Bastadin 21, a Novel Isobastarane Metabolite from the Great Barrier Reef Marine Sponge Ianthella quadrangulata

Bastadin 21, a novel tribrominated bastadin with the uncommon isobastarane skeleton, was isolated from the Great Barrier Reef marine sponge Ianthella quadrangulata. The structure was elucidated on the basis of the 1D and 2D NMR and MS data of bastadin 21 and its tetramethyl ether.