Synthesis of the tetrasaccharide repeating unit of the K-antigen from Klebsiella type 57.

Starting from D-galactose and D-mannose two disaccharide blocks, namely 2-(trimethylsilyl)-ethyl 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl-(1-->4)-6-O-(4-methoxybenz yl)- beta-D-galactopyranoside and ethyl 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl-(1-->3)-4-O-acetyl- 2,6-di-O-benzoyl-1-thio-beta-D-galactopyranoside, were synthesized which were then allowed to react, in the presence of dimethyl(methylthio)sulfonium triflate to give a tetrasaccharide derivative. This compound was converted to 2-(trimethylsilyl)ethyl 2,3,4,6-tetra-O-benzyl-alpha-D- mannopyranosyl-(1-->3)-4-O-acetyl-2,6-di-O-benzoyl-beta-D-galactopyranos yl- (1-->3)-[2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl-(1-->4)]-tert-but yl (2-O-acetyl-beta-D-galactopyranosid)uronate which, on treatment with sodium methoxide followed by hydrogenolysis, afforded the methyl [2-(trimethylsilyl)ethyl glycosid]uronate of the tetrasaccharide repeating unit of the K-antigen from Klebsiella type 57.