Voltammetric study of GR127935 at a glassy carbon electrode, and optimized conditions for its determination by high-performance liquid chromatography with coulometric detection

Abstract

Systematic studies, employing cyclic voltammetry at a planar glassy carbon electrode, have revealed that the orally active 5-HT_1D receptor antagonist GR127935 is electroactive. Results indicate that the electrode process involves a diffusion controlled, irreversible, 1 electron–1 proton oxidation of the compound's anisolic methoxy group (E_pa approximately + 1 V versus Ag/AgCl) to yield a reactive radical anion that is considered to undergo further oxidation to the semiquinone. It is likely that other follow-up chemical reactions proceed to generate non-electroactive species; however, some reductive behaviour occurs because two small cathodic waves are seen on the reverse voltammetric scans. Subsequent forward scans reveal three additional anodic waves when sweep rates are >50 mV s^–1. One cathodic and the more anodic of these latter waves are considered to arise from the quasi-reversible behaviour of the semiquinone generated on the first forward scan. GR152077, the major metabolite of GR127935 identified in toxicokinetic studies, is not electroactive. The GR127935 oxidation process was utilized for the development of an analytical method employing HPLC with electrochemical (coulometric) detection (HPLC–ECD). This method can detect 20 pg of GR127935 injected on-column (using a 100 µl sample volume). The intra-assay precision for standard solutions containing either 1.14 or 8.41 ng ml^–1 of GR127935 is 3.60% or 2.11%, respectively (n= 6).