Identification of Prostaglandins in the Gorgonian, Plexaura homomalla

Hexane extracts of the air‐dried cortex of the gorgonian Plexaura homomalla (Esper) were found to contain (15 R )‐hydroxy‐9‐oxo‐prost‐5,10,13‐trienoic acid [ i.e. (15. R )‐prostaglandin A 2 ] and its 15‐acetate methyl ester in 0.2% and 1.3% yield from the cortex by Weinheimer and Spraggins in 1969. Chloroform‐methanol extracts of this organism have now been shown to contain these two compounds as major prostaglandin constituents, but also a more complex mixture of prostaglandin derivatives including 11α, (15 R )‐dihydroxy‐9‐oxo‐prost‐5,13‐dienoic acid [ i.e. (15 R )‐prostaglandin E 2 ] and the methyl esters of (15 R )‐prostaglandin E 2 and (15 R )‐prostaglandin A 2 . (15 R ) Prostaglandin E 2 was identified by its chromatographic behavior, by the chromatographic behavior and mass spectrum of its O ‐methyloxime, methyl ester, tri‐methylsilyl ether derivative, and by oxidative ozonolysis to fragments of established structure. The configuration of the 15‐hydroxyl group was determined in the cleavage fragment 2‐hydroxy‐heptanoic acid by gas‐liquid chromatography of its methyl ester (–)‐menthyloxycarbonyl derivative. Similar degradations of material with chromatographic properties equivalent to prostaglondin A 2 and prostaglandin E 2 yielded 2‐hydroxyheptanoate with the S configuration, demonstrating the presence of small amounts of (15 S )‐prostaglandins in the lipid extract.