Acta Crystallographica Section E

Structure Reports Online

Volume 69, Part 8 (August 2013)

organic compounds

Acta Cryst. (2013). E69, o1237-o1238    [ doi:10.1107/S1600536813018369 ]

Tenulin 0.25-hydrate, a sesquiterpene lactone isolated from Helenium amarum

K. S. Knight, C. T. Smith, T. G. Waddell and B. Noll

Abstract: 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 [beta]-position. In the crystal, each water mol­ecule inter­acts with four tenulin mol­ecules via O-H...O 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-H...OA and a donor of OA-H...OB hydrogen bonds, mol­ecule B is an acceptor of the latter hydrogen bond and the donor of an OB-H...Owater hydrogen bond. In the crystal, these O-H...O hydrogen bonds link the tenulin and water mol­ecules into layers parallel to the ac plane.

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