Unified mechanism for polyunsaturated fatty acid autoxidation. Competition of peroxy radical hydrogen atom abstraction, .beta.-scission, and cyclization

Abstract

The photooxidation of benzoylformic acid (la) in benzene gave peroxybenzoic acid, hydrogen peroxide, and phenyl benzoate. The addition of -methylstyrene to the oxidation system afforded the epoxide together with acetophenone as a C-C cleaved product, and the ester yield was significantly increased at the expense of the peracid. The photooxidation of la was not sensitized by methylene blue or other sensitizers, but was efficiently accelerated by pyridine or other weakly basic solvents such as ethers. Pyridine effectively catalyzed the photoepoxidation as well as the photodecarboxylation of la to benzaldehyde.The photoepoxidation gave predominantly trans epoxides, and the relative reactivities of olefins were similar to the photoepoxidation with benzoin (i.e., PhC03•) and quite different from the peracid epoxidation. Similar results were obtained by other a-keto acids or the corresponding esters. These facts suggest that the photoepoxidation proceeds via radical epoxidation by acylperoxy radical, affording trans epoxide predominantly. Contrary to previous reports, the photooxidation of -keto acids via an *02 reaction was not substantiated. The photodecarboxylation of la to afford benzaldehyde was selectively catalyzed by water, and its undissociated form was about tenfold more reactive than the corresponding carboxylate ion.

Coexistence of Oxidized Lipids and α-Tocopherol in All Lipoprotein Density Fractions Isolated From Advanced Human Atherosclerotic Plaques

“…52,53 Preliminary results indicate that in advanced human lesions cis,trans predominate over trans,trans Ch18:2-O(O)H isomers, 56 suggesting that most oxidized Ch18:2 detected were indeed formed in the presence of vitamin E.…”

Methods for Evaluation of the Oxidative Stability of Lipid-Containing Foods.

“…Polyunsaturated fatty acids (PUFA) such as arachidonic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), containing 4, 5 and 6 double bonds, respectively, are much less stable than linoleic and linolenic acids. Arachidonic acid is oxidized 2.9 times faster than linoleic acid (Porter et al, 1981). Ethyl esters of EPA and DHA oxidized rapidly even at 5'C in the dark after an induction period of 3-4 days, whereas the induction period of linoleate and linolenate under similar conditions are 20 and 60 days, respectively.…”

Formation of Highly Reactive Cyclopentenone Isoprostane Compounds (A3/J3-Isoprostanes) in Vivo from Eicosapentaenoic Acid

“…Pathway for the formation of the A 3 /J 3 -IsoPs by the nonenzymatic peroxidation of EPA. For simplicity, the stereochemistry of both the lipid peroxidation intermediates and final IsoPs is not shown, although it has been extensively characterized previously utilizing other fatty acids (32,55).…”