Synthetic directions of acidic hexasaccharide repeating unit of the O-antigen of Cronobacter sakazakii HPB 2855 using one pot glycosylation

Abstract

Synthesis of a hexasaccharide repeating unit of the O-antigen of Cronobacter sakazakii HPB 2855 has been achieved by sequential glycosylations and one-pot glycosylation-deprotection techniques. The synthetic method relies on the use of a p-methoxybenzyl ether as an in situ-removable protecting group to reduce the number of reaction steps significantly. All the glycosylations have been accomplished by the activation of the only one class of simple and stable thioglycosyl donors using NIS in the presence of sulfuric acid immobilized on silica (H2SO4-silica) as a Brönsted acid catalyst to work as a promoter. The stereo outcomes of all the glycosylation steps were excellent with satisfactory yield. TEMPO mediated selective oxidation of the primary hydroxyl group has been carried out at the late stage of the synthetic strategy to achieve the required uronic acid motif.