Plants oxylipins

An interesting example of regioselective CM with ethylene as a tool in natural product degradation was recently disclosed by Hawaiian authors [149]. Thus, CM using catalyst C and ethylene gas was used to degrade the plant polyacetylene oxylipin (+)-falcarindiol (342) with uncertain stereochemistry at C3. As the reaction provided a meso product (343) in 81% yield by regioselective attack at the aliphatic side chain, the natural compound 342, isolated from a Hawaiian endemic plant, had the 3R,8S configuration shown in Scheme 66. 

The alcohol moiety is produced in a different manner from that of the acid moiety. The alcohol moiety resembles the plant hormone jasmonic acid (JA) (26) generated from linolenoyl moiety of lipids via (13,S )-hydroperoxy-linolenic acid (22), (12.13,S )-epoxylinolenic acid (23), and 12-oxo-cis-10.15-phytodienoic acid (24) by the oxylipin or octadecanoid pathway (Fig. 3) [31]. In fact, 13C was incorporated at pyrethrolone (1) carbon positions that agreed with those predicted to be labeled when the alcohol moiety is produced via the pathway (Fig. 3) [30]. Figure 3 illustrates that m-jasmone (25) is hydroxylated to yield jasmololone (4), which is then dehydrogenated to yield pyrethrolone (5). However, it has not yet been determined if this is actually the case. 

Fig. 3 Biosynthetic pathways to pyrethrins. The identified enzymes involved in biosynthesis are shown in orange. Note that green leaf volatiles and the plant hormone jasmonic acid share the oxylipin pathway. The phosphate moiety is indicated as P ...

Bouarab K, Adas F, Gaquerel E, Kloareg B, Salaun J-P, Potin P (2004) The innate immunity of a marine red alga involves oxylipins from both the eicosanoid and octadecanoid pathways. Plant Physiol 135 1838-1848... 

Blee, E. (2002). Impact of phyto-oxylipins in plant defense. Trends Plant Sci., 7,315-321. 

FROELICH, J.E., ITOH, A., HOWE, G.A., Tomato allene oxide synthase and fatty acid hydroperoxide lyase, two cytochrome P450s involved in oxylipin metabolism, are targeted to different membranes of chloroplast envelope., Plant Physiol., 2001,125,306-317. 

Jasmonate is one of several lipid-derived plant growth regulators referred to as oxylipins... 

Beyond these various defense compoimds, plants synthesize a wide variety of signaling molecules (oxylipins, brassinosteroids, gibberel-lins, cytokinins, strictolactones) [25], pigments (chlorophylls, carotenoids) [26], and fatty acids and sterols [27]. In the perspective of this chapter, it is worth noting that the production of many of these plant compoimds depends on both chlo-roplast enzymes, which include a small number of soluble P450s, and endoplasmic reticulum enzymes, which include the bulk of membrane-bound P450s. 

Hamberg, M. (1993) Pathways in the biosynthesis of oxylipins in plants,]. Lipid Mediators 6, 375-384... 

Since AA is only a minor fatty acid in higher plants, eicosanoids are not of major importance for plant physiology. However, the oxygenation metabolites of linoleic acid and a-linolenic acid, called oxylipins [5,6], do play a role in plant defence reactions, in the formation of phytohormones and in the synthesis of cutin monomers [6,40-43]. Oxylipins constitute a family of lipids that are formed from free fatty acids by a cascade of reactions involving at least one step of dioxygen-dependent oxidation. The biosynthesis of oxylipins proceeds via a large number of metabolic pathways, most of which involve an unsaturated hydroperoxy fatty acid as intermediate (Scheme 10). Conversion of the hydroperoxide via the peroxide lyase pathway, the allene oxide pathway and the recently discovered peroxygenase pathway, leads to a complex pattern of oxidized lipid mediators. 

Oxylipins, oxygenated fatty acid derivatives and especially eicosanoids, the 20-carbon examples, have long been known to play a regulatory role in animals. More recently, these compounds have been shown to be important in lower vertebrates, invertebrates and plants as well [1]. While there are scattered earlier reports, our understanding of oxylipins in fungi has only emerged in the last decade or so. 

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