Enantioselective reduction, using enzymes

For this type of C-C bond formation both stereoisomers of the hydroxyphenyl-propanone can be obtained using either the BFD mentioned above or the benz-aldehyde lyase (BAL). Both of these enzymes are dependent on thiamine diphosphate (ThDP) as cofactor [22]. For the enantioselective reduction of the intermediate also, both stereoisomers can be obtained by using two different ADH enzymes. Thus all four possible stereoisomers of the diol can be obtained in high optical purity (see Scheme. 3.1.1) [23]. 

Electroenzymatic reactions are not only important in the development of ampero-metric biosensors. They can also be very valuable for organic synthesis. The enantio- and diasteroselectivity of the redox enzymes can be used effectively for the synthesis of enantiomerically pure compounds, as, for example, in the enantioselective reduction of prochiral carbonyl compounds, or in the enantio-selective, distereoselective, or enantiomer differentiating oxidation of chiral, achiral, or mes< -polyols. The introduction of hydroxy groups into aliphatic and aromatic compounds can be just as interesting. In addition, the regioselectivity of the oxidation of a certain hydroxy function in a polyol by an enzymatic oxidation can be extremely valuable, thus avoiding a sometimes complicated protection-deprotection strategy. 

This article will focus on new developments on the field of NAD(P)-depen-dent dehydrogenases, in particular on new alcohol dehydrogenases applicable for preparative chemistry. Biochemical properties of dehydrogenases useful for the synthesis of chiral hydroxy esters and alcohols are summarized in this contribution with respect to more recent studies on enantioselective reduction of prochiral ketones and to new enzymes for this purpose. Reviews covering earlier works in this field can be found in [42-44],... 

At the same time, activity of the enzyme was lost when very high concentrations of the ions were used. The optimum activity was observed when the ion concentration was within 0.3-0.8 M. But unlike stability and activity, enantioselectivity of protease seemed to markedly decrease with reduction in ee of protease with increasing kosmotropicity of both cations and anions of the ILs. 8 Value, i.e., the difference in viscosity B values of anion and cation, is indicative of overall kosmotropicity of cations and anions of ILs. Enantioselectivity of the enzymes increases in ILs having high 5 value [92,115]. 

Organic solvents have been used widely for esterifications and transesterifications using hydrolytic enzymes to shift the equilibrium towards esterification by avoiding hydrolysis. Organic solvents can also be used for reductions using dehydrogenases198-109. They can be used to control the overall enantioselectivity of the reduction, when there are more than two competing enzymes with different enantioselectivities, KM and kmax-... 

A more recent EMR-process for the enantioselective reduction of 2-oxo-4-phenylbutyric acid (OPBA) to (R)-2-hydroxy-4-phenylbutyric acid (HPBA, e.e.>99.9%) with NADH-de-pendent D-lactate dehydrogenase (D-LDH) from Staphylococcus epidermidis and FDH/for-mate for co-factor recycling uses free NADH instead of PEG-NADH [100, 101] (Fig. 3). Within the selected residence time of 4.6 h, a cycle number for the co-factor of 1000 can easily be achieved. Instead of NADH, the less expensive NAD+ is used. A second reason for the application of the native co-enzyme is the fact that the activity of D-LDH is reduced to one tenth when PEG-enlarged co-enzyme is used instead of the native co-enzyme. HPBA produced by this method with a space-time yield of 165 g 1 d-1 is of considerably higher enantiomeric purity and the process shows competitive economy in comparison with chemical... 

Oxidoreductases are of special interest for the enantioselective reduction of prochiral ketones [49]. Formate dehydrogenase from Candida boidinii was found to be stable and active in mixtures of [MMIM][MeS04] with buffer. The apphcation of alcohol dehydrogenases for enzyme-catalyzed reactions in the presence of water-miscible ionic liquids could make use of another advantage of these solvents they increase the solubility of hydrophobic compounds in aqueous systems. By addition... 

The alcohol dehydrogenase from Lactobacillus brevis was used to catalyze the enantioselective reduction of 2-octanone to (i )-2-octanol on the expense of the reduced cofactor NADPH. The same enzyme is able to regenerate NADPH from... 

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