Genistein-3′-sulfonic acid dihydrate

In the title compound [systematic name: 5-(5,7-dihydroxy-4-oxo-4H-chromenyl)-2-hydroxybenzenesulfonic acid dihydrate], C15H10O8S·2H2O, the benzopyranone ring is not coplanar with the phenyl ring, the dihedral angle between them being 41.35 (3)°. No H atom was placed on the sulphonic acid group because it was not possible to distinguish between the two S=O bonds and the S—O bond. In the crystal, the molecules are linked by classical O—H⋯O and C—H⋯O intra- and intermolecular hydrogen bonds and aromatic π–π stacking interactions [centroid–centroid distance of 3.4523 (14) Å between the 1, 4-pyranone rings and the benzene rings, and 3.6337 (14) Å between the benzene rings] into a supramolecular structure.

In the title compound [systematic name: 5-(5,7-dihydroxy-4-oxo-4H-chromenyl)-2-hydroxybenzenesulfonic acid dihydrate], C 15 H 10 O 8 SÁ2H 2 O, the benzopyranone ring is not coplanar with the phenyl ring, the dihedral angle between them being 41. 35 (3) . No H atom was placed on the sulphonic acid group because it was not possible to distinguish between the two S O bonds and the S-O bond. In the crystal, the molecules are linked by classical O-HÁ Á ÁO and C-HÁ Á ÁO intra-and intermolecular hydrogen bonds and aromaticstacking interactions [centroid-centroid distance of 3.4523 (14) Å between the 1, 4-pyranone rings and the benzene rings, and 3.6337 (14) Å between the benzene rings] into a supramolecular structure.

Comment
Genistein is an isoflavone that can be extracted from plants such as soybean, trifolium, puerarin (Curnow et al. 1955;Kaufman et al., 1997). It has physiological functions of anti-tumour, anti-arteriosclerosis, anti-bone loss (Fritz et al., 1998;Zhu et al., 2006). It can also reduce plasma lipids and kill various cancer cells without damaging normal cells (Fanti et al., 1998;Lamartiniere, 2000). Nevertheless, its medical applications are restricted because of its poor solubility in water and fat (Suo et al.,2005). One effective way to increase the solubility of these compounds is to involve a sulfonate group (Kopacz, 1981;Pusz et al., 2001;Xie et al. 2002).
We present here the structure of (I, Fig. 1), a new derivative of Genistein. In (I) the molecules are linked by classic O-H···O and C-H···O intra-and intermolecular hydrogen bonds (Table 1). Adjacent benzopyranone rings are aligned in a parallel and alternatively inverse fashion, with a centroid-centroid distance of 3.4523 (14)Å between 1, 4-pyranone rings and benzene rings, and 3.6337 (14)Å between the benzene rings (Table 2), indicating significant stacking interactions that form columns running along the a axis. The hydrogen bonding and π-π stacking interactions extend the structure into a 3-D supramolecular structure ( Fig. 2 and Fig. 3).

Experimental
In a 100 ml flask are placed 40 ml 98% sulfuric acid and 10 g (37 mmol) genistein with stirrer. The resulting mixture is stirred at room temperature for 6 h. The reaction mixture is carefully diluted by addition of 40 ml ice water. The resulting yellow solid is filtered, and recrystallized from 50 ml of 90% acetonitrile to give 9.1-11 g (70-85%) of the title compound yellow crystals.

Refinement
The analysis indicated that all three O atoms of the sulfonate group are disordered and therefore the refinement did not converge satisfactorily. Two sulfonate groups, with an occupancies of 0.53740 (O6A, O7A, O8A) and 0.46260(O6B, O7B, O8B), respectively, could be detected and refined. No H atom was added to the sulfonate group because it was not possible to distinguish between the 2 S=O bonds and the S-O bond. The disorder in the SO 3 group was treated with the tools available in SHELXL97 (Sheldrick, 2008).
H atoms bonded to C atoms were placed in calculated positions, with C-H = 0.93 Å and U iso (H) = 1.2Ueq(C), and were included in the refinement in the riding-model approximation. The H atoms of water molecules were located in difference  Fig. 1. The asymmetric unit of (I), with displacement ellipsoids drawn at the 30% probability level.       Symmetry code: (i) -x, 2-y, 1-z. α is dihedral angle between the planes, DCC is the length of the CC vector (centroid-centroid), τ is the angle(s) subtended by the plane normal(s) to CC. Cg1 is the centroid of ring O4, C1, C2, C7-C9 and Cg2 is the centroid of ring C2-C7.