Conversion Of Hydroperoxide Research Articles

EPOXIDATION OF 1-OCTENE BY TERT-BUTYL HYDROPEROXIDE IN THE PRESENCE OF TITANIUM COMPOUNDS

The epoxidation reaction of 1-octene by tert-butyl hydroperoxide in the presence of TiB2, TiC and TiSi2 was investigated. It is shown that the titanium compounds catalyzed the reaction and exhibited different activity. It is established that TiSi2 is the best choice for theepoxidation reaction which provided 73 % of hydroperoxide conversion and 75 % of selectivity of epoxide formation. The performance of TiSi2 after three runs indicated it’s excellent reusability.

A quantum chemical and molecular dynamics simulation study on photo-oxidative aging of polyethylene: Mechanism and differences between crystalline and amorphous phases

It is well known that polyethylene (PE) generates CO2 during photo-oxidative aging; however, there is still some ambiguity in the exact mechanistic steps involved. In this work, the photo-oxidative aging mechanism of PE is considered via quantum chemical (QC) calculations. This demonstrates that it is difficult for some previously proposed Norrish I mechanisms to occur because of the high energy required and forbidden transitions. A synergistic effect between oxygen and ultraviolet (UV) radiation is shown to promote the initiation of photo-oxidative aging, providing a more reasonable description of photo-oxidation than existing mechanisms. The charge differential density (CDD) indicates that UV radiation alters the electron distribution so that the electron transfer from the secondary C–H bond to the H–OO bond promotes the formation of HOO·. As is well established, after the initiation reaction, the formed radical is converted into hydroperoxide. UV radiation promotes the conversion of hydroperoxide into ketones via cleavage of the O–OH bonds and the formation of hydroxyl radicals. The hydroxyl radicals can further react with ketonic carbonyls, resulting in carbonic acid. Finally, the carbonic acid decomposes into CO2. The difference in photo-oxidative aging between the crystalline and amorphous phases of PE was studied by molecular dynamics (MD) simulation. The MD results show that the crystalline phase is more difficult to photo-oxidize than the amorphous phase because of the poorer permeation ability and solubility but not the diffusion ability of O2.

Hydroperoxide bicyclase CYP50918A1 of Plasmodiophora brassicae (Rhizaria, SAR): Detection of novel enzyme of oxylipin biosynthesis

The genome of the cabbage clubroot pathogen Plasmodiophora brassicae Woronin 1877 (Cercozoa, Rhizaria, SAR), possesses two expressed genes encoding the P450s that are phylogenetically related to the enzymes of oxylipin biosynthesis of the CYP74 clan. The cDNA of one of these genes (CYP50918A1) has been expressed in E. coli. The preferred substrate for the recombinant protein, the 13-hydroperoxide of α-linolenic acid (13-HPOT), was converted to the novel heterobicyclic oxylipins, plasmodiophorols A and B (1 and 2) at the ratio ca. 12:1. Compounds 1 and 2 were identified as the substituted 6-oxabicyclo[3.1.0]hexane and 2-oxabicyclo[2.2.1]heptane (respectively) using the MS and NMR spectroscopy, as well as the chemical treatments. The 18O labelling experiments revealed the incorporation of a single 18O atom from [18O2]13-HPOT into the epoxide and ether functions of products 1 and 2 (respectively), but not into their OH groups. In contrast, the 18O from [18O2]water was incorporated only into the hydroxyl functions. One more minor polar product, plasmodiophorol C (3), identified as the cyclopentanediol, was formed through the hydrolysis of compounds 1 and 2. Plasmodiophorols A–C are the congeners of egregiachlorides, hybridalactone, ecklonialactones and related bicyclic oxylipins detected before in some brown and red algae. The mechanism of 13-HPOT conversions to plasmodiophorols A and B involving the epoxyallylic cation intermediate is proposed. The hydroperoxide bicyclase CYP50918A1 is the first enzyme controlling this kind of fatty acid hydroperoxide conversion.

Does lysine drive the conversion of fatty acid hydroperoxides to aldehydes and alkyl-furans?

During the oxidation of lipids in food or in vivo, fatty acids are initially converted to hydroperoxides, which undergo decomposition to various secondary decomposition products, including aldehydes and alkyl-furans. Aldehydes and alkyl-furans reduce the sensory quality of food by contributing to rancidity, and aldehydes reduce nutritional value by reacting with some essential nutrients such as lysine and thiamine. In vivo, reactions of aldehyde with proteins and DNA contribute to the pathogenesis of physiological disorders. Conversion of fatty acid hydroperoxides to aldehydes is generally believed to involve free radical reactions. However, it was recently hypothesized that lysine can catalyze the non-radical conversion of hydroperoxides to aldehydes. Thus the aim of the present study was to determine such lysine-catalysed conversion of linoleic acid hydroperoxides to aldehydic products. Linoleic acid hydroperoxides were prepared by the photosensitized oxidation of linoleic acid. The mixture of hydroperoxides was reacted with lysine, in the presence of a radical scavenger, and the organic fraction analysed by gas chromatography-mass spectrometry (GC-MS). Hexanal was detected as a major aldehydic product. The alkylfuran, 2-pentylfuran was also surprisingly detected under these conditions, and a pathway for its lysine-catalysed formation via the highly cytotoxic aldehyde, 4-hydroxy-2-nonenal proposed. The results of this study imply that, in the prevention of lipid oxidation-associated food deterioration and development of physiological disorders, more attention should be paid to pathways not involving free radical reactions, and which cannot be prevented by radical scavenging antioxidants.

Anion effect on the cumene hydroperoxide decomposition in the presence of Cu(II) 1,10-phenanthrolinates

Kinetics of the cumene hydroperoxide catalytic decomposition in the presence of Cu(II) salt complexes with 1,10-phenanthroline (Phen) has been investigated in the water: ethanol (1:1) solvent mixture. Catalytic properties of Cu(CH3COO)2 - Phen complex were confirmed: after full hydroperoxide conversion its new portion had been added to the reaction mixture. The hydroperoxide decomposition rate constant observed on the second cycle was the same. The salt anion effect on the complex catalytic activity has been revealed. The rate constant of the cumene hydroperoxide catalytic decomposition increases in the following row of anions: SO42− < Cl− < CH3COO−, the hydroperoxide decomposition in the presence of Cu(II) nitrate in the same experimental conditions was not observed. The effect of the anion nature in the reaction of cumene hydroperoxide catalytic decomposition may be associated with both the structure of the Cu(II) complex with Phen, as well as the structure of the hydroperoxide - catalyst complex. In addition, the double activation effect is observed in the reaction considered. The hydroperoxide molecule is chemically activated by the corresponded Cu(ІІ) salt. The Cu(ІІ) salt reactivity by-turn is activated in the presence of 1,10-phenanthroline and can be regulated by means of variation in corresponded salt anion.

Conversion of hydroperoxides to carbonyls in field and laboratory instrumentation: Observational bias in diagnosing pristine versus anthropogenically controlled atmospheric chemistry

AbstractAtmospheric volatile organic compound (VOC) oxidation mechanisms under pristine (rural/remote) and urban (anthropogenically‐influenced) conditions follow distinct pathways due to large differences in nitrogen oxide (NOx) concentrations. These two pathways lead to products that have different chemical and physical properties and reactivity. Under pristine conditions, isoprene hydroxy hydroperoxides (ISOPOOHs) are the dominant first‐generation isoprene oxidation products. Utilizing authentic ISOPOOH standards, we demonstrate that two of the most commonly used methods of measuring VOC oxidation products (i.e., gas chromatography and proton transfer reaction mass spectrometry) observe these hydroperoxides as their equivalent high‐NO isoprene oxidation products – methyl vinyl ketone (MVK) and methacrolein (MACR). This interference has led to an observational bias affecting our understanding of global atmospheric processes. Considering these artifacts will help close the gap on discrepancies regarding the identity and fate of reactive organic carbon, revise our understanding of surface‐atmosphere exchange of reactive carbon and SOA formation, and improve our understanding of atmospheric oxidative capacity.

Change of the catalytic activity of copper(II) chelates in the decomposition of hydroperoxides depending on the nature of the solvent

A fundamental difference in the catalytic activity of complex compounds of copper(II), bis(2-phenyliminomethylene-3-hydroxybenzyl[b]thiophenate) copper(II) (CuL2) and bis(2-acetylacetonate) copper(II) (Cu(acac)2), in the decomposition of cyclohexenyl and tetralyl hydroperoxides in solvents of different natures is established. Aprotic solvent chlorobenzene and ethanol, capable of forming intermolecular hydrogen bonds, are used. In chlorobenzene, catalyst deactivation occurs at a small depth of conversion of hydroperoxides, while in alcohol, no deactivation is observed. A possible mechanism explaining the absence of catalyst passivation in an alcoholic medium is proposed.

Gold peroxide complexes and the conversion of hydroperoxides into gold hydrides by successive oxygen-transfer reactions

Gold catalysts are widely studied in chemical and electrochemical oxidation processes. Computational modelling has suggested the participation of Au-OO-Au, Au-OOH or Au-OH surface species, attached to gold in various oxidation states. However, no structural information was available as isolable gold peroxo and hydroperoxo compounds were unknown. Here we report the syntheses, structures and reactions of a series of gold(III) peroxides, hydroperoxides and alkylperoxides. The Au-O bond energy in peroxides is weaker than in oxides and hydroxides; however, the Au-OH bond is also weaker than Au-H. Consequently Au-OH compounds are capable of oxygen-transfer generating gold hydrides, a key reaction in a water splitting cycle and an example that gold can react in a way that other metals cannot. For the first time it has become possible to establish a direct connection from peroxides to hydrides: Au-OO-Au→Au-OOH→Au-OH→Au-H, via successive oxygen-transfer events.

Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

Olefin epoxidation with cyclohexyl hydroperoxide offers great perspective in increasing the yield from industrial cyclohexane oxidation and the production of epoxides in an apolar medium. Two competing hydroperoxide conversion routes, namely direct epoxidation and thermal decomposition, were identified. The formation of radicals seemed to play a role in both mechanisms. However, olefin epoxidation was found to solely take place at the catalyst. Allylic oxidation of cyclohexene occurs under reaction conditions primarily by molecular oxygen and only constitutes a minor route. The presence of molecular oxygen was found to increase the overall yield of the process by solvent oxidation yielding new cyclohexyl hydroperoxide. Hydrolysis and isomerization of the epoxide were found to be negligible reactions, although the epoxide gets converted at higher concentrations, presumably by the radical initiated polymerization. UV-Vis spectroscopy provided proof for the formation of titanium-hydroperoxide species as the active catalytic site in the direct epoxidation reaction.

Liquid-phase oxidation of benzothiophene and dibenzothiophene by cumyl hydroperoxide in the presence of catalysts based on supported metal oxides

The liquid-phase oxidation of benzothiophene and dibenzothiophene by cumyl hydroperoxide in the presence of supported metal oxide catalysts was carried out in octane in an N2 atmosphere at 50–80°C. The cumyl hydroperoxide, benzothiophene, and dibenzothiophene conversions and the yield of sulfones were determined for catalysts of various natures. In the presence of MoO3/SiO2, the most efficient and most readily regenerable catalyst, the benzothiophene conversion was ∼60% and the dibenzothiophene conversion was as high as 100% upon almost complete consumption of cumyl hydroperoxide. The influence of unsaturated and aromatic compounds (oct-1-ene, toluene) on the catalytic effect was studied. The kinetics of substrate oxidation and cumyl hydroperoxide decomposition and an analysis of the cumyl hydroperoxide conversion products suggested a benzothiophene and dibenzothiophene oxidation mechanism including the formation of an intermediate complex of the hydroperoxide with the catalyst and the substrate and its transformation via heterolytic and homolytic routes.

Kinetics and mechanism of the liquid-phase oxidation of tert-butyl phenylacetate

The oxidation of tert-butyl phenylacetate in ortho-dichlorobenzene at 140°C occurs with short chains. The primary nonperoxide reaction products (tert-butyl α-hydroxyphenylacetate, tert-butyl α-oxophenylacetate, and benzaldehyde) are formed by the decomposition of a hydroperoxide (tert-butyl α-hydroperoxyphenylacetate) and (or) by the recombination of peroxy radicals with and without chain termination. Benzaldehyde and tert-butyl α-hydroxyphenylacetate undergo radical chain oxidation in a reaction medium to result in benzoic acid and tert-butyl α-oxophenylacetate. Homolytic hydroperoxide decomposition is responsible for process autoacceleration and results in benzaldehyde, which is also formed from hydroperoxide by a nonradical mechanism, probably, via a dioxetane intermediate. Both of the reactions are catalyzed by benzoic acid. Benzoic acid has no effect on hydroperoxide conversion into tert-butyl α-oxophenylacetate, which most likely occurs as a result of hydroperoxide decomposition induced by peroxy radicals. The rate constants of the main steps of the process and kinetic parameters have been calculated by solving an inverse kinetic problem.

Parameters of Epoxidation of Cyclohexene by tert-Butyl Hydroperoxide

The process of epoxidation of cyclohexene by tert-butyl hydroperoxide in the presence of Mo(CO)6 as the catalyst has been investigated by applying statistical methods of experimental design. The influence of essential process parameters on the hydroperoxide conversion, the selectivity of transformation to the epoxy compound with regard to the hydroperoxide consumed, the cyclohexene conversion, and the selectivity of transformation to the epoxy compound with regard to the cyclohexene consumed (response functions Ŷ1−Ŷ4, respectively) have been described by regression equations in the form of polynomials of second order. The analysis of the obtained regression equations and the technological parameters allows the optimum ranges of the reaction parameters for cyclohexene epoxidation with tert-butyl hydroperoxide to be established as follows: reaction time, 2.4−5 h; temperature, 90−120 °C; and molar ratio of alkene to tert-butyl hydroperoxide, (2.1−4.4):1.

Parameters of the epoxidation of 1‐octene by t‐butyl hydroperoxide

AbstractThe epoxidation of 1‐octene with t‐butyl hydroperoxide in the presence of Mo(CO)6 has been studied. The influence of the crucial parameters on the yield of 1,2‐epoxyoctane in relation to hydroperoxide, on the hydroperoxide conversion, on the selectivity of the transformation of 1‐octene to epoxy compound and on the yield of 1,2‐epoxyoctane in relation to 1‐octene has been described by the use of regression functions in the form of a second order polynomial. The optimal values of parameters: reaction time, temperature, olefin to hydroperoxide mol ratio, Mo(CO)6 to hydroperoxide mol ratio, ensuring the maximum values of these functions have been determined.

Antioxidative and antimycotic effects of turmeric, lemon-grass, betel leaves, clove, black pepper leaves andGarcinia atriviridis on butter cakes

Turmeric, lemon-grass, Garcinia atriviridis and clove were found to be effective in retarding mould growth in butter cakes. Betel leaves and black pepper leaves showed no antimycotic activity and may even promote mould growth in butter cakes. Turmeric, betel leaves and clove effectively retarded the rancidity of butter cakes and extended their storage life from 2 weeks (control) to more than 4 weeks. Lemon-grass, G atriviridis and butylated hydroxy toluene (BHT) extended the butter cake storage life to 4 weeks, while butylated hydroxy anisole (BHA) was only able to extend the storage life to 3 weeks. The thiobarbituric acid value (TBAV), peroxide value (PV) and anisidine value (AV) of cakes containing these extracts (0.1% w/w butter) and control cakes were significantly different (p < 0.05) during the 4 weeks of storage. Turmeric and betel leaves had the best antioxidative activities (TBAV = 0.62f, 0.64f; PV = 10.2cde, 15.29bc; AV = 3.05e, 3.63e; Totox V = 23.55b, 34.21b respectively), performing better than BHA or BHT (TBAV = 1.62c, 1.21cde; PV = 9.77de, 5.46ef; AV = 12.52c, 15.16b; Totox V = 32.06b, 26.08b respectively). Same letters superscripted on the mean values of samples indicate insignificant difference between them. The oxidative values of BHA and BHT in cakes were insignificantly different (p < 0.05) except in AV analysis, but significantly lower than control cakes (TBAV = 2.43b; PV = 23.09a; AV = 23.10a; Totox V = 69.27a). Clove and lemon-grass were also better than BHA/BHT and had the next strongest antioxidant activity (TBAV = 0.81ef, 0.98def; PV = 15.45b, 12.50bcd; AV = 3.11e, 7.20d; Totox V = 34.03b, 32.20b respectively). The AVs of cakes containing G atriviridis (25.03a) were similar to control cakes (23.10a) but the PVs were low (0.94f) throughout the storage period, indicating that G atriviridis increased the rate of conversion of hydroperoxides to aldehydes. Black pepper leaves appeared to be pro-oxidative (TBAV = 2.91a; PV = 10.45bcde; AV = 8.52d; Totox V = 29.40b). © 1999 Society of Chemical Industry

Epoxidation of chloromethylbutenes by t-butyl hydroperoxide

The epoxidation of chloromethylbutenes by t-butyl hydroperoxide in the presence of Mo(CO)6 has been investigated. The influence of important parameters on hydroperoxide conversion, selectivity of transformation to epoxy compound in relation to hydroperoxide used, yield in relation to olefin introduced (response function) has been described by regression equations in the form of a second order polynomial. The optimum values of: temperature, olefin to hydroperoxide molar ratio, reaction time, molar ratio of Mo(CO)6 catalyst to hydroperoxide, ensuring the maximum values of these functions, have been determined. ©1997 SCI

Epoxidation of chloromethylbutenes byt-butyl hydroperoxide

The epoxidation of chloromethylbutenes by t-butyl hydroperoxide in the presence of Mo(CO) 6 has been investigated. The influence of important parameters on hydroperoxide conversion, selectivity of transformation to epoxy compound in relation to hydroperoxide used, yield in relation to olefin introduced (response function) has been described by regression equations in the form of a second order polynomial. The optimum values of: temperature, olefin to hydroperoxide molar ratio, reaction time, molar ratio of Mo(CO) 6 catalyst to hydroperoxide, ensuring the maximum values of these functions, have been determined.

Mechanism of linoleic acid hydroperoxide reaction with alkali.

Treatment of (13S,9Z,11E)-13-hydroperoxy-9,11-octadecadienoic acid (13S-HPODE) with strong alkali resulted in the formation of about 75% of the corresponding hydroxy acid, (13S,9Z,11E)-13-hydroxy-9,11-octadecadienoic acid (13S-HODE), and the remaining 25% of products was a mixture of several oxidized fatty acids, the majority of which was formed from (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid by Favorskii rearrangement (Gardner, H.W., et al. (1993) Lipids 28, 487-495). In the present work, isotope experiments were completed in order to get further information about the initial steps of the alkali-promoted decomposition of 13S-HPODE. 1. Reaction of [hydroperoxy-18O2] 13S-HPODE with 5 M KOH resulted in the formation of [hydroxy-18O] 13S-HODE and [epoxy-18O](9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoi c acid; 2. treatment of a mixture of [U-14C] 13S-HODE and [hydroperoxy-18O2] 13S-HPODE with KOH and analysis of the reaction product by radio-TLC showed that 13S-HODE was stable under the reaction conditions and did not serve as precursor of other products; 3. reaction of a mixture of [U-14C] 13-oxo-9,11-octadecadienoic acid (13-OODE) and [hydroperoxy-18O2] 13S-HPODE with KOH resulted in the formation of [U-14C-epoxy-18O]99Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octad ecenoic acid; 4. treatment of a mixture of [hydroperoxy-18O2] 13S-HPODE and [carboxyl-18O1] 13S-HPODE with KOH afforded (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid having an 18O-labeling pattern which was in agreement with its formation by intermolecular epoxidation. It was concluded that (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid is formed from 13S-HPODE by a sequence involving initial dehydration into the alpha, beta-unsaturated ketone, 13-OODE, followed by epoxidation of the delta 11 double bond of this compound by the peroxyl anion of a second molecule of 13S-HPODE. Rapid conversion of hydroperoxides by alkali appeared to require the presence of an alpha, beta-unsaturated ketone intermediate as an oxygen acceptor. This was supported by experiments with a saturated hydroperoxide, methyl 12-hydroperoxyoctadecanoate, which was found to be much more resistant to alkali-promoted conversion than 13S-HPODE.

Purification and characterization of a lentil seedling lipoxygenase expressed in E. coli: Implications for the mechanism of oxodiene formation by lipoxygenases

Lentil seedlings contain at least six lipoxygenase isoenzymes, which are difficult to separate by classical enzyme purification techniques. The aim of this work was to study one particular lentil seedling lipoxygenase, as previous work indicated possible interesting characteristics of this enzyme with respect to oxodiene formation. Since it proved to be difficult to obtain this enzyme in significant quantities in a pure state, we expressed it in Escherichia coli. Using an expression vector based on the T7 RNA polymerase promoter (pET11d) we achieved of a fully functional lentil seedling lipoxygenase in E. coli, which was purified to homogeneity by DEAE ion-exchange chromatography and gel-filtration. The products obtained from linoleic acid were analysed. This recombinant lipoxygenase corresponds to that found in the lower part of the epicotyl and in the hypocotyl of the lentil seedling. It produces predominantly 13-( S)-hydroperoxy-(9 Z,11 E)-octadecadienoic and minor amounts of 9( S)-hydroperoxy-(10 E,12 Z)-octadecadienoic acids, as well as significant amounts of C 18-oxodienes with a regiospecificity different from hydroperoxide formation. The latter mixture was found to consist of equal amounts of 13-oxo-(9 Z,11 E)-octadecadienoic and 9-oxo-(10 E,12 Z)-octadecadienoic acids. It is concluded that (1) oxodienes formed by this lentil enzyme do not originate from a secondary conversion of hydroperoxides, but rather from a different lipoxygenase-catalysed reaction and (2) this lipoxygenase shows similarities to pea lipoxygenase G, with both representing a novel type of legume lipoxygenase.

97 ELECTRON PARAMAGNETIC RESONANCE (EPR) MONITORING OF ASCURBATE FREE RADICAL (A*) AS MARKER OF INCREASED IRON-MEDIATED OXIDATIVE DAMAGE (MOD) IN PLASMA OF NEONTES

In common neonatal disorders (hemolytic disease, asphyxia, hypoperfusion) as well as in red cell transfusion the oxidative risk can increase, as free iron is released from damaged tissues and promotes conversion of hydroperoxides into the highly reactive hydroxyl/alkoxyl radicals. In this reaction ascorbate is concurrently oxidized to A−. To investigate the capability of neonatal plasma to counteract IMOD, samples of pre-term (11 subjects, GA 28-35 wks) and term infants (11 normals, GA 38-42 wks) were challenged with scalar amounts of Fe++, as well as plasma of 7 adult controls. The reaction was evaluated by EPR monitoring of the A− produced.RESULTS: 1) althought A− production was slighly lower than in adults, the Fe++ μM which triggered the reaction were significantly smaller in pre-term and term infants (21.1 ± 6.0 and 31.1 ± 10.3 vs. 43.7 ± 4.6; P<0.001 and < 0.05). This difference was not referable to a different saturation of transferrin since the total and latent iron binding capacity of plasma was similar both in neonatal and adult samples. 2) in contrast with adults, in pre-term and term infants (P<0.001) the EPR segnal persisted for a longer time and after 15 min. A− values were still 69.2 ± 8.9 and 63.5 ± 23.3 per cent of initial peak. CONCLUSIONS: 1) Neonates have a reduced tolerance to IMOD; 2) In this condition ascorbate behaves as a pro-oxidant, instead of antioxidant compound and its administration can be dangerous; 3) Prevention of IMOD should be directed to the search for effective iron chelators.

Hydroperoxides of α‐ketols

Metabolism of [1-14C]linolenic acid, 13-hydroperoxy-8(Z),11(E),15(Z)-[1-14C]octadecatrienoic acid (13-HPOT) and 9-hydroperoxy-10(E),12(Z),15(Z)-[1-14C]octadecatrienoic acid (9-HPOT) was studied by enzyme preparations from flax, wheat and corn seeds, containing two enzymes of fatty acid metabolism, namely, lipoxygenase and hydroperoxide dehydrase. Along with the previously known products of the hydroperoxide dehydrase pathway, the radiolabel was incorporated into some more polar metabolites. These polar products 1 and 4, formed from 13-HPOT and 9-HPOT, respectively, were purified by reversed-phase and normal-phase HPLC, and investigated by ultraviolet spectroscopy, chemical-ionization and electron-impact mass spectrometry, and 1H-NMR. The data obtained suggest that metabolites 1 and 4 are 9-hydroperoxy-12-oxo-13-hydroxy-10(E),15(Z)-octadecadienoic acid and 9-hydroxy-10-oxo-13-hydroperoxy-11(E),15(Z)-octadecadienoic acid, respectively. 12-oxo-13-hydroxy-9(Z),15(Z)-[1-14C]octadecadienoic acid (12,13-alpha-ketol) and 9-hydroxy-10-oxo-12(Z),15(Z)-[1-14C]octadecadienoic acid (9,10-alpha-keto) are the direct precursors of metabolites 1 and 4, respectively. Metabolites 1 and 4 are formed from the corresponding HPOT precursors in two stages; (a) conversion of hydroperoxide into the alpha-ketol by hydroperoxide dehydrase and (b) the lipoxygenase oxidation of the alpha-ketol. Different lipoxygenases were found to oxidize alpha-ketols. Oxidation of the 3(Z)-buten-1-onyl moiety of alpha-ketols presents an unusual and previously unknown type of lipoxygenase reaction.