Junceellolides E-G, new briarane diterpenes from the West Pacific Ocean gorgonian Junceella fragilis

Three new diterpenes, junceellolides E-G (1-3), along with an unnamed known diterpene 4, possessing the briarane carbon skeleton, have been isolated from the gorgonian Junceella fragilis collected in Taiwanese tropical waters. The structures of the new metabolites 1-3 were elucidated by extensive spectral analyses. The six-membered rings in junceellolides E and F (1 and 2) were found to exist in boat conformations. The structure, including the relative configuration of junceellolide E (1) was further confirmed by a single-crystal X-ray analysis.