Alcohol dehydrogenase stereospecificity

We can thus deduce that alcohol dehydrogenase stereospecifically removes the pro-R hydrogen from the prochiral methylene. 

Davis J, Jones JB (1979) Enzymes in organic synthesis. 16. Heterocyclic ketones as substrates of horse liver alcohol dehydrogenase. Stereospecific reductions of 2-substituted tetrahydropyran-4-ones. J Am Chem Soc 101 5405-5410... 

NAD (P) " -dependent enzymes are stereospecific. Malate dehydrogenase, for example, transfers a hydride to die pro-/ position of NADH, whereas glyceraldehyde-3-phosphate dehydrogenase transfers a hydride to die pro-5 position of the nicotinamide. Alcohol dehydrogenase removes a hydride from the pro-i position of edianol and transfers it to die pro-i position of NADH. 

The liver alcohol dehydrogenase mentioned in the preceding section has the same pro-R stereospecificity for NAD and ethanol as yeast alcohol dehydrogenase. Furthermore, the oxidation of ethanol by a microsomal oxidizing system, or by catalase and H2O2, likewise proceeds with pro-R stereospecificity for the ethanol77>. The catalase-H2C>2 system is so very different, however, from the pyridine nucleotide dehydrogenase, that one wonders whether the similarity in stereospecificity for ethanol is fortuitous. 

The chiral compounds (/ )- and (5)-bis(trifluoromethyl)phenylethanol are particularly useful synthetic intermediates for the pharmaceutical industry, as the alcohol functionality can be easily transformed without a loss of stereospecificity and biological activity, and the trifluoromethyl functionalities slow the degradation of the compound by human metabolism. A very efficient process was recently demonstrated for the production of the (5)-enantiomer at >99% ee through ketone reduction catalyzed by the commercially available isolated alcohol dehydrogenase enzyme from Rhodococcus erythropolis (Figure 9.1). The (7 )-enantiomer could be generated at >99% ee as well using the isolated ketone reductase enzyme KRED-101. 

The stereospecificity depends upon the enzyme in question. Let us consider the enzyme alcohol dehydrogenase, which is involved in the ethanol to acetaldehyde interconversion. It has been deduced that the hydrogen transferred from ethanol is directed to the Re face of NAD+, giving NADH with the AR configuration, hi the reverse reaction, it is the 4-pro-R hydrogen of NADH that is transferred to acetaldehyde. 

The latter were transformed into (+)-64, (-)-65 and (+)-66, respectively, in good yields. Lactone (+)-66 was also prepared in 37 % yield by stereospecific Horse Liver Alcohol Dehydrogenase (HLADH) catalyzed oxidation of the meso-diol 67. Lactones (-)-64 and (+)-64 are potentially interesting starting materials for the... 

Bradshaw, C.W., Fu, H., Shen, G.J. and Wong, C.H. (1992) APseudomonas sp alcohol-dehydrogenase with broad substrate-specificity and unusual stereospecificity for organic-synthesis. J. Org. Chem., 57, 1526-1532. 

Nicotinamide-dependent enzymes operate in a highly stereospecific manner. This phenomenon was first demonstrated for alcohol dehydrogenase which catalyzes the direct and stereospecific transfer of the pro-(R) hydrogen at C-l of ethanol to the re face of NAD+, or, in the reverse direction, the pro-(R) hydrogen of NADH to the re face of acetaldehyde (equation 2) (B-71MI11001, B-79MI11000). Many other nicotinamide-dependent... 

The results of the temperature dependence of the reaction rates of the enantiomers of secondary alcohols with a secondary alcohol dehydrogenase (SADE1) from the thermophilic bacterium Thermoanaerobacter ethanolicus demonstrated a temperature-dependent reversal of stereospecificity (Pham, 1990) (Figure 5.16). At T < 26°C, (S)-2-butanol was a better substrate than (i )-2-butanol on the basis of kCSLt/KM values however, at T> 26°C, (R)-2-butanol was a better substrate than (S)-2-butanol. (S)-2-Pentanol was the preferred substrate at T < 60°C however, the data predict that (i )-2-pentanol would be preferred at T > 70°C. (S)-2-Elexanol was predicted to be the preferred enantiomer only at T > 240°C. Therefore, the concept of isoinversion temperature is as valid for enzyme reactions as for others only the range of catalytically accessible temperatures is smaller. 

C. Heiss, M. Laivenieks, G. J. Zeikus, and R. S. Phillips, The stereospecificity of secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus is partially determined by active site water,... 

KP Lok, TJ Jakovac, JB Jones. Enzymes in organic synthesis. 34. Preparation of enantiomerically pure exo- and endo-bridged bicyclic [2.2.1] chiral lactones via stereospecific horse liver alcohol dehydrogenase catalyzed oxidations of meso di-ols. J Am Chem Soc 107 2521-2526, 1985. 

CW Bradshaw, H Fu, GJ Shen, C-H Wong. A Pseudomonas sp. alcohol dehydrogenase with broad specificity and unusual stereospecificity for organic synthesis. J Org Chem 57 1526-1531, 1992. 

The 3-carbamidopyridinium ring is the chemically active portion of the enzymatic cofactors, NAD and NADP (nicotinamide adenine dinucleotide and its phosphate). A typical reaction involving NAD is the stereospecific (with respect to both cofactor and substrate) oxidation of ethanol to acetaldehyde catalyzed by the enzyme, alcohol dehydrogenase (Eq. 33). 

The coenzyme stereospecificity of glyceraldehyde 3-phosphate dehydrogenase is the opposite of that of alcohol dehydrogenase... 

Exploitation of the complementary specificities of enzymes from different sources towards the same racemic substrate permits very precise control of the product stereochemistry. For example, any one of the three diastereomeric 2-decalols (94)-(96) can be obtained at will from ( )-tra/iJ-2-decalone (81 R = H) using the alcohol dehydrogenases HLADH, MJADH or CFADH, respectively (Scheme 40). The stereospecificities of these three enzymes are well documented and a simple active site model of predictive value is available for each. 55 Racemic bridged bicyclic ketones are similarly discriminated, either... 

Thus, the role of zinc in the dehydrogenation reaction is to promote deprotonation of the alcohol, thereby enhancing hydride transfer from the zinc alkoxide intermediate. Conversely, in the reverse hydrogenation reaction, its role is to enhance the electrophilicity of the carbonyl carbon atom. Alcohol dehydrogenases are exquisitely stereospecific and, by binding their substrate via a three-point attachment site (Figure 12.11), they can distinguish between the two methylene protons of the prochiral ethanol molecule. 

Sodium borohydride and potassium borohydride react regioselectively with the formyl group of alkyl 2-formylcyclopropanecarboxylates lithium aluminum hydride is unseleetive. Stereospecific reduction of the formyl group was observed when formyl-cyclo-propanes were subjected to yeast alcohol dehydrogenase. ei Furthermore, regiospecific reduction of the aldehyde function in a 2-cyclopropylprop-2-enal derivative was performed using a mixture of sodium borohydride and cerium(III) chloride. 

The ability of alcohol dehydrogenases to distinguish the methylene protons of ethanol is a paradigm of enzymic stereospecificity. Many alcohol dehydrogenases can function with both primary and secondary alcohols thus their ability to show selectivity toward the chirality of the secondary alcohols is remarkable. An example of the difficulties associated with stereospecificity of secondary alcohol dehydrogenases is illustrated by the thermophilic alcohol dehydrogenase from Thermoanaerobacter ethanolicus (57). At low temperatures the enzyme preferentially uses the 5 isomer of 2-pentanol or 2-butanol. The enantiomeric discrimination, however, is temperature dependent. Above a temperature 7, at which there is no enantiomeric discrimination, the enzyme shows the opposite preference and uses the R isomer. The value of 7, is a function of the substrate for... 

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