The stereochemistry of the addition of glycerol to D-galactal, catalyzed by beta-D-galactosidase.

On incubation with beta-D-galactosidase, D-galactal-2-d (1) plus glycerol yielded 1-deoxyglycerol-1-yl 2-deoxy-beta-D-lyxo-hexopyranoside-2(S)-d. By 1H-n.m.r. analysis, it was shown that the hydrogen atom introduced on C-2 is trans-related to the aglycon moiety. In contrast to this stereospecific, enzyme-catalyzed addition, the reaction of phenol with peracetylated 1, catalyzed by p-toluenesulfonic acid, which yields phenyl 3,4,6-tri-O-acetyl-2-deoxy-alpha-D-lyxo-hexopyranoside-2-d, was shown to entail both a trans and a cis addition.