ENZYMATIC-SYNTHESIS OF -[-BETA-D-GLCNAC-(1-]6)]-ALPHA-D-GALNAC-OC6H4NO2-P AS A CARBOHYDRATE UNIT OF MUCIN-TYPE-2 CORE

We have established a synthetic method for obtaining -beta-D-Gal-(1 -- > 3)-[beta-D-GlcNAc-(1 --> 6)]-alpha-D-GalNAc-OC6H4NO2-p (1), which is a carbohydrate unit of mucin-type 2 core. A beta-N-acetyl-D-hexosamin idase from Nocardia orientalis catalyzed the synthesis of the desired compound 1 with its isomers beta-D-GalNAc-(1 --> 6)-beta-D-Gal-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p (2) beta-D-GlcNAc-(1 --> 3)-beta-D-Glc-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2-p (3) through N-acetylglucosaminyl tra nsfer from N,N'-diacetylchitobiose and beta-D-Gal-(1 --> 3)-alpha-D-Ga lNAc-OC6H4NO2-p. The enzyme formed the trisaccharides 1,2, and 3 in 14 % overall yield based on beta-D-Gal-(1 --> 3)-alpha-D-GalNAc-OC6H4NO2- p as an acceptor substrate, and in the ratio of 44:32:24. In this way, N-acetylglucosaminyl transfer favored O-6 of the acceptor rather than O-6', and occurred to a lesser extent at O-3'. This reaction was effi cient enough to allow a one-pot preparation of the desired carbohydrat e unit of mucin-type 2 core. When beta-D-Gal-(1 --> 3)-beta-D-GalNAc-O C6H4NO2-p was used as an acceptor, the enzyme also synthesized three k inds of trisaccharides in the same regioselectivity with respect to O- 6 and O-6' versus O-3' of the acceptor.