Discovery of New Chlorinated Briaranes from Junceella fragilis

Four briarane-type diterpenoids, including two new chlorinated metabolites, fragilides F (1) and G (2), along with two known compounds, junceellonoid D (3) and juncin Z (4), were isolated from the gorgonian coral Junceella fragilis. The structures of new briaranes 1 and 2 were elucidated by spectral data analysis and the absolute configuration of 1 was directly determined by a single-crystal X-ray diffraction analysis. The relationships between proton chemical shifts and conformations of the methylenecyclohexane ring in briaranes possessing a C-11/20 carbon-carbon double bond are described. Briarane 4 was found to exhibit significant cytotoxicity toward the CCRF-CEM tumor cells.