Diethylhydrogensilyl cyclic diethylsilylene derivatives in gas chromatography-mass spectrometry of hydroxylated steroids. II. Pregnanes with a hydroxylated 17.BETA.-side-chain.

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Abstract
The gas chromatographic-mass spectrometric properties of diethylhydrogensilyl cyclic diethylsilylene derivatives of hydroxypregnanes were studied. Pregnanes with a sterically hindered 11.beta.-hydroxyl group were smoothly silylated with a new silylating agent, N,O-bis(diethylhydrogensilyl)-trifluoroacetamide, under mild conditions. The mass spectra of these derivatives were characterized by the appearance of the intense molecular ion peak, which provides convenient and reliable confirmation of the molecular weight of these hydroxypregnanes. The most characteristic fragment ions were those at m/z 185 for 17,20-diols and at m/z 287 for 17,20,21-triols, which were produced by cleavage at the C(13)-C-(17) and C(15)-C(16) bonds with hydrogen atom transfer. This indicates that all of the major fragmentations are directed by the cyclic diethylsilylene group. Another fragmentation common to the spectra was the successive loss of diethylhydrogensilanol from the molecular ion. A remarkable difference in the appearance of peaks was observed between DEHS-DES derivatives of a 17.alpha.,20.alpha.,21-triol and its 20.beta.-isomer. Structures are proposed for some of these fragment ions.

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