Received 10 July 2013
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.
For the discovery and structural identification of tenulin, see: Clark (1939); Herz et al. (1975); Braun et al. (1956); Barton et al. (1956). For biological activity that has been observed for tenulin and its analogs, see: Lee et al. (1977); Li et al. (2008); Hodge et al. (1995, and references therein). For the crystal structure of tenulin, see: Knight et al. (2013). For the crystal structure of bromoisotenulin, see: Mazhar-Ul-Haque et al. (1974).
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CV5424 ).
Acknowledgements are made to the National Science Foundation MRI Program (CHE-0951711) and the Grote Chemistry Fund at the University of Tennessee at Chattanooga for their generous support of our work.
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