Synthesis of penta- and hexasaccharide fragments corresponding to the O-antigen of Escherichia coli O150

The chemical synthesis of a pentasaccharide and a hexasaccharide corresponding to the O-antigen of Escherichia coli O150 has been achieved using sequential glycosylation and [3+3] block glycosylation strategies. Suitably protected monosaccharide synthons have been prepared from the commercially available reducing sugars and then stereoselectively coupled to give the pentasaccharide and a hexasaccharide in excellent yields. 4-Methoxyphenyl and 2-(4-methoxyphenoxy) ethyl groups have been used as the anomeric-protecting groups in the target pentasaccharide and a hexasaccharide, respectively.