Convenient Synthesis of the Branched Hexasaccharide Repeating Unit of the Cell Wall O-Antigen of Escherichia coli O80 Strain

Abstract

Chemical synthesis of a branched hexasaccharide corresponding to the cell wall O-antigen of Escherichia coli (E. coli) O80 strain has been achieved in very good yield with satisfactory stereochemical outcome around the glycosidic linkages by applying a regio- and stereoselective [4+2] block glycosylation strategy. The tetrasaccharide diol derivative was synthesized from suitably functionalized monosaccharide intermediates using sequential stereoselective glycosylations and the disaccharide thioglycoside donor was obtained applying a regio- and stereoselective orthogonal armed-disarmed glycosylation strategy using protected thioglycoside derivatives. A late-stage TEMPO and bis(acetoxy)iodobenzene (BAIB) mediated regioselective oxidation of the primary hydroxyl group of the protected hexasaccharide derivative to the carboxylic acid was achieved leaving secondary hydroxyl groups unaffected.