A Novel Chemoenzymatic Synthesis of Sulfated Type 2 Tumor-Associated Carbohydrate Antigens by Transglycosylation of Sulfated Lewis X Oxazoline Catalyzed by Keratanase II

Abstract

Sulfated type 2 carbohydrate chains are known tumor-associated carbohydrate antigens (TACAs). Many reports on cancer vaccines employing TACAs as specific antigens have been published, but structurally specified sulfated TACAs have not been used because of the low natural abundance and difficulties in chemical synthesis. We demonstrate for the first time the synthesis of the sulfated type 2 TACAs with an l-fucose branch by keratanase-II-catalyzed transglycosylation of the sulfated Lewis X (Galβ(1→4)[Fucα(1→3)]GlcNAc(6-OSO₃^- ); su-Le^x ) oxazoline derivative. Two keratanase IIs (from Bacillus sp. Ks36 and Bacillus circulans KsT202) efficiently catalyzed the transglycosylation reaction of the su-Le^x oxazoline derivative, thereby giving the su-Le^x dimer as the main product in good yields. Structural analysis of the oligomers confirmed exclusive formation of the β(1→3) glycosidic bond.

Keywords: Lewis X; enzyme catalysis; glycosylation; transition states; tumor-associated carbohydrate antigens.