Preparation of fatty acid cholesterol ester hydroperoxides by photosensitized oxidation

Abstract

Preparation of fatty acid cholesterol ester hydroperoxides was undertaken with the purpose of evaluating their biological effects on cell growth. Cholesterol stearate, oleate, linoleate and α-linolenate were oxidized using methylene blue as a photosensitizer. The structures of all compounds were established by mass spectrometry and by nuclear magnetic resonance. The photosensitized oxidation of cholesterol oleate gave two hydroperoxide isomers: 9-hydroperoxy- trans-10-octadecenoate, and 10-hydroperoxy- trans-8-octadecenoate. In the case of the cholesterol linoleate, hydroperoxide isomers formed were: 9-hydroperoxy- trans-10, cis-12-octadecadienoate; 10-hydroperoxy- trans-8, cis-12-octadecadienoate; 12-hydroperoxy- cis-9, trans-13-octadecadienoate; 13-hydroperoxy- cis-9, trans-11-octadecadienoate. The oxidation of the cholesterol α-linolenate gave a mixture of six hydroperoxide isomers, at positions 9, 10, 12, 13, 15 and 16 of the fatty acid chain. The photosensitized oxidation of cholesterol stearate produced a formation of hydroperoxide at position 5α of cholesterol. The same hydroperoxide isomers on the fatty acid chain were obtained as described in the literature for the fatty acid methyl esters.