commercially available 4-acetoxyazetidin-2-one 4. Chiral ruthenium catalysts are used in the hydrogenation step to control the β-stereochemistry at the 1-position, and a π-allylpalladium ring-closure strategy is used to form the functionalized carbapenem skeleton.
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  • 23
    ISSN: 1434-193X
    Keywords: Surfactants ; H aggregates ; Ion pairs ; Copper(II) binding ; Copper ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A novel, single-chained ammonium amphiphile that carries an o-hydroxyazobenzene unit at the terminus of its hydrophobic chain has been synthesized. This compound forms ordered thread-like aggregates upon dispersion in water. These aggregates exhibit a phase transition at 56 °C. The o-hydroxyazobenzene unit binds several transition-metal ions in a 2:1 stoichiometry. Binding of these metal ions results in a lowering of the critical aggregation concentration. From the changes in the UV absorption spectrum it is concluded that the Cu2+ complex forms more tightly packed aggregates in water than the Zn2+ and Ni2+ complexes.
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  • 24
    ISSN: 1434-193X
    Keywords: Hydroaminomethylation ; Rhodium ; Catalysis ; Carbonylation ; Heterofunctionalised allylic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Heterofunctionalised allylic ethers 1, silanes 5, and amines 9 are hydroformylated in the presence of primary or secondary amines 2 to form the corresponding γ-amino- and δ-amino-functionalised compounds. The rhodium(I)-catalysed reaction sequence proceeds by aldehyde formation and subsequent reductive amination to generate the corresponding functionalised secondary or tertiary amines. This selective one-pot hydroaminomethylation procedure establishes access to γ-amino- and δ-amino-functionalised ethers, amines or silanes with potential biological activity.
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  • 25
    ISSN: 1434-193X
    Keywords: Aziridines ; N-Heterocycles ; Fatty acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first successful preparation of the aziridines methyl cis-9,10;cis-12,13-diepiminooctadecanoate (3) derived from linoleic acid, and methyl cis-9,10;cis-12,13;cis-15,16-triepiminooctadecanoate (6) derived from linolenic acid, is reported. Remarkably, the bis- and trisaziridine were obtained in a reaction sequence that consists of only two steps, using technically pure methyl esters of epoxidized sunflower and linseed oil. The conversion of methyl 9,10;12,13-diepoxyoctadecanoate (1), with sodium azide and ammonium chloride in ethanol in the presence of water, yielded the new diazidodihydroxy compound methyl 9(10),12(13)-diazido-10(9),13(12)-dihydroxyoctadecanoate (2) in the first step. 2 was obtained as a regioisomeric mixture. The reaction of 2 with triphenylphosphane led to the bisaziridine 3. The analogous conversion of methyl 9,10;12,13;15,16-triepoxyoctadecanoate (4), via the new triazidotrihydroxy compound methyl 9(10),12(13),15(16)-triazido-10(9),13(12),16(15)-trihydroxyoctadecanoate (5), afforded trisaziridine 6.
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  • 26
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 679-683 
    ISSN: 1434-193X
    Keywords: Biomimetic oxidations ; Cytochrome P450 ; Metalloporphyrins ; Denaverine ; Metabolism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The behavior of denaverine (1) in various chemical model systems based on metalloporphyrins as catalysts was investigated to determine the possible oxidative metabolism. The resulting derivatives were compared to a biological model system and in vivo metabolism in rat and human.
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  • 27
    ISSN: 1434-193X
    Keywords: Single-electron transfer ; Ring contractions ; 1,4-Dihydro-1,2,4-triazine ; Photochemical reduction ; Chemical reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Chemical reduction (Zn/AcOH) of the arene 1 and of 2(4),5-dihydro-1,2,4-triazine 7 has been reinvestigated, resulting in the amendment of literature data concerning this reaction. Chemical, electrochemical, and photochemically induced reductions and ring contractions of 1,2,4-triazine derivatives have been compared. The first example of a triaryl-1,4-dihydrotriazine has been prepared. Some further evidence is presented that supports the proposed mechanism of the photochemically induced reduction and ring contraction of 1,2,4-triazines.
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  • 28
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 703-706 
    ISSN: 1434-193X
    Keywords: 4-Methylpyrimidine ; Ylides ; Quantum chemical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -For the first time in the pyrimidinium ylides series we present a theoretical and experimental study concerning the structure, stability and reactivity of pyrimidinium ylides and interesting correlations between these properties. 4-Methylpyrimidinium ylides are relatively stable compounds, their stability varying with the nature of the ylide carbanion substituent. The more electron-withdrawing these substituents, the more the anionic charge is delocalized and therefore the higher the stability. The data from experiments and quantum chemical calculations are in agreement with each other. The quantum chemical calculations show the possibility of using pyrimidinium ylides as nucleophilic reagents as well as 1,3-dipoles in reaction with appropriate reagents. Eight new pyrimidine compounds (4 salts and 4 ylides) were obtained.
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  • 29
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 707-736 
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Erinnerungen an Karl Johann Freudenberg (1886-1983)
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  • 30
    ISSN: 1434-193X
    Keywords: Glycosphingolipids ; Ganglioside ; GM3 ; Starfish ; Luidia maculata ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A ganglioside molecular species, LMG-2 (1), has been obtained from the water-soluble lipid fraction of the chloroform/methanol extract of the starfish Luidia maculata. On the basis of chemical and spectroscopic findings, the structure of 1 has been elucidated. 1 is a ganglioside molecular species of starfish resembling the mammalian ganglioside GM3. In addition, 1 shows neuritogenic activity toward the rat pheochromocytoma cell line PC-12 cell.
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  • 31
    ISSN: 1434-193X
    Keywords: Monoynes ; Polyynes ; Alkali metals ; Liquid NH3 ; Hexamethylphosphoric triamide ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Efficient procedures have been developed for the stereospecific reduction by alkali metals of disubstituted acetylenes with long carbon chains. Acetylenes containing two or more (isolated) triple bonds are reduced considerably more easily than are monoynes.
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  • 32
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 771-774 
    ISSN: 1434-193X
    Keywords: Natural products ; Glycosphingolipids ; Gangliosides ; Starfish ; Linckialaevigata ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A ganglioside molecular species [LLG-3 (1)] has been obtained from the water-soluble lipid fraction of the CHCl3/MeOH extract of the starfish Linckialaevigata. On the basis of chemical and spectroscopic findings, the structure of 1 has been elucidated. Negative-ion FABMS provided important information concerning both the structure of the sugar moiety and the molecular mass of the ganglioside. On the other hand, positive-ion FABMS/MS of [M + Na]+ ions obtained in the positive-ion FABMS of the ceramide lactoside (4) derived from 1 indicated the structure of the fatty acid chain of the ceramide moiety. 1 represents a new ganglioside molecular species possessing a 2→11-linked tandem-type disialosyl moiety.
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  • 33
    ISSN: 1434-193X
    Keywords: Epoxidations ; Diastereoselectivity ; Allylic alcohols ; Homogeneous catalysis ; Methyltrioxorhenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (Es) or Charton (ν). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m-chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130° is suggested.
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  • 34
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 791-795 
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Sulfur heterocycles ; Cyclisations ; Cesium effect ; ππ* transitions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two series of [8]metacyclophanes with cis or trans configurated double bonds or triple bonds in the bridges were prepared; the first series 6, 8, and 10 contains phenylethynyl, the second series 13, 14, and 15 phenylethenyl substituents so that ππ interactions between the π centres in the bridge and the π centres of the basic chromophores tolan and trans-stilbene, respectively, can be studied.
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  • 35
    ISSN: 1434-193X
    Keywords: Phenylselenenyl sulfate ; Selenium-catalyzed reactions ; Stereoselective syntheses ; Dihydrofurans ; Tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A stereoselective multi-step one-pot procedure for converting 2-methoxycarbonyl-3-alkenols into 3-methoxycarbonyl-2,5-dihydrofurans, using only catalytic amounts of diphenyl diselenide and an excess of ammonium persulfate, has been developed. The erythro alkenols give the trans dihydrofurans, while the threo stereoisomers give the corresponding cisproducts. The configurations of the starting alkenols were deduced from those of the intermediate phenylseleno tetrahydrofurans, which were independently obtained from reactions of the alkenols with stoichiometric amounts of phenylselenenyl sulfate.
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  • 36
    ISSN: 1434-193X
    Keywords: Aminophenols /Asymmetric synthesis ; C-C coupling ; Reductions ; Conformation analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Enantiopure o-hydroxybenzylamines 2a-i were synthesized by diastereoselective reduction of the 2-imidoylphenols (R)-1a-i. Conformational analysis enabled the assignment of the absolute configurations of compounds 2a-i. The accessible o-hydroxybenzylamine (R,R)-2h serves as an effective catalyst precursor for highly enantioselective addition of diethylzinc to aliphatic and aromatic aldehydes. This pathway represents a practical and operationally very simple methodology for the enantioselective synthesis of both the enantiomers of secondary alcohols 7a-f.
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  • 37
    ISSN: 1434-193X
    Keywords: Cyclizations ; Hydrocarbons ; Isomerizations ; Kinetics ; Polycycles ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Whereas 1,5-dimethylsemibullvalene (1b) equilibrates with 1,5-dimethylcyclooctatetraene (2b), the semibullvalene-2,6-dicarbonitriles 13 rearrange irreversibly to afford mixtures of the isomeric cyclooctatetraene-1,5-dicarbonitriles 14 and 15. Arrhenius and Eyring parameters of these thermal isomerisation reactions have been determined for the gas phase (1b → 2b) and [D6]benzene solutions (1b → 2b, 13 → 14 + 15). Furthermore, the activation parameters of the known rearrangement of octamethylcyclooctatetraene (3) to octamethylsemibullvalene (4) have been determined. - The data for these compounds, together with those for related compounds previously reported in the literature, show that substituents not only influence the relative stabilities of the semibullvalene and cyclooctatetraene systems but also the height of the energy barrier for their interconversion. Those substituents that lower the barrier toward the degenerate Cope rearrangement of semibullvalenes simultaneously accelerate their rearrangement to cyclooctatetraenes thus limiting the thermal stability of the former.
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  • 38
    ISSN: 1434-193X
    Keywords: C-Disaccharide ; C-Glycosides ; Carbohydrates ; Glycosylation ; Sugar lactone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -We have stereoselectively synthesized the analogues of the methyl β-glycosides of (1→6)-β-D-galacto-oligosaccharides (up to tetrasaccharide), in which the interglycosidic oxygen atoms are replaced by a methylene group.
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  • 39
    ISSN: 1434-193X
    Keywords: Cavitands ; Nuclear waste ; Actinide/lanthanide separation ; Solvent extraction ; Sulfur atoms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Cavitands with phosphane sulfide moieties 4 and 8a,b were prepared in good yields from their phosphane oxide analogues, as more stable alternatives for the dithiophosphinic acids used at present. The cavitands 7a and 7b with flexible butoxyphosphane oxide ligating sites are more efficient than cavitand 3 having rigid methylphosphane oxide groups as was studied with EuIII picrate extractions. Due to the absence of an ionic functionality in the phosphane sulfides 4 and 8a,b AmIII and EuIII are not extracted, not even in the presence of synergents (e.g. TBP, TOPO, HDNNS). Cavitand 10 with phosphinic acid groups efficiently extracts EuIII in 1:1 or 2:1 complexes, depending on the metal-to-ligand concentration ratio (extraction constants Kex1 = 3.9·10-5M2 and Kex2 = 1.9·102M, respectively). Furthermore, in the case of 10 EuIII is preferentially extracted over AmIII with a separation factor SEu/Am up to 5.
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  • 40
    ISSN: 1434-193X
    Keywords: Carbohydrates ; 4-Thiofuranosides ; Nucleosides ; Reaction mechanisms ; NOE measurements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.
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  • 41
    ISSN: 1434-193X
    Keywords: Corticium sp. ; Steroids ; Alkaloids ; Secondary metabolites ; Cytotoxic activity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Five new steroidal alkaloids, plakinamines C (1) and D (2), and the related compounds 3-5 have been isolated from the Vanuatu sponge Corticium sp. Their structures have been elucidated by a detailed spectroscopic analysis, including 2D-HMBC and ROESY correlation experiments. The new compounds show significant in vitro cytotoxicity against human bronchopulmonary non-small-cell lung carcinoma cells (NSCLC-N6) with IC50 values of 〈 3.3-5.7 μg/mL. When tested against T leukemia virus type one (HTLV-I), compounds 1, 4 and 5 were found to exhibit slight anti-HIV activity.
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  • 42
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 751-756 
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Streptenol A ; Synthetic methods ; Natural products ; SAMP/RAMP hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The asymmetric synthesis of (+)-streptenol A was carried out in ten steps and with high enantioselectivity (ee ≥ 96%). The key steps are the α-alkylation of 2,2-dimethyl-1,3-dioxan-5-one RAMP hydrazone A (1), subsequent deoxygenation and elaboration of the side chain via aldehyde B to furnish (+)-streptenol A in 23% overall yield. In analogy, the enantiomer (-)-streptenol A was synthesized using the corresponding SAMP hydrazone in 18% overall yield.
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  • 43
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 737-750 
    ISSN: 1434-193X
    Keywords: Baeyer-Villiger oxidation ; Ketones ; Monopersulfate ; Peracids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -In the present review, we report the discovery of the formation of esters and lactones by oxidation of ketones with a peroxide derivative, namely the Baeyer-Villiger reaction. This reaction was first reported by Adolf von Baeyer and Victor Villiger a century ago in 1899, just one year after the oxidant they used (KHSO5) has been described. Furthermore, Baeyer and Villiger established the composition of this new inorganic peroxide and showed that its instability was the reason of a controversy between several European chemists between 1878 and 1893. For the first 50 years the mechanism of the Baeyer-Villiger reaction was a matter of debate. A side product, 1,2,4,5-tetraoxocyclohexane, was ruled out as an intermediate in the ester formation by Dilthey. Criegee postulated a nucleophilic attack of the oxidant on the carbonyl group. This mechanism was confirmed by von E. Doering by a labeling experiment with [18O]benzophenone. The rearrangement step occurs with retention of the stereochemistry at the migrating center. The competitive migration and the rate-determining step are also discussed in this review.
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  • 44
    ISSN: 1434-193X
    Keywords: Transglycosylation ; Glycosidases ; Thermus thermophilus ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The aim of this paper is to test the ability of a β-glycosidase from Thermus thermophilus to catalyse transglycosylation reactions in the presence of nitrophenyl glycosides as donors and other monosaccharides as acceptors. Our results show that this enzyme is able to induce such reactions either with nitrophenylgalactosides, -glucosides and -fucosides. With the two former donors, the autocondensation of the donor, which thus acts also as an acceptor, is faster than the transglycosylation with other acceptors. Furthermore, as the regioselectivity of the reactions is mainly of the β-[1→3] type, good yields are obtained for the synthesis of 2-nitrophenyl-β-D-galactopyranosyl-[1→3]-β-D-galactopyranoside and 2-nitrophenyl-β-D-glucopyranosyl-[1→3]-β-D-glucopyranoside. Conversely, in the presence of p-nitrophenylfucoside, the autocondensation is very limited, and with methyl-α-D-galactoside as an acceptor, the regioselectivity is mainly of the β-[1→6]-type resulting in the synthesis of methyl-β-D-fucopyranosyl-[1→6]-α-D-galactopyranoside.
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  • 45
    ISSN: 1434-193X
    Keywords: Polymer-supported organotin hydride ; Steroids ; Iodinated estrogens ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Iodoestrogen derivatives were prepared by iododestannylation of insoluble polymer-supported organotin precursors.
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  • 46
    ISSN: 1434-193X
    Keywords: Fluorine ; Cycloadditions ; Nitrones ; Asymmetric induction ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3-(Fluoroalkyl)isoxazolidines 6 and -2,3-dihydroisoxazoles 8 have been obtained in enantiomerically pure form with good diastereoselectivity by 1,3-dipolar cycloaddition of diethyl fumarate and dimethylacetylene dicarboxylate, respectively, to the chiral fluorinated nitrone (R)-5. The latter has been prepared from the β-fluoromethyl-β-oxo sulfoxide (RS)-1, by a synthetic sequence where the chiral and enantiomerically pure sulfinyl function acts as a removable source of chirality. Reductive opening of isoxazolidines 6 then afforded amino fluoromethyl diols 7 in good yields.
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  • 47
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Imidazole ; Glycosidases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Some naturally occurring carbohydrates, of which several hydroxy groups had been selectively protected, were condensed with formamidine to give the expected imidazole derivatives in the D-arabino (9), D-lyxo (12), L-xylo (17), D-threo (21), and in the L- and D-erythro (24) series. Introduction of a strong leaving group at the remaining free alcohol function of these products led at once to intramolecular SN2 cyclisation to the corresponding bicyclic aza sugar derivatives. This was followed by total deprotection to give the target aza sugars in the L-xylo (7), L-ribo (14), D-arabino (19), as well as in the D-threo (22) and the L- and D-erythro (26) series. Inhibitory assays with four glycosidases showed that the D-arabino aza sugar 19 is the only potent inhibitor (for an α-mannosidase of jack bean).
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  • 48
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; 4-Octulose derivatives ; Aminations ; Double cyclization ; Polyhydroxyindolizidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Reaction of 3 with (cyanomethylene)triphenylphosphorane in refluxing dichloromethane or methanol gave mixtures of 4a and 4b in ratios of about 3:1 and 1:3, respectively. The same reaction performed with the furanoid isomer 5 afforded 6a and 6b in (E)/(Z) ratios of approximately 9:1 and 1:2, respectively. Catalytic hydrogenation of the α,β-unsaturated nitriles 4 and 6 with either 10% Pd-C or Raney nickel afforded the saturated nitriles 7 and 9, or the 1-amino-1,2,3-trideoxy-4-octulose derivatives 8 and 10, respectively. In an attempt to transform 6a into the appropriate polyhydroxylated branched-chain pyrrolidine 15, (5R,8S,9R,10S)-8,9,10-trihydroxy-1-aza-6-oxaspiro[4.5]decane, which was identified as its peracylated derivative 16, was isolated. Following an alternative synthetic strategy, partial hydrolysis of compound 9 afforded 17 which was regioselectively transformed into the corresponding derivative 22 via its 8-O-p-toluenesulfonyl derivative 18. Removal of the 4,5-O-isopropylidene group in 22 with aqueous trifluroacetic acid gave the free octulose 23, which was hydrogenated in the presence of 10% Pd-C, to afford the expected (6S,7R,8R,8aR)-6,7,8-trihydroxyindolizidine (1-deoxycasta-nospermine, 11).
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  • 49
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Diradicals ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm-1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
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  • 50
    ISSN: 1434-193X
    Keywords: Catenanes ; Mechanically interlocked molecules ; Molecular recognition ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A [2]catenane, able to bind π-electron-rich guests inside the cavity of one of its two macrocyclic components has been designed and synthesized using supramolecular assistance. This recognition motif has been exploited to template the formation of a so-called rotacatenane - i.e., a molecule composed of a dumbbell-shaped component threaded through the cavity of one of the two mechanically interlocked macrocyclic components of a [2]catenane. The structure of this [2]catenane, as well as that of a model [2]catenane, have been characterized unequivocally by single-crystal X-ray analyses. Furthermore, some of the co-conformational changes associated with these mechanically interlocked molecules in solution have been probed by variable-temperature 1H-NMR spectroscopy.
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  • 51
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 923-930 
    ISSN: 1434-193X
    Keywords: Bridged benzo[a]phenoxazinium salts ; Diazo compounds ; Cyclocondensation ; Absorption ; Fluorescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -By condensation of bridged 4-arylazo-substituted 3-hydroxyanilines 18 and bridged or unbridged 4-arylazo-substituted 1-naphthylamines 19-23 with bridged 1-naphthylamines 15-17 and 3-aminophenols 14, respectively, in the presence of perchloric acid, bridged naphthoxazinium perchlorates 24-30 have been prepared. The spectral properties of the products have been compared with those of the bridged phenoxazinium salt 31 as well as with data for some unbridged analogues.
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  • 52
    ISSN: 1434-193X
    Keywords: Nucleosides ; Phosphonates ; Nucleophilic additions ; C-C coupling ; Reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Acyclic carba-nucleoside phosphonates, modelled on natural deoxyribonucleotides have been prepared starting from DNA nucleobases and tert-butyl acrylate. The products obtained from a Michael-type reaction were elongated to β-oxo esters that were first reduced to β-hydroxy esters and then transformed into protected β-hydroxy aldehydes. Wittig-Horner-Emmons reaction with the anion of tetraisopropyl methylenebisphosphonate gave, after deprotection, the desired 4-hydroxy-6-purinyl- or -6-pyrimidinyl-1-hexenylphosphonic acids. A dimer, potential precursor of acyclic polynucleotides (APN), homomorphous with DNA, was also prepared.
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  • 53
    ISSN: 1434-193X
    Keywords: Iminium salts ; Triflic anhydride ; Arylamines ; 2-Trifluoromethyl quinolines ; 3-Trifluoromethyl-cinnamaldehydes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of iminium triflates 2 and 7 with various aromatic amines were investigated. The 2-Rf-substituted quinolines 3 and 8 were prepared in excellent yields by the reaction of 2 and 7, respectively, with substituted anilines. The reactions of 2 and 7 with diarylamines proceeds, suprisingly, to afford the corresponding 3-Rf-substituted cinnamaldehydes 4 and 9.
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  • 54
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 943-947 
    ISSN: 1434-193X
    Keywords: Thiolane 1-oxides ; Oxidations ; δ-Sultines ; [Bis(trifluoroacetoxy)iodo]benzene ; Asymmetric synthesis ; Carbanions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -2-(Alkylthio)-2-benzylthiolane 1-oxides (1a, b) and 2-(alkylthio)-2-(α-hydroxybenzyl)thiolane 1-oxides (1c, d) are oxidized with [bis(trifluoroacetoxy)iodo]benzene (PIFA). Under ring enlargement the corresponding cyclic sulfinate esters (δ-sultines) 2 are formed. Only (1R*,2S*)-1b is reactive whereas (1R*,2R*)-1b is not attacked. This observation is explained with the formation of a cyclic intermediate 3.
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  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 955-958 
    ISSN: 1434-193X
    Keywords: Tetraethylammonium peroxydicarbonate ; Tetraethylammonium carbonate ; N-alkylated pyrroles ; Electrochemistry ; Electrogenerated bases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Electrochemically generated tetraethylammonium peroxydicarbonate (TEAPC) and tetraethylammonium carbonate (TEAC) react under very mild conditions with pyrroles affording, after addition of a suitable alkylating agent, the corresponding N-alkylated pyrroles in high yields. C-Alkylated pyrroles have not been isolated in any case reported.
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  • 56
    ISSN: 1434-193X
    Keywords: Natural products ; Dimeric steroids ; Crellastatins ; Sponge ; Crella sp. ; 2D NMR ; Antitumor agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Seven new cytotoxic dimeric steroids, namely crellastatins B-H (2-8), have been isolated from the Vanuatu sponge Crella sp. They have been structurally characterized on the basis of 2D-NMR (500 MHz) and FAB-MS data. All the new compounds show the same unprecedented junction between the monomeric units, formed via their side-chains, whereas they differ from A (1) in the hydroxylation pattern of the two tetracyclic cores. Like crellastatin A (1), crellastatins B-H (2-8) exhibit in vitro antitumor activity against human bronchopulmonary non-small-cell lung carcinoma cell lines (NSCLC) with IC50 values in the range of 2-10 μg/mL.
    Additional Material: 4 Ill.
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  • 57
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
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  • 58
    ISSN: 1434-193X
    Keywords: Cross-coupling ; Isomerizations ; Cycloisomerization ; Palladium ; Homogeneous catalysis ; Bicyclic vinylcyclopropanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Palladium-catalyzed cyclizations of the 2-bromo-1,6-diene 6 with an acetoxymethyl substituent on the bromoalkenyl moiety did not only lead to the expected 1-acetoxymethyl-1,3-diene 40 but also to the bicyclic vinylcyclopropane 35, the 1,3-diene 36 and the triene 37 (a dendralene). All these compounds result from an initial 5-exo-trig cyclization of the 2-bromo-1,6-diene. By proper choice of the reaction conditions (ligand, base, allylic leaving group) each of these compounds could be formed selectively. Small amounts (3-5%) of the isomerized 1-acetoxymethyl-1,3-diene 38 and the 6-endo product 39 were also isolated. With the acetoxymethyl substituent on the alkenyl moiety (compound 27) only the 1,4-diene 44 was formed. The related 1,6-enyne 57 with a methoxycarbonyloxymethylene substituent on the triple bond gave in 36% yield the 2,3-bis(bicyclo[3.1.0]hex-1-yl)-substituted 1,3-butadiene 63, which can be regarded as a dehydrodimer of the vinylcyclopropane 35. The presumption that the formation of 63 involves the alkenylpalladium species 65 was supported by its successful inter- as well as intramolecular trapping with formate as a hydride source to yield the vinylcyclopropane 35. The reaction pathways leading to the vinylcyclopropane derivatives 35 and 63 have in common that an alkylpalladium species rather undergoes a 3-exo-trig cyclization than an internal rotation followed by a β-hydride elimination.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98406_s.pdf or from the author.
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  • 59
    ISSN: 1434-193X
    Keywords: Crystalline diazonium trifluoroacetate salts ; Quinone diazides ; Pd-catalyzed C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -We have developed a very mild procedure for the synthesis of crystalline aryldiazonium trifluoroacetate salts in high yields under anhydrous conditions. Over thirty mono- or polyfunctional aniline derivatives have been diazotized by this method, including water- and acid-sensitive substrates. The o- and p-hydroxyaryldiazonium salts, derived from the corresponding anilines, could be deprotonated by treatment with K2CO3 to yield pure diazoquinones. NMR and UV/Vis spectra have been recorded for all the synthesized salts; the data are in good agreement with the rather limited published data and constitute a first extensive report of 13C-NMR chemical shifts in diazonium salts. An excellent linear relationship emerged between Brown's substituent constants s+p and the 13Cipso chemical shifts. The diazonium salts obtained proved to be much more soluble in organic solvents than their tetrafluoroborate counterparts. They were tested in Pd-mediated coupling reactions of various Carbon-Carbon double bonds, and were found to give good yields within short reaction times under very mild conditions. We believe that diazonium trifluoroacetates represent a very attractive alternative to diazonium tetrafluoroborates.
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  • 60
    ISSN: 1434-193X
    Keywords: Peptidomimetics ; Octahydro[2H]pyrazino[1,2-a]pyrazine ; Diastereoselectivity ; Tripeptides ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new route to octahydrospiro(cyclopropane-1,1′-[2H]-pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones 12-15 has been developed. Michael additions of primary amines onto methyl 2-Me or tert-butyl 2-tBu 2-chloro-2-cyclopropylideneacetates, followed by DCC- or EDC-induced coupling with Boc- or FmocGlyOH, deprotection and cyclization led to α-amino esters 4a-c and chlorohexahydrodiazepinediones 5a-c, or in the case of 2-tBu to the α-amino ester 7 exclusively. This reaction sequence with (S)-BocPheOH and (S)-BocTrpOH diastereoselectively gave (3′R,5′S)-9a,b and (2′S,6′R)-11a,b as the main products. Further peptide coupling, deprotection and cyclization with 4a-c yielded octahydrospiro(cyclopropane-1,1′-[2H]pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones (7′S,9a′S)-12a-d, (6a′S,11a′S)-12e, (7′S,9a′R)-13a-d and (6a′S,11a′R)-13e which were easily separated. The α-amino esters 9a,b yielded (4′S,9a′R)-14a (≡15a) and (4′S,9a′R)-14b (≡15b), (4′S,7′S,9a′R)-14c and (4′R*,7′S*,9a′S*)-15c. The formation of compounds with three stereogenic centers 14c and 15c was accompanied by partial racemization. The versatility of the reported reaction sequence is limited by the steric availability of the secondary amino group in the intermediates 4, 9 and 10, as well as in the Michael adducts formed from primary amines and 2-Me.
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  • 61
    ISSN: 1434-193X
    Keywords: Catenanes ; Diastereoselectivity ; Molecular Recognition ; Self-Assembly ; Template-Directed Synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two chiral π-electron-rich crown ethers incorporating either a binaphthol or two D-mannitol units have been synthesized and their abilities to bind bipyridinium guests demonstrated. Both crown ethers could be interlocked mechanically with cyclobis(paraquat-p-phenylene) to afford two chiral [2]catenanes. Furthermore, these crown ethers were also mechanically interlocked with a tetracationic cyclophane incorporating a 2,2′-dihydroxy-1,1′-binaphthyl spacer to afford mixtures of diastereoisomeric [2]catenanes. The composition of these mixtures was determined by 1H-NMR-spectroscopic and HPLC analyses which revealed that modest diastereoselection (56:44-67:33) occurs during the kinetically controlled self-assembly of the catenanes. The free energy barriers (12.8-16.8 kcal mol-1) associated with the circumrotation of one macrocyclic component through the cavity of the other and vice versa were determined by variable-temperature 1H-NMR spectroscopy. In addition, another dynamic process involving the “rocking” of the mean planes of the mechanically interlocked macrocycles with respect to each other was also identified and the associated free energy barriers (10.3-10.4 kcal mol-1) determined.