Nitrile biotransformations for the practical synthesis of highly enantiopure azido carboxylic acids and amides, ‘click’ to functionalized chiral triazoles and chiral β-amino acids

Under very mild conditions, biotransformations of racemic azido nitriles using Rhodococcus erythropolis AJ270, a nitrile hydratase/amidase-containing microbial whole-cell catalyst, afforded highly enantiopure, (R)-α-arylmethyl- and (+)-α-cyclohexylmethyl-β-azidopropanoic acids and their (S)- and (−)-carboxamide derivatives in excellent yields. The resulting functionalized chiral organoazides were converted in a straightforward fashion to a pair of antipodes of α-benzyl-β-amino acids (R)-13 and (S)-13. Azido carboxamide (S)-11a and azido carboxylic acid (R)-12a underwent ‘click’ reactions with diethyl acetylenedicarboxylate and phenylacetylene to produce functionalized chiral triazoles 14 and 15, respectively. The easy preparation of the starting nitrile substrates, highly efficient and enantioselective biotransformation reactions, and versatile utility of the resulting functionalized azido carboxylic acids and amide derivatives, render this method very attractive and practical in organic synthesis.