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The use of liquid chromatography/thermospray mass spectrometry with on‐line ultraviolet diode array and radiochemical detection: Characterization of the putative metabolites of U‐78875 in female rat faeces
Author(s) -
Speed W.,
Parton A. H.,
Martin I. J.,
Howard M. R.
Publication year - 1994
Publication title -
biological mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1052-9306
DOI - 10.1002/bms.1200230102
Subject(s) - thermospray , mass spectrometry , chromatography , ultraviolet , chemistry , line (geometry) , high performance liquid chromatography , feces , chromatography detector , biology , materials science , tandem mass spectrometry , optoelectronics , microbiology and biotechnology , selected reaction monitoring , geometry , mathematics
Abstract The metabolites of an anxiolytic drug candidate U‐78875 {3‐(5‐cyclopropyl‐1,2,4‐oxadiazol‐3‐yl)‐5‐(1‐methylethyl)‐imidazo[1,5‐α]quinoxalin‐4(5 H )‐one; I} were investigated in female rat faecal extracts following a single oral dose of ( 14 C)I. Initial metabolite profiling was performed by high‐performance liquid chromatography incorporating homogeneous (i.e. liquid scintillant added post‐column) radiochemical detection (radio‐HPLC). This indicated the presence of parent drug and one minor metabolite. Because liquid scintillant is incompatible with thermospray interfaces, subsequent analysis by thermospray/HPLC/MS (TSP/LC/MS) incorporated radiochemical detection in heterogeneous (i.e. solid scintillant) mode and ultraviolet (UV) diode array detection. This revealed that the peak thought previously to be parent drug contained two components: a metabolite (major) and parent drug (minor). The UV spectrum and TSP/LC/MS/MS daughter ion analysis led to the proposition of a bisamide structure for the major metabolite. Chemical synthesis was used to confirm this structure. TSP/LC/MS indicated that the molecular weight of the minor metabolite was 16 u higher than the bisamide, suggesting an oxidized analogue. Attempts to obtain a daughter ion spectrum on this minor metabolite proved unsuccessful. On‐line radiochemical and UV diode array detection greatly facilitates the TSP/LC/MS characterization of metabolites from studies using radiolabelled drugs.