Synthesis and evaluation of glycosyl donors with novel leaving groups for transglycosylations employing beta-galactosidase from bovine testes.

Novel aryl beta-d-galactopyranosides were synthesized employing phase-transfer catalysis, and assayed as potential galactose donors in the presence of beta-galactosidase from bovine testes using pNP-Gal as a reference. The aglycones were represented mainly by nitrophenols containing halogens, hydroxymethyl, aldehyde, carboxyl, ester or amino functions. An unusual intermolecular acetyl migration onto the benzylic alcohol group was observed during galactosylation of hydroxymethylnitrophenols. Pyridyl glycosides were obtained by reaction with the corresponding silver pyridinolates. Glycosides of halo-, hydroxymethyl- or methoxycarbonyl-nitrophenols as leaving groups gave virtually the same yields of transglycosylation products. A minor increase was achieved with nitrosalicylaldehyde as leaving group, whereas carboxy or amino derivatives gave very low or no yield of the transglycosylation product. Commercially available donors such as resorufinyl and 4-methylumbelliferyl beta-d-galactopyranosides exhibited a lower transglycosylation potential than these novel pNP-Gal derivatives.