Asymmetric reduction by transition metals complexes and biocatalysts

In the last years the importance of α- and -amnimoacids is increased since these molecules are interesting synthons for the preparation of unnatural peptides and bioactive compounds, in particular antibiotics or anticancer. They can be easily obtained in optically pure form by reduction using metal catalyzed asymmetric hydrogenation1(chemocatalysis) or by enzyme mediated reduction2 (biocatalysis). In particular with the biocatalytical approach we used whole cells of different microorganisms endowed with enantioselective dehydrogenases, in chemocatalysis we used essentially Ir(I) and Ru(II) complexes of different atropoisomeric diphosphines. In both cases our research efforts let us to obtain chiral enriched unnatural aminoacids by reduction of prochiral ketones3 and by reduction of tetra substituted double bonds4, which are generally very low active. Our research will show that the process robustness and stereochemical outcome is strongly dependent on thermodynamic parameters but also on the presence of additives. We will discuss in detail nature and function of such compounds and we will demonstrate that it is possible to combine metal enantioselective reduction with stereoselective biocatalytic one. 1. E. Cesarotti; I. Rimoldi, P. Spalluto, F. Demartin Tetrahedron Asymmetry. 2007, 18, 1278-1283. 2. R. Gandolfi, E. Cesarotti, F. Molinari; D. Romano; I. Rimoldi Tetrahedron Asymmetry. 2009, 20, 411-414. 3. I. Rimoldi, E. Cesarotti, D. Zerla, F. Molinari, D. Albanese, R. Gandolfi submitted 4. R. Gandolfi, E. Cesarotti, D. Zerla, F. Molinari, I. Rimoldi submitted