Detection, isolation and characterization of principle synthetic route indicative impurity in telmisartan

An unknown impurity was detected in the telmisartan bulk drug (active pharmaceutical ingredient - API) using an isocratic reversed-phase high performance liquid chromatography (HPLC). This impurity was isolated by preparative HPLC. Spectral data of the isolated impurity were collected. Based on the spectral data deriving from two dimensional nuclear magnetic spectroscopy (2D-NMR) and mass spectrometry (MS), the impurity was characterized as “methyl 4′,4′-dibromo methyl biphenyl-2-carboxylate”. The arrived structure was further confirmed by theoretical studies.