The Absolute Structure of (+)-Aplysulfurin

The spongian diterpene aplysulfurin (C22H28O5) is a marine natural product whose relative stereochemistry has been previously elucidated by X-ray crystallography and NMR, but its absolute structure has only been proposed on biogenetic grounds. Herein we have determined the absolute structure of (+)-aplysulfurin by anomalous dispersion effects of a highly redundant data set collected with Cu-K alpha radiation. We have found that the four chirotopic centres have the absolute configuration C7(R), C10(S), C15(S) and C16(S).