1-O-Acetyl-β-d-galactopyranose: a novel substrate for the transglycosylation reaction catalyzed by the β-galactosidase from Penicillium sp.

1-O-Acetyl-β-d-galactopyranose (AcGal), a new substrate for β-galactosidase, was synthesized in a stereoselective manner by the trichloroacetimidate procedure. Kinetic parameters (KM and kcat) for the hydrolysis of 1-O-acetyl-β-d-galactopyranose catalyzed by the β-d-galactosidase from Penicillium sp. were compared with similar characteristics for a number of natural and synthetic substrates. The value for kcat in the hydrolysis of AcGal was three orders of magnitude greater than for other known substrates. The β-galactosidase hydrolyzes AcGal with retention of anomeric configuration. The transglycosylation activity of the β-d-galactosidase in the reaction of AcGal and methyl β-d-galactopyranoside (1) as substrates was investigated by 1H NMR spectroscopy and HPLC techniques. The transglycosylation product using AcGal as a substrate was β-d-galactopyranosyl-(1→6)-1-O-acetyl-β-d-galactopyranose (with a yield of ∼70%). In the case of 1 as a substrate, the main transglycosylation product was methyl β-d-galactopyranosyl-(1→6)-β-d-galactopyranoside. Methyl β-d-galactopyranosyl-(1→3)-β-d-galactopyranoside was found to be minor product in the latter reaction.