What is "portentol"

Portentol is a complex polyketide first isolated in 1967 from the lichen Roccella portentosa and has since been extracted from various other lichen. It has exhibited moderate activity toward several cancer cell lines. Of greater interest is the structural skeleton and chemical space the molecule possesses, which were ultimately determined by detailed NMR studies and X-ray analysis. The spiro tricyclic core contains nine consecutive stereocenters, two of which are adjacent quaternary centers, and a β-keto-δ-lactone moiety. The densely functionalized natural product offered an exciting challenge to total synthesis.