Antifeedant and antifouling briaranes from the South China Sea gorgonian Junceella juncea

A new briarane diterpene, juncin ZII (1), along with three known briaranes (2-4), was isolated from the EtOH/CH2Cl2 extracts of the South China Sea gorgonian Junceella juncea. The structure of 1 was established by extensive spectroscopic analysis, including 1D and 2D NMR data. For compounds 1-4 and eight other briaranes (5-12) isolated from J. juncea previously, the antifeedant activity against second-instar larvae of Spodoptera litura and cytotoxicity against S. litura cells were investigated, and it was observed that they all exhibit medium antifeedant activity. Compounds 1, 8, 9, and 12 also showed potent antifouling activity against the larval settlement of barnacle Balanus amphitrite at nontoxic concentrations with EC50 values of 0.004, 0.005, 2.82, and 0.447 mu g/mL, respectively, while all compounds did not show obvious cytotoxicity against tumor cell lines K562, A549, Hela, and Hep-2. Their structure-activity relationship was discussed.