During the course of the biotransformation process, the molecular integrity of the glycolic unit was completely retained, no loss of the migrating deuterium occurred by exchange with the medium, and the 1,2-deuterium shift was intramolecular. A diol dehydrataselike mechanism could explain the enzymatic cleavage of the ether bond of 2-phenoxyethanol, provided that an intramolecular H/OC 6 H 5 exchange is assumed, giving rise to the hemiacetal precursor of acetaldehyde. However, an alternative mechanism is proposed that is supported by the well recognized propensity of ␣-hydroxyradical and of its conjugate base (ketyl anion) to eliminate a ␤-positioned leaving group.

The conversion of 2‐phenoxyethanol to phenol and acetate by the anaerobic bacterium Acetobacterium sp. strain LuPhet1 proceeds through acetaldehyde with concomitant migration of a H‐atom from C(1) to C(2) of the glycolic moiety. Separate feeding experiments with (R)‐ and (S)‐2‐phenoxy(1‐2H)ethanol, prepared via chemoenzymatic syntheses, indicate that the H‐atom involved in the 1,2‐shift is the pro‐S one of the enantiotopic couple of the alcohol function.

18 O-Substituted propane-1,2-diols and meso-butane-1,2-diols were synthesized and fed to growing cells of Lactobacillus brevis. Propan-1-ol and butan-2-ol, prepared from such diols through diol-dehydratase-catalyzed dehydration followed by intracellular reduction, were analyzed for their 18 O-content. For each propane-1,2-diol enantiomer, partial retention or complete loss of the isotope appeared to be related to the mode of substrate binding. Specific retention of the O-atom linked to the (R)-configured C-atom of meso-butane-1,2-diol indicates that the diol dehydratase handles this substrate like (R)-propane-1,2-diol.

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