Antisettlement and narcotic action of analogues of diterpene marine natural product antifoulants from octocorals

Previous studies have determined that the octocorals Renilla reniformis and Leptogorgia virgulata contain diterpenes that are potent inhibitors of barnacle settlement. These antifoulants-the renillafoulins and pukalide-are, however, comparatively complex and thus are not amenable to commercial exploitation. The present study examined 19 analogues, based on the functional groups of lactone and furan rings in the parent molecules, for antisettlement activity and toxicity. The latter parameters are presented as EC50 values for inhibition of cypris settlement and naupliar swimming, respectively. Assays of a subset of the analogues indicated that they were active in solution rather than when bound to a surface and that at relatively high concentrations they had a narcotic action. The mechanism whereby some of the analogues were able to inhibit settlement at nontoxic concentrations has yet to be explained but suggests that there is merit in the present approach to antifoulant development.