Parthenolide
Parthenolide is a sesquiterpene lactone of the germacranolide class which occurs naturally in the plant feverfew, after which it is named, and in the closely related tansy. It is found in highest concentration in the flowers and fruit. Parthenolide's molecular structure depiction is often incorrect regarding the stereochemistry of the epoxide, although X-ray single crystal structures are available.
Lack of solubility in water and bioavailability limits the potential of parthenolide as a drug.