A chemoenzymatic reduction of conjugated C=C double bonds has been developed by Diederik J. Opperman, Frank Hollmann and co-workers, University of the Free State, South Africa, and Delft University of Technology, The Netherlands, respectively.

Chiral carbonyl compounds can be prepared by the enoate reductase (ER)-catalyzed asymmetric reduction of conjugated C=C double bonds. Conventional processes use the expensive nicotinamide cofactor [NAD(P)H] to regenerate the primary reductant, which necessitates an additional recycling strategy to ensure cost-effective use of the cofactor.

Based on the fact that the nicotinamide does not play a direct role in the catalytic mechanism, the group have developed NAD(P)-independent regeneration of ERs by using the rhodium catalyst [Cp*Rh(bpy)(H₂O)]²⁺. This catalyst, with good activity and stability at high temperature, is an excellent candidate for thermophilic oxidoreductions. The robust and readily available ER homologue chromate reductase (CrS) was used as a model enzyme in the reduction of conjugated C=C double bonds.

The combination of CrS and [Cp*Rh(bpy)(H₂O)]²⁺ provides a system much simpler than the classical ones and shows promising catalytic performance. Optimization and upscaling of the chemoenzymatic reduction system are currently underway.

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• Chemoenzymatic Reduction of Conjugated C=C Double Bonds,
  J. Bernard, E. van Heerden, I. W. C. E. Arends, D. J. Opperman, F. Hollmann,
  ChemCatChem 2012, 4, 196–199.
  DOI: 10.1002/cctc.201100312

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