Aplysinopsin Dimers from a Stony Coral. Tubastraea aurea

Five novel bis(indole) alkaloids, which were composed of two molecules of aplysinopsin have been isolated from a stony coral, Tubastraea aurea.Their structures were elucidated on the basis of spectroscopic methods.The secondary metabolites of the stony corals have not been studied so extensively as those of soft corals, based on the assumption that their calcareous bodies likely eliminate the requirement for defensive metabolites.However, they have been proven to be a source of many different types of compounds: anthraquinoid derivatives, 1 a phenol, 2 alkaloids, 3 macrolides, 4 and acetylenes. 5Many of these compounds exhibited interesting biological activities, such as antiviral, 6 antifungal, 6 and cytotoxic activity. 7 We examined the chemical constituents of the stony coral, Tubastraea aurea, collected in the Odomari area, Kagoshima Prefecture.A methanol extract of the animal was partitioned between CH 2 Cl 2 and water, and then the aqueous part was extracted with n-BuOH.Neither extract exhibited biological activity (e.g.antibacterial, antifungal, or cytotoxic activity) in our initial screening.Nevertheless, we tried to isolate the aromatic compounds from the dichloromethane extract, because aromtic signals were observed in the 1 H NMR spectrum of the extract.The extract was subjected to silica gel chromatography and reversed-phase HPLC and yielded three unprecedented bis(indole) alkaloids named tubastrindoles A-C (1-3), dimers of aplysinopsin. 8Further investigation has led to the isolation of five new bis(indole) alkaloids, tubastrindoles D-H (4-8).In this paper, we describe the isolation and structure elucidation of these compounds.