Synthesis of amidrazones using an engineered papain nitrile hydratase

To demonstrate the usefulness of an engineered papain nitrile hydratase as a biocatalyst, a peptide amidrazone was prepared by incubation of the nitrile MeOCO-Phe-Alanitrile with the Gln19Glu papain mutant in the presence of salicylic hydrazide as a nucleophile. The amidrazone results from nucleophilic attack by salicylic hydrazide at the imino carbon of the thioimidate adduct formed between the enzyme and the peptide nitrile substrate. Compared to wild-type enzyme, the engineered nitrile hydratase causes a better than 4000-fold increase in the rate of amidrazone formation and yields a product of much higher purity. The advantages over other nitrile-hydrolyzing enzymes and current limitations of the papain nitrile hydratase are discussed.