Multigram-Scale Asymmetric Alkene Reduction Catalyzed by a Thermostable Flavin Ene-Reductase

Chiral-substituted carbonyl compounds can be sustainably obtained via asymmetric alkene reduction catalyzed by ene-reductases from the Old Yellow Enzyme (OYE) family. Yet OYEs are seldom implemented in scale-up reactions due to low turnover numbers (TONs). Herein, we demonstrate multigram 150 g/L scale reactions with the thermostable OYE from Thermus scotoductus (0.2 wt %) for the asymmetric reduction of monoterpenes. Best results were achieved with (S)-carvone (7.5 g), affording a record TON of 123,000, with 90% isolated yield and >99% enantiomeric excess of (2R,5S)-dihydrocarvone, and an environmental E-factor of 11.6.