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.
Wilcox
A L
AL
A. B. Hancock, Jr., Memorial Laboratory of Cancer Research, Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146.
Marnett
L J
LJ
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