An Electron Spin Resonance Investigation of Radical Intermediates in Cholesterol and Related Compounds: Relation to Solid-State Autoxidation

Article abstract of DOI:10.1021/j100404a035

This work reports an investigation of the free-radical chemistry of cholesterol and a number of cholesterol derivatives and analogues.The initial radicals formed in solid oxygen-free cholesterol samples after γ-irradiation at 77 K are found to be a tertiary side-chain radical and an allylic radical in the cholesterol A and B rings.At 300 K only the allylic radical is found.The structure of the allylic radical is confirmed by experiments on two analogues of cholesterol, 7-OH cholesterol, and the selectively deuterated 7-D-7-OH cholesterol, both of which produce the allylic radical after γ-irradiation by loss of the hydroxyl group. Cholesterol samples with oxygen present provide evidence for formation of two distinct peroxy radicals originating with the two carbon radicals found in the oxygen-free samples.These peroxy radicals are suggested to have different reactivities resulting from the different motional freedom each possesses.We suggest that the products found after radiation-induced autoxidation at or near room temperature are consistent with the different reactivities of the peroxy radicals.It is found for four cholesterol esters, one cholesterol derivative, and one sterol that the only radical stable at room temperatures in oxygen-free samples is the allylic radical.In only one ester, cholesterol chloroacetate, is the allylic radical not the stable room temperature radical.