Enzyme-catalyzed enantioselective reductions of ketones and keto esters have become popular for the production of homochiral building blocks which are valuable synthons for the preparation of biologically active compounds at industrial scale. Among many kinds of biocatalysts, dehydrogenases/reductases from various microorganisms have been used to prepare optically pure enantiomers from carbonyl compounds. The enzyme belongs to the short-chain dehydrogenase/reductase family. It catalyzes the NAD+ dependent stereospecific oxidation of (S)-alkylaromatic alcohols to respective ketones but also the reverse reaction, i.e. NADH - dependent enantioselective reduction of ketones to (S)-alcohols (precisely alcohols Prelog orientation).
The enzyme can be obtained as a recombinant protein in easy to grow E.coli strain. The enzyme exhibits an excellent storage time (up to 4 years), high resistance to range of organic solvents and substrate loadings (up to 0.5 M). The conversions can be carried out in a batch reactor using and isopropanol as reaction solvent and co-substrate for NADH recovery. It is also possible to deploy the catalyst as cell-extracts with added NADH or with enzyme immobilized on monolytic support providing a convenient plug-flow reactor system. Ketones can be converted to the respective secondary alcohols with excellent enantiomeric excesses and high productivities with substrate loading in the range of 50-300 mM.
The enzyme was demonstrated to be an efficient catalysts in asymmetric reduction of prochiral ketones and β-keto esters to enantiopure secondary alcohols.
- The cost of the catalyst (recombinant enzyme produced in E.coli) is very low, especially in case of a bigger batch.
- The process does not involves any transition metals, toxic organic compounds and solvents.
- The process does not requires any sophisticated chemical installation, proceeds in room temperature under aerobic atmosphere.
- The catalysts is stable (up to 30 days in 30oC, up to 6 months in 4oC for purified enzyme, up to 4 years in -70oC for cells)
- Use of the whole-cells catalysts and cofactor recovery system eliminates a requirement for a high-cost cofactors
- The catalysis can be deployed both as a GMM whole-cell or as a cell extract (does not require GMM permit)