title: 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.
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-alpha]quinoxalin-4(5H)-one; I] were investigated in female rat faecal extracts following a single oral dose of (14C)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.
authors.affiliation: Upjohn Laboratories-Europe, Crawley, UK.
authors.forename: W
authors.initials: W
authors.lastname: Speed
authors.forename: A H
authors.initials: AH
authors.lastname: Parton
authors.forename: I J
authors.initials: IJ
authors.lastname: Martin
authors.forename: M R
authors.initials: MR
authors.lastname: Howard
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000032:analysis* / Q000493:pharmacokinetics; D001711:Biotransformation; D002853:Chromatography, Liquid; D005243:Feces / Q000737:chemistry*; D005260:Female; D013058:Mass Spectrometry; D010069:Oxadiazoles / Q000032:analysis* / Q000493:pharmacokinetics; D011810:Quinoxalines / Q000032:analysis* / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013056:Spectrophotometry, Ultraviolet
chemical_list: D014151:Anti-Anxiety Agents; D010069:Oxadiazoles; D011810:Quinoxalines; C069443:panadiplon