Chemical investigation of the South China Sea soft coral Lemnalia sp. afforded 13 structurally diverse terpenoids, including three new neolemnane sesquiterpene lineolemnene, E-G (1-3); a new aristolane-type sesquiterpenoid, 2-acetoxy-aristolane (4); four new decalin-type bicyclic diterpenes, named biofloranate A-D (5-8); a new serrulatane, named euplexaurene D (9); and a new aromadendrane-type diterpenoid cneorubin K (10), together with three known related compounds (11-13). The structures of the new compounds were elucidated by NMR spectroscopy, the Mosher's method, and ECD analysis. Compounds 1-13 were tested in a wide panel of biological assays. Lineolemnene J (3) showed weak cytotoxicity against the CCRF-CEM cancer cell line. The isolated new diterpenes, except euplexaurene D (9), demonstrated moderate antimicrobial activity against Bacillus subtilis and Staphylococcus aureus with a MIC of 4-64 μg/mL. Compound 2 exhibited a mild inhibitory effect against influenza A H1N1 virus (IC50 = 5.9 µM).
Keywords: Lemnalia sp.; antimicrobial activity; cytotoxicity; soft coral; terpenoids.