Galactosyl transfer ability of β-(1→4)-galactosyltransferase toward 5a-carba-sugars

Bovine β-(1→4)-galactosyltransferase was assayed with a series of 5a-carba-sugars, i.e., sugar analogues in which the ring oxygen of pyranose is replaced by a methylene group. The analogues are 5a-carba-sugar of 2-acetamido-2-deoxy-α-dl-galactopyranose, both α and β anomers of 2-acetamido-2-deoxy-dl-glucopyranose (5a-carba-dl-GlcNAc), and 2-acetamido-2-deoxy-dl-mannopyranose. Of these analogues, both α and β anomers of 5a-carba-dl-GlcNAc act as an acceptor. Enzymatic synthesis using the α and β anomers of 5a-carba-dl-GlcNAc afforded the corresponding d-Gal-β-(1→4)-5a-carba-α-d-GlcNAc and d-Gal-β-(1→4)-5a-carba-β-d-GlcNAc on a practical scale, and these structures were confirmed by NMR spectroscopy. These results indicate that the ring oxygen atom in the 5a-carba-d-GlcNAc is not used for specific recognition by bovine β-(1→4)-galactosyltransferase.