Bioreduction of N-(3-oxobutyl)heterocycles with flexible ring by yeast whole-cell biocatalysts.

This study explored the bioreduction of N-(3-oxobutyl)heterocycles with (partially) saturated heterocyclic moieties using whole-cell forms of wild-type yeast strains and commercially available baker's yeast (Saccharomyces cerevisiae). Eleven wild-type yeast strains and baker's yeast were screened for ketoreductase activity on a series of five flexible N-heterocycles with prochiral carbonyl group in the N-(3-oxobutyl) substituent. Among the yeast strains tested, Candida parapsilosis (WY12) proved to be the most efficient biocatalyst in the bioreductions, resulting in the corresponding enantiopure alcohols-being promising chiral fragments with high level of drug-likeness-with good to excellent conversions (83-99%) and high enantiomeric excess (ee > 99%). Other strains, such as Pichia carsonii (WY1) and Lodderomyces elongisporus (WY2), also showed promising ketoreductase activities with certain substrates. After screening as lyophilized whole cells, C. parapsilosis cells were immobilized in the form of calcium, zinc, nickel, and copper alginate beads. The whole-cell immobilization enabled recycling, with considerable residual activity of the biocatalyst over multiple cycles. Additionally, the study explored the scalability of these bioreductions, with immobilized C. parapsilosis delivering promising results. The use of immobilized cells simplified the work-up process and resulted in chiral alcohols with similar or even higher conversions to those observed in the screening reactions. Molecular docking of the five flexible N-heterocycles with prochiral carbonyl group into the active site of the experimental structure of the carbonyl reductase of C. parapsilosis rationalized their biocatalytic behavior and confirmed the assigned (S)-configuration of forming enantiopure alcohols. KEY POINTS: • Ketoreductase activity of eleven wild-type yeast strains and baker's yeast were examined. • Candida parapsilosis was subjected to whole-cell immobilization and recycling. • Enantiopure alcohols with flexible N-heterocyclic units were produced at preparative scale.