Streptococcus pneumoniae type XIV polysaccharide: synthesis of a repeating branched tetrasaccharide with dioxa-type spacer-arms.

beta-Glycosides of 2-acetamido-2-deoxy-D-glucopyranose were synthesised, using either 7-methoxycarbonyl-3,6-dioxa-1-heptanol or 8-azido-3,6-dioxa-1-octanol. Selective beta-lactosylation of 7-methoxycarbonyl-3,6-dioxaheptyl 2-acetamido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside with hepta-O-acetyl-lactosyl-trichloroacetimidate, followed by beta-galactosylation of the secondary hydroxyl group with O-(2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl)trichloroacetimida te, catalytic hydrogenolysis, and O-deacetylation, gave 7-methoxycarbonyl-3,6-dioxaheptyl 2-acetamido-2-deoxy-4-O-beta-D-galactopyranosyl-6-O-(4-O-beta-D- galactopyranosyl-beta-D-glucopyranosyl)-beta-D-glucopyranoside. Selective beta-lactosylation of 8-azido-3,6-dioxaoctyl 2-acetamido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside with hepta-O-acetyl-lactosyl bromide in the presence of silver triflate, followed by condensation with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of silver triflate, catalytic hydrogenolysis, and O-deacetylation, gave 8-azido-3,6-dioxaoctyl 2-acetamido-2-deoxy-4-O-beta-D-galactopyranosyl-6-O-(4-O-beta-D- galactopyranosyl-beta-D-glucopyranosyl)-beta-D-glucopyranoside.