Cytotoxic Diterpenoids from the Soft Coral Sarcophyton crassocaule

Five new cembrane diterpenoids, sarcrassins A−E (15) along with a known compound, emblide (6), have been isolated from the soft coral Sarcophyton crassocaule collected from the Bay of Sanya, Hainan Island, China. The structures of 15 were determined by spectroscopic methods including 1D and 2D NMR techniques. Their relative configurations were determined by NMR data and NOESY experiments. Compounds 2, 4, and 6 exhibited significant cytotoxic activities against KB cell lines with IC50 values of 5.0, 4.0, and 5.0 μg/mL, respectively, while compounds 1 and 5 showed moderate cytotoxicity toward KB cell lines with IC50 values of 19.0 and 13.0 μg/mL, respectively.