A unique chemoenzymatic synthesis of α-galactosyl epitope derivatives containing free amino groups:: Efficient separation and further manipulation

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 alpha(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 alpha-Gal-(1-->3)-beta-Gal-(1-->4)-GlcNH(2) (2), tetrasaccharide beta-Gal-(1-->4)-beta-GlcNH(2)-(1-->3)-beta-Gal-(1-->4)-beta-Glc-N-3 (7), to pentasaccharide alpha-Gal-(1-->3)-beta-Gal-(1-->4)-beta-GlcNH(2)-(1-->3)-beta-Gal-(1-->4)-beta-Glc-N-3 (15). Compounds 2 and 15 are derivatives of natural alpha-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.