Concise synthesis of sialic acid containing hexasaccharide corresponding to group B Streptococcus type IX capsular polysaccharide

Abstract

A convenient block [3 + 2+1] glycosylation strategy has been developed for the synthesis of sialic acid containing hexasaccharide repeating unit having a 2-aminoethyl linker at the reducing end corresponding to the capsular polysaccharide of Group B Streptococcus type IX strain. A disaccharide thioglycoside has been prepared applying “orthogonal latent-active” glycosylation of a thioglycoside acceptor with a thioglycoside donor. A specially designed sialic acid thioglycoside donor has been used to furnish α-glycosidic linkage. Thioglycosides were used as glycosyl donors throughout the synthetic strategy. A combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4–SiO2), a solid acid substitute, was used as a thiophilic promoter for the activation of thioglycosides.