Dictyterpenoids A and B, two novel diterpenoids with feeding-deterrent activity from the brown alga Dilophus okamurae.

In our continuing efforts to study the presence of biologically active compounds that control seaweed-herbivore interactions, we examined the presence of such chemicals in freshly collected Dilophus okamurae Dawson. Our results demonstrated the presence of two diterpenoids, named dictyterpenoid A (1) and dictyterpenoid B (2), having a novel carbon skeleton, along with 10 known diterpenes, 3-12. The structures of these novel metabolites were elucidated by spectroscopic and chemical methods. The isolated compounds showed feeding-deterrent activity against the young abalone Haliotis discus hannai.