Convenient synthesis of Thr and Ser carrying the tumor associated sialyl-(2 -> 3)-T antigen as building blocks for solid-phase glycopeptide synthesis

Sialyl-T antigens have been synthesized, conveniently and in high yield, by a block condensation approach. Glycosylation of the D-GalN(3) derivative w ith the suitably protected sialyl-alpha-(2-->3)-D-galactopyranosyl trichlor oacetimidate by using trimethylsilyl trifluoromethanesulfonate (TMS-OTf) as a-promoter in dichloromethane gave the trisaccharide in high yield. Cleava ge of the tert-butyldimethylsilyl ether (TBDM) at the anomeric position of the sialic acid containing trisaccharide derivative, using tetrabutylammoni um fluoride (TBAF) in pyridine, occurred in very high yield. After conversi on to the trichloroacetimidate coupling of the sialyl-containing trisacchar ide derivative with Fmoc-Thr/Ser-OPfp, using silver trifluoromethanesulfona te (AgOTf) as a promoter in dichloromethane, gave the target building block s-in good yields.