The Stereochemistry of the Conversion of D and L 1,2-Propanediols to Propionaldehyde

Abstract

Abstract When D-1,2-propanediol is converted to propionaldehyde in the presence of dioldehydrase and dimethylbenzimidazolylcobamide coenzyme, 1 of 2 C-1 hydrogens of the substrate is stereospecifically transferred to position C-2. The hydrogen transferred is the hydrogen introduced into D-1,2-propanediol by horse liver alcohol dehydrogenase when D-lactaldehyde is reduced to D-1,2-propanediol. When L-1,2-propanediol reacts, the other C-1 hydrogen exclusively is transferred. The displacement of the secondary hydroxyl group of propanediol by hydrogen, which takes place when D- or L-1,2-propanediol is converted to propionaldehyde, occurs with inversion of configuration at C-2. These results suggest that the removal of the secondary hydroxyl group may proceed through a displacement reaction in which the hydride functions as displacing nucleophile. It was also shown that the reduction of D- and L-lactaldehyde with horse liver alcohol dehydrogenase and α-deuterated reduced diphosphopyridine nucleotide leads to D- and L-propanediol of identical configuration at C-1. Therefore, the stereochemical course of the reduction by horse liver alcohol dehydrogenase is not influenced by the configuration of the carbon adjacent to the center which is reduced.