Gas chromatography—mass spectrometry of epimeric 19-norandrostan-3-ol-17-ones as the trimethylsilyl ether, methyloxime. Trimethylsilyl ether and trimethylsilyl-enol trimethylsilyl ether derivatives

Abstract

The capillary gas chromatographic and mass spectrometric properties of trimethylsilyl (TMS), methyloxime-trimethylsilyl (MO-TMS) and trimethylsilyl-enol trimethylsilyl (TMS-enol-TMS) ether derivatives of four stereoisomeric 19-norandrostan-3-ol-17-ones are presented. The best gas chromatographic separation was obtained with the TMS ethers. Their electron-impact mass spectra show identical fragmentation pathways. However, the isomeric steroids can be differentiated by the characteristic relative intensities of their structurally informative ions. The separation of various epimeric pairs is reduced by changing from TMS to MO-TMS and TMS-enol-TMS ether derivatives. The mass spectra of MO-TMS derivatives are dominated by intense [M — 31] + and [M — (31 + 90)] + ions, whereas those of the TMS-enol-TMS ethers exhibit prominent ions at M + and [M — 15] +. Evidence is presented for the formation of 16-hydroxy-19-norandrosterone TMS derivatives when vigorous conditions were used for the preparation of the TMS-enol-TMS ether derivatives. The mechanisms giving rise to various characteristic fragment ions were investigated with the corresponding [ 2H 9]TMS derivatives. Gas chromatographic properties and mass spectrometric features are discussed.