Characterization of sterols by gas chromatography‐mass spectrometry of the trimethylsilyl ethers

Abstract

The utility of combined gas chromatography-mass spectrometry in the analysis and characterization of sterols has been explored. Methylene unit (MU) values and principal mass spectrometric data are presented for trimethylsilyl ethers of 28 sterols, including the major natural sterols. The diagnostic value of the fragmentation of trimethylsilyl ethers of Delta(5)-3 beta-hydroxysteroids has been confirmed. Characteristic fragmentations of Delta(4)-3 beta-trimethylsilyloxysteroids, and of Delta(5,7)-3 beta-trimethylsilyloxysteroids were also found. Location of side-chain hydroxyl groups is facilitated by the alpha-cleavages typical of the trimethylsilyl ethers. Fragmentations of saturated sterols, and of Delta(7), Delta(8(9)) and Delta((14)) stenols, are less influenced by trimethylsilyl ether formation, but the derivatives still afford satisfactory mass spectra. The combination of gas chromatographic and mass spectrometric information allows positive identification of any of the sterols examined, whereas application of either technique alone may give inconclusive results.

Microaerobic steroid biosynthesis and the molecular fossil record of Archean life

“…Arrows indicate mass shifts of selected fragment ions resulting from incorporation of 13 C from labeled glucose, which produces multiisotopologue ion clusters shifted to masses higher than the unlabeled compound. Ionization was by electron impact at 70 eV; fragment ion assignments are after Brooks et al (41) Our calculations show that, to provide the O 2 outgassing fluxes described in these models, the average concentration in ocean regions contributing to the sea-to-air O 2 flux would be at least 40 nM, which is well above our experimental determination of the concentration required for steroid biosynthesis. Even if the total flux were far below the lower limit considered by Zahnle et al (22), dissolved O 2 concentrations in higher-productivity hot spots ("oxygen oases"), would likely have been high enough to allow steroids to be made.…”

Phycomysterols and Other Sterols from the Fungus Phycomyces blakesleeanus

“…Mass spectra of TMS-ethers of compounds 4, 5, 7, 8, 10, and 12-15 matched those previously described. 12,13 Interpretation of the MS from the TMS-ethers of compounds 6, 9, 11, and 16-20 was carried out on the basis of their fragmentation patterns 12,14 and was facilitated by the previously reported MS of the corresponding free sterols and their acetyl derivatives. [8][9][10][15][16][17][18] Semipreparative HPLC yielded compounds 4-8, 11, 12, and 16.…”

“…TMS-ethers of sterols were used for GC-MS analysis, instead of free sterols, because the former have better chromatographic properties and afford highly characteristic modes of fragmentation from which structural details may be inferred. 12 In the mass spectrum of 1, as the TMS-ether, the molecular ion was consistent with the TMS derivative of a sterol with the molecular formula C 27 H 40 O, containing four double bonds. The fragment ions [M -TMSOH -C 9 H 17 ] + , [M -TMSOH -C 6 H 11 ] + , and [M -(C 6 H 11 + H)] + indicated a side chain with nine carbon atoms and a double bond.…”

“…These include the new natural sterols (1-3; Chart 1) with a 19-norergostane skeleton and an aromatic B ring. Previous studies of sterols from Phycomyces at the University College of Wales yielded a number of new sterols (4)(5)(6)(7)(8)(9)(10)(11)(12)(13) and certain aspects of fungal ergosterol biosynthesis were resolved. [7][8][9][10][11] However, some sterols present in the fungus were not identified.…”

Molecular biogeochemistry of modern and ancient marine microbes

“…Incorporation of C -glucose results in broad peaks in the mass spectrum, shifted to higher masses than the unlabeled compound. Fragment ion assignments are after Brooks et al (1968 span roughly four orders of magnitude, so overall the model is not expected to be highly sensitive to the precise physics of gas exchange.…”