Polyunsaturated fatty acid alkoxyl radicals exist as carbon-centered epoxyallylic radicals: a key step in hydroperoxide-amplified lipid peroxidation.
13-Hydroperoxyoctadeca-9,11,15-trienoic acid was reacted with a catalytic amount of 5,10,15,20-tetraphenyl-21H,23H-porphyrin iron(III) chloride in dichloromethane containing 2,4,6-tri-tert-butylphenol. The principal products were identified as 13-oxooctadeca-9,11,15-trienoic acid, 13-oxotrideca-9,11-dienoic acid, and a series of isomeric epoxyaryl ethers [9-(2,4,6-tri-tert-butylphenoxy)-12,13-epoxyoctadec-10-enoic acids and 11-(2,4,6-tri-tert-butylphenoxy)-12,13-epoxyoctadec-9-enoic acids]. The epoxyaryl ethers are coupling products of 2,4,6-tri-tert-butylphenoxyl radical and an epoxyallylic radical formed by cyclization of an intermediate alkoxyl radical. The high yield of epoxyaryl ethers relative to 13-oxotrideca-9,11-dienoic acid suggests the equilibrium between alkoxyl radical and epoxyallylic radical lies predominantly toward epoxyallylic radical. This cyclization appears to be a key step in the amplification of lipid peroxidation by polyunsaturated fatty acid hydroperoxides.
A. B. Hancock, Jr., Memorial Laboratory of Cancer Research, Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146.
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Wilcox
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Marnett
D000975:Antioxidants; D002851:Chromatography, High Pressure Liquid; D003500:Cyclization; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D005609:Free Radicals; D006861:Hydrogen Peroxide; D007502:Iron Chelating Agents; D008042:Linolenic Acids; D015227:Lipid Peroxidation; D008054:Lipid Peroxides; D010636:Phenols / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry
D000975:Antioxidants; D005231:Fatty Acids, Unsaturated; D005609:Free Radicals; D007502:Iron Chelating Agents; D008042:Linolenic Acids; D008054:Lipid Peroxides; D010636:Phenols; D011166:Porphyrins; C057375:13-hydroperoxy-9,11,15-octadecatrienoic acid; C016136:tetraphenylporphine sulfonate; C019584:2,4,6-tri-tert-butylphenol; D006861:Hydrogen Peroxide