Effect of organic solvents on asymmetric reduction of β-keto esters using cyanobacterium Synechocystis sp. PCC 6803

Abstract The asymmetric reduction of tert-butyl 3-oxobutanoate by cyanobacterium Synechocystis sp. PCC 6803 under illumination with red LED light at 25 °C for 24 h afforded the corresponding (R)-β-hydroxy ester in 79% enantiomeric excess (ee) (81% yield), while the addition of toluene (1% (v/v)) to the system gave the corresponding (S)-β-hydroxy ester in >99% ee (87% yield). Organic solvents such as chloroform, benzene, ethylbenzene, cyclohexane, and methylcyclohexane showed similar effects and afforded the corresponding (S)-β-hydroxy ester in >99% ee. However, polar organic solvents, such as DMSO, THF, and ethanol, as well as dodecane—a hydrophobic solvent with a straight long-chain—did not exhibit such effects.