Synthesis of Carbohydrate-Antigenic Structures ofMycobacterium Tuberculosisusing an Iodonium Ion Promoted Glycosidation Approach

Syntheses of deoxy analogues of methyl 3,6-di-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside for studies of the binding site of concanavalin A

All of the monodeoxy analogues of methyl 3,6-di-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside have been synthesized together with two dideoxy (2,3'- and 4,3'-) analogues. The 2'- and 2"-deoxy functions were introduced by NIS-promoted couplings with 2,3,4-tri-O-acetyl-D-glucal as donor, followed by reduction of the resulting 2'- and 2"-iodo derivatives, whereas the 3'-, 3"-, 4'-, 4"-, 6'-, and 6"-deoxy functions were introduced by using known deoxyglycosyl chlorides as donors in coupling reactions promoted by silver trifluoromethanesulfonate. The 2- and 4-deoxy functions on the central mannose residue were introduced by displacement, using triiodoimidazole and triphenylphosphine, of a hydroxyl group by iodine on suitably protected derivatives followed by reduction of the resulting iodo analogues.

Synthesis of a pentasaccharide fragment of Polysaccharide II of Mycobacterium tuberculosis

Stereocontrolled, stepwise synthesis of decyl glycosides of alpha-(1-->2)-linked di- to pentaglucosides (1-5) is described; these constitute fragments of Polysaccharide II of Mycobacterium tuberculosis. Phenyl 3,4,6-tri-O-acetyl-2-O-benzyl-1-thio-alpha-D- glucopyranoside (7) was used as the single key intermediate, obtained from 1,3,4,6-tetra-O-acetyl-2-O-benzyl-beta-D-glucopyranose (6) and PhSSiMe3. Halogenolysis of 7 afforded the isolated beta bromide (10) and beta chloride (13). Solvolysis of 10 with decanol without heavy metal salts gave decyl 3,4,6-tri-O-acetyl-2-O-benzyl-alpha-D-glucopyranoside (14) in a highly stereoselective reaction, in high yield. Subsequent, iterative hydrogenolytic removal of the O-benzyl group and glycosylation with the beta-chloride 13 under catalysis by silver salts afforded the protected di- to penta-saccharide glycosides 16, 19, 21, and 23, which were conventionally deblocked.

Modulation of antibody affinity by synthetic modifications of the most exposed pyranose residue of a trisaccharide epitope

When the Salmonella trisaccharide epitope, methyl 3-O-(3,6-dideoxy-alpha-D-xylo-hexopyranosyl)-2-O-(alpha-D-galactopyra nos yl)- alpha-D-mannopyranoside 12 is bound by a monoclonal antibody Se155.4, the 3,6-dideoxy-alpha-D-hexose is completely buried, while the galactopyranosyl mannopyranosyl units lay across the protein surface. Crystallography of an antibody complexed with 12 also shows that the galactose residue is the most exposed saccharide. A simplified strategy to synthesize 12 and analogues modified at the galactose residue is described. Monosaccharide building blocks containing benzyl ether and ester protecting groups were used for efficient assembly of trisaccharides that can be deprotected by a single hydrogenolysis step, or occasionally preceded by a transesterification stage. Glycosylation of methyl 2-O-benzoyl-4,6-di-O-benzyl-alpha-D- mannopyranoside 4 by 2,4-di-O-benzyl-3,6-dideoxy-D-xylo-hexopyranosyl chloride 8 affords after transesterification the disaccharide acceptor 10. This disaccharide serves as a universal acceptor for glycosylation by glycosyl donors that lead, following facile deprotection, to the alpha- and beta-D-galacto, alpha- and beta-D-gluco, and 2-amino-2-deoxy-alpha-D-galacto trisaccharides 12, 14, 17, 18 and 21. Only a small change in binding energy delta (delta G) occurs when the alpha-D-galactopyranosyl residue of 12 is replaced by either an alpha-D-glucopyranosyl 17 or a 2-amino-2-deoxy alpha-D-galactopyranosyl unit 21. Whereas binding of the beta-D-glucopyranose congener 18 was tolerated by the antibody, the beta-D-galactopyranose analogue 14, showed a 250 fold loss of affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of 5-aminopentyl mono- to tri-saccharide haptens related to the species-specific glycopeptidolipids of Mycobacterium avium-intracellulare serovars 8 and 21

The preparation of pyruvate acetal-containing 5-aminopentyl mono-, di-, and tri-saccharide fragments related to serovars 8 and 21 of the species-specific glycopeptidolipid of Mycobacterium avium-intracellulare is described. The saccharides were constructed by sequential coupling of the suitably protected 4,6-O-[(S)-1-methoxycarbonylethylidene]-D-glucopyranosyl trichloroacetimidates 6 and 7 to Z-protected 5-aminopentanol, to give the serovar 21 monosaccharide fragment 9 upon deblocking; and to ethyl 2-O-benzoyl-4-O-benzyl-1-thio-alpha-L-rhamnopyranoside (18), to give the corresponding ethyl 1-thio-disaccharides 21 and 23, respectively. Subsequent N-iodosuccinimide-promoted coupling of the latter with Z-protected 5-aminopentanol followed by deblocking of the products afforded the corresponding disaccharide fragments 26 (serovar 8) and 27 (serovar 21), respectively. Condensation of 21 with Z-protected 5-aminopentyl 3,4-di-O-benzyl-6-deoxy-alpha-L-talopyranoside (28) and subsequent deblocking of the resulting trisaccharide gave the serovar 8 fragment 5-aminopentyl O-(4,6-O-[(S)-1-carboxyethylidene]-3-O-methyl-beta-D-glucopyranosyl)- (1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)-6-deoxy-alpha-L-talopyranos ide (30).