Nitriles hydrolyzing enzymes: promising green catalysts for the synthesis of high bio-valued molecules

In an industrial society in which the requests of green strategies and sustainable methodologies are always more demanding and mandatory, the biocatalysis offers unique and innovative solutions and possibilities, representing today a well-established field of research at a crossroad between organic synthesis and biotechnology, dealing with the application of biological systems such as microorganisms, enzymes or catalytic antibodies to the synthesis of organic compounds. Nitriles hydrolyzing enzymes remain still largely unknown biocatalysts for the common organic chemistry synthesist, although they possess an enormous potentiality for the development of synthons useful in the preparation of molecules with important chemical-physical and/or biological properties. In nature, the biotransformation of nitriles proceeds via two different pathways: the direct nitrilase-catalyzed reaction to yield the corresponding carboxylic acids and ammonia, or a two-step indirect reaction, in which nitriles are first transformed to amides by nitrile hydratase, and then the amides are transformed to the corresponding carboxylic acids and ammonia by an amidase. In this work, examples concerning the chemo-enzymatic synthesis and their biotransformations of novel nitrile-cyclitols useful as synthons in the preparation of biologically important molecules, such as cyclophellitol, are presented. Examples of biotrasformations aimed to the enantio-preparation of non steroidal anti-inflammatory drugs belonging to the profen family are shown too. Finally, very recent experiments involving the synthesis and biotransformations of ferrocenyl nitrile derivatives incorporating elements of planar chirality are described.