Amaroxocanes A and B: Sulfated Dimeric Sterols Defend the Caribbean Coral Reef Sponge Phorbas amaranthus from Fish Predators

Two new dimeric steroids, amaroxocanes A (1) and B (2), were isolated from Phorbas amaranthus collected on shallow coral reefs off Key Largo, Florida. The two compounds are comprised of two sulfated sterol cores bridged by an oxocane formed by different oxidative side-chain fusions. The structures were characterized by interpretation of MS and NMR spectroscopic data. The compounds are the primary components of a fraction that deters feeding of the bluehead wrasse, Thalassoma bifasciatum, in aquarium assays. When the pure compounds were assayed at eight times the natural concentration, amaroxocane B (2) was found to be an effective antifeedant, but A (1) was not.