title: Electron ionization mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols.
abstract: The electron ionization (EI) mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols was investigated. Interesting fragmentation processes involving a transannular cleavage of the epoxide ring after transfer of the trimethylsilyl group are significant in the case of 4,5-epoxysterol trimethylsilyl ethers (affording abundant fragment ions at m/z 403 and 404). Different pathways, which have been substantiated by deuterium labelling, are proposed in order to explain the formation of these ions. In contrast, this transfer is not significant in the case of 5,6-epoxysterol trimethylsilyl ethers. The EI mass spectra of these latter compounds appear to be very complex and to differ slightly according to the stereochemistry of the epoxy group. Acetate and trifluoroacetate derivatives of 4,5-epoxysterols display interesting EI mass spectra dominated by a fragment ion at m/z 332 resulting from cleavage of the steroid ring A.
authors.affiliation: Laboratoire de Microbiologie de Géochimie et d'Ecologie Microbienne (UMR 6117), Centre d'Océanologie de Marseille (OSU), Campus de Luminy-case 901, 13288 Marseille, France. rontani@com.univ-mrs.fr
authors.forename: J-F
authors.initials: JF
authors.lastname: Rontani
authors.forename: C
authors.initials: C
authors.lastname: Aubert
mesh_terms: D004083:Cholestanol / Q000032:analysis; D002783:Cholestenones / Q000032:analysis; D004852:Epoxy Compounds / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014297:Trimethylsilyl Compounds / Q000032:analysis
chemical_list: D002783:Cholestenones; D004852:Epoxy Compounds; D014297:Trimethylsilyl Compounds; C000475:cholest-4-en-3-one; D004083:Cholestanol