Studies on the selectivity between glycosylation and intermolecular aglycone transfer of thioglucoside in synthesis of lactose derivatives

Glycosylation reaction of 2,3-di-O-benzoyl-protected galactosyl donors with ethyl thioglucoside acceptor to prepare lactose derivatives was investigated. The presence of benzyl ether moieties at the 4 and 6 positions of the donor drove the glycosylation reaction to completion and blocked the intermolecular aglycone transfer reaction with thioglucoside. On the other hand, the presence of benzoyl moieties at those positions promoted the intermolecular aglycone transfer reaction with thioglucoside.