4, 5-Dichlorophthaloyl Group for Amino Protection in Carbohydrate Chemistry

Abstract

Phthaloyl (Phth) is a valuable amino-protecting group for use in synthetic carbohydrate chemistry. Its strong 1, 2-trans-directing nature in a glycosylation reaction, when it is introduced to the C__--2 position of a glycosyl donor, makes the construction ofβ-GlcNAc or β-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 elevated temperature when applied to a large oligosaccharide. We studied the 4, 5-dichlorophthaloyl (DCPhth) group as an alternative to Phth. A thioglycoside carrying a DCPhth group at the C__--2 position was reacted with alcohol by the action of PhSeNPhth-TMSOTf to selectively give the correspondingβ-glycoside. DCPhth Could then be .removed under mild conditions by using ethylenediamine or hydrazine/MeOH at room temperature.