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A carbonyl reductase variant, SmCRM5, from Serratia marcescens was obtained through structure-guided directed evolution. The variant showed improved specific activity (U mg−1) towards most of the 16 tested substrates and gave high stereoselectivities of up to 99% in the asymmetric synthesis of 13 γ-/δ-lactones. In particular, SmCRM5 showed a 13.8-fold higher specific activity towards the model substrate, i.e., 5-oxodecanoic acid, and gave (R)-δ-decalactone in 99% ee with a space–time yield (STY) of 301 g L−1 d−1. The preparative synthesis of six δ-lactones in high yields and with high enantiopurities showed the feasibility of the biocatalytic synthesis of these high-value-added chemicals, providing a cost-effective and green alternative to noble-metal catalysis. [ABSTRACT FROM AUTHOR]

Structurally diverse γ‐ and δ‐lactones were efficiently synthesized stereoselectively using an engineered carbonyl reductase from Serratia marcescens (SmCRV4). SmCRV4 exhibited improved activity (up to 500‐fold) and thermostability toward 14 γ‐/δ‐keto acids and esters, compared with the wild‐type enzyme, with 110‐fold enhancement in catalytic efficiency (kcat/Km) toward methyl 4‐oxodecanoate. The preparative synthesis of alkyl and aromatic γ‐ and δ‐lactones with 95 %–>99 % ee and 78 %–90 % yields was demonstrated. The highest space‐time yield, 1175 g L−1 d−1, was achieved for (R)‐γ‐decalactone. [ABSTRACT FROM AUTHOR]