Bioreductions Catalyzed by an Alcohol Dehydrogenase in Non‐aqueous Media

Abstract Highly productive biocatalytic reductions were established using an isolated alcohol dehydrogenase (ADH) under water‐deficient conditions. First, a solvent‐free system was evaluated for the reduction of 2‐butanone catalyzed by ADH evo‐1.1.200 promoted by the “smart cosubstrate” 1,4‐butanediol. ADH evo‐1.1.200 excelled by its activity and stability under high reagent concentrations and hence was the enzyme of choice. However, conversion of 2‐butanone was limited to <1 % in 10 days under the solvent‐free conditions. Therefore, water‐immiscible organic solvents were evaluated whereby the highest conversions were achieved in MTBE and toluene. MTBE was chosen as its different boiling point compared to other reaction components (e.g., 2‐butanone, 2‐butanol, diol cosubstrate, and lactone coproduct) would simplify the downstream processing. Further on, by tuning substrate loading, the productivity of the ADH evo‐1.1.200 was successfully increased to a turnover number (TON) of 64 000.