Rhodococcus amidase/nitrile hydratase system

Figure 18 Stereospecific formation of the anti-inflammatory agent (S)-naproxen by the stereoselective amidase/nitrile hydratase system from two Rhodococcus strains.

Enantioselective transformations of several cyclopropane or oxirane-containing nitriles were studied using nitrile-transforming enzymes [78]. Microbial Rhodococcus sp. whole cells containing a nitrile hydratase/amidase system hydrolyzed a number... 

With both these strains, the enzymatic system is composed of nitrile hydratases and amidases. The nitrile hydratase gene of Brevibacterium R312 is cloned, sequenced (ref. 17) and over expressed in Rhodococcus rhodochrous ATCC12674 (pKRNH2) (ref. 18). The best selectivity which can be hoped for with this nitrile hydratase is 93 % (ref. 4). Moreover, the cyanovaleramide with its poor solubility must not be accumulated and requires a biocatalyst with a superactivated amidase activity. The nitrile hydratase is less stable than amidase and the biocatalyst with these two enzymes would not be sufficiently robust for an industrial application. 

In 2003, Griengl s group reported the hydrolysis of cyanohydrins by treatment with bacterial cells of Rhodococcus erythropolis NCIMB 11540, which have a highly active nitrile hydratase/amidase enzyme system. In this manner, (R)-2-chloromandelic acid and (R)-2-hydroxy-4-phenylbutyric acid, two important pharmaceutical intermediates, could be prepared in high optical and chemical yield after short reaction times (3 and 1.5 h, respectively) (Scheme 3.43). 

The stereospecific nitrilase of this strain was also able to convert naproxen nitrile to (5 )-naproxen [(5 )-2-(6-methoxy-2-napthyl)propionic acid]. However, a high enantioselec-tivity was only found at the expense of a low chemical yield (Fig. 11). (S)-Naproxen was furthermore synthesized by stereospecific nitrile hydratase/amidase enzyme systems from oth i Rhodococcus strains (Fig. 18). 

Figure 17 Racemic resolution of (/ ,5)-2-arylpropionitriles by stereoselective nitrile hydratase/ amidase systems from Rhodococcus sp. SP 361 and Agrobacterium tumefaciens d3.

Predominantly Rhodococcus species have been isolated as biocatalysts bearing stereoselective nitrile-converting enzymes. It has been assumed that rhodococci generally contain a nitrile hydratase/amidase system [128], but to regard this as a rule might be... 

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