Isotenulin, C17H22O5, is a sesquiterpene lactone isolated from sneezeweed Helenium amarum.It crystallizes with two independent molecules in the asymmetric unit.In each molecule, two five-membered generic baby picture rings (cyclopentenone and lactone) are trans-fused to the central seven-membered ring.The five-membered rings each adopt envelope verragio paradiso conformations.
The seven-membered ring adopts a twist-chair conformation.In the crystal, the molecules are linked by C—H.O interactions, which generate a three-dimensional network.