Discovery and photosynthesis of sinuaustones A and B, diterpenoids with a novel carbon scaffold isolated from soft coral Sinularia australiensis from Hainan

Two novel diterpenoids, sinuaustones A (1) and B (2), featuring an unprecedented tricyclo[9.3.1.0(3.15)]tetradecane carbon framework, along with a new spatane-type diterpenoid 3 and two related known compounds 4 and 5, were isolated from the South China Sea soft coral Sinularia australiensis. The structures of the new compounds were established by detailed spectroscopic, X-ray diffraction analysis and quantum chemical computation methods. Photosynthesis of 1 and 2 starting from co-isolated 5 was completed giving insight into the plausible biosynthetic pathway of 1 and 2, as well as their structural relationship with co-occurring 3-5. In the in vitro bioassay, compounds 1, 2, 3, and 5 exhibited inhibitory effects on lipopolysaccharide (LPS)-induced inflammatory responses in RAW264.7 cells with IC50 values of 20.9, 75.1, 9.1, and 30.4 mu M, respectively.

Automated summary

Two novel compounds were isolated from South China Sea soft coral, featuring a unique carbon framework. A new diterpenoid and two related known compounds were also discovered. These compounds showed inhibitory effects on inflammatory responses in cells.