Crystal structure and Hirshfeld analysis of (1aS,3aR,4aS,5aR)-15-acetoxylinden-7(11),8-trieno-12,8-lactone

The title compound, isolated from the Chloranthus japonicus Sieb., is a typical lindenane-type sesquiterpenoid. Hirshfeld surface analysis illustrates that the most important contributions are from O⋯H/H⋯O contacts (34.6%).


Chemical context
Lindenanolides are precursors for various sesquiterpene dimer derivatives (Uchida et al., 1980;Wang et al., 2009;Shi et al., 2016). Inspired by the clinical application of artemisinin, these compounds have become a products library for screening antimalarial drugs (Dondorp et al., 2010;Zhou et al., 2017). The roots of Chloranthus japonicus (called Yinxiancao) were reported to exhibit antifungal and anti-inflammatory activities, and have been used as traditional Chinese medicine to treat malaria (Kawabata & Mizutani, 1989). Chloranthalactone C was characterized as an ,,,-unsaturated -lactone and was converted into desacetyl enol lactone hydrate and ketoalcohol under moderate alkaline conditions (Uchida et al., 1980). Because of the unique stereostructure in lindenane, these lactone derivatives have been studied extensively and serve as precursors for screening cytotoxicity against mouse lymphosarcoma, liver cancer and human cervical cancer cells, the expression of cell adhesion molecules and the mode of antiplasmodial agents (Uchida et al., 1980;Zhang et al., 2012;Zhou et al., 2017). Based on the antiwiggler activity, we are currently searching for a biological pesticide preparation to inhibit flyblow breeding in vegetable production (Shi et al., 2016) and report here the structure of the title compound.

Supramolecular features
In the crystal of the title compound, the molecules are linked via multiple C-HÁ Á ÁO weak hydrogen bonds, generating twodimensional (2D) layers propagating along the c-axis direction ( Fig. 2 and Table 1). Details of the hydrogen-bonding interactions and the symmetry codes are given in Table 1.

Figure 1
The molecular structure of the title compound, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Isolation and crystallization
The title sesquiterpenoid was isolated as a colourless solid from the EtOAc soluble fraction of C. japonicus by chromatography over silica gel, and eluted with a mixture of ethyl acetate and hexane (1:20 to 5:1 v/v gradient) to yield the title compound. Crystals were obtained after recrystallization from

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically (C-H = 0.96-0.98 Å ) and refined as riding, with U iso (H) = 1.2U eq (C) for CH hydrogens or 1.5U eq (C) for methyl H atoms.   Data collection: SMART (Bruker, 2002); cell refinement: SMART (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.