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  • 11
    ISSN: 0170-2041
    Keywords: Cyanohydrins and cyanohydrin esters, optically active ; Resolutions, kinetic enzyme-catalyzed ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 71). - Enantioselective Esterification of Racemic Cyanohydrins and Enantioselective Hydrolysis or Transesterification of Cyanohydrin Esters by LipasesPure cyanohydrin enantiomers (S)-1/(R)-1 and their O-acyl derivatives (R)-3/(S)-3 are obtained from three different lipasecatalyzed reactions: i) enantioselective hydrolysis of aliphatic and aromatic racemic cyanohydrin esters 3, ii) enantioselective acylation of racemic cyanohydrins 1, iii) enantioselective transesterification of 3 with primary alcohols. Both the cyanohydrin esters and the free cyanohydrins (which are prone to racemization) are isolated as enantiomers with high optical purity on a preparative scale. Hydrolysis of the racemic butyrates 3b, e with Candida cylindracea lipase and pseudomonas sp. lipase, respectively, for example, affords the free (S)-cyanohydrins (S)-2-hydroxypentanenitril [(S)-1a] and (S)-mandelonitrile [(S)-1b)] in high yield with 97 and 96% ee, respectively. (S)-1a is obtained with the same optical purity by candida sp. lipase-catalyzed transesterification of 3b with 1-octanol.
    Additional Material: 4 Tab.
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  • 12
    ISSN: 0170-2041
    Keywords: Carbohydrates ; Furanoses, 3,6-anhydro ; Glycosides, pyruvylated ; Anhydrofuranoses ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of methyl 2,3-di-O-acyl-D-glycopyranosides 1 of glucose and mannose with catalytic amounts of trifluoromethanesulfonic acid afforded the corresponding bis(5-O-acyl-3,6-anhydro-D-glycofuranose) 1,2′:2,1′-dianhydrides 6 in 12-58% yield the structure of which was confirmed for the α-D-glucose derivative 6a by an X-ray analysis. In addition, in the presence of methyl pyruvate (2a) or methyl 2-acetoxy-acrylate (2b) various amounts of diastereomeric 3,6-anhydro-5-O-benzoyl-1,2-O-(1-methoxycarbonyl)ethylidene-α-D-glucofuranoses 5 and acylated methyl α-D-glucopyranosides 3 and 4, respectively, were formed.
    Additional Material: 1 Ill.
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  • 13
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pyruvated galactosyl donors, 2,3-di-O-benzoyl-4,6-O-[1-(R)-methoxycarbonyl(ethylidene)]-α-D-galactopyranosyl chloride (6) and trichloroacetimidate 13, were coupled to position 3 of suitably protected mono and disaccharide benzyl glucoside acceptors. For both donors, an unusual high content of the α-(1 → 3)-linked products was obtained. The corresponding β-(1 → 3)-linked di- and trisaccharides are related to exopolysaccharides of Rhizobium leguminosarum.
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  • 14
    ISSN: 0947-3440
    Keywords: Glycosides, pyruvated ; Sponge, marine ; Microciona prolifera ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of phenyl 2,3,6,2′,3′-penta-O-benzoyl-1-thio-β-D-lactoside (7) with BF3 in methyl pyruvate afforded the corresponding phenyl 4′,6′-O-[(R)-1-(methoxycarbonyl)ethylidene]-1-thio-β-D-lactoside (9) in 91% yield. The latter was converted via bromide 10 into the corresponding lactal 11 the azidonitration of which afforded an unseparable mixture of the „gluco“- and „manno“-configurated azido nitrates 12 (97%). As an alternative, benzyl O-(β-D-galactopyrnosyl)-(1→4)-2-azido-2-deoxy-α-D-glucopyranoside (15) was prepared in two steps and 91% yield from the corresponding fully acetylated 2-azido-2-deoxylactosyl bromide 13 and was further modified in four steps to give the benzoylated benzyl 4′,6′-O-benzylidene-2-deoxy-2-[(2,2,2-trichloroethoxycarbonyl)amino]-α-D-lactoside 18 in 78% overall yield. The benzylidene acetal of the latter was cleaved to give the diol 19 the pyruvation of which as for compound 9 afforded the corresponding pyruvated lactosamine derivative 20 (81%). Hydrogenolysis of 20 followed by treatment with trichloroacetonitrile gave the corresponding pyruvated disaccharide trichloroacetimidate 22 (77%). Coupling of the latter with Z-protected 5-amino-1-pentanol followed by deblocking of the intermediates furnished 5-aminopentyl 2-acetamido-4′,6′-O-[(R)-1-carboxyethylidene]-2-deoxy-β-D-lactoside (2). Similarly, condensation of 22 with 5-[(benzyloxycarbonyl)amino]-pentyl 2,4-di-O-benzyl-β-L-fucopyranoside (25) followed by deblocking of the intermediate trisaccharide afforded 5-aminopentyl O-{4,6-O-[(R)-1-carboxyethylidene]-β-D-galactopyranosyl}-(1→4)-2-acetamido-2-deoxy-β-D-glucopyranoside-(1→3)-β-L-fucopyranoside (3). Saccharides 2 and 3, represent fragments of the Microciona prolifera aggregation factor.
    Additional Material: 2 Tab.
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