Linolenic acid epoxidation

Biosynthesis of triene pheromone components with a triene double bond system that is n-3 (3,6,9-) are probably produced from linolenic acid [49]. Moths in the families Geometridae, Arctiidae, and Noctuidae apparently utilize linoleic and linolenic acid as precursors for their pheromones that must be obtained in the diet,since moths can not synthesize these fatty acids [50]. Most of the Type II pheromones are produced by chain elongation and decarboxylation to form hydrocarbons [51]. Oxygen is added to one of the double bonds in the polyunsaturated hydrocarbon to produce an epoxide [49]. 

Studies on the biosynthesis of lactones have shown that epoxidation of unsaturated fatty acids like, e.g., linoleic and linolenic acid may represent a common pathway to oxygenated derivatives of fatty acids. Epoxy fatty acid hydrolases were identified as key enzymes that exhibit high regioselectivity and enantiose-lectivity [25, 26]. 

Two general classes of pheromone compound have been identified in moths, and these have some broad, although not uniform, associations with certain taxa. The polyene hydrocarbons and epoxides of various chain lengths are pheromones found in some subfamilies of the Geometridae and Noctuidae, and in the Arctiidae and Lymantridae (Millar, 2000). These compounds are probably derived from dietary Unoleic and linolenic acids. The other major class of pheromone compounds includes acetate, alcohols, and aldehydes, which are found in the Tortrici-dae, Pyralidae, Gelechiidae, Sessiidae, and Noctuidae. This class of compounds is derived from the insect s fatty acid synthesis pathway, with enzymatic modifications discussed above. Both classes of pheromone are broadly represented in the Noctuidae but are typically found in different subfamilies (Am et al., 1992,2003). 

In plants a-dioxygenases (Chapter 18) convert free fatty acids into 2(R)-hydroperoxy derivatives (Eq. 7-3, step d).32a These may be decarboxylated to fatty aldehydes (step e, see also Eq. 15-36) but may also give rise to a variety of other products. Compounds arising from linoleic and linolenic acids are numerous and include epoxides, epoxy alcohols, dihydroxy acids, short-chain aldehydes, divinyl ethers, and jasmonic acid (Eq. 21-18).32a... 

A considerable amount of knowledge has accumulated about how pheromone components are produced in female moths since the first pathway was identified some 20 years ago. It appears that most female moths produce their pheromone through modifications of fatty acid biosynthesis pathways. For moths that utilize aldehydes, alcohols, or esters biosynthesis occurs in the pheromone gland. The exceptions are those that utilize linoleic or linolenic acids, which must be obtained from the diet. However, modifications of these fatty acids occur in the gland. For moths that utilize hydrocarbons or epoxides of hydrocarbons, the hydrocarbon is produced in oenocyte cells and then transported to the pheromone gland where the epoxidation step takes place. 

An interesting system that is applied in the epoxidation of soybean oil is MTO immobilized on niobia combined with UHP as oxidant. The different components of soybean oil have been studied separately, and it was found that oleic acid can be epoxidized completely with 1 mol% MT0/Nb205 in 2 h at room temperature. When raising the temperature to 50°C and lowering the catalyst amount to 0.2 mol%, complete epoxidation is reached in as little as 10 min. In applying the same procedure to linoleic and linolenic acid, excellent yields of epoxidized product are obtained within 30 min. In attempts to reuse the catalyst in this reaction, it was found that the catalyst remains active for three runs, although no numerical data is provided to underline this [39, 76]. 

In contrast, the hemolymph of females of the arctiid moth Spilosoma imparilis were found to contain significant levels of the polyunsaturated hydrocarbons corresponding to the epoxide pheromone components produced by this species (Wei el al., 2003). In a biosynthetic study with the arctiid Syntomoides imaon, the pheromone of which consists of a blend of 3Z,6Z,9Z-21 H and 1,3Z,6Z,9Z-21 H (Matsuoka el al., 2008), the lipids extracted from oenocytes and peripheral fat bodies associated with the abdominal integument contained both (llZ,14Z,17Z)-eicosa-ll,14,17-trienoic acid and (13Z,16Z,19Z)-docosa-13,16,19-trienoic acid, the intermediates predicted by elongation of linolenic acid by one or two cycles of 2-carbon chain extension (Ando et al., 2008). The latter acid is likely to be the direct biosynthetic precursor to 3Z,6Z,9Z-21 H (Ando et al., 2008). 

Hydrogen abstraction also increases at elevated temperature as thermal energy decreases bond dissociation energy. Typical H abstraction rates for ROO at room temperature are < 1 M s, but this increases to 10 -10" L M s at 65°C (223). For example, in linolenic acid autoxidized neat at room temperature to PV 1113, products were not quantified, but estimates from intensities of HPLC peaks gave about 40% LnOOH, 12% dihydroperoxides, 12% hydroperoxy epidioxides, and 4% epoxides (228). At 40°C, H abstraction occurred more as a secondary process. Hydroperoxides per se were still the main products, but fewer were present as mono- and dihydroperoxides (36% total) and more had formed after cyclization or addition (31%). Data are not available to distinguish whether this... 

Double bonds are present in all PUFAs. As a consequence epoxides of linoleic and linolenic acid are formed by injury of plant tissue (see Scheme 16). For instance epoxides of linoleic and linolenic acid were detected in rice plants after infection with the rice blast fungus [237,238]. These epoxides turned out to be highly toxic and were therefore called lipotoxins . 

Recently, Bouh and Espenson reported that MTO supported on niobia catalyzed tlie epoxidation of various fatty oils using UHP as the terminal oxidant (Scheme 12). Oleic acid, linoleic acid and linolenic acid were all epoxidized in high yields (80-100%) within less than 2 h. Moreover, the catalyst could be recycled and reused without any loss of activity. 

Fatty acid epoxides have numerous uses. In particular, oils and fats of vegetable and animal origin represent the greatest proportion of current consumption of renewable raw materials in the chemical industry, providing applications that cannot be met by petrochemicals [64]. Polyether polyols produced from methyl oleate by the Prileshajev epoxidation (using peracetic acid) are an example. Epoxidized soybean oil (ESBO) is a mixture of the glycerol esters of epoxidized linoleic, linolenic, and oleic acids. It is used as a plasticizer and stabilizer for poly (vinyl chloride) (PVC) [1] and as a stabilizer for PVC resins to improve flexibility, elasticity, and toughness [65]. The ESBO market is second to that of epoxy resins and its world wide production... 

Workers at Lilly have reported the synthesis of 8,9-LTA3 (51), 8,9-LTC3 (52a), and 8,9-LTD3 (52b),leukotrienes that are reported to be produced from dihomo-y-linolenic acid in ionophore-stimulated murine mastocytoma cells. The natural stereochemistry was assumed to be (85,9/f,10,12 ,14Z) by analogy with arachidonic acid metabolism in the same cell system. The chiral synthesis was achieved (93% ee) via Sharpless epoxidation of an appropriate allylic alcohol (53) (Scheme 5.17). 

It seems, then, that epoxidized methyl esters of oleic, linoleic, and linolenic acid contribute equally to yellowing, taking into consideration die added amount of crosslinker. The observed yellowing with epoxidized methyl ricinoleate is rather poor, and the reason for fliat is not yet fully understood. For all of the model compounds under investigation, it can be concluded that the films show poor coating characteristics after heat-curing. The films are too brittle and do not resist the standard re-versed-impact tests. It is likely fliat epoxide functionalities between 1 and 3 per alkyl chain are too low to form flexible three-dimensional networks. 

Monooxygenase metabolism of essential fatty acids has received comparatively little attention. DiAugustine and Fonts found that in liver microsomes, linoleic acid, linolenic acid and arachidonic acid induced spectral changes of type I, which are associated with metabolism, but the products were not identified [394]. These polyunsaturated fatty acids could be expected to be wl- and w2-hydroxylated like their saturated counterparts and to be transformed into hydroxylated cis,trans conjugated products by chemical peroxidation (autooxidation) as discussed above. Recent studies show that cytochrome P-450 can metabolise polyunsaturated fatty acids to a large extent by epoxidation. The epoxides are rapidly hydrolysed to vicinal diols by microsomal or soluble enzymes. 

Linoleic and linolenic acid are metabolised by hepatic microsomes of the rabbit and NADPH in an analogous way [404,405], Linolenic acid is thus transformed into three 1,2-diols, viz. 15,16-dihydroxy-9,12-octadecadienoic acid, 12,13-dihydroxy-9,15-octadecadienoic acid and 9,10-dihydroxy-12,15-octadecadienoic acid. They were the major metabolites formed and apparently stem from hydrolysis of the w3-, 6-and (0 9-epoxides of linolenic acid, respectively. Linoleic acid can also be w6-w9-epoxidised by this system [395,404,405],... 

Modern biobased lubricants are mainly based on rapeseed oil, sunflower oil, soybean oil, and animal fats. These oils easily undergo oxidation due to their content of polyunsaturated fatty acids such as linoleic acid and linolenic acid. Efforts have been made to modify the oils to provide a more stable material and a product more competitive in performance to mineral oil-based lubricants. This modification can involve partial hydrogenation of oil and a shifting of its fatty acids to high oleic acid content [21]. Other reported changes that address the problem of unsaturation include alkylation, acylation, hydroformylation, hydrogenation, oligomerization (polymerization), and epoxidation [20, 22]. 

Lipoxygenase (LOX) converts polyunsaturated fatty acids, such as linoleic and linolenic acids, to lipid hydroperoxides (Figure 2)(52,73,74). The lipid hydroperoxides then form hydroperoxide radicals, epoxides, and/or are degraded to form malondialdehyde. These products are also strongly electrophilic, and can destroy individual amino acids by decarboxylative deamination (e.g., lysine, cysteine, histidine, tyrosine, and tryptophan) cause free radical mediated cross-linking of protein at thiol, histidinyl, and tyrosinyl groups and cause Schiff base formation (e.g., malondialdehyde and lysine aldehyde) (39,49,50,74-78). 

LOX destroys linoleic and linolenic acids via their oxidation to lipid hydroperoxides. These lipid hydroperoxides subsequently form hydroperoxides, hydroperoxide free radicals, epoxides and malondialdehyde which can impair the nutritive quality of protein via mechanisms similar to those mediated by POD and PPO. These unsaturated fatty acids are essential for normal larval growth and maturation. 

Roots of Echinacea purpurea contain up to 0.2% essential oil [4, 14,15, 21, 67, 69, 74]. According to Becker [75] and Martin [76] it is composed of 2.1% caryophyl-lene, 0.6% humulene and 1.3% caryophyllene epoxide. Heinzer et al. [14] have analyzed the essential oil by gas chromatography-mass spectrometry (GC-MS) and found compounds of the type dodeca-2,4- dien-l-yl-isovalerate, as well as palmitic and linolenic acid, vanillin, p-hydroxycinnamic acid methyl ester and germacrene D, which had already been reported by Bohlmann and Hoffmann [27] for the aerial parts of the plant. Nevertheless, . purpurea roots are not a typical essential oil drug, and therefore analysis of the essential oil has not been used often for standardization purposes of phytopreparations. However, gas chromatography of the essential oil can be used for the discrimination of the species (see Fig. 1) [14]. 

The last route is important for the formation of jasmonic acid. The action of allene oxide synthase on 13-hydroperoxy linolenic acid initially results in the generation of 12,13-epoxy-octadecatrienoic acid. This unstable epoxide is either chemically hydrolyzed to a- and y-ketols and racemic 12-oxo-phytodienoic acid or, in the presence of allene oxide cyclase (AOC), is further converted to enantiomeric pure 12-oxo-PDA [7]. The ring double bond of PDA is then reduced in a NADPH dependent reaction by 12-oxo-PDA reductase and after shortening of the side chain containing the carboxy group by 3 rounds of fi>-oxidation, the biosynthesis of jasmonic acid is completed. 

Seeds contain steroidal s onins (proto-dioscin, oligofurostanosides) large amounts of NaOH-soluble polysaccharides " carotenoids (mutatoxanthin epimers, antheraxanthin, P-carotene, P-cryptoxanthin, lutein, cap-santhin, capsanthin 5,6-epoxide, eapsorubin, neoxanthin, violaxanthin, zeaxanthin) and 15.3% oil composed of 43.47% arachidie, 22.16% oleic, 11.52% palmitic, 11.34% lino-leic, 5.78% behenic, 3.59% stearic, 2.14% linolenic acids, and 1.43% unsaponifiable matter consisted mostly of P-sitosterol. ... 

Today palm oil is widely used in food applicahons and preferred for frying and baking applications because of its good oxidative stability and high solid fat content. Palm oil contains about 50% saturated (42 8% palmitic and 4-5% stearic acids) and 50% unsaturated fatty acids (37-41% linoleic and 9-11% linolenic acids). The fatty acid composition of palm kernel oil resembles that of the coconut oil rather than that of palm oil. Palm kernel oil is rich in lauric (about 48%), myristic (16%) and oleic (15%) acids. Both palm oil and pahn kernel oil are commercially separated into stearin (solid) and olein (liquid) fractions for special applications. The stearin fraction obtained from palm kernel can be used as a cocoa butter substitute. The olein fraction is used in baked goods and soap manufacturing. Imitation palm-oil-based cheese, hand and body lotion, fatty acid methyl esters for use as fuel or solvent, and epoxidized pahn oil to produce plasticizers and stabilizers for conventional polyvinyl chloride plastics are some of the other products that are produced from palm oil (Basiron, 2005). 

---