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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1609-1621 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Tab.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrazole 1 is a new β-glucosidase inhibitor (IC50=8·10-5 M, Emulsin), obtained (92%) by deprotection of 22, the product of an intramolecular cycloaddition of the azidonitrile 20. This azidonitrile was formed as an intermediate by treating the L-ido-bromide 14 or the L-ido-tosylate 19 with NaN3 at 110-120°. It was isolated in a separate experiment. The yield of 22 from 19 reached 70%; 21 was formed as by-product (10%). The bromide 14 (42%) and the iodide 15 (30-35%) were obtained from the nitrile 13, together with the 2,5-anhydro-L-idononitrile 16, which was formed in ca. 35-45%. The tosylate 19 was obtained from 18 (97%). To obtain 18, the nitrile 13 was oxidized according to Swern (→17, 92%) and then reduced (NaBH4, CeCl3), leading to 18and 13 (92%, 18/13 93:7). Reduction of the tetrahydropyridotetrazole 22 with LiAlH4 afforded 83 % of the piperidine 23, which was deprotected to (+)-1-deoxynojirimycin hydroacetate (2·AcOH, 86%) and further converted into the corresponding hydrochloride and into the free base 2.
    Additional Material: 1 Ill.
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 9-(2′-deoxy-à-D-threo-pentofuranosyl)adenine (=9-(2′-deoxy-à-D-xylofuranosyl)adeninc, xAd; 2) was protected at its 6-NH2 group with cither a benzoyl (5a) or a (dimethyfamino)methylidcnc (6a) residue and with a dimethoxytntyl group at 5′-OH (5b, 6b). Compounds 5b and 6b were then converted into the 3′-phosphonates 5c and 6c; moreover, the 2-cyanoethyl phosphoramidite 6d was synthesized starting from fib. The DNA building blocks were used for solid-phase synthesis of d[(xA)122-A] (8). The latter was hybridized with d[(xT)12-T] (Tm = 35°); in contrast, with d(T12), complex formation was not observed. Moreover, xAd and xTd were introduced into the self-complementary dodccamcr d(G-T-A-G-A-A-T-T-C-T-A-C) (12) at different positions lo give the oligomcrs 13-16. All oligonucleotides were characterised by temperature-dependent CD and UV spectroscopy, and in addition, 14 by T-jump experiments. From concentration-dependent Tm measurements, the thermodynamic paraneters of the melting as well as the tendency of hairpin formation of the oligonucleotides were deduced. Oligemer 14 was hydrolyzed by snake-venom phosphodiesterase in a discontinuous way implying a fast hydrolysis of unmodified 3′- and 5′-flanks followed by a slow hydrolysis of the remaining modified tetramer. In contrast to this, oligonucleotide 16 was hydrolyzed in a continuous reaction. In both cases, calf-spleen phosphodiesterase hydrolyzed the oligomer only marginally.
    Additional Material: 7 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The antibiotic myxovirescine M2 was synthesized from seven building blocks (1-7, Scheme 1), with the following chiral starting materials being employed: (S)-malic acid, (+)-D-ribonolactone, (S)-2-(hydroxymethyl)butanoate, and (2R,4S)-5-hydroxy-2,4-dimethylpenLanoate. Three new nucleophilic reagents, 8-10, for C-C bond formation have been used. The key steps of the synthesis are: a Suzuki coupling between an alkyl borane and a vinyl bromide (4 + 12e → 13), a Julia olefinalion (14 + 17 → 18), and a Yamaguchi macrolactonizalion to form the 28-membered lactone (18 → 19), This extremely convergenl synthetic approach will allow the preparation of a number of the 31 known myxovirescine molecules.
    Additional Material: 1 Ill.
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variety of model compounds for the pyrimidinediyl-based rigid-rod polyamide poly[imino-(pyrimidine-2,5-diyl)-imino-tetraphthaloyl] (PPYMT) was prepared, in order to compare their conformations to several model compounds of the related, fully aromatic polymer poly(p-phenyleneterephthalamide) (PPTA). In particular, the structures of N-(2-pyrimidyl)benzamide (PYMB) and its complexed form bis[(N-pyrimidin-2-yl)benzamide]nickel(II) dichloride (NiPYMB) were determined by X-ray diffraction. The molecular packing in these crystals provides us with a model for the possible ‘cross-linking’ of PPYMT fibers. The structures of the trimer model compounds N,N′ -bis(2-pyrimidyl)terephthalamide (PYTA) and N,N′ -bis(benzoyl)-2,5-diaminopyrimidine (BDAP) yield information about the conformation of PPYMT chains and are compared to analogous model compounds of PPTA.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of pyridine exchange on trans-[MO2(py)4]+ have been followed by 1H-NMR in CD3NO2 for M = Re, Tc: k298S-1 = (5.5 ± 0.1) × 10-6, 0.04 ± 0.02; ΔH≠/kJmol-1 = 111 ± 3, 101 ± 9; ΔS≠/JK-1mol-1 = +28 ± 10, +68 ± 35. For the Rev complex, pyridine and oxygen exchanges have been measured simultaneously by 1H- and 17O-NMR in deuterated water: k298/s-1 = (8.6 ± 0.2) × 10-6 (py), (14.5 ± 0.3) × 10-6 (oxygen); ΔH≠/kJmol-1 = 111 ± 1, 91 ± 1; ΔS /JK-1mol-1 = +32 ± 3, -32 ± 4. For both complexes, the rate law for pyridine exchange is first-order in complex and zero-order in pyridine; together with the activation parameter values, and the fact that the rate does not depend significantly on the nature of the solvent, this strongly implies the operation of a dissociative mechanism. The ratio of pyridine exchange rates for the Tc and Re complexes at room temperature is ca. 8000. The consequences of these observations for radiopharmaceutical synthesis are discussed.
    Additional Material: 1 Ill.
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  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of the title compound, 7a and ent-7a, and of substituted analogues are synthesized. The absolute configuration of 7a is deduced from that of (tert-butyl 2-tert-butyl)-3-methyl-4-oxoimidazolidin-1-carboxylate (15) and from the trans-configuration of the intermediate 17a which in turn is assigned on the basis of 1H-NMR nuclear Overhauser effect (NOE) measurements. Instead of 15, the 2-isopropyl-substituted analogue 21 can also be employed. Its preparation from glycine, methylamine, isobutyraldehyde, and (Boc)2O, and the resolution through the bis-O,O′-(4-toluyl)tartrate salt 20 are described. In two functional tests (rat neocortical slice and frog hemisected spinal cord preparation) the (S)-enantiomer 7a (SDZ EAB 515) is shown to be a very potent, selective competitive NMDA antagonist.
    Additional Material: 10 Tab.
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Synthesis of (2S,6S)-2,6-Diaminoheptanedioic Acid and of Unsymmetrical Derivatives of meso-2,6-Diaminoheptanedioic AcidSpecific inhibition of enzymes of the diaminopimelate pathway (L-lysine biosynthesis) should, in principle, lead to selective antibacterial agents or herbicides. For this purpose, enantioselective syntheses were devised for (2S, 6S)-2, 6-diaminoheptanedioic acid (L, L-diaminopimelate, 1), (2R,6S)-2,6-diamino-2-methylhept-3-enedioic acid (10), (2R, 6S)-2, 6-diaminohept-3-enedioic acid (9), (2R, 6S)-2, 6-diamino-4-fluorohept-3-enedioic acid (42), and (2S, 6S)-2, 6-diamino-3-chloroheptanedioic acid (5). The Schöllkopf bislactim-ether methodology was applied to control the configuration of C(2) and C(6) of 1, C(2) of 10, as well as C(6) of 9 and 42. Semialdehyde derivatives of L-glutamate afforded C(6) of 10 and 5, while the (R)-configurated C(2) of 9 and 42 were derived from L-serine. For this purpose, the synthesis of the Garner aldehyde 32 has been improved. As chromatographic purifications and the low temperatures for the reduction of the carboxylic acid are eliminated, this valuable intermediate can now be prepared in bulk quantities. An enantio- and diastereoselective aldol addition of a glycine titanium-enolate was applied for the construction of 5 (C(2) and C(3)). As all chiral building blocks and reagents used are available in both enantiomeric forms, these routes should also be suitable for the selective synthesis of the other stereoisomers of these bis(α-amino acids).
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 940-940 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 2-Substituted and 2,3-Disubstituted Alkyl- und Aryl-thiophenes and Related 2,3-Anellated Thiophene Derivatives, Using Ketones and Carbonodithioic Acid O-Ethyl S-(2-Oxoethyl) Ester as the Building BlocksA simple method to synthesize 2-substituted and 2,3-disubstituted alkyl- and aryl-thiophenes as well as related 2,3-anellated thiophenes 6, starting from ketones 1 as C2-fragment and the S-protected carbonodithionic-acid derivative 3 as a C2S-fragment is described. The aldols 4 are intermediates of the two step process.
    Additional Material: 1 Tab.
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