Vagiallene, a Rearranged C15 Acetogenin from Laurencia obtusa.

Vagiallene (1), a rearranged C15 acetogenin with a molecular formula and a carbon skeleton unprecedented in natural products, was isolated as a trace constituent from the organic extract of the red alga Laurencia obtusa from Lefkada island. The planar structure and the relative configuration of 1 were established on the basis of extensive analysis of its spectroscopic data, while its absolute configuration was determined by comparison of its experimental and quantum-mechanically predicted electronic circular dichroism spectra.