(E)-3-(2,3-Dimethoxyphenyl)-1-(2-hydroxy-4-methoxyphenyl)prop-2-en-1-one

The molecular conformation of the title compound, C18H18O5, is stabilized by a strong intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The C=C double bond displays an E configuration while the carbonyl group shows an S-cis configuration relative to the double bond. The dihedral angle between the two rings is 15.0 (1)°.

The molecular conformation of the title compound, C 18 H 18 O 5 , is stabilized by a strong intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The C C double bond displays an E configuration while the carbonyl group shows an S-cis configuration relative to the double bond. The dihedral angle between the two rings is 15.0 (1) .
Data collection: SMART-NT (Bruker, 2001); cell refinement: SAINT-NT (Bruker, 1999); data reduction: SAINT-NT; program(s) used to solve structure: SHELXTL-NT (Sheldrick, 2008); program(s) used to refine structure: SHELXTL-NT; molecular graphics: SHELXTL-NT; software used to prepare material for publication: SHELXTL-NT. This behavior is attributed to the intense H-bonding interaction between the 2'-hydroxyl proton and the acetyl moiety of the acetophenone, which is preserved in the derivatives like 2'-hydroxy-chalcones. This structural characteristic of the title compound has been recognized to play a key role in its biological activity and seems to be the basis to its potential as an anti carcinogenic agent. In fact 2'-hydroxychalcones have been found to be cytotoxic against human tumor cells. In the particular case of the title compound this was found to be a potent cytotoxic agent against human lymphocytic and also to monocytic cell linies (Rao et al., 2004). It has been also proved to be a potent antiproliferative agent against tumor cell lines without being more cytotoxic to normal cells (Rao et al., 2004).
The structure of the title compound displays two phenyl rings connected through a three carbon propenone moiety. As shown in Figure 1, one phenyl ring is substituted at positions 2 and 3 with methoxy groups, while the other is substituted at positions 2' and 4' with one hydroxy and one methoxy group respectively.
The hydroxy substitution at 2' produces a six-membered intramolecular O-H···O hydrogen bond with the keto group (Desiraju, 2002). This hydrogen bond is present with almost no exception through the series of compounds with this core, startintg with 2'-Hydroxy-4-methylchalcone (Shoja, 1999). This intramolecular bond leads the carbonyl group to display an S-cis configuration in relation to the double bond. The double bond displays an E configuration.
The molecule is significantly planar, as reflected in the values determined for the torsion angles. This is also true for molecules substituted with methoxy and/or hydroxy groups at different points of both phenyl sub-systems (Fronczek et al., 1987;Wallet et al., 1995;Subbiah Pandi et al., 2003;Chu et al., 2004;Wafo et al., 2005;Radha Krishna et al., 2005;Wu et al., 2005;Usman et al., 2006).
The packing shows no significant intermolecular hydrogen bonding.

Experimental
The title compound was prepared as follows: A solution of the 2,3-dimethoxybenzaldehyde, (7.34 mmol in ethanol, 20 ml) was added dropwise to a mixture of 2'-hydroxy-4'-methoxyacetophenone (7.34 mmol, in ethanol, 20 ml) and potassium hydroxide (2 g in 10 ml distilled water) with stirring. The mixture was allowed to react overnight, was then diluted with distilled water (200 ml), neutralized with hydrochloric acid and extracted with ethyl acetate (4 x 50 ml). The combined supplementary materials sup-2 organic phases were concentrated in a rotatory evaporator, redissolved in ethanol and allowed to crystallize, as yellow crystals (31%); mp 98-101 °C.

Refinement
The hydrogen atoms positions were calculated after each cycle of refinement with SHELXL (Bruker,1999) using a riding model for each structure, with C-H distances in the range 0.95 to 0.98 Å. U iso (H) values were set equal to 1.5U eq of the parent carbon atom for methyl groups and 1.2U eq for the others. The exception were the hydroxyl hydrogen atom which were located in the Fourier and then refined with the O-H distance constrained to be 0.84 Å and the U eq free to refine.