Process intensification for substrate-coupled whole cell ketone reduction by in situ acetone removal

Three different reactor configurations for in situ acetone removal in whole cell biotransformation processes with substrate-coupled cofactor regeneration were applied. The reduction of 2,5-hexanedione to the corresponding (2R,5R)-hexanediol was catalyzed by recombinant Escherichia coli cells expressing an alcohol dehydrogenase from Lactobacillus brevis. The reaction was carried out in a substrate-coupled cofactor regeneration approach using 2-propanol as redox equivalent for intracellular cofactor regeneration. In contrast to a process without acetone removal, where 54% yield could be reached, the yield was increased to >90 % when a pervaporation system was applied or when acetone was removed by sparging air through the reaction mixture. In a third system, conversion was driven using a biphasic system to extract acetone continuously from the biocatalyst containing aqueous phase and to allow high concentrations of the hydrophobic substrate 1-phenyl-2-propanone. When methyl tert-butyl ether was applied as the non-aqueous phase, only 24% yield was achieved. When the ionic liquid 1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfony-1)amide was applied as the non-aqueous phase, >95% yield was reached as a result of the preferential partitioning behaviour of acetone over 2-propanol into the ionic liquid.