Synthesis of Two Hexasaccharides Related to the Repeating Unit of the O-Antigen from Escherichia coli TD2158

摘要

Efficient strategies for the synthesis of two hexasaccharides related to the O-antigen polysaccharide of E. coli TD2158 are reported. Both of the oligosaccharides were prepared by the sequential glycosylation of rationally functionalized monosaccharide synthons derived from commercially available sugars. Azido and phthalimido groups were utilized as the precursors for the natural acetamido functionality depending on the stereochemical requirement of the glycosidic bond. The target oligosaccharides were prepared in the form of their 4- methoxyphenyl (OPMP) glycoside to leave the scope for further glycoconjugate formation. All glycosylation reactions were performed through the activation of thioglycosides using NIS and H2SO4-silica resulting in desired stereoselectivity and good to excellent yields.