Biotransformations of nitrile ferrocenes catalyzed by nitrilase: first examples of molecular recognition and enantioselectivity of a chiral planar substrate

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 unexploited 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, for the first time, different purified nitrilases were tested and found able to recognize the ferrocene framework, a very versatile and important scaffold for the synthesis of bioactive compounds. Moreover, the first example of chiral recognition of this enzymatic class toward compounds with planar chirality is illustrated.