Synthesis of the pentasaccharide repeating unit corresponding to the capsular polysaccharide of Escherichia coli O20:K83:H26

Abstract

A concise synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit of the capsular polysaccharide of Escherichia coli (E. coli) strain applying block [2 + 3] stereoselective glycosylation. A functionalized disaccharide thioglycoside donor prepared using “armed-disarmed” glycosylation concept, was coupled with suitably protected trisaccharide glycosyl acceptor in the presence of a combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4–SiO2) to give the target pentasaccharide derivative in 65% yield. A late-stage regioselective oxidation of the primary hydroxyl group using a combination of TEMPO and Bis(acetoxy)iodobenzene (BAIB) furnished d-galacturonic acid moiety in the functionalized pentasaccharide derivative.