Hydrogen sulfide adducts of methyltrans,trans- 9,11-octadecadienoate

Hydrogen sulfide was added to methyltrans, trans- 9,11-octadecadienoate in benzene solution at 25 C with ultraviolet radiation. GC-MS and GLC analysis of the reaction product showed the presence of methyl oleate, methyl stearate, geometric isomers of methyl 9,11-octadecadienoate, methyl 9,12-epoxy-octadeca-9, 11-dienoate, an unknown compound with an apparent molecular weight of 306, methyl 8-(2′,5′-hexylthienyl) octanoate, an unidentified sul-fur ] containing C₁₈ ester with an apparent molecular weight of 326, methyl 9,12-epithiostearate, an adduct of methyltrans,trans- 9,11-octadecadienoate and ben-zene [bicyclo (4.4.0)-deca-2,5,7-triene-l-(Ω-carboxy-methyl heptyl)-4 hexyl] and a probable mixture of methyl 9,11-epidithiostearate, methyl 9,12-epidithio-stearate, and methyl 10,12-epidithiostearate.     

Synthesis of phenyl substituted C18 furanoid fatty esters

Methyl 9,12-epoxy-10-phenyl-9,11-octadecadienoate was prepared by acid catalyzed cyclization of methyl 9,12-dioxo-10-phenyloctadecanoate, which was derived from the oxidation of methyl 9-hydroxy-12-oxo-10-phenyloctadecanoate. The latter was exclusively obtained from methylcis-9,10-epoxy-12-oxooctadecanoate with phenyllithium in the presence of copper (I) bromide. A mixture of positional isomers, methyl 9,12-epoxy-10(11)-phenyl-9,11-octadecadienoates, was also prepared by another route. The spectroscopic properties of the various intermediates and products were studied. The positional isomers of the phenyl substituted furanoid fatty esters were characterized by¹³C nuclear magnetic resonance spectrometry.     

Epoxidation reactions of unsaturated fatty esters with potassium peroxomonosulfate

Epoxidation of the double bond in methyl oleate, octadec-11E-en-9-ynoate, ricinoleate (12-hydroxy-octadec-9Z-enoate), iso-ricinoleate (9-hydroxy-octadec-12Z-enoate), and 12-oxo-octadec-9Z-enoate with potassium peroxomonosulfate (oxone, 2 KHSO₅.K₂SO₄) in the presence of trifluoroacetone or methyl pyruvate gave the corresponding monoepoxy derivatives. Reaction of Oxone^® with methyl linoleate and octadeca-9Z,11E-dienoate furnished the corresponding diepoxystearate derivative. Methyl 9,12-dioxo-octadec-10Z-enoate was obtained when a C₁₈ furanoid fatty ester (methyl 9,12-epoxy-9,11-octadecadienoate) was treated with Oxone^®. The yield of these reactions was very high (85–99%), and the epoxy derivatives were readily isolated by solvent extraction. The products were identified by spectroscopic methods.     

Inhibition of bacterial urease by autoxidation of furan C-18 fatty acid methyl ester products

Autoxidation products of synthetic methyl 9,12-epoxy-octadeca-9,11-dienoate (MEFA) were investigated by gas chromatography-mass spectrometry analysis and tested for bacterial urease inhibition. A suspension of oxidized MEFA in 10% Tween 80 was an effective inhibitor for bacterial urease extract fromHelicobacter pylori (I₅₀=1.3 mM) and for commercial urease fromBacillus pasteurii (I₅₀=0.06 mM). The urease inhibitory effect was cancelled by adding cysteine to the reaction mixture. The total content of biologically active oxidized products in the mixture was found to be 6.2%. Dioxo-ene derivatives of MEFA on the thin-layer chromatography plate surface were converted into more stable compounds, whose formation in the mixture reduced inhibition ofB. pasteurii to about 2% of the former level. The mechanism of urease inhibition is supposed to involve the interaction of the thiol groups of the enzyme’s active center with the inhibitor molecules.     

An efficient ultrasound-assisted zinc reduction of fatty esters containing conjugated enynol and conjugated enynone systems

Reduction of methyl 8-hydroxy-11-E/Z-octadecen-9-ynoate (1) with zinc in either aqueous n-propanol or water under concomitant ultrasound irradiation furnished a mixture of methyl 8-hydroxy-9Z,11E-octadecadienoate (3a) and methyl 8-hydroxy-9Z, 11Z-octadecadienoate (3b) (96% yield). Reduction of methyl 8-oxo-11-E/Z-octadecen-9-ynoate (2) under similar conditions gave methyl 8-oxo-10-Z-octadecenoate exclusively (4, 70%). The latter compound was epoxidized and converted to a C₁₈ furanoid fatty ester (6, methyl 8,11-epoxy-8,10-octadecadienoate) in 70% yield.     

Fatty acids: XXIII. A rapid method for the preparation of C18 furanoid fatty ester involving dry-column chromatography

A rapid method for the synthesis of methyl 9,12-epoxyoctadeca-9,11-dienoate from methyl ricinoleate was developed. Methyl ricinoleate was oxidized to the corresponding keto ester, which was treated with mercury (II) acetate to give the required furanoid ester. Dry column silica gel chromatography was used for the purification process and was found to be reliable and efficient.     

Synthesis of trisubstituted C18 pyrrole fatty ester derivatives

Reaction of methyl 10(11)-dicarbethoxymethyl-9,12-dioxooctadecanoate (1a,1b) with ammonium acetate furnished a mixture of positional isomers of a pyrrole derivative, methyl 9,12-imino-10(11)-dicarbethoxymethyl-9,11-octadecadienoate (2a,2b). Decarboxylation of the mixture of compounds 2a,2b with sodium carbonate in aqueous methanol yielded a mixture of compounds 3a,3b containing a CH₂COOCH₃ group at the 3- or 4-position of the pyrrole ring after esterification. Heating of the hydrolyzed mixture of compounds 3a,3b at 180°C for 1 h gave the desired trisubstituted pyrrole derivatives, methyl 9,12-imino-10(11)-methyl-9,11-octadecadienoate (4a,4b), containing a methyl group at the 3- or 4-position of the pyrrole nucleus. The structures of the products and intermediates were confirmed by infrared, and by¹H and¹³C nuclear magnetic resonance spectroscopy.     

Reaction of α-tocopherol in heated bulk phase in the presence of methyl linoleate (13S)-hydroperoxide or methyl linoleate

α-Tocopherol and methyl (9Z, 11E)-(S)-13-hydroperoxy-9, 11-octadecadienoate (13-MeLOOH) were allowed to stand at 100°C in bulk phase. The products were isolated and identified as methyl 13-hydroxyoctadecadienoate (1), stereoisomers of methyl 9,11,13-octadecatrienoate (2), methyl 13-oxo-9, 11-octadecadienoate (3), epoxy dimers of methyl linoleate with an ether bond (4), a mixture of methyl (E)-12, 13-epoxy-9-(α-tocopheroxy)-10-octadecenoates and methyl (E)-12, 13-epoxy-9-(α-tocopheroxy)-11-(α-tocopheroxy)-9-octadecenoates (5), a mixture of methyl 9-(α-tocopheroxy)-10,12-octadecadienoates and methyl 13-(α-tocopheroxy)-9, 11-octadecadienoates (6), α-tocopherol spirodiene dimer (7), and α-tocopherol trimer (8). α-Tocopherol and 13-MeLOOH were dissolved in methyl myristate, and the thermal decomposition rate and the distributions of reaction products formed from α-tocopherol and 13-MeLOOH were analyzed. α-Tocopherol disappeared during the first 20 min, and the main products of α-tocopherol were 5 and 6 with the accumulation of 1–4 which were the products of 13-MeLOOH. The results indicate that the alkyl and alkoxyl radicals from the thermal decomposition of 13-MeLOOH could be trapped by α-tocopherol to produce 5 and 6. The reaction products of α-tocopherol during the thermal oxidation of methyl linoleate were compounds 6 and 7. Since the radical flux during the autoxidation might be low, the excess α-tocopheroxyl radical reacted with each other to form 7.     

Synthesis of oxygenated fatty acid esters from santalbic acid ester

The reaction of methyl octadec-trans-11-en-9-ynoate (1) with mercuric sulfate in the presence or absence of sulfuric acid is described. Treatment of 1 with mercuric sulfate in absolute methanol yielded methyl 9(10)-oxoocta-dec-trans-11-enoates (Product A). This product, upon treatment withm-chloroperbenzoic acid, afforded methyltrans-11,12-epoxy-9-oxooctadecanoate (4) and methyl 10-oxooctadec-trans-11-enoate (2). Sodium borohydride reduction of A furnished the corresponding hydroxy esters. The treatment of 1 with mercuric sulfate in the presence of sulfuric acid gave as major product methyl 9(10)-oxo-11(12)-methoxyoctadecanoates and methyl 9(10)-oxoocta-dec-trans-11-enoates as a minor product. When methyl 11,12-epoxyoctadec-9-ynoate was reacted with acid in methanol, methyl 12-hydroxy-11-methoxyoctadec-9-ynoate was formed, which on treatment with zinc chloride in CCl₄ yielded methyl 9,12-epoxyoctadec-9,11-dienoate exclusively. The preparation of oxo fatty esters from the total methyl esters ofSantalum album was also demonstrated. The structures of the products were established by chemical derivatization and spectral characterization.     

Furan fatty acids determined as oxidation products of conjugated octadecadienoic acid

The objective of this study was to identify oxidation products of conjugated linoleic acid (CLA), a series of octadecadienoic acids with conjugated double bonds, which have been reported to have antioxidant and anticarcinogenic properties. Reference materials of CLA were oxidized in different concentrations of water/methanol; for example, 0.5 g octadecadienoic acid was dissolved in 50 mL methanol, and 100 mL water was added; this suspension was heated at 50°C and continuously aerated. Aliquots of 5 mL were taken over time, extracted with ether, treated with diazomethane and examined by gas chromatography/mass spectrometry and/or gas chromatography with flame-ionization detection. Products identified included the following furan fatty acids (FFAs): 8,11-epoxy-8,10-octadecadienoic; 9,12-epoxy-9,11-octadecadienoic; 10,13-epoxy-10,12-octadecadienoic; and 11,14-epoxy-11,13-octadecadienoic. Conjugated dienes should be considered as a possible source of FFAs, and CLA may have products common to furans in their overall oxidative scheme.     

Chemical and enzymatic preparation of acylglycerols containing C18 furanoid fatty acids

C₁₈ furanoid triacylglycerol [glycerol tri-(9,12-epoxy-9,11-octadecadienoate)] was prepared by chemical transformation of triricinolein isolated from castor oil. The procedure involved oxidation, epoxidation and cyclization of the epoxy-keto intermediate with sodium azide and ammonium chloride in aqueous ethanol. The furanoid triacylglycerol was also obtained by esterification of C₁₈ furanoid fatty acid with glycerol using Novozyme 435 (Novo Nordisk A.S., Bagsvaerd, Denmark) as biocatalyst. When Lipozyme (Novo Nordisk A.S.) was used, a mixture of the furanoid 1(3)-rac-monoacylglycerol and 1,3-diacylglycerol was obtained. In order to obtain the C₁₈ furanoid 1,2(2,3)-diacylglycerol, selective hydrolysis of the furanoid triacylglycerol was achieved using procine pancreatic lipase intris(hydroxymethyl) methylamine buffer. Interesterification of triolein with methyl C₁₈ furanoid ester in the presence of Lipozyme showed maximum incorporation of 34% of furanoid fatty acid. Extension of the interesterification to vegetable oils (olive, peanut, sunflower, corn and palm oil) allowed a maximum of 24% furanoid acid incorporation to be achieved.     

Isolation of unsaturated diols after oxidation of conjugated linoleic acid with peroxygenase

Oat seeds are a rich source of peroxygenase, an iron heme enzyme that participates in oxylipin metabolism in plants. An isomer of CLA, 9(Z), 11(F)-octadecadienoic acid (1), believed to have anticarcinogenic activity, was used as a substrate for peroxygenase in an aqueous medium using t-butyl hydroperoxide as the oxidant. After acidification of the reaction medium, the products were extracted with ethyl ether, converted to their methyl esters, and characterized using HPLC. Major products after reaction for 24 h showed resonances from ¹H NMR spectroscopy that were further downfield than the expected epoxides and were thought to be diol hydrolysis products. However, analyses by HPLC with atmospheric pressure chemical ionization MS (APCI-MS) of the putative allylic diols or their bis-trimethylsilyl ether derivatives gave incorrect M.W. The M.W. of the diols could be obtained by APCI-MS after removal of unsaturation by hydrogenation or by EI-MS after conversion of unsaturation by hydrogenation or by EI-MS after conversion of the allylic 1,2-diols to cyclic methyl boronic esters. Data from MS in conjunction with analyses using ¹H and ¹³C NMR showed that the methylated products from 1 were methyl 9,10(threo)-dihydroxy- 11(E)-octadecenoate, methyl 9,10(erythro)-dihydroxy-11(E)-octadecenoate, methyl 9,12(threo)-dihydroxy-10(E)-octadecenoate. Solid-phase extraction without prior acidification and conversion of the products to methyl esters allowed identification of the following epoxides: methyl 9,10(Z)-epoxy-11(E)-octadecenoate (6M), methyl 9,10(E)-epoxy-11(E)-octadecenoate, and methyl 11,12(E)-epoxy-9(Z)-octadecenoate. At times of up to at least 6h, 6M accounted for approximately 90% of the epoxide product. Product analysis after the hydrolysis of isolated epoxide 6M showed that hydrolysis of epoxide 6 could largely account for the diol products obtained from the acidified reaction mixtures.     

A novel method for the introduction of a methyl group into the furan ring of a 2,5-disubstituted C18 furanoid fatty estervia a malonic acid function

Furan ring opening with benzohydroxamic acid of methyl 9,12-epoxy-9,11-octadecadienoate gave a mixture of positional isomers of conjugated methyl 3-phenyl-1,4,2-dioxazolyl C₁₈-enone esters 6a,6b. Michael addition of diethyl malonate anion to the conjugated enone system of 6a,6b furnished the corresponding malonyl intermediates 7a,7b, which upon removal of the dioxazole ring by hydrolysis gave methyl 10- and 11-dicarbethoxymethyl-9,12-dioxooctadecanoate 8a,8b. Cyclization of the latter gave the trisubstituted C₁₈ furanoid fatty esters 9a,9b, containing the malonate ester function at the 3-/4-position of the furan ring. Base hydrolysis of compounds 9a,9b gave the corresponding tricarboxylic acid derivatives 10a,10b, which were esterified to the trimethyl esters 11a,11b in BF₃/MeOH. When a mixture of 9a,9b was refluxed with Na₂CO₃/MeOH, hydrolysis of the malonate ester function was followed by decarboxylation to yield a-CH₂COOH substituent at the 3-/4-position of the furan ring (12a, 12b). Esterification of the latter with BF₃/MeOH gave the corresponding methyl diester derivatives 13a,13b. When a mixture of tricarboxylic acids 10a,10b was heated at 160–180°C for 6 hr, exhaustive decarboxylation of malonic acid function furnished a methyl group at the 3-/4-position of the furan nucleus. Esterification of the decarboxylated product gave a mixture of trisubstituted furanoid compounds 14a,14b (overall yield 28%). The procedure constitutes a novel method for the introduction of a methyl groupvia a malonic acid group to the 3-/4-position of the furan ring of a 2,5-disubstituted C₁₈ furanoid fatty ester.     

Oxygenated fatty acid constituents of soybean phosphatidylcholines

Bitter-tasting phosphatidylcholines from hexane-defatted soybean flakes were chromatographically separable from ordinary soy phosphatidylcholines (SPC). The bitter-tasting SPC contain 32% oxygenated fatty acids in addition to palmitic, stearic, oleic, linoleic, and linolenic acids. Identification of these oxygenated acids was based on infrared, ultraviolet, proton nuclear magnetic resonance, and mass spectral characteristics of methyl ester derivatives which were separated and purified by column and thin layer chromatography. The fatty acid methyl esters identified were (a) 15, 16-epoxy-9, 12-octadecadienoate, (b) 12, 13-epoxy-9-octadecenoate, both with double bonds and epoxide groups predominantly ofcis configuration; (c) 13-oxo-9,11-and 9-oxo-10, 12-octadecadienoates; (d) 13-hydroxy-9, 11- and 9-hydroxy-10, 12-octadecadienoates; (e) 9, 10, 13-trihydroxy-11- and 9,12,13-trihydroxy-10-octadecenoates. In addition, trace amounts of (f) 11-hydroxy-9,10-epoxy-12-and 11-hydroxy-12,13-epoxy-9-octadecenoates; (g) 13-oxo-9-hydroxy-10-and 9-oxo-13-hydroxy-11-octadecenoates; (h) 9,10-dihydroxy-12- and 12, 13-dihydroxy-9-octadecenoates; and (i) 9,12,13-dihydroxyethoxy-10- and 9,10,13-dihydroxyethoxy-11-octadecenoates were indicated by mass spectrometry. Dihydroxyethoxy compounds (i) were possibly formed upon extraction of the SPC from flakes by 80% ethanol. Except for the first two epoxy compounds, labelled a and b, the oxygenated fatty acids are similar to the products formed by homolytic decomposition of linoleic acid hydroperoxide. The first two compounds with predominantlycis configuration may occur by action of fatty acid hydroperoxides on an unsaturated fatty acid. Presented in part at the 13th World Congress of the International Society for Fat Research, Marseille, France, August 31–September 4, 1976.     

Reaction of mono-epoxidized conjugated linoleic acid ester with boron trifluoride etherate complex

The reaction of methyl 11, 12-E-epoxy-9Z-octadecenoate (1) with boron trifluoride etherate furnished a mixture of methyl 12-oxo-10E-octadecenoate (3a) and methyl 11-oxo-9E-octadecenoate (3b) in 66% yield. Methyl 9, 10-Z-epoxy-11 E-octadecenoate (2) with boron trifluoride etherate furnished a mixture of methyl 9-oxo-10 E-octadecenoate (4a, 45%) and methyl 10-oxo-11 E-octadecenoate (4b, 19%). A plausible mechanism is proposed for these reactions, which involves the attack on the epoxy ring system by BF₃, followed by deprotonation, oxo formation, and double bond migration to give a mixture of two positional α,β-unsaturated C₁₈ enone ester derivatives (3a/3b, 4a/4b). The structures of these C₁₈ enone ester derivatives (3a/3b, 4a/4b) were identified by a combination of NMR spectroscopic and mass spectrometric analyses.     

Gas chromatographic analysis of diels-alder adducts of geometrical and positional isomers of conjugated linoleic acid

This research demonstrates the gas chromatographic analysis of the 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) adducts derived from standards of cis,trans-9,11-octadecadienoic acid, trans,trans-9,11-octadecadienoic acid, and cis,cis-9,11-octadecadienoic acid. Methyl cis,trans-9,11-octadecadienoate and methyl trans,trans-9,11-octadecadienoate formed Diels-Alder addition products with MTAD to produce adducts with similar mass spectral fragmentation patterns but different retention times determined by gas chromatography/ mass spectrometry. Methyl cis,cis-9,11-octadecadienoate reacted slowly and produced two adducts with similar fragmentation patterns and different retention times. These results were comparable to those reported for an analogous series of conjugated hexadienes. Based on hexadiene reactions, methyl cis,trans-9,11-octadecadienoate produced a trans adduct as a major product while methyl trans,trans-9,11-octadecadienoate formed a cis adduct. Methyl cis,cis-9,11-octadecadienoate reacted slowly under the conditions used leaving mostly unreacted material. Of the adducts observed from this isomer, a major trans adduct and a minor cis adduct were formed.     

Gas chromatographic study on high-temperature thermal degradation products of methyl linoleate hydroperoxides

Chromatographic techniques were used to separate secondary products generated by thermal degradation of methyl linoleate hydroperoxides (MLHP). The MLHP were obtained by oxidation, selected, and concentrated by solid-phase extraction (SPE) and thin-layer chromatography (TLC). The purified MLHP were then thermo-degraded in the gas-chromatographic glass liner and analyzed on-line by gas chromatography-mass spectrometry (GC-MS). The MLHP were also thermodegraded and collected in a short silicic acid-packed column, eluted, separated by TLC, and then analyzed by GC. By considering the elution in TLC, the GC retention times and the GC-MS analyses, it was possible to characterize the mono- and the dioxygenated secondary products, particularly those having a boiling point higher than methyl linoleate. The peaks that corresponded to the mono-oxygenated products (epoxy, hydroxy, and keto) were identified, and, on the basis of their MS spectra, molecular structures were proposed. A specific elution order was suggested for keto derivatives: 9-keto,Δ^10,12- and 13-keto,Δ^9,11-octadecadienoate. The hydroxy derivatives, which show the typical fragmentations of 9-hydroxy,Δ^10,12- and 13-hydroxy,Δ^9,11-octadecadienoate, were also identified. On the other hand, identification of the di-oxygenated compounds was more difficult, and, therefore, it was not possible to indicate each positional isomer; however, their elution order could be epoxy-hydroxy and epoxy-keto derivatives.     

Reaction of α-tocopherol with alkyl and alkylperoxyl radicals of methyl linoleate

α-Tocopherol was reacted with alkyl and alkylperoxyl radicals at 37°C in bulk phase. The lipid-free radicals were generated by the reaction of methyl linoleate with the free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN) under air-insufficient conditions. The products were isolated by high-performance liquid chromatography. Their structures were identified as 2-(α-tocopheroxy)-2,4-dimethylvaleronitrile (1), a mixture of methyl 9-(8a-peroxy-α-tocopherone)-10(E),12(Z)-octadecadienoate and methyl 13-(8a-peroxy-α-tocopherone)-9(Z),11(E)-octadecadienoate (2), methyl 9-(α-tocopheroxy)-10(E),12(Z)-octadecadienoate (3a), methyl 13-(α-tocopheroxy)-9(Z),11(E)-octadecadienoate (3b), α-tocopherol spirodiene dimer (4) and α-tocopherol trimer (5). When methyl linoleate containing α-tocopherol was oxidized with AMVN under airsufficient conditions, the main products were 8a-alkyl-peroxy-α-tocopherones (2). In addition to these compounds, 6-O-alkyl-α-tocopherols (1, 3a and 3b) were formed when the reaction was carried out under air-insufficient conditions. The results indicate that α-tocopherol can react with both alkyl and alkylperoxyl radicals during the autoxidation of polyunsaturated lipids.     

Linoleate hydroperoxides are cleaved heterolytically into aldehydes by a Lewis acid in aprotic solvent

Treatment of isomeric methyl linoleate hydroperoxides with a Lewis acid, BF₃, in anhydrous ether led to a carbon-to-oxygen rearrangement that caused cleavage into shorter-chain aldehydes. Methyl (9Z,11E)-13-hydroperoxy-9,11-octadecadienoate afforded mainly hexanal and methyl (E)-12-oxo-10-dodecenoate, whereas methyl (10E,12Z)-9-hydroperoxy-10,12-octadecadienoate cleaved into 2-nonenal and methyl 9-oxononanoate. The 2 aldehydes obtained from each hydroperoxide isomer were uncharacteristic of the complex volatile profile usually obtained by β-scission of oxy radicals derived from homolysis of the hydroperoxide group. Rather, the reaction resembled the one catalyzed by the plant enzyme, hydroperoxide lyase. Presented in part at the American Oil Chemists' Society Meeting, Chicago, Illinois, May 8–12, 1983. The mention of firm names or trade products does not imply that they are endorsed or recommended by the USDA over other firms or similar products not mentioned.     

Hydroperoxide formation during autoxidation of conjugated linoleic acid methyl ester

The aim of this study was to investigate whether hydroperoxides are formed in the autoxidation of conjugated linoleic acid (CLA) methyl ester both in the presence and absence of α‐tocopherol. The existence of hydroperoxide protons was confirmed by D₂O exchange and by chemoselective reduction of the hydroperoxide groups into hydroxyl groups using NaBH₄. These experiments were followed by nuclear magnetic resonance (NMR) spectroscopy. The ¹³C and ¹HNMR spectra of a mixture of 9‐hydroper‐oxy‐10‐trans,12‐cis‐octadecadienoic acid methyl ester (9‐OOH) and 13‐hydroperoxy‐9‐cis, 11‐trans‐octadecadienoic acid methyl ester (13‐OOH), which are formed during the autoxidation of methyl linoleate, were studied in detail to allow the comparison between the two linoleate hydroperoxides and the CLA methyl ester hydroperoxides. The ¹³CNMR spectra of samples enriched with one of the two linoleate hydroperoxide isomers were assigned using 2D NMR techniques, namely Correlated Spectroscopy (COSY), gradient Heteronuclear Multiple Bond Correlation (gHMBC), and gradient Heteronuclear Single Quantum Correlation (gHSQC). The ¹³C and ¹H NMR experiments performed in this study show that hydroperoxides are formed during the autoxidation of CLA methyl ester both in the presence and absence of α‐tocopherol and that the major isomers of CLA methyl ester hydroperoxides have a conjugated monohydroperoxydiene structure similar to that in linoleate hydroperoxides.