SYNTHETIC OLIGOSACCHARIDES RELATED TO GROUP-B STREPTOCOCCAL POLYSACCHARIDES .4. SYNTHESIS OF A TRISACCHARIDE AND A TETRASACCHARIDE FRAGMENT OF THE CAPSULAR POLYSACCHARIDE OF TYPE-III GROUP-B STREPTOCOCCUS

Syntheses of the propyl glycosides (1-3) of β-d-Galp-(1→4)-β-d-GlcpNAc, β-d-Glcp-(1→6)-[β-d-Galp-(1→4)]-β-d-GlcpNAc, and β-d-Galp-(1→4)-β-d-Glcp-(1→6)-[β-d-Galp-(1→4)]-β-d-GlcpNAc, respectively, are reported. Reaction of allyl 2-acetamido-3-O-benzyl-2-deoxy-6-O-(4-methoxybenzyl)-β-d-glucopyranoside with 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide under Hg(CN)2 catalysis, followed by oxidative removal of the 4-methoxybenzyl group, gave allyl 2-acetamido-3-O-benzyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d-glucopyranoside (10) O-deacetylation of which, followed by hydrogenolysis/hydrogenation, gave 1. Reaction of 10 with β-d-glucopyranose penta-acetate and β-lactose octa-acetate, under catalysis by trimethylsilyl trifluoromethanesulfonate, and treatment of the products as for 10 gave 2 and 3, respectively. Attempted glycosylation of 10 with 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl bromide under catalysis by Hg(CN)2 or silver trifluoromethanesulfonate gave an orthoester. Complete assignments of the 1H- and 13C-n.m.r. spectra of 1-3 are reported together with their carbon spin-lattice relaxation times which indicate that 3 assumes a compact instead of an extended shape. © 1990.