To make a glycoprotein with a definite molecular weight

Glycoproteins, naturally occurring hybrid macromolecules composed of a protein and oligosaccharide chains, show various important biological activities in medical and pharmaceutical sciences. In spite of strong demand for glycoproteins having a definite structure, its specific preparation is still an unsolved problem in the field of synthetic organic chemistry. Here we propose an efficient strategy for synthesis of glycoproteins via 1,2-oxazoline derivatives as glycosyl donors for enzymatic transglycosylation. We developed a facile method for synthesis of sugar oxazoline derivatives by the intramolecular dehydration reaction of the corresponding unprotected 2-acetamido-sugars in water using 2-chloro-1,3-dimethylimidazolinium chloride (DMC) as a dehydrating agent. According to this method, disialo-oligosaccharides can be converted to the corresponding 1,2-oxazoline derivatives in high yields without protecting the hydroxy groups. A transglycosylation of the resulting oxazoline derivative to the GlcNAc moiety on a protein has successfully been demonstrated catalyzed by a mutant of A'-acetylglucosaminidase-M, giving rise to a monodispersed disialo-type glycoprotein.