Regioselective biotransformation of the dinitrile compounds 2-, 3- and 4-(cyanomethyl) benzonitrile by the soil bacterium Rhodococcus rhodochrous LL100–21

The cyanomethyl benzonitrile compounds used for this study contain two cyano groups: a −CH2CN side chain, plus a cyano group attached to the benzene ring. The ortho, meta and para −CH2CN substituted compounds were biotransformed using whole cell suspensions of the bacterium Rhodococcus rhodochrous LL100–21. The bacterium had previously been grown on the mono-nitrile compounds propionitrile, benzonitrile or acetonitrile, inducing the formation of nitrile hydrolyzing enzymes. Suspensions of R. rhodochrous LL100–21 that had been grown on propionitrile or benzonitrile converted the aliphatic group of 2-(cyanomethyl) benzonitrile (a) to the corresponding carboxylic acid, 2-(cyanophenyl) acetic acid (d) with excellent recovery of the product and no evidence for any other products. Conversely, when grown on acetonitrile the bacterium converted 2-(cyanomethyl) benzonitrile (a) to the amide derivatives 2-(cyanophenyl) acetamide (k) and 2-(cyanomethyl) benzamide (l) but only in low yields. Biotransformations of 3-(cyanomethyl) benzonitrile (b) and 4-(cyanomethyl) benzonitrile (c), by suspensions of bacteria that had been grown on benzonitrile or propionitrile, resulted in hydrolysis of the aromatic nitrile to produce 3- and 4-(cyanomethyl) benzoic acid (j) and (m), respectively, both with a high yield. Low concentrations of other products were also detected, for example the diacids 3- and 4-(carboxyphenyl) acetic acid (h) and (i). When the bacterium was grown on acetonitrile it could biotransform 3- and 4-(cyanomethyl) benzonitrile (b) and (c) to different products indicating less regiospecificity by the nitrile hydratase enzyme. Comparison of the initial rates of conversion of the aliphatic cyano side chain of 2-(cyanomethyl) benzonitrile (a) and other substituted benzonitriles indicated that electronic effects did not affect the initial rate of the reaction as they would require transmission through an SP3 methylene carbon atom.