Isolation and characterization of benazepril unknown impurity by chromatographic and spectroscopic methods

The presence of unknown impurity of the order of 0.2% was identified in benazepril using liquid chromatographic technique employing binary gradient system comprising acetic acid and ammonia in water and acetonitrile as the mobile phase. LCMS data corresponds to hydroxylated benazepril (OHB) derivative possessing the molecular formula C24H28N2O6. This impurity was isolated using isocratic system containing ammonium acetate and acetonitrile and the product was characterized using FT-IR, 1H and 13C NMR and mass spectroscopy to ascertain the structure of the impurity. The spectroscopic analysis revealed the presence of hydroxyl function on C17 carbon atom of benazepril molecule. The plausible mechanism for the formation of OHB species is proposed.