β-Galactosidase-catalyzed intramolecular transglycosylation

A novel transglycosylation strategy for efficient preparation of N-acetyllactosamine (Galβ1→4GlcNAc, LacNAc) and sialyl LacNAc was developed using β-galactosidase from Bacillus circulans. In order to minimize the competing hydrolysis by forcing the enzymatic transglycosylation to proceed in an intramolecular manner, a novel substrate 9 carrying the donor (galactose) and the acceptor (N-acetylglucosamine) components linked via a 2-hydroxy-5-nitro-benzylalcohol derived tether was prepared. Treatment with β-galactosidase from B. circulans afforded the transglycosylation product 11 in 26% yield. Furthermore, addition of sialyltransferase and CMP–sialic acid to this system gave sialyl LacNAc 18 in 39% yield.