Synthesis of the tetrasaccharide repeating unit of the antigen from Klebsiella type 20

Starting from d-mannose, d-galactose and d-glucuronolactone, two disaccharide blocks, namely methyl 4,6-di-O-benzyl-2-O-(2,3,4,6-tetra-O-benzyl-β-d-galactopyranosyl)-α-d-mannopyranoside, acting as acceptor, and ethyl 4,6-di-O-acetyl-2-O-ally-3-O-(methyl 2,3,4-tri)-O-acetyl-β-d-glucopyranosyluronate)-1-thio-β-d-galactopyranoside, acting as donor, were synthesised. The two disaccharides were then allowed to react to give, after deprotection, methyl 2-O-β-d-galactopyranosyl-3-O-(3-O-β-d-glucopyranosyluronic acid-α-d-galactopyranosyl)-α-d-mannopyranoside which is the methyl glycoside of the tetrasaccharide repeating unit of the said antigen.