An Electrochemical Pipette for Study of the Drug Metabolites
Authors: Rafiee Mohammad , Nikzad Nastaran 
Published: August 2024

The similarity between electrochemical and biological redox reactions, particularly in the realm of CYP450-catalyzed oxidation, provides the basis for using electrochemistry to simulate drug metabolism and to synthesize complex drug candidates. The tunability of electrochemical reactions, mild reaction conditions, and the avoidance of toxic reagents are the characteristics of electrochemical reactions in mimicking enzymatic drug metabolites. The acquired insights from these techniques can be used to assess the metabolites' potential toxicity and pharmacological properties. These features along with insights from electrochemical drug metabolism enable chemists to accomplish transformations on complex, functionalized molecules with high selectivity and hold great promise for improving the processes used for pharmaceutical synthesis. An instance is exemplified by acetaminophen (APAP), for which adverse side effects have been ascribed to the oxidative generation of a metabolite known as N-acetyl-p-benzoquinone imine (NAPQI). This well-established area showcased impressive examples of the ability of electrochemistry to replicate phase I and II APAP metabolism reactions. Yet, it is often limited to an analytical scale, hampering comprehensive characterization and complete metabolic behavior elucidation. The synthetic scale preparation of metabolites for quantitative analysis and their further studies is a valuable complementary approach to EC-MS techniques.

Recently, we designed a thin layer electrode that the electrode can be pulled and pushed, like a pipette inside a glass tube, allowing for the taking in and expelling of the sample into and from the thin layer, respectively.1 The thin layer electrochemical pipette allows rapid electrolysis on a microscale making it suitable for the study of the products or intermediates of drug metabolites. The required time for electrolysis or voltammetric experiments in this TLE is in order of minutes, shorter than traditional electrolysis cells, and longer than many of the electroanalytical techniques. This allows us to detect and investigate the drug metabolites with a minute scale half-life. Herein, we showcase the utilization of microscale electrolysis to investigate drug metabolites, specifically elucidating the oxidation pathways of paracetamol and acebutolol drugs using thin-layer electrolysis (TLE) and cyclic voltammetry (CV). We successfully identified well-defined redox peaks of p-benzoquinone and hydroquinone, which remain undetectable through conventional electrolysis, whether in short or extended durations. Additionally, employing a microelectrode in the TLE facilitates the real-time examination of concentration profiles for both redox-active and inactive components involved in electrosynthesis reactions, allowing us to extract valuable kinetic information. Conducting CV experiments within the framework of (TLE) not only yielded detailed electrochemical insights into the mechanisms but also produced micromole-scale products, which can be fully characterized via chromatographic or spectroscopic methods.

1. B.T. Punchihewa, V. Minda, W.G. Gutheil, M. Rafiee, Electrosynthesis and Microanalysis in Thin Layer: An Electrochemical Pipette for Rapid Electrolysis and Mechanistic Study of Electrochemical Reactions. Angew. Chem. Int. Ed.
2023,
62, e202312048.