Synthesis of the tetrasaccharide repeating unit of the antigen from Klebsiella type 2.

The disaccharide ethyl 2,4,6-tri-O-acetyl-3-O-(2,3,4,6-tetra-O-benzyl-alpha- D-glucopyranosyl)-1-thio-beta-D-glucopyranoside (6) and methyl 2,6-di-O-benzyl-3-O-(methyl 2,3,4-tri-O-benzyl-alpha-D- glucopyranosyluronate)-beta-D-mannopyranoside (21) have been synthesized and condensed in the presence of methyl triflate to afford a tetrasaccharide derivative. Removal of protecting groups gave methyl 3-O-(methyl alpha-D-glucopyranosyluronate)-4-O-(3-O-alpha-D- glucopyranosyl-beta-D-glucopyranosyl)-beta-D-mannopyranoside (23), the repeating unit of the antigen from Klebsiella type 2, in the form of its methyl ester methyl glycoside.