Electron ionization mass spectral fragmentation of cholestane-3beta,4alpha,5alpha-triol and cholestane-3beta,5alpha,6alpha/beta-triol bis- and tris-trimethylsilyl derivatives.
The electron ionization (EI) mass spectral fragmentation of the bis- and tris-trimethylsilyl derivatives of cholestane-3beta,4alpha,5alpha-triol, cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol was investigated. The EI mass spectrum of the 3beta,4alpha-bis-trimethylsilyl derivative of cholestane-3beta,4alpha,5alpha-triol exhibits interesting fragment ions at m/z 142 and 332 resulting from the initial loss of TMSOH between the carbons 2 and 3 and subsequent retro-Diels-Alder (RDA) cleavage of the ring A. Trimethylsilyl transfer between the 4alpha- and the 5alpha-hydroxy groups acts significantly before RDA cleavage affording an ion at m/z 404. Complete silylation of cholestane-3beta,4alpha,5alpha-triol strongly stabilizes the molecule, affording an abundant molecular ion at m/z 636 and decreasing the abundance of the RDA cleavage. Loss of water (from the non-silylated 5alpha-hydroxy group) plays a very important role during the decomposition of the molecular ion of 3beta,6alpha/beta-bis-trimethylsilyl derivatives of cholestane-3beta,5alpha,6alpha/beta-triols. These derivatives appear to be very useful in assigning the configuration of the carbon 6. This assignment is based on the abundance of the fragment ions at m/z 321, 367 and 403, which are more prominent in the EI mass spectrum of the beta-isomer. In contrast, EI mass spectra of the tris-trimethylsilyl derivatives of cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol differ only slightly and appear to be poorly informative.
Rontani
J-F
JF
Laboratoire de Microbiologie de Géochimie et d'Ecologie Marines (UMR 6117), Centre d'Océanologie de Marseille (OSU), Campus de Luminy-case 901, 13288 Marseille, France. rontani@com.univ-mrs.fr
Aubert
C
C
D002777:Cholestanols / Q000737:chemistry* / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry* / Q000378:metabolism; D006888:Hydroxycholesterols / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014297:Trimethylsilyl Compounds / Q000737:chemistry / Q000378:metabolism
D002777:Cholestanols; D006888:Hydroxycholesterols; D014297:Trimethylsilyl Compounds; C000474:cholestane-3,5,6-triol; C099828:cholest-5-ene-3,4-diol; D002784:Cholesterol