Abstract: This process makes it possible to prepare a compound of controlled enantiomeric purity, D-P or L-P respectively, from a substrate S consisting of the oxidized form of the corresponding D/L-P racemate or of the said D/L-P racemate, or else of the optical isomer which is the inverse of that which it is wished to prepare. In accordance with this process, the said substrate S, the said D/L-P racemate or the optical isomer inverse of that which it is wished to prepare, respectively, is introduced into an electrochemical reactor together with an oxidoreductase enzyme capable of catalyzing the oxidation of the optical isomer which is the inverse of that which it is wished to prepare; a potential difference is applied between the electrodes in order to perform the nonstereospecific cathodic reduction of the said substrate S until the isomer having the required enantiomeric purity is obtained; and the cosubstrate of the said enzyme is regenerated by anodic oxidation in the said electrochemical reactor.