A Unique Chemoenzymatic Synthesis of α-Galactosyl Epitope Derivatives Containing Free Amino Groups: Efficient Separation and Further Manipulation

Abstract

A novel chemoenzymatic approach for the synthesis of oligosacchrides containing free amino groups has been developed in which thermophilic glycosidases and a fusion enzyme containing catalytic domains of uridine-5‘-diphospho-galactose 4-epimerase and α(1→3) galactosyltransferase were used. This methodology, in conjunction with a convenient purification procedure employing ion exchange chromatography, facilitates the lengthy and high-cost process of carbohydrate synthesis. The prepared oligosaccharides range from disaccharide lactosamine (1a), trisaccharide α-Gal-(1→3)-β-Gal-(1→4)-GlcNH2 (2), tetrasaccharide β-Gal-(1→4)-β-GlcNH2-(1→3)-β-Gal-(1→4)-β-Glc-N3 (7), to pentasaccharide α-Gal-(1→3)-β-Gal-(1→4)-β-GlcNH2-(1→3)-β-Gal-(1→4)-β-Glc-N3 (15). Compounds 2 and 15 are derivatives of natural α-Gal epitopes. Both of them have shown comparable activities with their natural parent compounds toward human anti-Gal IgG. This method provides a practical approach for the preparation and purification of oligosaccharides containing free amino groups, which can be further derivatized for the enhancement of biological activities.