Junceellolides J-L, 11,20-epoxybriaranes from the Gorgonian coral Junceella fragilis

Three new 11,20-epoxybriarane diterpenoids, junceellolides J-L (1-3), along with a known metabolite, 4, have been isolated from the gorgonian coral Junceella fragilis. The structures of these metabolites were elucidated using spectroscopic methods. The cyclohexane rings were found to exist in boat form in briaranes I and 4 and in chair form in 2 and 3. The structure of I was further confirmed by chemical conversion and single-crystal X-ray diffraction analysis. The relationship between C-13 NMR chemical shifts and the conformation of the cyclohexane ring in briaranes possessing an 11,20epoxy group are described. The briaranes 2 and 4 showed mild inhibitory effects on human neutrophil elastase release.