Nitrile converting enzymes

As illustrated in Figure A8.3 nitrilases catalyse conversions of nitriles directly into the corresponding carboxylic adds (route A), while other nitrile converting enzymes, die nitrile hydratases, catalyse the conversion of nitriles into amides (route B) which, by the action of amidases usually present in the whole cell preparations, are readily transformed into carboxylic adds (route C). 

Martinkova, L. and Mylerova, V. (2003) Synthetic applications of nitrile-converting enzymes. Current Organic Chemistry, 7, 1279-1295. 

Wieser, M. and Nagasawa, T. (2000) Stereoselective nitrile-converting enzymes, in Stereoselective Biocatalysis (ed. R.N. Patel), Marcel Dekker, New York, Chapter 17. 

PAN was for a long time thought to be resistant to microbial attack. However, various bacteria that produced nitrile-converting enzymes were isolated from waste-waters of factories producing PAN fibre. Eor example, a nitrile hydratase/amidase enzyme system was studied from Mesorhizobium sp. E28 [68]. Also, bacteria (namely Ralstonia solanacearum and Acidovorax avenae) were used for the removal of acrylic acid from such waste-waters [69]. Later, on the basis of NMR... 

Despite the fact that early experiments suggested low selectivity of nitrile-converting enzymes with respect to the substrate chirality (Faber, 1992), many recent works report the successful enantioselective bioconversion of nitriles catalyzed by nitrilases or nitrile hydratases, even if the stereoselectivity of nitrile hydratases remains often lower that that of coupled amidases. 

The enantioselective synthesis of 2-phenylisoserine derivatives is an attractive goal and several attempts, such as the application of acylase (36), lipase [37], and, more recently, bakers yeast reductase enzymes [38], were made to prepare the taxol side chain (see Section 15.1). No nitrile-converting enzymes have been investigated so far. The chemical instability of 2-hydroxy-3-amino-3-phenylpropionitrile (a cyanohydrin) in aqueous solution afforded the preparation of the cyclic protection products tron.s-( )-8a and ds-( )-9a (Figure 15.2). 

Nitrile Converting Enzymes Involved in Natural and Synthetic Cascade Reactions... 

Figure 11.4 Biotransformations of benzonitrile analogs (R = CI chloroxynil R = Br bro-moxynil R = l ioxynil) by nitrile-converting enzymes in rhodococci [17],...

Previous reviews of this field of research focused mainly on the biocatal5dic uses of nitrilases [1], structure and function of nitrilases [2, 3], nitrilases in filamentous fungi [4], stereoselective biotransformations catalyzed by nitrile-converting enz5nnes [5], and the structure, function, and uses of nitrile hydratases [6]. For a comprehensive review of nitrile-converting enzymes known at the time, the study by Banerjee et al. [7] has been helpful. Some of the most recent reviews focused on nitrilases, specifically their sources, properties, and use, [8], and on methodologies for their screening [9]. 

NITRILE-CONVERTING ENZYMES AND THEIR SYNTHETIC APPLICATIONS... 

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