An effective sialylation method using N-Troc- and N-Fmoc-protected β-thiophenyl sialosides and application to the one-pot two-step synthesis of 2,6-sialyl-T antigen

We describe an efficient sialylation method using β-thiosialosides with various N-protecting groups. Modification of the C-5 amino group of β-thiosialosides into N-Fmoc and N-Troc derivatives enhanced their reactivity in glycosidation. In addition, a minimum amount of MS-3 Å was effective to improve the yield of α-linked sialoside. Branched type one-pot glycosylation initiating glycosidation of the N-Troc-protected β-thiophenyl sialoside at a primary alcohol provided the protected 2,6-sialyl-T antigen in good yield, which was converted to the fully deprotected glycosyl amino acid.