Enzymatic synthesis of glycosides using the β-galactosidase of Escherichia coli: regio- and stereo-chemical studies

β-Galactosyl transfer from lactose to acceptor alcohols (R)-(–)-butan-2-ol, (RS)-butan-2-ol, (S)-(+)-propane-1,2-diol, (RS)-propane-1,2-diol, (S)-(+)-butane-1,3-diol, (RS)-butane-1,3-diol, propane-1,3-diol, (S)-(+)-isopropylideneglycerol (1,2-O-isopropylidene-sn-glycerol) and (RS)-iso-propylideneglycerol (rac-1,2-O-isopropylideneglycerol) was studied, catalysed by the β-galactosidase (β-D-galactoside galactohydrolase EC 3.2.1.23) of Escherichia coli. Preference for galactosyl transfer to the R-enantiomers of chiral alcohols was observed, although selectivity was not pronounced. Higher selectivity for transfer to the primary hydroxy groups of the primary–secondary diols was observed. The results are interpreted in terms of a proposed active site model for the enzyme.