Synthesis of the acidic pentasaccharide repeating unit of the cell wall O-antigen of Providencia alcalifaciens O45:H25 strain

Abstract

Synthesis of an acidic pentasaccharide repeating unit corresponding to the cell wall O-antigen of the human pathogen, Providencia alcalifaciens O45:H25 strain has been achieved by multi-step stereoselective glycosylations. p-Methoxybenzyl (PMB) group was used as in situ removable protecting group, which was removed from the glycosylated products in the same pot after stereoselective glycosylations. The d-glucuronic acid moiety in the pentasaccharide derivative was installed by converting the primary hydroxyl group of the d-glucose moiety to a carboxylic group using a late-stage TEMPO-bis(acetoxy)iodobenzene (BAIB) mediated selective oxidation condition. Only thioglycoside donors were used for glycosylation steps with satisfactory stereochemistry and chemical yields.