Investigation of the biotransformation pathway of verapamil using electrochemistry/liquid chromatography/mass spectrometry – A comparative study with liver cell microsomes

► The oxidative metabolism of the drug verapamil was successfully mimicked by electrochemistry/LC/MS. ► Accurate mass data and tandem mass spectrometry were used for product identification. ► All of the most important verapamil metabolites were found after oxidation on boron-doped diamond electrodes. ► The data obtained by electrochemistry/LC/MS correlate well with those based on liver cell microsome experiments. The biotransformation pathway of verapamil, a widely prescribed calcium channel blocker, was investigated by electrochemistry (EC) coupled online to liquid chromatography (LC) and electrospray mass spectrometry (ESI-MS). Mimicry of the oxidative phase I metabolism was achieved in a simple amperometric thin-layer cell equipped with a boron-doped diamond (BDD) working electrode. Structures of the electrochemically generated metabolites were elucidated on the basis of accurate mass data and additional MS/MS experiments. We were able to demonstrate that all of the most important metabolic products of the calcium antagonist including norverapamil (formed by N-demethylation) can easily be simulated using this purely instrumental technique. Furthermore, newly reported metabolic reaction products like carbinolamines or imine methides become accessible. The results obtained by EC were compared with conventional in vitro studies by conducting incubations with rat as well as human liver microsomes (RLMs, HLMs). Both methods showed good agreement with the data from EC/LC/MS. Thus, it can be noted that EC is very well-suited for the simulation of the oxidative metabolism of verapamil. In summary, this study confirms that EC/LC/MS can be a powerful tool in drug discovery and development when applied complementary to established in vitro or in vivo approaches.