Sialylations reactions: Expanding the effect of silicon protecting groups at C-4.

As a part of a general research goal into evaluating the effect of O-protecting groups in sialylation reactions, we compared the reactivities of phenylthio α- and ß-sialyl donors protected at C-4 with tert-butyldimethyl silyl (TBDMS) and tri-isopropylsilyl (TIPS) groups in the coupling with primary and secondary galactosyl acceptors. The effect of the solvent and the donor's anomeric configuration were investigated and compared to previously published data. It is demonstrated that silicon groups at C-4 have a significant influence on sialylation reactions, and in general their overall performance is optimized with the use of acetonitrile.