Oxylipin

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. 

Oxylipin is a term that has not yet fully entered the scientific vocabulary. Indeed, a new word for oxidized fatty acid-derived compounds was needed, as the older terms - prostanoids, eicos-anoids - proved to be too narrow for an ever-widening spectrum of discoveries. Much of this research has come from the laboratory of the authors of Chapter 4. Their account demonstrates the... 

The term oxylipin is redefined here as an encompassing term for oxidized compounds which are formed from fatty acids by reaction(s) involving at least one step of mono- or dioxygenase-dependent oxidation [1]. Thus, this term includes eicosanoids as well as biosynthetically related compounds of longer and shorter chain length. 

Studies of the natural products of the antipatharian (Hexacorallia), Leiopathes sp., obtained during an expedition to the South Indian Ocean, led to the isolation of one novel oxylipin, (+)- 10P-hydroxydocosa-7Z, 11E, 13Z, 16Z, 19Z-pentaenoic acid (= leiopathic acid, 31), as well as two known compounds,... 

Another barnacle species, Elminius modestus, was found to produce mono and trihydroxy fatty acids [146]. Analysis of the extract of whole animal homogenates by TLC provided two hatching factor active bands. The more polar band was tentatively identified as a trihydroxy fatty acid (THFA) band. The less polar band had an / r value similar to a 5-HETE standard. The compounds from this latter band were eluted from the TLC plate, methylated, and trimethylsilylated. GC-MS analysis detected several HEPE s and small amounts of monohydroxy derivatives of Ci8 1, C18 2, and C22 fatty acids. Hydrogenation and subsequent GC-MS analysis allowed identification of the major compound as 8-HEPE (ca. 70%). Five to ten percent of 9-, 11-, and 15-HEPE and minor amounts of 5-, 6-, 12-, and 13-HEPE were also detected. No stereochemical features of these oxylipins were determined. 

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