Ionic Liquids as Performance Additives for Electroenzymatic Syntheses

Electroenzymatic syntheses combine oxidoreductase‐catalysed reactions with electrochemical reactant supply. The use of ionic liquids as performance additives can contribute to overcoming existing limitations of these syntheses. Here, we report on the influence of different water‐miscible ionic liquids on critical parameters such as conductivity, biocatalyst activity and stability or substrate solubility for three typical electroenzymatic syntheses. In these investigations promising ionic liquids were identified and have been used as additives for batch electrolyses on preparative scale for the three electroenzymatic systems. It was possible to improve the space‐time‐yield for the electrochemical regeneration of NADPH by a factor of three. For an amino acid oxidase catalysed resolution of a methionine racemate with ferrocene‐mediated electrochemical regeneration of the enzyme‐bound cofactor FAD a 50 % increase in space time yield and 140 % increase in catalyst utilisation (TTN) were achieved. Furthermore, for the chloroperoxidase‐catalysed synthesis of (R)‐phenylmethylsulfoxide with electrochemical generation of the required cosubstrate H2O2 the space time yield and the catalyst utilisation were improved by a factor of up to 4.2 depending on the ionic liquids used. The best of three worlds? Ionic liquids can act both as co‐solvents and conducting salts and are therefore superior additives for electroenzymatic syntheses. The benefits of this combination are described for three preparative electrolyses (see figure). In addition to increased substrate solubility and enzyme stability, the productivity of the reactions could be increased in all cases.