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).