Mass spectrometry characterization of the 5 alpha-, 7 alpha-, and 7 beta-hydroxy derivatives of beta-sitosterol, campesterol, stigmasterol, and brassicasterol

The 5 alpha-hydroperoxides of beta-sitosterol, campesterol, stigmasterol, a nd brassicasterol were obtained by photooxidation of the respective sterols in pyridine in the presence of hematoporphyrine as sensitizer. The reducti on of the hydroperoxides gives the corresponding 5 alpha-hydroxy derivative s. The 7 alpha- and 7 beta-hydroperoxides of the sterols were obtained by a llowing an aliquot of the 5 alpha-hydroperoxides to isomerize to 7 alpha-hy droperoxides, which in turn epimerize to 7 beta-hydroperoxides. The reducti on gave the corresponding 7 alpha- and 7 beta-hydroxy derivatives. The 5 al pha-, 7 alpha-, and 7 beta-hydroxy derivatives of beta-sitosterol, campeste rol, stigmasterol, and brassicasterol were identified by comparing thin-lay er chromatography mobilities, specific color reactions, and mass spectral d ata with those of the corresponding hydroxy derivatives of cholesterol, whi ch were synthesized in the same manner. The phytosterols had the same behav ior to photooxidation as cholesterol and, moreover, the different phytoster ols photooxidized at about the same rate. The mass spectra of the trimethyl silyl ethers of the hydroxy derivatives of the phytosterols investigated an d of the corresponding hydroxy derivatives of cholesterol have the same fra gmentation patterns and similar relative ion abundances.