Enzyme-catalyzed stereoselective

The enzyme-catalyzed stereoselective synthesis of (/ )- and (S )-cyanohydrins allows a simple access to compounds which can be easily transformed into the corresponding a-hydroxy-car-boxylic acids (see Table 2)20,21,23, a-hydroxyaldehydes26 or acyloins27, without racemization. 

Enzyme-catalyzed stereoselective hydrolysis allows the preparation of enantio-merically enriched lactones. For instance. Pseudomonas sp. lipase (PSL) was found to be a suitable catalyst for the resolution of 5-undecalactone and 5-dodecalactone (Figure 6.20). Relactonization of the hydroxy acid represents an efficient method for the preparation of both enantiomers of a lactone [67]. 

A similar enzyme-catalyzed stereoselective synthesis of enantiomers of propanolamines has been recently reported30. Addition of a lipozyme from the fungus Mucor miehei to the epoxide ( )-8 in toluene and then a slightly more than one half molar equivalent of 2-propylamine gave a 29% conversion of ( )-8 to (S)-9 with an ee of 90%. For some benzene ring-substituted epoxides, both the percent conversion of the epoxide and the ee of product are slightly higher30. 

The enzyme-catalyzed stereoselective oxidations of 1,2-dithiane and l,4-dihydro-2,3-benzodithiin were also investigated <2002CC1452>. Using naphthalene dioxygenase and chloroperoxidase, enantiomerically enriched sulfoxides (1,2-dithiane 1-oxides) were obtained l,4-dihydro-2,3-benzodithiin yielded a product of 32—47% ee with an excess of the (6)-configuration while 1,2-dithiane yielded almost enantiopure (96% ee) (R)-configured 1-oxide. Finally, 1,4-dihydro-2,3-benzodithiin 2-oxide was also prepared by perborate oxidation <1988JOC2608>. 

The Baeyer-Villiger reaction occurs with retention of stereochemistry at die migrating center. This stereoselectivity has been utilized in a practical method for the preparation of isotopically chiral metiiyl acetic acid (5) ftom [2- H]cyclohexanone (4) prepared by enzyme-catalyzed stereoselective exchange of the pro-R a -proton and enantioconvergent exchange of the a-proton with deuterium (Scheme 2). As a cautionary note, prior epimerization of an acyl group prior to oxidation has been observed. ... 

Enzyme-Catalyzed Stereoselective Reactions in Continuous-Flow Systems... 

Uwai K, Konn N, Kitamura S, Ohta S, Takeshita M. Purification and characterization of rat liver enzyme catalyzing stereoselective reduction of acetylpyridines. Chirality 2005 17 494-500. 

ENZYME-CATALYZED STEREOSELECTIVE C-C BOND FORMATION REACTIONS IN TOTAL SYNTHESES... 

Enzyme-Catalyzed Stereoselective C C Bond Formation Reactions in Total Syntheses... 

The vast majority of enzyme-catalyzed stereoselective hydroxylations are carried out by the cytochrome P450-dependent monoxygenases [4]. The membrane-bound nature of the majority of these enzymes, together with their functional dependence on the presence of cofactors and their related electron transport proteins, has ensured that preparative biocatalytic hydroxylations are most usefully performed with whole-cell catalysts. The exceptions to this generality, the lipoxygenases and haloperoxidases, will be considered in Sec. n.B. 

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