Enzymes metal combination

This chapter deals with recent developments in this area, in particular DKR by enzyme-metal combinations. Each successful DKR is exempfified with several substrates and novel metal catalyst. Asymmetric transformations of achiral substrates via DKR of racemic intermediates also are described. 

DYNAMIC KINETIC RESOLUTIONS BY ENZYME-METAL COMBINATIONS... 

Kim M-J, Kim HM, Kim D et al (2004) Dynamic kinetic resolution of secondary alcohols by enzyme-metal combinations in ionic liquid. Green Chem 6 471-474... 

But in order to utilise these reactions, a few conditions must be met. A selective enzyme is crucial and the organometallic catalyst must facilitate a fast racemisation of the substrate. Last, but not least, the catalyst should not influence the enzyme in terms of selectivity and reactivity. In the ideal case, the enzyme transforms one enantiomer of the substrate, giving rise to the corresponding product, which is not susceptible to metal-catalysed racemisation. Three major types of enzyme-metal combinations—lipase-ruthenium, sub-tilisin-ruthenium and lipase combined with a metal other than ruthenium—have been developed primarily as the catalysts for the DKRs of various secondary alcohols but also for diols, amines and esters. Meanwhile, the lipase-ruthenium combination has been the most used method up to the present time. 

Kim, M.-J., Ahn, Y., Park, J. Dynamic kinetic resolution and asymmetric transformations by enzyme-metal combination. In Biocatalysis in the Pharmaceutical and Biotechnology Industries (ed. Patel, R.N.), 2007, CRC Press, Boca Raton, FL, 249-272. 

The coupling of enzyme-catalyzed resolution with metal-catalyzed racemization constitutes a powerful DKR methodology for the synthesis of enantioenriched alcohols, amines, and amino acids. In many cases, the metalloenzymatic DKRs provide high yields and excellent enantiopurities, both approaching 100%, and thus provide useful alternatives to the chemical catalytic asymmetric reactions employing transition metals (complexes) or organocatalysts. The wider applications of a metalloenzymatic DKR method, however, are often limited by the low activity, narrow substrate specificity, or modest enantioselectivity of the enzyme employed. The low activities of metal-based catalysts, particularly in the racemization of amines and amino acids, also limit the wider applications of DKR. It is expected that fm-ther efforts to overcome these limitations with the developments of new enzyme-metal combinations will make the metalloenzymatic DKR more attractive as a tool for asymmetric synthesis in the future. 

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