Influence of the 6-trimethylsilyl group on the fragmentation of the trimethylsilyl derivatives of some 6-hydroxy- and 3,6-dihydroxy-steroids and related compounds

The 25 eV mass spectra of the trimethylsilyl derivatives of a number of 6-hydroxy and 3,6-dihydroxy steroids together with deuterium and 18O-labeled analogs have been examined to determine the influence of the 6-OTMS group on fragmentation patterns. Ions in the cholestane series at m/z 321 and 403 were the most characteristic ions derived from the 6-OTMS function; their relative abundances, although low in the spectra of 6-OTMS steroids themselves, were considerably elevated when a 3-OTMS or 3-oxo group was present. Similar ions were present in the spectra of androstane and pregnane derivatives. No correlation was found between the abundance of these ions and the stereochemistry at C3, C5, or C6. Fragmentation mechanisms and gas chromatographic data are discussed.