Nirmolendu Roy

Synthesis of the Trisaccharide Repeating Unit of the O‐Antigen Related to the Enterohemorrhagic Escherichia coli Type O26:H

l‐Fucose was converted to the 2‐azido‐2‐deoxy‐l‐fucose derivative, which together with the monosaccharide synthons prepared from l‐rhamnose and d‐glucosamine hydrochloride were utilized for the synthesis of the p‐ethoxyphenyl glycoside of the trisaccharide repeating unit of the antigen from enterohemorrhagic Escherichia coli type O26:H.

Synthesis of the tetrasaccharide repeating-unit of the polysaccharide from Klebsiella type 23

Methyl 2-O-allyl-4-O-benzyl-3-O-(2,3,4,6-tetra-O-acetyl-beta-D- glucopyranosyl)-alpha-L-rhamnospyranoside was obtained by condensing methyl 2-O-allyl-4-O-benzyl-alpha-L-rhamnopyranoside with tetra-O-acetyl-alpha-D-glucopyranosyl bromide. Benzylation, removal of the allyl group, and condensation of the product with ethyl 6-O-acetyl-2,3,4-tri-O-benzyl-1-thio-beta-D-glucopyranoside gave methyl 2-O-(6-O-acetyl-2,3,4-tri-O-benzyl-alpha-D-glucopyranosyl)-4-O-benzyl-3- O- (2,3,4,6-tetra-O-benzyl-beta-D-glucopyranosyl)-alpha-L-rhamnopyranoside. O-Deacetylation, condensation of the product with methyl (2,3,4-tri-O-acetyl-alpha-D-glucopyranosyl bromide)-uronate, and removal of the protecting groups gave methyl 3-O-beta-D-glucopyranosyl-2-O-[6-O-(beta-D-glucopyranosyluronic acid)-alpha-D-glucopyranosyl]-alpha-L-rhamnopyranoside (13).

Chemical and immunochemical studies of the O-antigen from enteropathogenic Escherichia coli O158 lipopolysaccharide

The O-specific polysaccharide isolated from Escherichia coli O158 smooth lipopolysaccharide contains L-rhamnose, D-glucose and 2-acetamido-2-deoxy-D-galactose in the molar ratios 1:2:2. Studies on composition, methylation analysis and specific degradations together with a 1H and 13C NMR spectral study established that the O-antigen is built up from a pentasaccharide repeating unit having the following structure: [formula: see text] The most effective inhibitory part of the oligosaccharide from E. coli O158 lipopolysaccharide has been serologically characterized by an ELISA-inhibition study using different sugars. The results showed that methyl alpha- and beta-D-GalpNAc are the most effective inhibitors among the monosaccharides tested, while the main antibody specificity lies on the main-chain trisaccharide repeating unit.

Synthesis of a di- and a tri-saccharide related to the k-antigen of Klebsiella type 10 and a study of their inhibition in the precipitin reaction

Syntheses of methyl 3-O-alpha-D-galactopyranosyl-alpha-D-mannopyranoside (10) and methyl 3-O-alpha-D-galactopyranosyl-2-O-(beta-D-glucopyranosyluronic acid)-alpha-D-mannopyranoside (11) in good yield are described. Both 10 and 11 significantly inhibit antigen-antibody precipitation in the Klebsiella Type 10 immune system. The results provide more evidence for the structure (1) of the antigen from Klebsiella K-10 and its immunodominant grouping.

AN IMPROVED METHOD FOR THE PREPARATION OF SOME ETHYL 1-THIOGLYCOSIDES

Abstract Ethyl 1-thioglycosides were prepared in almost quantitative yield from sugar peracetates in 3:2 chloroform-ether, with boron trifluoride diethyl etherate as catalyst. d -Galactose, d -glucose, and 2-deoxy-2-phthalimido- d -glucose yielded almost exclusively β anomers, whereas l -rhamnose and d -mannose resulted predominantly in the α anomers.

SYNTHESIS OF SOME GALACTOFURANOSYL DISACCHARIDES USING A GALACTOFURANOSYL TRICHLOROACETIMIDATE AS DONOR

Abstract 2,3,5-Tri- O -benzoyl-6- O -benzyl- β - d -galactofuranosyl trichloroacetimidate has been prepared for the first time and utilised as glycosyl donor for the synthesis of several disaccharides containing the β -linked galactofuranoside moiety.

Synthesis of the Trisaccharide Repeating Unit of the K-Antigen from Klebsiella Type-63

Abstract Starting from L-fucose, D-glucose and lactose, methyl O-[2,3-di-O-benzoyl-4, 6-O-(4-methoxybenzylidene)-β-D-glucopyranosyl]-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside and methyl O-(2,3,4,6-tetra-O-benzyl-β-D-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate)-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside were synthesized. Removal of protecting groups gave the tetrasaccharide repeating unit of the antigen from Klebsiella type-16 in the form of its methyl ester methyl glycoside.

Synthesis of di- and tri-saccharides related to the polysaccharide from Streptococcus pneumoniae type 23 and a study of their inhibition in the precipitin reaction

Syntheses of methyl 2-O-beta-L-rhamnopyranosyl-beta-D-galactopyranoside (9), methyl 2-O-alpha-L-rhamnopyranosyl-beta-D-galactopyranoside (13), and methyl 4-O-beta-D-glucopyranosyl-2-O-alpha-L-rhamnopyranosyl-beta-D- galactopyranoside (16) in good yields are described. Both 13 and 16 significantly inhibit antigen-antibody precipitation in the S. pneumoniae Type 23 immune system. The results indicate that the rhamnosyl group in the side chain of the repeating unit of the antigen is alpha and not beta as reported previously, and that the trisaccharide related to 16 is the immunodominant group.

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)

Synthesis of the pentasaccharide related to the repeating unit of the antigen from Shigella dysenteriae type 4 in the form of its methyl ester 2-(trimethylsilyl)ethyl glycoside.

Starting from D-mannose, D-glucose and L-fucose, the pentasaccharide derivative methyl 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl-(1-->3)-2-O-acetyl-4,6-O-benzylidene-alpha-D-mannopyranosyl-(1-->3)-2-O-acetyl-6-O-benzyl-4-O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-alpha-D-mannopyranosyl-(1-->4)-[2-(trimethylsilyl)ethyl 2,3-di-O-benzyl-beta-D-glucopyranosid]uronate was synthesized. This compound with two alpha-mannopyranosyl units was transformed, via Walden inversion and subsequent deprotection, into the alpha-D-glucosamine-type target compound, namely methyl alpha-L-fucopyranosyl-(1-->3)-2-acetamido-2-deoxy-alpha-D-glucopyranosyl-(1-->3)-2-acetamido-2-deoxy-4-O-(alpha-L-fucopyranosyl)-alpha-D-glucopyranosyl-(1-->4)-[2-(trimethylsilyl)ethyl beta-D-glucopyranosid]uronate which is related to the repeating unit of the O-antigen from Shigella dysenteriae type 4.