New Cembrane‐Type Diterpenoids from the South China Sea Soft Coral Sinularia nanolobata

Comprehensive Summary In the present study, nine new cembrane‐type diterpenoids, namely ximaonanolobatins A—I (1—9), together with six related known analogs (10—15) and four known tetraprenylated alkaloids malonganenones D, E, H, and K (16—19) were isolated from the soft coral Sinularia nanolobata collected off the Ximao Island in the South China Sea. The structures of 1—9 were robustly established by a combination of detailed spectroscopic analyses, chemical reactions, quantum mechanical (QM)‐NMR methods, biogenetic consideration, and the comparison with those literature data. The absolute configuration of 1 was confirmed by X‐ray diffraction analysis, and the absolute configuration of 2 was determined by QM‐NMR calculations and chemical transformation. In addition, the absolute configuration of 3 was determined using the modified Mosher's method. All these isolates were evaluated for their anti‐inflammatory and anti‐tumor activities. The results showed that only compound 15 exhibited potential anti‐inflammatory effect against LPS‐induced TNF‐ α release in RAW264.7 macrophages with an IC 50 value of 12.6 μmol/L.