Helleborus of the Ranunculaceae family are well known flowering plants native to Europe and Asia and are mostly documented to be mildly toxic, especially when in contact with the skin. There are reports of fatal incidents while ingesting copious amounts of such plants, and many gardeners develop contact dermatitis upon continued exposure for an elongated period of time. Although all parts of the Helleborus plant are toxic, the nature of the chemicals in the root and the ones in the other parts of the plant are vastly different in terms of molecular structure. While the toxins identified in the roots are steroid-based, others are mostly unsaturated lactones (or their progenitors, see Ranunculin below) bearing an conjugated exo-methylene group that are notorious potent Michael acceptors with a vicious appetite for thiol appengages present in biomolecules.
The main skin irritant, Ranunculin, a simple glucoside with an unsaturated γ-lactone sidechain. Ranunculin is unstable and readily decomposes into other organic compounds such as Anemonin that also possesses some bioactivity:
Draw a plausible mechanism and identify the intermediates for the decomposition of Ranunculin upon contact with air, moisture and light.
For reference:
Maior, M., & Dobrotă, C. (2013).
“Natural compounds with important medical potential found in Helleborus sp.”
Open Life Sciences, 8(3).
doi: 10.2478/s11535-013-0129-x