Oxylipin family

It comes as no surprise that this useful methodology has also found an application in natural product synthesis (473, 474). The trans-cyclopropane motif is a prevalent structural feature of some members of the oxylipin family (475). Kumaraswamy and co-workers have recently described the synthesis of an eicosa-noid (555) (473) and a lactonealdehyde (556) (474). While 555 is believed to be an important intermediate in the biogenetic route towards different members of the oxylipin family (473), 556 is an advanced synthetic intermediate towards solandelactones A and B (557 and 558) (474), which were isolated in 1996 from the hydroid Solanderia secuda, collected off the Korean coast (476). 

Scheme 118 Cinchona alkaloid-catalyzed cyclopropanation in the synthesis of members of the oxylipin family...

Halicholactone 214, a marine metabolite with lipoxygenase inhibitory activity, belongs to the family of oxylipins which all contain a lactone moiety substituted by a /ra r-disubstituted cyclopropane subunit. Stereoselective RCM for the formation of the nine-membered lactone core in 214 was the penultimate step (212 —> 213) in a asymmetric... 

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. 

The lactones and peroxylactones have structures very similar to those mentioned above, and this whole family of compounds may be derived by the action of lipooxyge-nases on fatty acids with 18-22 carbon atoms, by mechanisms similar to those resulting from the peroxidation of arachidonic acid (Casteel, 1992). This justifies the inclusion of these derivatives among the oxylipins (Gerwick, Nagle, and Protean, 1993). 

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