Heliespirones B and C: Two New Plant Heliespiranes with a Novel Spiro Heterocyclic Sesquiterpene Skeleton

From the medium, polar bioactive fractions of leaf aqueous extract of Helianthus annuus L., heliespirones B (2) and C (3) have been isolated. The structural elucidation was based on extensive spectral studies. A probable biogenesis of heliespirone skeleton is proposed and discussed. The structure of heliespirone B has been confirmed by X-ray diffraction analysis.