Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.
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