(1E,4E)-1-(2-Nitrophenyl)-5-(2,6,6-trimethylcyclohex-1-en-1-yl)penta-1,4-dien-3-one

In the title curcumin–ionone derivative, C20H23NO3, the dihedral angle between the cyclohexene and benzene rings is 21.03 (8)°, with both double bonds in the interlinking olefinic chain adopting E conformations. Two of the methylene groups of the β-ionone ring are disordered over two sets of sites with occupancy ratios of 0.50:0.50 and 0.60:0.40. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds into zigzag chains extending along the b axis.


Comment
Ionone is an important intermediate in the metabolism of terpenoids, and has been isolated from many sources, and represents a promising candidate for chemopreventive applications. Ionone has been used for in vivo and in vitro protection against various types of cancer cells (Asokkumar et al., 2012). Curcumin is a yellow compound isolated from the rhizome of the herb Curcuma longa L, which has been used for centuries as a dietary pigment, spice, and traditional medicine in India and China (Kuttan et al., 1985). Several clinical trials involving curcumin are currently being conducted on patients with pancreatic cancer, multiple myeloma, rheumatoid arthritis, cystic fibrosis, inflammatory bowel disease, psoriasis, and other disorders (Hsu & Cheng, 2007). Our previous studies also showed that some monocarbonyl analogues of curcumin without the β-diketone moiety exhibited better anti-inflammatory activities than those of curcumin (Liang et al., 2007;Zhao, Cai et al., 2010;Zhao, Yang et al., 2010).
In the present study, we designed and synthesized a series of ionone-based monocarbonyl analogues of curcumin by incorporating ionone and monocarbonyl dienone into one chemical entity. One of these was the title compound, C 20 H 23 NO 3 and its structure is reported here. In the molecule (  (Table 1), giving zigzag chains which extend down the b-cell direction.

Experimental
To the mixture of β-ionone (2.5 mmol, 0.481 g) and 2-nitrobenzaldehyde (2.5 mmol) in 10 ml of ethanol, 1 ml of 10% NaOH was added and the mixture was stirred for 12 h at room temperature. After addition of 10 ml of water, the solution was extracted by 3×10 ml of CH 2 Cl 2 . The crude product was obtained from the combined organic layers, and was purified by silica gel column chromatography (elutant: EtOAc/hexane). Crystals of the title compound suitable for X-ray analysis were obtained from an ethanol/chloroform solution (1:3, v/v) at 293 K.

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 F2 against all reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional Rfactors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating Rfactors (gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on all data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (