Synthesis, purification and characterization of 7-ketocholesterol and epimeric 7-hydroxycholesterols.

Various methods were assessed for the synthesis of 7-ketocholesterol and epimeric 7-hydroxycholesterols. Upon the oxidation of cholesteryl acetate with t-butyl chromate, the resulting ketosterol acetate crystallized from methanol consisted of about 25% unoxidized cholesteryl acetate. After the sterol acetates were hydrolyzed in an aqueous K(2)CO(3) medium, preparative TLC was used to fractionate the ketone from cholesterol.Of all the reducing agents employed, only LiAlH(4) reduced completely the purified 7-ketocholesterol to 7-hydroxycholesterols without side reaction products and ketone contamination. Yields of 21.3 mg of 7alpha-hydroxycholesterol and 72.6 mg of 7beta-hydroxycholesterol were obtained by preparative TLC of a diol mixture prepared by the LiAlH(4)-reduction of 100 mg of 7-ketocholesterol. To accomplish the preparative TLC separation of diol bands without overlapping, a double development of a chromatoplate with ethyl ether-cyclohexane (90ratio10, v/v) and ethyl ether was essential.Data on the melting point, optical rotation and infrared spectra, as well as TLC and GLC characteristics, were obtained for purified 7-ketocholesterol and epimeric 7-hydroxycholesterols.