Synthesis of the pentasaccharide repeating unit of the O-antigenic polysaccharide of enteroaggregative Escherichia coli O44:H18 strain

Abstract

A straightforward synthetic strategy has been developed for the synthesis of the branched pentasaccharide repeating unit of the O -antigenic polysaccharide of enteroaggregative Escherichia coli O44: H18 strain involving functional group directed stereoselective β- d -mannosylation together with α-glycosylations of d -glucose and d -mannose moieties using suitably protected thioglycoside as glycosyl donors. A combination of N -iodosuccinimide (NIS) and perchloric acid supported over silica (HClO 4 –SiO 2 ) was used as thiophilic glycosylation promoter in all glycosylation reactions. The yields of the glycosylations were very good with satisfactory stereochemical outcome. • Branched pentasaccharide corresponding to Escherichia coli O44:H18 was synthesized. • A combination of NIS and HClO 4 –SiO 2 was used as glycosylation activator. • p -Methoxybenzyl (PMB) was used as H-bond mediating functional group for β-mannosylation. • β- d -mannosylation was achieved in very good yield with high stereochemical outcome. • HClO 4 –SiO 2 has been used as a solid acid catalyst.