Assistance of the C-7,8-Picoloyl Moiety for Directing the Glycosyl Acceptors into the α-Orientation for the Glycosylation of Sialyl Donors.

An efficient α-sialylation method for many primary hydroxyl acceptors that include 6-OH glycosides has been developed. 7,8-Di-O-picoloyl sialyl glycoside was used as the glycosyl donor, and α-glycoconjugation was controlled by using the 7,8-di-O-picoloyl moiety in CH2 Cl2 . The methodology was successfully applied to the total synthesis of ganglioside Hp-s1 possessing neuritogenic activity.