Stereoselective oxidoreduction

The oxidoreductase of most current utility is horse liver alcohol dehydrogenase (HLADH), and its application in the stereoselective oxidoreduction of ketones and alcohols has been explored. It requires an NAD coenzyme which becomes expensive if reactions have to be performed on a preparative (up to 5 g) scale. In fact, this cofactor sells for as much as 250,000 per mole ... 

Hoch U, ScheUer G, Schmitt M, Schreier P, Adam W, Saha-MoUer CR (1995) Enzymes in synthetic organic chemistry selective oxidoreductions catalyzed by the metaUoenzymes lipoxygenase and peroxidase. In Werner H, Simdermeyer J (eds) Stereoselective reactions of metal-activated molecules, 2nd Symposium. Vieweg, Braimschweig, p 33 Adam W, Korb MN (1997) Tetrahedron Asymmetry 8 1131... 

AJ Irwin, JB Jones. Stereoselective horse liver alcohol dehydrogenase catalyzed oxidoreductions of some bicyclic [2.2.1] and [3.2.1] ketones and alcohols. J Am Chem Soc 98 8476-8482, 1976. 

Asymmetric oxidoreductions performed in isopropyl ether allow syntheses of optically active alcohols with ee >95% on a 1-10 mmol scale. Nakamura et al. investigated the effect of organic solvents on the reduction of ot-keto esters mediated by bakers yeast [140]. The reduction of ethyl 2-oxoheptanoate was tested in various solvents. Best results were achieved with benzene so further experiments were performed with benzene. Conversion only takes place in the presence of small amounts of water. The reduction of six ot-keto esters was examined regarding the stereoselectivity of the corresponding ot-hydroxy esters. The reactions were performed in aqueous systems as well as in benzene. In aqueous systems, the formed hydroxy esters show (S)-stereoselectivity while the stereochemistry of the reaction shifts markedly towards the production of (/ )-ot-hydroxy esters in benzene. 

Reactions of oxidoreduction are an example of chiral inversion that takes place by the intermediacy of two opposing metabolic processes. The alcohol/ketone equilibrium mediated by alcohol dehydrogenase enzyme is an abundant reaction. The dehydrogenation of secondary alcohols to a ketone proceeds with substrate stereoselectivity in oxidation, while the hydrogenation of the ketone metabolite is product selective to one face of the carbonyl group. The consequence of the metabolism of the secondary alcohols may involve chiral inversion of this center, which can result in an altered proportion of the two enantiomers or epimers. 

Horse liver alcohol dehydrogenase (HLADH) catalyzes the oxidoreduction of a variety of compounds [61,62]. It has been demonstrated that HLADH catalyzes the stereospecific oxidation of only one of the enantiopic hydroxyl groups of acyclic and monocyclic me o-diols [63,64]. The oxidation of meso-exo- and enfto-7-oxabicyclo[2.2.1]heptane dimethanol to the corresponding enantiomerically pure y-lactones by HLADH has been demonstrated. Nicotinamide adenine dinucleotide (NAD" ) and flavin adenine dinucleotide (FAD) were required for the stereoselective oxidation of substrate. Due to the high cost of enzyme and required cofactors, this process for preparing chiral lactones was econom-... 

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See also in sourсe #XX -- [ ]

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