Reaction engineering studies on β-ketoester reductions with whole cells of recombinant Saccharomyces cerevisiae

A recombinant Saccharomyces cerevisiae strain over-expressing the fatty acid synthase of S. cerevisiae and the glucose dehydrogenase of Bacillus subtilis was applied for enantioselective reduction of ethyl 4-chloro acetoacetate (CAAE) to ethyl (S)-4-chloro-3-hydroxybutanoate (S-CHBE) as well as the reduction of ethyl benzoylacetate (EBA) to ethyl (S)-3-hydroxy-3- phenylpropionate (S-HPPE). The reaction conditions for these asymmetric reductions were optimised by combining simple screening procedures and a stochastic search strategy (Genetic Algorithm). Complete conversion of 200 mM CAAE was achieved within 8 h in a two liquid phase system (water/n-butyl acetate). The S-CHBE yield (94%) and the product/biocatalyst ratio (1.9 mmol S-CHBE/g cell dry weight) were improved by 50 and 450%, respectively, compared to published data. The enantiomeric excess was 90%. Nearly complete conversion of 55 mM EBA was achieved within 48 h without addition of an organic solvent. The S-HPPE yield (74%) and the product/biocatalyst ratio (0.7 mmol S-HPPE/g cell dry weight) were improved by 20 and 350%, respectively, compared to published data. The enantiomeric excess was >97% in the case of S-HPPE production.