New cytotoxic spongian-class rearranged diterpenes from a marine sponge

Chemical investigation of an Okinawan marine sponge resulted in the isolation of two new spongian-class diterpenes 1 and 2 together with two known compounds, chromodorolide B (3) and chromodorolide C (4). Compound 1, named chromodorolide D, is an example of a diterpenoid with a highly rearranged chromodorane carbon skeleton, while compound 2 retains the open side chains. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis and chemical conversion. Compounds 1-4 exhibited significant cytotoxicity against NBT-T2 rat bladder epithelial cells.