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-α-d-glucopyranosyl)-1-thio-β-d-glucopyranoside(6) and methyl 2,6-di-O-benzyl-3-O-(methyl 2,3,4-tri-O-benzyl-α-d-glucopyranosyluronate)-β-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 α-d-glucopyranosyluronate)-4-O-(3-O-α-d-glucopyranosyl-β-d-glucopyranosyl)-β-d-mannopyranoside(23), the repeating unit of the antigen from Klebsiella type 2, in the form of its methyl ester methyl glycoside.