Pw. Albro et al., DOUBLY ALLYLIC HYDROPEROXIDE FORMED IN THE REACTION BETWEEN STEROL 5,7-DIENES AND SINGLET OXYGEN, Photochemistry and photobiology, 60(4), 1994, pp. 310-315
Ergosterol and 7-dehydrocholesterol, common 5,7-conjugated diene stero
ls, react with photochemically produced singlet oxygen very efficientl
y 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, respec
tively. 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 endo
peroxide to hydroperoxide was constant (16:5) with two different react
ion solvents, two different photosensitizers, and at all time points b
etween 5 min and 3 h from the start of irradiation. Ergosterol did not
react with either hydrogen peroxide or superoxide ion under our react
ion conditions. Inhibition studies with nitrogen, 2,5-dimethylfuran, b
eta-carotene, and tert-butanol confirmed the involvement of singlet ox
ygen in these reactions. The unstable hydroperoxide would be expected
to have undesirable biological consequences if formed in vivo.