A novel diterpenoid, sinunanolobatone A (1), featuring an unprecedented bicyclo[13.1.0]pentadecane carbon framework, along with two new casbane diterpenoids (2 and 3), and five known related ones (4-8) were isolated from the Sanya soft coral Sinularia nanolobata. The structures of the new compounds were established by detailed spectroscopic analysis, X-ray diffraction analysis, chemical reactions, or quantum chemical computation method. A plausible biosynthetic pathway of 1 and its biogenetic relationship with co-occurring casbanes was proposed. In bioassay, the novel compound 1 showed significant inhibitory activity against lipopolysaccharide (LPS) induced inflammation in BV-2 microglial cells.

A novel norditerpenoid, sinusiaetone A (1), featuring an uncommon bicyclo[11.3.0]­hexadecane carbon skeleton, and four polyoxygenated cembranoids (2–5) were isolated from the Hainan soft coral Sinularia siaesensis. Their structures were established by spectroscopic analysis, X-ray diffraction, quantum chemical computational approaches, and/or a modified Mosher’s method. A plausible biosynthetic pathway of 1 and its biogenetic relationship with 2–5 were proposed. New compounds 1–3 displayed an interesting inhibitory activity against lipopolysaccharide-induced inflammation in BV-2 microglial cells.

Eight new cembranoids (sarcophytembranoids A–H, 1–8) and 10 known terpenoids (9–18) were obtained from the soft coral Sarcophyton trocheliophorum of Ximao Island. Notably, 11, 15, and 16 were obtained from a natural source for the first time. The structures of the new isolates were elucidated by extensive spectroscopic analysis, optical rotatory dispersion, and X-ray diffraction experiments. Although the isolated compounds did not show significant activity against the tested tumor cell lines, compounds 3, 7, 8, and 10–15 exhibited anti-inflammatory activities at 10 μM, and compounds 17 and 18 showed moderate protein tyrosine phosphatase 1B inhibition activities with the minimum inhibitory concentrations of 22.19 and 11.26 μM, respectively.