Baker’s yeast-mediated asymmetric reduction of ethyl 3-oxobutanoate in deep eutectic solvents

• The DES were evaluated for yeast-mediated reduction of ethyl 3-oxobutanoate.
• Among tested DES the sugar containing ones possess the best biocompatibility.
• Enantioselectivity is influenced by the water content in DES and/or DES itself.
• The DES are promising candidates for green whole-cell biocatalysis.

Cholinium-based deep eutectic solvents (DES) were evaluated as solvents for yeast-mediated reduction of ethyl 3-oxobutanoate to ethyl 3-hydroxybutanoate. The type of hydrogen bond donor and the amount of water present in DES considerably influenced the reaction yield. At water content of 50% (w/w), sugar and alcohol containing DES were the most appropriate solvents for the given reduction, with yields similar to those obtained in phosphate buffer (<93.0%), while in DES based on acids or amide poor yields were observed regardless water content (<49.3%). The results suggest that pH value of reactiom medium and cell viability are the curtail variables influencing bioreduction yield. Furthermore, by changing the water content in DES and/or DES itself it is possibly to alter enantioselectivity. Overall, the results suggest that sugar containing DES possess good biocompatibility with yeast cells and can be applied as green reaction medium for yeast-mediated bioreduction.

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