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At least 1,531 records · Page 85Linked to original sources
PubMed1986

Catalytic versatility of trehalase: synthesis of alpha-D-glucopyranosyl alpha-D-xylopyranoside from beta-D-glucosyl fluoride and alpha-D-xylose.

Trehalase was previously shown (see ref. 5) to hydrolyze alpha-D-glucosyl fluoride, forming beta-D-glucose, and to synthesize alpha, alpha-trehalose from beta-D-glucosyl fluoride plus alpha-D-glucose. Present observations further define the enzyme's separate cosubstrate requirements in utilizing these nonglycosidic substrates. alpha-D-Glucopyranose and alpha-D-xylopyranose were found to be uniquely effective in enabling Trichoderma reesei trehalase to catalyze reactions with beta-D-glucosyl fluoride. As little as 0.2mM added alpha-D-glucose (0.4mM alpha-D-xylose) substantially increased the rate of enzymically catalyzed release of fluoride from 25mM beta-D-glucosyl fluoride at 0 degrees. Digests of beta-D-glucosyl fluoride plus alpha-D-xylose yielded the alpha, alpha-trehalose analog, alpha-D-glucopyranosyl alpha-D-xylopyranoside, as a transient (i.e., subsequently hydrolyzed) transfer-product. The need for an aldopyranose acceptor having an axial 1-OH group when beta-D-glucosyl fluoride is the donor, and for water when alpha-D-glucosyl fluoride is the substrate, indicates that the catalytic groups of trehalose have the flexibility to catalyze different stereochemical reactions.

Disaccharides↗
PubMed1986

Synthesis of protected purpurosamine B and 6-epipurpurosamine B.

In relation to the synthesis of antipseudomonal drugs, namely, gentamicin C2 and 3-de-O-methylsporaricin A, a protected purpurosamine B (15) and 6-epipurpurosamine B (13) were synthesized. The key intermediate, methyl 2,3,4,7- tetradeoxy-6-O-(methylsulfonyl)-2-phthalimido-beta-L-lyxo-++ +heptopyranoside (8), was obtained in 48% yield by Grignard addition to methyl 2,3,4-trideoxy-2-phthalimido-alpha-D-erythro-hexodialdo-1,5-pyrano side (7) proceeding in accordance with Cram's chelate rule, followed by methylsulfonylation. From 8, compound 15 was readily obtained by introduction of the azide group with inversion of configuration at C-6. Compound 13 was obtained by introduction of the azide group with retention of configuration.

Anti-Bacterial Agents↗
PubMed1986

Cyclic platelet-activating factor analogues derived from 2-deoxy-D-erythro-pentose.

A method for the synthesis of chiral cyclic analogues of platelet-activating factor (PAF) is reported. Treatment of suitably substituted derivatives of 2-deoxy-D-erythro-pentose with phosphorus oxychloride, followed by choline p-toluenesulfonate generates cyclic phospholipids in good yield. Further chemical modification produces other compounds including optically active gamma-butyrolactones such as 2-deoxy-5-O-hexadecyl-3-O-phosphocholyl-D-erythro-pentono-1, 4-lactone and 2-deoxy-3-O-hexadecyl-5-O-phosphocholyl-D-erythro-pentono-1, 4-lactone. All phospholipids were poor antagonists of PAF-induced aggregation of human platelets, and two analogs were poor agonists. The chemistry presented should be useful for the syntheses of other conformationally restricted analogues of PAF.

4-Butyrolactone↗
PubMed1986

3-Methoxy-4-(2-nitrovinyl)phenyl glycosides as potential chromogenic substrates for the assay of glycosidases.

Selective glycosidation of 2,4-dihydroxybenzaldehyde with either 2,3,4, 6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide, 2-acetamido-3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl chloride, or 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide afforded the corresponding 4-O-glycosyl derivatives. Subsequent O-methylation, O-deacetylation, and condensation with nitromethane afforded the appropriate beta-glycoside of 3-methoxy-4-(2-nitrovinyl)phenol. The phenol is highly coloured at alkaline pH so that these glycosides may be suitable as chromogenic substrates for the assay of glycosidases.

Chemical Phenomena↗
PubMed1986

Bioactive chitin derivatives. Activation of mouse-peritoneal macrophages by O-(carboxymethyl)chitins.

The effect of O-(carboxymethyl)chitins (CM-chitins) on the activation of mouse-peritoneal macrophages in vivo and their mitogenic activity on mouse spleen-cells were investigated. The induction of cytotoxic macrophages is enhanced by an increase of negative charge at O-6 and decreased by further modification at O-3 of the GlcNAc residue. CM-Chitins had a minor effect on mitogenic activity that was independent of the site of modification; partially N-deacetylated chitins had little activity. Although there was remarkable enhancement of accessibility to lysozyme upon modification at O-6 of the GlcNAc residue, the accessibility was decreased by further substitution at O-3.

Animals↗
PubMed1987

Demonstration that the galactosyl and arabinosyl residues in the cell-wall arabinogalactan of Mycobacterium leprae and Mycobacterium tuberculosis are furanoid.

By a complex process involving methylation, partial hydrolysis with acid, reduction with sodium borodeuteride, ethylation, further hydrolysis and reduction, and subsequent capillary gas-liquid chromatography-mass spectrometry of the derived alditol acetates, it was established that the arabinogalactans of Mycobacterium leprae and Mycobacterium tuberculosis contain arabinofuranyosyl and galactofuranosyl residues exclusively. Thus, the covalently bound, highly immunogenic arabinogalactan of mycobacteria, and presumably of other actinomycetes, is highly unusual, in that all of the glycosyl residues are in the furanoid form. Furthermore, by establishing that the galactofuranosyl residues are either 5-, 6-, or 5,6-linked, their linkage pattern was established, and the literature is corrected on this point.

Arabinose↗
PubMed1987

Structure of the capsular polysaccharide of Klebsiella serotype K40.

The capsular polysaccharide from Klebsiella Serotype K40 contains D-galactose, D-mannose, L-rhamnose, and D-glucuronic acid in the ratios of 4:1:1:1. Methylation analysis of the native and carboxyl-reduced polysaccharide provided information about the glycosidic linkages in the repeating unit. Degradation of the permethylated polymer with base established the identity of the sugar unit preceding the glycosyluronic acid residue. The modes of linkages of different sugar residues were further confirmed by Smith degradation and partial hydrolysis of the K40 polysaccharide. The anomeric configurations of the different sugar residues were determined by oxidation of the peracetylated native and carboxyl-reduced polysaccharide with chromium trioxide. Based on all of these results, the heptasaccharide structure 1 was assigned to the repeating unit of the K40 polysaccharide. (Formula: see text)

Carbohydrate Conformation↗
PubMed1987

Synthesis of methyl 3-O-alpha-D-mannopyranosyl-alpha-D-talopyranoside and methyl 3-O-alpha-D-talopyranosyl-alpha-D-talopyranoside.

Methyl 2-O-benzyl-3-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)-alpha- D-mannopyranoside (4) and methyl 2-O-benzyl-3-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside (6) were prepared from a common intermediate, namely, methyl 2-O-benzyl-4,6-O-benzylidene-3-O-(2,3,4,6-tetra-O-acetyl-alpha-D- mannopyranosyl)-alpha-D-mannopyranoside. On treatment with tert-butylchlorodiphenylsilane, in N,N-dimethylformamide in the presence of imidazole, 4 and 6 afforded methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(2,3,4,6-tetra-O-acetyl -alpha-D- mannopyranosyl)-alpha-D-mannopyranoside (7), and methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(6-O-tert- butyldiphenylsilyl-alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (8), respectively. Compound 8 was converted into its 2,3-O-isopropylidene derivative (9), and oxidation of 7 and 9 with pyridinium chlorochromate, and reduction of the resulting carbonyl intermediates gave methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(2,3,4,6-tetra-O-acetyl -alpha-D- mannopyranosyl)-alpha-D-talopyranoside and methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(6-O-tert-butyldiphe nylsilyl- 2,3-O-isopropylidene-alpha-D-talopyranosyl)-alpha-D-talopyranoside , respectively. Removal of the protecting groups furnished the title disaccharides.

Disaccharides↗
PubMed1987

[Synthesis of modified tetrasaccharide sequences of N-glycoproteins].

The tetrasaccharides O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D- mannopyranosyl-(1----6)]-O-(4-deoxy-beta-D-lyxo-hexopyranosyl)-(1- ---4)-2- acetamido-2-deoxy-alpha, beta-D-glycopyranose (22) and O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D-mannopyranosyl-(1----6)]-O- beta-D-talopyranosyl-(1----4)-2-acetamido-2-deoxy-alpha, beta-D- glucopyranose (37), closely related to the tetrasaccharide core structure of N-glycoproteins, were synthesized. Starting with 1,6-anhydro-2,3-di-O-isopropylidene-beta-D-mannopyranose, the glycosyl donors 3,6-di-O-acetyl-2-O-benzyl-2,4-dideoxy-alpha-D-lyxo- hexopyranosyl bromide (10) and 3,6-di-O-acetyl-2,4-di-O-benzyl-alpha-D-talopyranosyl bromide (30), were obtained in good yield. Coupling of 10 or 30 with 1,6-anhydro-2-azido-3-O-benzyl-beta-D-glucopyranose to give, respectively, the disaccharides 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2-O-benzyl-4 -deoxy- beta-D-lyxo-hexopyranosyl)-beta-D-glucopyranose and 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2,4-di-O-ben zyl- beta-D-talopyranosyl)-beta-D-glucopyranose was achieved with good selectivity by catalysis with silver silicate. Simultaneous glycosylation of OH-3' and OH-6' of the respective disaccharides with 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl chloride yielded tetrasaccharide derivatives, which were deblocked into the desired tetrasaccharides 22 and 37.

Carbohydrate Conformation↗
PubMed1987

The chemistry of the 1-deoxynojirimycin system. Synthesis of 2-acetamido-1,2-dideoxynojirimycin from 1-deoxynojirimycin.

The synthesis of 2-acetamido-1,2-dideoxynojirimycin (2-acetamido-1,2,5-tri-deoxy-1,5-imino-D-glucitol) by a double inversion procedure starting from 1-deoxynojirimycin is reported. The key intermediates were the selectively protected N-benzyl-1,5-dideoxy-1,5-imino-4,6-O-isopropylidene-D-mannitol, the triflate ester N-benzyl-3-O-benzyl-1,5-dideoxy-1,5-imino-4,6-O-isopropylidene-2-O- (tri-fluoromethylsulfonyl)-D-mannitol, and 2-azido-N-benzyl-3-O-benzyl-1,2,5-tri-deoxy-1,5-imino-4,6-O- isopropylidene-D-glucitol, readily obtained in a sequence from 1-deoxynojirimycin. Thus 1-deoxynojirimycin served as a synthon compatible with the basic operations of carbohydrate chemistry.

1-Deoxynojirimycin↗
PubMed1987

Application of the trichloroacetimidate method to the synthesis of glycopeptides of the mucin type containing a beta-D-Galp-(1----3)-D-GalpNAc unit.

Mucin-type O-glycopeptides containing the beta-D-Galp-(1----3)-D-GalpNAc disaccharide core unit, which is also the T-antigenic determinant, were synthesized from D-galactose, 2-azido-2-deoxy-D-galactose, 2-azido-2-deoxylactose, and L-serine precursors by applying the trichloroacetimidate method. Thus, beta-D-Galp-(1----3)-alpha-D-GalpNAc-(1----3)-Ser (1) and beta-D-Galp-(1----4)-beta-D-GlcpNAac-(1----6)-[beta-D-Galp-(1----3 )]-alpha-D-GalpNAc-(1----3)-Ser (2) were obtained. A protected precursor of 2 having free OH groups at C-4 and C-6 of the inner sugar unit is a valuable intermediate for the synthesis of further O-glycopeptides of this core-unit type.

Acetylgalactosamine↗