Sequence of reactions which follows enzymic oxidation of propargylglycine

Abstract

The nonenzymatic reactions which follow enzymatic oxidation of the .gamma.-.delta. acetylenic amino acid propargylglycine (2-amino-4-pentynoate) [by hog kidney D-amino acid oxidase] were studied. The product which accumulates in solution was identified as 2-amino-4-hydroxy-3,4-pentadienoate .gamma.-lactone, formed by intramolecular attack of the carboxylate anion on the electrophilic 4th C of 2-iminium-3,4-pentadienoate. This previously unknown substance was characterized by its reactions in acid and base and by its NMR spectrum. The lactone is preceded in the pathway by 2-amino-2-penten-4-ynoate, a transient electron-rich species which binds tightly to D-amino-acid oxidase and induces a charge-transfer complex with the electron-deficient bound flavin coenzyme. The aminediene lactone is converted by base treatment to 2-amino-4-keto-2-pentenoate, which is also a strong inhibitor of D-amino-acid oxidase and induces a charge-transfer complex.