Homolytic decomposition of linoleic acid hydroperoxide: Identification of fatty acid products

Abstract

An isomeric mixture of linoleic acid hydroperoxides, 13‐hydroperoxy‐cis‐9,trans‐11‐octadecadienoic acid (79%) and 9‐hydroperoxy‐cis‐12,trans‐10‐octadecadienoic acid (21%), was decomposed homolytically by Fe(II) in an ethanol‐water solution. In one series of experiments, the hydroperoxides were decomposed by catalytic concentrations of Fe(II). The 10−5 M Fe(III) used to initiate the decomposition was kept reduced as Fe(II) by a high concentration of cysteine added to the reaction in molar excess of the hydroperoxides. Nine different monomeric (no detectable dimeric) fatty acids were identified from the reaction. Analyses of these fatty acids revealed that they were mixtures of positional isomers identified as follows: (I) 13‐oxo‐trans,trans‐(andcis,trans‐) 9,11‐octadecadienoic and 9‐oxo‐trans,trans‐ (andcis,trans‐) 10,12‐octadecadienoic acids; (II) 13‐oxo‐trans‐9,10‐epoxy‐trans‐11‐octadecenoic and 9‐oxo‐trans‐12, 13‐epoxy‐trans‐10‐octadecenoic acids; (III) 13‐oxo‐cis‐9,10‐epoxy‐trans‐11‐octadecenoic and 9‐oxo‐cis‐12, 13‐epoxy‐trans‐10‐octadecenoic acids; (IV) 13‐hydroxy‐9,11‐octadecadienoic and 9‐hydroxy‐10,12‐octadecadienoic acids; (V) 11‐hydroxy‐trans‐12, 13‐epoxy‐cis‐9‐octadecenoic and 11‐hydroxy‐trans‐9, 10‐epoxy‐cis‐12‐octadecenoic acids; (VI) 11‐hydroxy‐trans‐12, 13‐epoxy‐trans‐9‐octadecenoic and 11‐hydroxy‐trans‐9,10‐epoxy‐trans‐12‐octadecenoic acids; (VII) 13‐oxo‐9‐hydroxy‐trans‐10‐octadecenoic acids; (VIII) isomeric mixtures of 9, 12, 13‐dihydroxyethoxy‐trans‐10‐octadecenoic and 9, 10, 13‐dihydroxyethoxy‐trans‐11‐octadecenoic acids; and (IX) 9, 12, 13‐trihydroxy‐trans‐10‐octadecenoic and 9, 10, 13‐trihydroxy‐trans‐11‐octadecenoic acids. In another experiment, equimolar amounts of Fe(II) and hydroperoxide were reacted in the absence of cysteine. A large proportion of dimeric fatty acids and a smaller amount of monomeric fatty acids resulted. The monomeric fatty acids were examined by gas liquid chromatography‐mass spectroscopy. Spectra indicated that the monomers were largely similar to those produced by the Fe(III)‐cysteine reaction.

Metabolism of Fatty Acid Hydroperoxides by Chlorella pyrenoidosa

“…IR spectroscopy revealed absorptions at 1740 cm-' (ester carbonyl), 1700 and 1679 cm-' (a,f3-unsaturated ketone), 1635 cm-' (double bond a,f3 to a carbonyl), 980 cm-' (trans unsaturation), and 885 cm-' (trans epoxide) (14). NMR shifts were virtually identical to those reported by Gardner et al (4) for a mixture of 9,10-trans-epoxy-13-oxo-trans-11-and 12,13-trans-epoxy-9-oxo-trans-10-octadecenoic acids: 62.28 (t, methylene a to ester carbonyl), 62.93 (m, 1 H, epoxide proton a to methylene), 63.23 (dd, 1 H, epoxide proton a to a double bond), 66.45 (dd, 1 H, olefinic proton a to epoxide), 66.40 (s, 1 H, olefinic proton a to carbonyl), 62.51 (t, methylene a to conjugated carbonyl), multiplet centered on 65.44 (2 H, olefinic protons), 62.03 (m, methylene a to methyl and a to unsaturation).…”

“…They result from homolytic decomposition reactions catalyzed by Fe(II) (4). In our experiments with Chlorella, both metabolites were formed in the presence of enzyme extract, but were not produced when the extract was heat-treated for 5 min at 100°C.…”

Decomposition products of Dimers Arising from Secondary Oxidation of Methyl Linoleate Hydroperoxides

“…These oxygenated fatty acids (esters), except the dihydroxy (or .hydroperoxy) ester, have already been identified in the homolytic decompostion products of linoleic acid hydroperoxides by Gardner et a1. 17 ) Dihydroxy and trihydroxy esters were identified in the chemical reduction products of oxygenated linoleate hydroperoxides by Terao et al 19 ) Our present results, together with the previous papers,9-11) suggest the pathway for the formation of these hydroxy esters via dimers.…”

Vitamin E: Mechanism of Its Antioxidant Activity.

“…The results indicate that alkoxyl radical rearrangement to epoxide is an important pathway in the homolysis of 13-MeLOOH by heat. The conversion of lipid hydroperoxides to the corresponding lipid ketones usually accounts for a relatively large portion of end products and they can be derived from hydroperoxides via alkoxyl eoH RI~~\R2 Rlj~VR2 Rl~/~lA~E '.J'__ R2 radicals (Gardner et al, 1974;Hamberg, 1975). From 1 3-MeLOOH, the corresponding oxodiene, methyl 1 3-0xo-9, 1 1-0ctadecadienoate (b), was obtained, and high concentrations of a-tocopherol accelerated the formations of a and b.…”