Rationalisation of the stereochemical outcome of ene-reductase-mediated bioreduction of ?,?-difunctionalised alkenes

The OYE1-3-mediated reductions of some ?,?-difunctionalised alkenes, showing on the double bond a nitrile and ester group, are submitted to a careful stereochemical analysis, in order to identify which of the two electron-withdrawing groups (EWGs) is responsible for the activation of the CC double bond towards reduction and for establishing hydrogen bond interactions within the binding pocket of the enzymes. The results show that for most of these substrates the activating EWG is the CN moiety linked to the prostereogenic olefinic carbon atom. The final stereochemical outcome can be explained through the empirical model which has been recently developed for difunctionalised alkenes activated by carbonyl/carboxyl containing EWGs. In a single case the activation is due to the COOR group linked to the less substituted olefinic carbon atom: an alternative empirical model is established for this kind of substrates, taking into consideration the OYE-catalysed reductions of ?,??-disubstituted-?-monofunctionalised alkenes. © 2014 Elsevier B.V.