4,5-DICHLOROPHTHALOYL GROUP FOR AMINO PROTECTION IN CARBOHYDRATE-CHEMISTRY

Phthaloyl (Phth) is a valuable amino-protecting group for use in synth etic carbohydrate chemistry. Its strong 1,2-trans-directing nature in a glycosylation reaction, when it is introduced to the (C) under bar-2 position of a glycosyl donor, makes the construction of beta-GlcNAc o r beta-GalNAc glycosides quite straightforward. The Phth group can be removed by using an appropriate nucleophile, most typically hydrazine; however, this transformation often requires a long reaction time at e levated temperature when applied to a large oligosaccharide. We studie d the 4,5-dichlorophthaloyl (DCPhth) group as an alternative to Phth. A thioglycoside carrying a DCPhth group at the (C) under bar-2 positio n was reacted with alcohol by the action of PhSeNPhth-TMSOTf to select ively give the corresponding beta-glycoside. DCPhth could then be remo ved under mild conditions by using ethylenediamine or hydrazine/MeOH a t room temperature.