New Nitrogenous Spongian Diterpenes from the New Zealand Marine Sponge Darwinella Oxeata

During the course of this research five New Zealand marine sponges were investigated. Detailed examination of one of the species, Darwinella oxeata, has resulted in the isolation of ten compounds whose structures were elucidated using a variety of spectroscopic techniques and a simple derivatisation reaction. These compounds were identified as rearranged spongian diterpenes with the aplysulphurane backbone. Five of these compounds have been previously reported, though two of them were originally isolated from another marine sponge, Dendrilla membranosa. The five new compounds, oxeatamides C to G (25-29), were found to have the same diterpene portion as the oxeatamides already isolated from this sponge. They do, however, differ in the gamma-lactam side chain, which is proposed to be of amino acid origin. The new oxeatamides showed moderate levels of cytotoxicity against the HL-60 cell line in MTT assays.