Hopeahainol C monohydrate

In the structure of the title compound, C28H16O6·H2O [systematic name 3,11-bis(4-hydroxyphenyl)-4,12-dioxapentacyclo[8.6.1.12,5.013,17.09,18]octadeca-1(16),2,5(18),6,8,10,13(17),14-octaene-7,15-diol monohydrate], the hopeahainol C molecule lies about an inversion center with the solvent water molecule located on a crystallographic twofold axis. Hopeahainol C is an oligostillbenoid compound and was isolated from the bark of Shorea roxburghii G. Don. The five central fused rings are essentially planar with an r.m.s. deviation of 0.0173 (3) Å. The 4-hydroxyphenyl ring is twisted with respect to this plane, with the dihedral angle between the phenyl ring and the fused-ring system being 41.70 (10)°. The crystal features intermolecular O—H⋯O hydrogen bonds. These interactions link the hopeahainol C molecules into chains along the b axis. Water molecules are located interstitially between the hopeahainol C molecules linked by O(water)—H⋯O(hydroxy) and O(hydroxy)—H⋯O(water) hydrogen bonds. π–π interactions are also observed with centroid–centroid distances of 3.6056 (17) and 3.5622 (17) Å. Short O⋯O contacts [2.703 (2)–2.720 (3) Å] are also present in the crystal.

During the course of our research on searching for novel bioactive compounds from Thai dipeterocarpaceous plants, the title compound (I), known as hopeahainol C, was obtained from Shorea roxburghii G. Don. Hopeahainol C is an oligostilbenoid, which is a highly unsaturated resveratrol dimer, and it possesses potent antioxidant activity (Ge et al., 2009). Herein we report its crystal structure.
The molecule of the title oligostilbenoid (I) (Fig. 1), C 28 H 16 O 6 .H 2 O, is a symmetrical dimer. Its asymmetric unit contains one half-molecule. The complete molecule of hopeahainol C is generated by a crystallographic center of symmetry 1/2-x, 3/2-y, -z whereas the other hydrogen atom of the water molecule is generated by a two-fold rotation axis -x, y, 1/2-z.  (Allen et al., 1987).

Experimental
The dried powdered bark of Shorea roxburghii G. Don. (1 kg) which was collected during June-August 2010 from Sam Sung District, Khon Kaen province in the northeastern part of Thailand, was macerated in C 2 H 5 OH (2.5 L) for 7 days. The slurry was filtered and the ethanolic extract obtained was dried with a rotary evaporator under reduced pressure at 313 K.
The dried extract (98 g) was ground, dissolved in CH 3 OH, mixed with silica gel (118 g), and then dried in hot air oven at 333 supplementary materials sup-2 K for one day. The sample was separated by using a wet column chromatographic technique. The column was packed with 1 kg of silica gel (200-300 mesh) and was eluted with gradient mixtures of CHCl 3 and CH 3 OH (100:0 to 0:100), to give 8 major fractions (A-H). Fraction G was further isolated using sephadex column chromatography, eluted with 100% CH 3 OH.
Only the blue methanolic extract could be selectively collected and was pre-concentrated and heated for 5-10 minutes at 313-333 K before being left for 2-3 days at 298 K to allow crystallization of hopeahainol C. Colorless needle-shaped single crystals of the hopeahainol C suitable for X-ray structure determination were obtained from CH 3 OH by slow evaporation at room temperature after a few days.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.