Asymmetric synthesis of the chiral synthon ethyl (S)-4-chloro-3- hydroxybutanoate using Lactobacillus kefir

Lactobacillus kefir was used as the whole cell biocatalyst for the asymmetric reduction of ethyl 4-chloro acetoacetate 1 to the chiral synthon ethyl (S)-4-chloro-3-hydroxybutanoate 2. Ketoester 1 was obtained as micro-droplets, without the use of an organic solvent as substrate reservoir. 2 (1.2 M) was produced using 2-propanol as co-substrate with a final yield of 97% within 14 h. A high space-time yield and a high specific product capacity of 85.7 mmol/L h and of 24 mmol/g_DCW were measured. The enantiomeric excess of the (S)-alcohol 2 was 99.5%.