OYE-like ene reductases

Figure 3.1 Mechanism of C—C double bond reduction mediated by OYE-like ene reductases (exemplified with OYEl) (a) classical binding mode (b) flipped binding mode.

As an alternative approach to classical OYE-like ene reductases, also cell-free extracts of anaerobic bacteria such as Clostridium sporogenes were tested for the bioreduction of a library of nitroalkenes [106]. The iron-sulfur cluster dependent enoate reductases responsible for the C=C bioreduction in Clostridia showed the same stereopreference of OYEl-3 on ( )-81 and related nitroolefins. As with ene reductases, nonaromatic substrates were converted more slowly and a,P-disubstituted nitroalkenes yielded almost racemic products. The relatively low deuterium exchange rate at the a-position (employing a biphasic system) confirmed also in this case that the low optical purity of the products is mostly due to the bioreduction itself, rather than to chemical racemization. 

The biocatalytic counterpart for the stereoselective reductirai of alkenes is catalyzed by flavin-dependent ene-reductases, " EC 1.3.1.31], which are members of the old yellow enzyme family (OYE, Scheme 2.134) [968,969], first described in the 1930s [970]. These enzymes are widely distributed in microorganisms and in plants. Some of them occur in well-defined pathways, e.g., in the biosynthesis of fatty acids and secondary metabolites, such as morphine [971] and jasmonic acid [972]. Others are involved in the detoxification of xenobiotics [973], such as nitro esters [974] and nitro-aromatics [975] like trinitrotoluene (TNT) [976]. 

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