Synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of Escherichia coli O59 using iterative glycosylations in one pot

Abstract

Synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of Escherichia coli O59 has been achieved by orthogonal glycosylation and two iterative glycosylations in one pot. Synthesis of a β-d-mannosidic linkage present in the molecule has been successfully achieved with satisfactory yield by the activation of thioglycoside with a combination of 1-benzenesulfinyl piperidine (BSP) and triflic anhydride (Tf2O). The α-d-glucosaminyl moiety was achieved in moderate yield from the α-d-mannosyl moiety by azidolysis of C-2 hydroxy group with inversion of configuration. TEMPO mediated selective oxidation of the primary hydroxyl group has been carried out at the late stage of the synthetic strategy.