Cembranoid-Related Diterpenes, Novel Secoditerpenes, and an Unusual Bisditerpene from a Formosan Soft Coral Sarcophyton Tortuosum

Further chemical investigation of the ethyl acetate extract of the soft coral Sarcophyton tortuosum has led to the isolation of ten terpenoidal metabolites, including six new compounds, secoditerpenes secotortuosenes A and B (1 and 2), diterpenes tortuosenes C and D (3 and 4) and tortuosumol (5), and a biscembranoid bisotortuolide cyclobutane A (6), along with four known compounds, ketoemblide (7), sartrolide G (8), emblide (9), and sarcrassin E (10). Compounds 5 and 6 are metabolites of intra- and intermolecular [2+2] cyclizations, respectively. Notably, 1 and 2 are 12-membered carbocyclic compounds possessing a 2-methyl-3-oxopentanyl side chain and representing an unprecedented molecular skeleton, while compound 6 possesses a unique cyclobutanyl biscembranoid skeleton. The absolute configurations of 1 and 5 were determined by TDDFT ECD calculations. Bioassays showed that compound 5 exhibited selective cytotoxicity against the growth of the Molt-4 cell line, while 6 exhibited inhibitory activity against P388, K562, and HT-29 cancer cell lines. Compounds 3 and 57 showed effects for inhibition toward the generation of superoxide anion, while 3, 6, and 7 displayed inhibition activity against elastase release in fMLF/CB-induced neutrophils. In addition, compounds 6, 7, and 10 exhibited anti-inflammatory activity by inhibiting nitric oxide generation in the LPS-induced RAW 264.7 cell assay.