Oxyresveratrol from Mulberry as a dihydrate

The title compound {systematic name: 4-[(E)-2-(3,5-dihydroxyphenyl)ethenyl]benzene-1,3-diol dihydrate}, C14H12O4·2H2O, a derivative of resveratrol, was isolated from mulberry. The linking C=C double bond has a trans conformation and allows the formation of a conjugated system throughout the molecule. The dihedral angle between the benzene rings is 9.39 (9)°. In the crystal, molecules are connected into a three-dimensional architecture through O—H⋯O hydrogen bonds between hydroxy groups of oxyresveratrol and solvent water molecules.

In the title compound ( Fig. 1), the benzene rings form a dihedral angle of 9.39 (9)°. The presence of the trans C═C double bond allows the formation of a conjugated system, strongly stabilized through π-electron delocalization. The trans-double bond is the same as found in similar structures (Piao et al., 2009;Qiu et al., 1996;Hano et al., 1986). The molecules of the oxyresveratrol are connected into a three-dimensional architecture through O-H-O hydrogen bonds formed between its hydroxyl group and the solvent water molecules ( Fig. 2 and Table 1).

Experimental
The dried root bark of Morus alba L. (1 kg) was powdered and extracted with 95% ethanol at room temperature for 48 h.
After removal of the solvent under reduced pressure, a brown extract was suspended with water, and sequentially partitioned with petroleum ether, acetyl acetate and n-butanol. The acetyl acetate extract (9 g) was subjected to column

Figure 1
A view of the molecular structure of compound (I). The displacement ellipsoids are at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.