Selective hydrolysis of aliphatic dinitriles to monocarboxylic acids by a nitrilase from Arabidopsis thaliana

The hydrolysis of a variety of dinitriles including α,ω-dicyanoalkanes 1, β-substituted glutaronitriles 5, and γ-cyanopimelonitrile 7 with a recombinant plant nitrilase from Arabidopsis thaliana, expressed in E. coli, is described. Conversion rate and selectivity of the hydrolysis of dinitriles 1a-f to ω-cyanocarboxylic acids 2a-f depend on the chain length. The enzyme activity markedly increases from malononitrile (1a) to octanedinitrile (1f). The selectivity, however, does not correlate with the rates. Up to a chain length of 6 C-atoms, the cyanocarboxylic acid is the only product, even at complete conversion of the starting material. Pimelonitrile (1e) is hydrolyzed to the cyanocarboxylic acid 2e without formation of diacid (<1%) up to 73% conversion. Glutaronitriles 5a-c were also hydrolyzed to the corresponding cyanobutanoic acids 6a-c with perfect selectivity. The nitrilase hydrolyzes exclusively the primary cyano group of 7 to give 3,5-dicyanoheptanoic acid (8a), whereby the selectivity is slightly reduced compared to the unsubstituted pimelonitrile (1e). If the hydrolysis is terminated at conversions &le90%, pure 8a can be isolated in 72% yield (92% referred to conversion). After esterification of 8a to the methyl ester 8b, only the 5-cyano group but not the ester function was hydrolyzed enzymatically to give cyanoheptanedioic acid monoester (10).