In situ NMR spectroelectrochemistry for the structure elucidation of unstable intermediate metabolites

Abstract

In situ NMR spectroelectrochemistry is presented in this study as a useful hybrid technique for the chemical structure elucidation of unstable intermediate species. An experimental setting was designed to follow the reaction in real time during the experimental electrochemical process. The analysis of (1)H NMR spectra recorded in situ permitted us (1) to elucidate the reaction pathway of the electrochemical oxidation of phenacetin and (2) to reveal the quinone imine as a reactive intermediate species without using any trapping reaction. Phenacetin has been considered as hepatotoxic at high therapeutic amounts, which is why it was chosen as a model to prove the applicability of the analytical method. The use of 1D and 2D NMR experiments led to the elucidation of the major species produced from the oxidation process. We demonstrated that in situ NMR spectroelectrochemistry constitutes a fast way for monitoring unstable quinone imines and elucidating their chemical structures.

Electrochemistry-mass spectrometry to study reactive drug metabolites and CYP450 simulations

“…Other studies have described the formation of NAPQI after paracetamol (dehydrogenation) or phenacetin (aromatic ether dealkylation) oxidation and confirmed the quick, efficient trapping by GSH [14,30]. Moreover, electrochemical oxidation of phenacetin combined with pyridinium chemical trapping demonstrated the formation of an oxonium intermediate involved in the electrochemical mechanistic pathway (Fig.…”

“…2) [20,22,30] and acebutolol [9,31,32] were chosen as models of aromatic ether O-dealkylation. Lohmann et al reported the comparison between electrochemical oxidation and rat-liver microsome incubations for three active pharmaceutical ingredients [15].…”

Solution-phase electrochemistry-nuclear magnetic resonance of small organic molecules

“…Active transport necessitates the solution to be continuously introduced and removed to and from the probe/vial [19]. Passive transport by diffusion is slow, difficult to control and high conversion rates are hard to achieve [16,21]. This is true for both in-probe and in-situ set-ups [8].…”

“…WE, CE and RE are labelled and the NMR sensitive volume is marked instead of the position of the RF coils. {Adapted from [16] with kind permission from Springer Science and Business Media}.…”

Review of advances in coupling electrochemistry and liquid state NMR

“…More recently, Bussy et al [17] introduced a simplified spectroelectrochemical cell, based on carbon microfiber electrode proposed by Klod et al [16]. Carbon microfibers are inserted into a glass capillary tube.…”