Fe2+ catalyzes vitamin E-induced fragmentation of hydroperoxy and hydroxy endoperoxides that generates γ-hydroxy alkenals

The formation of cytotoxic gamma-hydroxyalkenals has been generally viewed as the consequence of free radical-induced oxidation of polyunsaturated fatty acyls through the decomposition of lipid peroxides. Vitamin E (Vit E) would be expected to inhibit such autoxidation. In a model study, we now find that fragmentation of a hydroperoxy endoperoxide generated the lactone of a gamma-hydroxyalkenal. With 1 equiv of Fe2+, or with a catalytic amount (0.1 equiv) of Fe2+ and 1 equiv of Vit E, the yields are 43-50%. However, Vit E alone did not promote the fragmentation, and a catalytic amount of Fe2+ alone only afforded a low yield (about 5%). Vit E could contribute to, as opposed to preventing, the formation of gamma-hydroxyalkenals by converting redox-active metal ions into their reduced forms that promote the rapid fragmentation of hydroperoxy endoperoxides.