Indole Derivatives as Potent Inhibitors of Larval Settlement by the Barnacle,Balanus amphitrite

A potent inhibitor of larval settlement by the barnacle, Balanus amphitrite, was isolated as 2,5,6-tribromo-1-methylgraimne from a marine invertebrate. In comparative tests on the activity of related compounds, such compounds as 2-methylgramine and 2-methyl-3-(morpholinomethyl)-indole exhibited potent inhibitory activity. The inhibitory activity toward larval settlement was found not to be due to toxicity but to a repellent effect.