Nanolobatone A, An Unprecedented Diterpenoid and Related New Casbanoids from the Hainan Soft Coral Sinularia nanolobata.

Nanolobatone A, featuring an unprecedented tricyclo[10.3.0.0 1,2 ]pentadecane carbon skeleton, along with four new polyoxygenated and four unusual endoperoxide-bridged casbane-type diterpenoids were isolated from the Hainan soft coral Sinularia nanolobata. The structures of the new compounds were established by extensive spectroscopic analysis, X-ray diffraction analysis, and time-dependent density functional theory/electronic circular dichroism calculations. A plausible biosynthetic pathway of new isolates was proposed. Bioassays revealed that nanolobatone A showed weak antibacterial activity against the Gram-positive bacteria Streptococcus pyogenes.