Nitriles biocatalytic hydrolysis

Biocatalytic hydrolysis or transesterification of esters is one of the most widely used enzyme-catalyzed reactions. In addition to the kinetic resolution of common esters or amides, attention is also directed toward the reactions of other functional groups such as nitriles, epoxides, and glycosides. It is easy to run these reactions without the need for cofactors, and the commercial availability of many enzymes makes this area quite popular in the laboratory. 

Figure 5.24 Unlike the chemical route, the biocatalytic hydrolysis of acrylonitrile to acrylamide is highly selective, owing to the specific function of the nitrile hydratase enzyme.

DuPont practices biocatalytic hydrolysis of nitriles using immobilized whole cells of P. chloioiaphis B23. The catalyst consumption is 0.006 kg/kg product. The conversion is higher and so... 

Oishi T, Yamaguchi K, Mizuno N. Catalytic oxidative synthesis of nitriles directly from primary alcohols and ammonia [J]. Angew Chem Int Ed 2009,121 (34) 6404-6406. Debabov V, Yanenko A. Biocatalytic hydrolysis of nitriles [J]. Rev Chem 2011, 1 (4) ... 

The biocatalytic differentiation of enantiotopic nitrile groups in prochiral or meso substrates has been studied by several research groups. For instance, the nitrilase-catalyzed desymmetrization of 3-hydroxyglutaronitrile [92,93] followed by an esterification provided ethyl-(Jl)-4-cyano-3-hydroxybutyrate, a useful intermediate in the synthesis of cholesterol-lowering dmg statins (Figure 6.32) [94,95]. The hydrolysis of prochiral a,a-disubstituted malononitriles by a Rhodococcus strain expressing nitrile hydratase/amidase activity resulted in the formation of (R)-a,a-disubstituted malo-namic acids (Figure 6.33) [96]. 

Another example of a biocatalytic transformation ousting a chemical one, in a rather simple reaction, is provided by the Lonza nitotinamide process (Fig. 2.34) (Heveling, 1996). In the final step a nitrile hydratase, produced by whole cells of Rh. rhodoccrous, catalyses the hydrolysis of 3-cyano-pyridine to give nitotinamide in very high purity. In contrast, the conventional chemical hydrolysis afforded a product contaminated with nicotinic acid. 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

A strategy to access lactones via enzymatic hydrolysis of y- and /3-hydroxy aliphatic nitriles to their corresponding acids with subsequent internal esterification was applied using commercially available enzymes from BioCatalytics Inc. A number of y- and /3-hydroxy aliphatic nitrile substrates (Table 8.11) were evaluated, with the greatest selectivity observed with y-hydroxy nonanitrile, which was converted by nitrilase NIT1003 to the precursor of the rice weevil pheromone in 30% yield, 88% ee with an enatiomeric ratio of = 23 [90],... 

Figure 2.20 (a) Mitsubishi s new route for the biocatalytic production of acrylamide (b) and (c) DuPont and Lonza bioroutes, respectively, for the hydrolysis of nitriles. 

Nifrilases catalyze the conversion of organonitriles directly to the corresponding carboxylic acids. Synthetic hydrolysis of nitriles into the corresponding amides and carboxylic acids requires severe reaction conditions. A typical synthetic approach would require the use of 70% H2SO4 and heat (13). Such a reaction condition is not compatible when selectivity and the conservation of other hydrolysable functional groups in a substrate are desired. Biotransformation of nitrites can be accomplished under mild conditions, in an aqueous environment (13). Additionally, enantioselectivity of the biocatalytic conversion of nitriles to chiral acids has been demonstrated (14-16). Therefore, nifrilases provide an alternative route for synthetic processes that require conversion of nitriles to corresponding acids. 

Another biocatalytic option is the hydrolysis of p-aminonitriles, compounds that are relatively easily synthesized. There are two hydrolytic routes for the enzymatic conversion of nitriles to the corresponding carboxylic acids. These transformations can be achieved either through a two-step cascade reaction involving a nitrile hydratase followed by an amidase that hydrolyzes the intermediate amide, or through use of a nitrilase, an enzyme able to perform the two sequential transformations (Scheme 14.4). The focus of this chapter is on nitrile hydrolysis enzymes. 

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