Cembrane- and Casbane-Type Diterpenes from the South China Sea Soft Coral Sinularia nanolobata.

Five new cembrane-type diterpenes (1-5), one new casbane-type diterpene (7), and ten known related ones (6, 8-16) were isolated from the South China Sea soft coral Sinularia nanolobata. The structures of new compounds were elucidated through comprehensive spectroscopic analysis, NMR calculation with DP4+ probability analysis, time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations, and comparison with the reported spectroscopic data of known analogs. Structurally, compounds 2-5 featured rare five- to seven-membered oxygen-containing heterocyclic rings with diverse joints, reflecting remarkable chemical diversity of secondary metabolites. In bioassays, all isolates were evaluated for their cytotoxic and anti-inflammatory effects. Although no significant cytotoxic or anti-inflammatory activity was observed, the structural novelty of these compounds expands the chemical diversity of this class of natural products, providing valuable leads for further structural modifications and biological investigations.