Ring-opening of aziridine-2-carboxamides with carbohydrate C1-O-nucleophiles. Stereoselective preparation of alpha- and beta-O-glycosyl serine conjugates.

The stereoselective formation of the alpha-GalNAc-Ser linkage via the ring opening of aziridine-2-carboxamides with pyranose C1-O-nucleophiles is described. The process is tolerant to the native C2-NHAc group, can be modulated to provide either the alpha- or beta-glycoside through judicious choice of solvent and metal counterion, and is amenable to other classes of O-glycosyl-Ser constructs such as the beta-GlcNAc-Ser and alpha-Man-Ser linkages. This coupling reaction also led to the development of the o-allylbenzyl (ABn) moiety as a new C-terminus carboxyl protective group, which allows for the use of novel methods for N- and C-terminus extension of amino acids following carbohydrate conjugation.