Novel perfluoroacyl derivatives of corticosteroids and related substances for potential use in quantitative gas chromatography mass spectrometry

We investigated the potential of perfluoroacylation for gas chromatographic mass spectro-metric determination of corticosteroids and related substances. Structure elucidation of the reaction products was performed with high and low resolution mass spectrometry and with proton and carbon nuclear magnetic resonance spectrometry. Besides the well known S-enol ester formation, 17 beta-methyl-18-nor-13(14)-ene steroids were formed via loss of the 17-alpha hydroxyl group followed by a Wagner-Meerwein rearrangement. Compounds that bear an 11 beta-hydroxy group formed additionally a 9(11) double bond when acetone was used as solvent, whereas acetonitrile or cyclohexane led to formation of 11 beta-perfluoroacyl esters. In particular, perfluoroacylation of cortisol led to a clearly defined product instead of complex mixtures observed before, which thus makes it a valuable alternative to methoxime formation-silylation of cortisol for quantitative gas chromatographic mass spectrometric analyses