Vanadium-catalyzed transformation of 13(S)-hydroperoxy-9(Z), 11(E)-octadecadienoic acid: Structural studies on epoxy alcohols and trihydroxy acids

Light-Driven Waste-To-Value Upcycling: Bio-Based Polyols and Polyurethanes from the Photo-Oxygenation of Cardanols

The upcycling of waste biomass into valuable materials by resource-efficient chemical transformations is a prime objective for sustainable chemistry. This approach is demonstrated in a straightforward light-driven synthesis of polyols and polyurethane foams from the multi-ton waste products of cashew nut processing. The photo-oxygenation of cardanol from nutshell oil results in the formation of synthetically versatile hydroperoxides. The choice of the workup method (i. e., reduction, hydrogenation, epoxidation) enables access to a diverse range of alcohols with tunable alkene and OH functions. Condensation with isocyanates to give rigid polyurethane foams provides a resource-efficient waste-to-value chain that benefits from the availability of cardanol and installation of OH groups from aerial O2 .

14,17,18-Trihydroxy-Eicosatetraenoic Acid: A Novel Pro-Resolving Lipid Mediator from Marine Microalgae

Specialized pro-resolving mediators (SPMs) are enzymatically oxygenated derivatives of polyunsaturated fatty acids that function as central immunoregulators in mammals. Among them are resolvins (Rvs) that stimulate the clearance of harmful stimuli and limit pro-inflammatory processes. Because of their beneficial features and their high potency, SPMs are promising molecules for anti-inflammatory therapy. Besides mammals, also marine algae form lipid mediators such as prostaglandins and leukotrienes. In particular, microalgae are attractive candidates for the production of bioactive high-value metabolites. Here, we identified the diatom Cylindrotheca closterium as a prolific producer of SPMs. The diatom forms RvE3 and novel structurally related eicosanoids, including 14S/R,17R,18R-trihydroxy-eicosatetraenoic acid, which displays inflammation-resolving and anti-inflammatory bioactivities. This pro-resolving compound might enable advancements in anti-inflammatory therapy in mammals.

An LC-MS/MS workflow to characterize 16 regio- and stereoisomeric trihydroxyoctadecenoic acids

Trihydroxyoctadecenoic acids (TriHOMEs) are linoleic acid-derived oxylipins with potential physiological relevance in inflammatory processes as well as in maintaining an intact skin barrier. Due to the high number of possible TriHOME isomers with only subtle differences in their physicochemical properties, the stereochemical analysis is challenging and usually involves a series of laborious analytical procedures. We herein report a straightforward analytical workflow that includes reversed-phase ultra-HPLC-MS/MS for rapid quantification of 9,10,13- and 9,12,13-TriHOME diastereomers and a chiral LC-MS method capable of resolving all sixteen 9,10,13-TriHOME and 9,12,13-TriHOME regio- and stereoisomers. We characterized the workflow (accuracy, 98-120%; precision, coefficient of variation ≤6.1%; limit of detection, 90-98 fg on column; linearity, R² = 0.998) and used it for stereochemical profiling of TriHOMEs in bronchoalveolar lavage fluid (BALF) of individuals with chronic obstructive pulmonary disease (COPD). All TriHOME isomers were increased in the BALF of COPD patients relative to that of smokers (P ≤ 0.06). In both COPD patients and smokers with normal lung function, TriHOMEs with the 13(S) configuration were enantiomerically enriched relative to the corresponding 13(R) isomers, suggesting at least partial enzymatic control of TriHOME synthesis. This method will be useful for understanding the synthetic sources of these compounds and for elucidating disease mechanisms.

Regio- and stereochemical analysis of trihydroxyoctadecenoic acids derived from linoleic acid 9- and 13-hydroperoxides

The methyl esters of 9S,10S,13R-trihydroxy-11E-octadecenoic acid, 9S,10R,13S-trihydroxy-11E-octadecenoic acid, and 9S,10R,13R-trihydroxy-11E-octadecenoic acid were prepared from 9S-hydroperoxy-10E,12Z-octadecadienoic acidvia the epoxy alcohols methyl 10R,11R-epoxy-9S-hydroxy-12Z-octadecenoate and methyl 10S,11S-epoxy-9S-hydroxy-12Z-octadecenoate. The trihydroxyesters, as well as four stereoisomeric methyl 9,12,13-trihydroxy-10E-octadecenoates earlier prepared [Hamberg, M.,Chem. Phys. Lipids 43, 55-67 (1987)], were characterized by thin-layer chromatography, gas-liquid chromatography, mass spectrometry, and by chemical degradation. Availability of these chemically defined trihydroxyoctadecenoates made it possible to design a method for regio- and stereochemical analysis of 9,10,13- and 9,12,13-trihydroxyoctadecenoic acids obtained from various sources. Application of the method revealed that the mixture of 9,10,13- and 9,12,13-trihydroxyoctadecenoic acids formed during autoxidation of linoleic acid in aqueous medium contained comparable amounts of the sixteen possible regio- and stereoisomers. Furthermore, hydrolysis of the allylic epoxy alcohol, methyl 9S,10R-epoxy-13S-hydroxy-11E-octadecenoate, yielded a major trihydroxyoctadecenoate,i.e., methyl 9S,10S,13S-trihydroxyl-11E-octadecenoate, together with smaller amounts of methyl 9S,10R,13S-trihydroxy-11E-octadecenoate, methyl 9S,12R,13S-trihydroxy-10E-octadecenoate, and methyl 9S,12S,13S-trihydroxy-10E-octadecenoate.

Efficient and specific conversion of 9-lipoxygenase hydroperoxides in the beetroot. Formation of pinellic acid

The linoleate 9-lipoxygenase product 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid was stirred with a crude enzyme preparation from the beetroot (Beta vulgaris ssp. vulgaris var. vulgaris) to afford a product consisting of 95% of 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid (pinellic acid). The linolenic acid-derived hydroperoxide 9(S)-hydroperoxy-10(E),12(Z),15(Z)-octadecatrienoic acid was converted in an analogous way into 9(S),12(S),13(S)-trihydroxy-10(E),15(Z)-octadecadienoic acid (fulgidic acid). On the other hand, the 13-lipoxygenase-generated hydroperoxides of linoleic or linolenic acids failed to produce significant amounts of trihydroxy acids. Short-time incubation of 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid afforded the epoxy alcohol 12(R),13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoic acid as the main product indicating the sequence 9-hydroperoxide → epoxy alcohol → trihydroxy acid catalyzed by epoxy alcohol synthase and epoxide hydrolase activities, respectively. The high capacity of the enzyme system detected in beetroot combined with a simple isolation protocol made possible by the low amounts of endogenous lipids in the enzyme preparation offered an easy access to pinellic and fulgidic acids for use in biological and medical studies.

Stereochemistry of hydrogen removal during oxygenation of linoleic acid by singlet oxygen and synthesis of 11(S)-deuterium-labeled linoleic acid

Exposure of unsaturated fatty acids to singlet oxygen results in the formation of hydroperoxides. In this process, each double bond in the acyl chain produces two regioisomeric hydroperoxides having an (E)-configured double bond. Although such compounds are racemic, the hydrogen removal associated with the oxygenation may, a priori, take place antarafacially, suprafacially or stereorandomly. The present study describes the preparation of [11(S)-²H]linoleic acid by two independent methods and the use of this stereospecifically labeled fatty acid to reveal the hidden stereospecificity in singlet oxygenations of polyunsaturated fatty acids. It was found that linoleic acid 9(R)- and 13(S)-hydroperoxides formed from [11(S)-²H]linoleic acid both retained the deuterium label whereas the 9(S)- and 13(R)-hydroperoxides were essentially devoid of deuterium. It is concluded that polyunsaturated fatty acid hydroperoxides produced in the presence of singlet oxygen in e.g., plant leaves are formed by a reaction involving addition of oxygen and removal of hydrogen taking place with suprafacial stereochemistry. This result confirms and extends previous mechanistic studies of singlet oxygen-dependent oxygenations.

Payne rearrangement during analysis of epoxyalcohols of linoleic and α-linolenic acids by normal phase liquid chromatography with tandem mass spectrometry

Hydroperoxides of polyunsaturated fatty acids can be transformed to epoxyalcohols and keto fatty acids by metal enzymes, hematin, and various catalysts. In the current study, we used hematin to transform 9-hydroperoxy-10E,12Z-octadecadienoic acid and 13-hydroperoxy-9Z,11E-octadecadienoic acid to epoxyalcohols (with trans epoxide configuration) and to keto fatty acids. The products were separated by normal phase high-performance liquid chromatography (NP-HPLC) and analyzed using postcolumn addition of isopropanol/water and online negative ion electrospray ionization mass spectrometry (MS). The tandem MS (MS/MS) spectra were studied using analogs prepared from [9,10,12,13-2H4]linoleic acid (18:2n-6) and from alpha-linolenic acid (18:3n-3). We also studied the MS/MS spectra of epoxyalcohols formed from 11-hydroperoxy- and 8-hydroperoxy-9Z,12Z-octadecadienoic acids. Results were confirmed by MS/MS analysis of a series of authentic standards. MS/MS ions of 9-keto-10E,12Z-octadecadienoic acid and 13-keto-9Z,11E-octadecadienoic acid could be explained by keto-enol tautomerism. MS/MS spectra of regioisomeric allylic epoxyalcohols differed in relative intensities of characteristic ions. The MS/MS spectra of the epoxyalcohols with 1-hydroxy-2,3-epoxy-4Z-pentene or 3-hydroxy-1,2-epoxy-4Z-pentene elements were virtually identical and showed two characteristic ions that differed by 30 in m/z values (CH(OH)). The results suggested that epoxide migration (Payne rearrangement) occurred during collision-induced dissociation. We conclude that regioisomeric allylic epoxyalcohols can be identified by their MS/MS spectra, whereas regioisomeric epoxyalcohols can be identified by MS/MS in combination with their retention times on NP-HPLC.

Aldehydic lipid peroxidation products derived from linoleic acid

Lipid peroxidation (LPO) processes observed in diseases connected with inflammation involve mainly linoleic acid. Its primary LPO products, 9-hydroperoxy-10,12-octadecadienoic acid (9-HPODE) and 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), decompose in multistep degradation reactions. These reactions were investigated in model studies: decomposition of either 9-HPODE or 13-HPODE by Fe(2+) catalyzed air oxidation generates (with the exception of corresponding hydroxy and oxo derivatives) identical products in often nearly equal amounts, pointing to a common intermediate. Pairs of carbonyl compounds were recognized by reacting the oxidation mixtures with pentafluorobenzylhydroxylamine. Even if a pure lipid hydroperoxide is subjected to decomposition a great variety of products is generated, since primary products suffer further transformations. Therefore pure primarily decomposition products of HPODEs were exposed to stirring in air with or without addition of iron ions. Thus we observed that primary products containing the structural element R-CH=CH-CH=CH-CH=O add water and then they are cleaved by retroaldol reactions. 2,4-Decadienal is degraded in the absence of iron ions to 2-butenal, hexanal and 5-oxodecanal. Small amounts of buten-1,4-dial were also detected. Addition of m-chloroperbenzoic acid transforms 2,4-decadienal to 4-hydroxy-2-nonenal. 4,5-Epoxy-2-decenal, synthetically available by treatment of 2,4-decadienal with dimethyldioxirane, is hydrolyzed to 4,5-dihydroxy-2-decenal.

An epoxy alcohol synthase pathway in higher plants: biosynthesis of antifungal trihydroxy oxylipins in leaves of potato

[1-14C]Linoleic acid was incubated with a whole homogenate preparation of potato leaves (Solanum tuberosum L., var. Bintje). The methyl-esterified product was subjected to straight-phase high-performance liquid chromatography and was found to contain four major radioactive oxidation products, i.e., the epoxy alcohols methyl 10(S),11(S)-epoxy-9(S)-hydroxy-12(Z)-octadecenoate (14% of the recovered radioactivity) and methyl 12(R), 13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoate (14%), and the trihydroxy derivatives methyl 9(S),10(S),11(R)-trihydroxy-12(Z)-octadecenoate (18%)and methyl 9(S), 12(S),13(S)-trihydroxy-10(E)-octadecenoate (30%). The structures and stereochemical configurations of these oxylipins were determined by chemical and spectral methods using the authentic compounds as references. Incubations performed in the presence of glutathione peroxidase revealed that lipoxygenase activity of potato leaves generated the 9- and 13-hydroperoxides of linoleic acid in a ratio of 95:5. Separate incubations of these hydroperoxides showed that linoleic acid 9(S)-hydroperoxide was metabolized into epoxy alcohols by particle-bound epoxy alcohol synthase activity, whereas the 13-hydroperoxide was metabolized into alpha- and gamma-ketols by a particle-bound allene oxide synthase. It was concluded that the main pathway of linoleic acid metabolism in potato leaves involved 9-lipoxygenase-catalyzed oxygenation into linoleic acid 9(S)-hydroperoxide followed by rapid conversion of this hydroperoxide into epoxy alcohols and a slower, epoxide hydrolase-catalyzed conversion of the epoxy alcohols into trihydroxy-octadecenoates. Trihydroxy derivatives of linoleic and linolenic acids have previously been reported to be growth-inhibitory to plant-pathogenic fungi, and a role of the new pathway of linoleic acid oxidation in defense reactions against pathogens is conceivable.

Linoleic acid peroxidation--the dominant lipid peroxidation process in low density lipoprotein--and its relationship to chronic diseases

Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions--these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH2-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10-100 higher concentration, compared to LDL from healthy individuals.

9-Hydroxy-traumatin, a new metabolite of the lipoxygenase pathway

9-Hydroxy-traumatin, 9-hydroxy-12-oxo-10E-dodecenoic acid, was isolated as a product of 13S-hydroperoxy-9Z,11E-octadecadienoic acid as catalyzed by enzyme preparations of both soybean and alfalfa seedlings. This suggested that 9Z-traumatin, 12-oxo-9Z-dodecenoic acid, was being converted into 9-hydroxy-traumatin in an analogous manner to the previously identified enzymic conversion of 3Z-nonenal and 3Z-hexenal into 4-hydroxy-2E-nonenal and 4-hydroxy-2 E-hexenal, respectively. Other metabolites of 13S-hydroperoxy-9Z,11E-octadecadienoic acid were similar for both soybean and alfalfa seedling preparations, and they are briefly described.

Strong dependence of the lipid peroxidation product spectrum whether Fe2+/O2 or Fe3+/O2 is used as oxidant

Catalytic amounts of Fe2+ or Fe3+ ions are widely applied to induce simulated biological lipid peroxidation reactions. Independently, whether Fe2+ or Fe3+ were used, similar products were obtained. We show in this paper that the product spectrum is indeed very different, whether one ion species, either Fe2+ or Fe3+, is present in excess; thus, decomposition of (13S,9Z,11E) 13-hydroxyperoxy-9, 11-octadecadienoic acid (13S-HPODE) generates in the presence of equimolar amounts of Fe2+ ions mainly the corresponding alcohol (13S, 9Z,11E) 13-hydroxy-9,11-octadecadienoic acid besides 12,13-epoxy-11-hydroxy-9-octadecenoic acid (12,13-epHOD) and 13-oxo-9,11-octa-decadienoic acid (13-KODE), while decomposition of 13S-HPODE with equimolar amounts of Fe3+ produces mainly 12,13-epHOD, hydrolysis products thereof and other oxidized products, e.g., hydroxyoxo acids. In addition, unusually large amounts of aldehydes are formed, e.g., the amount of 4-hydroxy-nonenal was found to exceed that obtained by Fe2+ induced air oxidation for a factor of about 100. Since these further oxidation products are suspected to cause cell damage, liberated Fe3+ ions seem to be responsible for generation of toxic products in inflammatory diseases, e.g., atherosclerosis.

Recent investigations into the lipoxygenase pathway of plants

The plant lipoxygenase (LOX) pathway is in many respects the equivalent of the 'arachidonic acid cascade' in animals. The LOX-catalyzed dioxygenation of the plant fatty acids, linoleic and linolenic acids, is followed by metabolism of the resulting fatty acid hydroperoxides by other enzymes. Although the physiological functions of the end-products do not appear to be fully defined at this time, hormonal and anti-fungal activities have been reported.

Hydroperoxide-dependent epoxidation of unsaturated fatty acids in the broad bean (Vicia faba L.)

Incubation of linoleic acid with the 105,000g particle fraction of the homogenate of the broad bean (Vicia faba L.) led to the formation of the following products: 13(S)-hydroxy-9(Z),11(E)-octadecadienoic acid, 9,10-epoxy-12(Z)-octadecenoic acid (9(R),10(S)/9(S)/10(R), 80/20), 12,13-epoxy-9(Z)-octadecenoic acid (12(S),13(R)/12(R)/13(S), 64/36), and 9,10-epoxy-13(S)-hydroxy-11(E)-octadecenoic acid (9(S),10(R)/9(R),10(S), 91/9). Oleic acid incubated with the enzyme preparation in the presence of 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid or cumene hydroperoxide was converted into 9,10-epoxyoctadecanoic acid (9(R),10(S)/9(S),10(R), 79/21). Two enzyme activities were involved in the formation of the products, an omega 6-lipoxygenase and a hydroperoxide-dependent epoxygenase. The lipoxygenase, but not the epoxygenase, was inhibited by low concentrations of 5,8,11,14-eicosatetraynoic acid and nordihydroguaiaretic acid. In contrast, the epoxygenase, but not the lipoxygenase, was readily inactivated in the presence of 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid. Studies with 18O2-labeled 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid showed that the epoxide oxygens of 9,10-epoxyoctadecanoic acid and of 9,10-epoxy-13(S)-hydroxy-11(E)-octadecenoic acid were derived from hydroperoxide and not from molecular oxygen.

Oxygen radical chemistry of polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFA) are readily susceptible to autoxidation. A chain oxidation of PUFA is initiated by hydrogen abstraction from allylic or bis-allylic positions leading to oxygenation and subsequent formation of peroxyl radicals. In media of low hydrogen-donating capacity the peroxyl radical is free to react further by competitive pathways resulting in cyclic peroxides, double bond isomerization and formation of dimers and oligomers. In the presence of good hydrogen donators, such as alpha-tocopherol or PUFA themselves, the peroxyl radical abstracts hydrogen to furnish PUFA hydroperoxides. Given the proper conditions or catalysts, the hydroperoxides are prone to further transformations by free radical routes. Homolytic cleavage of the hydroperoxy group can afford either a peroxyl radical or an alkoxyl radical. The products of peroxyl radicals are identical to those obtained during autoxidation of PUFA; that is, it makes no difference whether the peroxyl radical is generated in the process of autoxidation or from a performed hydroperoxide. Of particular interest is the intramolecular rearrangement of peroxyl radicals to furnish cyclic peroxides and prostaglandin-like bicyclo endoperoxides. Other principal peroxyl radical reactions are the beta-scission of O2, intermolecular addition and self-combination. Alkoxyl radicals of PUFA, contrary to popular belief, do not significantly abstract hydrogens, but rather are channeled into epoxide formation through intramolecular rearrangement. Other significant reactions of PUFA alkoxyl radicals are beta-scission of the fatty chain and possibly the formation of ether-linked dimers and oligomers. Although homolytic reactions of PUFA hydroperoxides have received the most attention, hydroperoxides are also susceptible to heterolytic transformations, such as nucleophilic displacement and acid-catalyzed rearrangement.

Fatty acid allene oxides. II. Formation of two macrolactones from 12,13(S)-epoxy-9(Z),11-octadecadienoic acid

An unstable fatty acid allene oxide, 12,13(S)-epoxy-9(Z),11-octadecadienoic acid, was recently identified as the product formed from 13(S)-hydroperoxy-9(Z), 11(E)-octadecadienoic acid in the presence of corn (Zea mays L.) hydroperoxide dehydrase (M. Hamberg (1987) Biochim. Biophys. Acta 920, 76-84). The present paper is concerned with the spontaneous decomposition of 12,13(S)-epoxy-9(Z),11-octadecadienoic acid in acetonitrile solution. Two major products were isolated and characterized, i.e. macrolactones 12-keto-9(Z)-octadecen-11-olide and 12-keto-9(Z)-octadecen-13-olide.