Antifouling activity against bryozoan and barnacle by cembrane diterpenes from the soft coral Sinularia flexibilis

In the present study, seven cembrane diterpenes were isolated from the soft coral Sinularia flexibilis by Toyopearl HW-40 column chromatography and High Performance Liquid Chromatography (HPLC). The diterpenes were identified as epoxycembrane A (1), sinularin (2), sinulariolide (3), (1R,13S,12S,9S,8R,55,4R)-9-acetoxy-5,8:12,13-diepoxycembr-15(17)-en-16,4-olide (4), 11-dehydrosinulariolide (5), (-)14-deoxycrassin (6) and dihydrosinularin (7). The antifouling activity of these compounds was examined by settlement assays, using the larvae of the bryozoan Bugula neritina and the barnacle Balanus albicostatus. With the exception of compound 2, all compounds indicated significant antifouling activity and a variety of EC50 values. In particular, compound 6 exhibited remarkable anti-settlement activity against the two biofoulers (EC50 for B. neritina 3.90 mu g ml(-1); EC50 for B. albicostatus 21.26 mu g ml(-1)) as well as low toxicity against B. albicostatus larvae (LC50 > 100 mu g ml(-1)), suggesting its potential as an environmentally friendly antifoulant. This is the first report on the antifouling activity of compounds 1 and 4-7, further demonstrating the involvement of cembrane diterpenes in the chemical defense of soft corals against surface fouling. (C) 2017 Elsevier Ltd. All rights reserved.