Doubly allylic hydroperoxide formed in the reaction between sterol 5,7-dienes and singlet oxygen.
Ergosterol and 7-dehydrocholesterol, common 5,7-conjugated diene sterols, react with photochemically produced singlet oxygen very efficiently to yield, in parallel pathways, the corresponding 5,8-endoperoxides and the 7 beta-hydroperoxy-5,8(9),22-trienol or -5,8(9)-dienol, respectively. The hydroperoxides decompose in an acid-catalyzed reaction to generate hydrogen peroxide and the 5,7,9(11),22-tetraenol or 5,7,9(11) trienol, respectively, with 1:1 stochiometry. The molar ratio of endoperoxide to hydroperoxide was constant (16:5) with two different reaction solvents, two different photosensitizers, and at all time points between 5 min and 3 h from the start of irradiation. Ergosterol did not react with either hydrogen peroxide or superoxide ion under our reaction conditions. Inhibition studies with nitrogen, 2,5-dimethylfuran, beta-carotene, and tert-butanol confirmed the involvement of singlet oxygen in these reactions. The unstable hydroperoxide would be expected to have undesirable biological consequences if formed in vivo.
Albro
P W
PW
Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709.
Corbett
J T
JT
Schroeder
J L
JL
D000498:Allyl Compounds; D003684:Dehydrocholesterols / Q000737:chemistry*; D004875:Ergosterol / Q000737:chemistry*; D015227:Lipid Peroxidation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010100:Oxygen; D010777:Photochemistry; D026082:Singlet Oxygen
D000498:Allyl Compounds; D003684:Dehydrocholesterols; D026082:Singlet Oxygen; C016705:7-dehydrocholesterol; D010100:Oxygen; D004875:Ergosterol