Absolute stereostructures of novel cytotoxic metabolites, gymnastatins A–E, from a Gymnascella species separated from a Halichondria sponge

Gymnastatins A–E have been isolated from a strain of Gymnascella dankaliensis originally separated from the sponge Halichondria japonica, and their absolute stereostructures have been established on the basis of spectroscopic analyses using 1D and 2D NMR techniques and some chemical transformations. Among them gymnastatins A–C exhibited significant cytotoxicity against cultured P388 cells.