organic compounds
Open access
The asymmetric unit of the title compound, C17H22O5·0.25H2O [systematic name: 2-hydroxy-2,2a,6,9a-tetramethyl-2a,4a,5,6,6a,9a,9b,9c-octahydro-2H-1,4-dioxadicyclopent[cd,f]azulene-3,9-dione 0.25-hydrate], a natural product isolated from Helenium amarum, contains two independent tenulin molecules and half a water molecule of crystallization situated on a twofold rotation axis. The hydroxy group of the hemiketal moiety is in a β-position. In the crystal, each water molecule interacts with four tenulin molecules via O—HO hydrogen bonds. The two independent tenulin molecules (A and B) differ only in the character of their participation in hydrogen bonding. Specifically, while A is an acceptor of Owater—HOA and a donor of OA—HOB hydrogen bonds, molecule B is an acceptor of the latter hydrogen bond and the donor of an OB—HOwater hydrogen bond. In the crystal, these O—HO hydrogen bonds link the tenulin and water molecules into layers parallel to the ac plane.
organic compounds
Open access
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 rings (cyclopentenone and lactone) are trans-fused to the central seven-membered ring. The five-membered rings each adopt envelope conformations. The seven-membered ring adopts a twist-chair conformation. In the crystal, the molecules are linked by C—HO interactions, which generate a three-dimensional network.