(Z)-1-(2-Hydroxyethyl)-4-(2-methoxybenzylidene)-2-methyl-1H-imidazol-5(4H)-one

In the title compound, C14H16N2O3, an analog of the chromophore in green fluorescent protein, the methoxyphenyl substituent and the imidazole N adopt a Z conformation with respect to the C=C bond. Aside from the hydroxyethyl group, the molecule is approximately planar, with the five- and six-membered ring planes forming a dihedral angle of 9.3 (1)°. An intramolecular C—H⋯N contact occurs. In the crystal, O—H⋯N hydrogen bonds link the molecules, forming chains along the b-axis direction. C—H⋯O hydrogen bonds are also observed.

In the title compound, C 14 H 16 N 2 O 3 , an analog of the chromophore in green fluorescent protein, the methoxyphenyl substituent and the imidazole N adopt a Z conformation with respect to the C C bond. Aside from the hydroxyethyl group, the molecule is approximately planar, with the five-and sixmembered ring planes forming a dihedral angle of 9.3 (1) . An intramolecular C-HÁ Á ÁN contact occurs. In the crystal, O-HÁ Á ÁN hydrogen bonds link the molecules, forming chains along the b-axis direction. C-HÁ Á ÁO hydrogen bonds are also observed.
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008). The title compound is an analog of the chromophore in green fluorescent protein (GFP). GFP was first identified and separated from the jellyfish Aequorea victoria in the 1960s. Since then, GFP has found broad use in many areas of science and medicine, especially as fluorescent labels for cell biology and biotechnology. (Shimomura et al., 1962;Shimomura, 2009;Remington, 2006;Tsien, 1998;Chalfie et al., 1994) Though the GFP is a protein composed of more than two hundred amino acid residues, its chromophore (p-hydroxybenzylidene-imidazol-5-one) is relatively small. In nature, the GFP chromophore is formed via the sequential cyclization-oxidation-dehydration of the Ser 65 -Tyr 66 -Gly 67 tripeptide motif. (Prasher et al., 1992) Preparation of the title compound starts with the Erlenmeyer azlactone synthesis, which involves the condensation of hippuric acid derivatives with aromatic aldehydes (Yampolsky et al., 2005;Bailly et al., 2004), Fig. 1. Further reaction of the resulting azlactone with ethanolamine leads to the formation of the title compound. We report the crystal structure of the compound here, which shows the compound has a Z-configuration. The compound is used as a model compound in our study of E, Z-isomerization of chromophores in fluorescent proteins.
The structure of the molecule is shown in Fig. 2. The Z configuration is evidenced by the torsion angle N2-C3-C7-C8 3.33 (14)° about the central double bond. The hydroxyethyl group is twisted away from coplanarity with the rest of the molecule (C1-N1-C4-C5 torsion angle -74.77 (9)°), but otherwise, the molecule is relatively planar, with the phenyl and imidazole rings forming a dihedral angle of 9.3 (1)°.
The OH group O3 forms a near-linear intermolecular hydrogen bond to the imidazole nitrogen atom N2 (at -x, y-1/2, 1z), forming chains in the b direction, propagated by the screw axis. Several intermolecular C-H···O hydrogen bonds and an intramolecular C-H···N contact also exist, as given in Table 1.

Experimental
A mixture of o-anisaldehyde (6.95 g, 50.0 mmol), N-acetylglycine (5.97 g, 50.5 mmol) and anhydrous sodium acetate (4.35 g, 52.5 mmol) were dissolved in 20 ml acetic anhydride. The mixture was stirred at 100° C for 6 h. Upon completion, the reaction mixture was cooled to room temperature. After the addition of 10 ml ice-cold water, the resulting precipitate was collected by gravity filtration. The filtrand was then washed three times with ice-cold water and dried in vacuum, yielding (1) as a yellow powder (8.41 g, 64.7%). Title compound (2) was synthesized by reacting (1) with ethanolamine in 2-propanol. To a suspension of compound (1) (3.30 g, 15.2 mmol) in dried 2-propanol (30 ml), ethanolamine (1.14 ml, 18.8 mmol) was added gradually. The reaction mixture was refluxed for 8 h. The solvent was then removed under vacuo. The crude product was recrystallized from a n-butanol/diethyl ether (1/1, v/v) mixture. Yellow crystals of the title compound (2) were obtained in a yield of 2.77 g (58%). The sample crystal was grown by evaporation from methanol.

Refinement
H atoms on C were located from difference maps, but were placed in idealized positions with C-H distance 0.95 -0.99 Å, depending on atom type. A torsional parameter was refined for each methyl group. Coordinates for the hydroxy H atom were refined. U iso for H were assigned as 1.2 times U eq of the attached atoms (1.5 for methyl and OH). Refinement of the Flack (1983) parameter was inconclusive; however, analysis of the Bijvoet pairs by the Hooft et al. (2008) method yielded a P2(true) value of 1.000. Although the molecule is not inherently chiral, we consider the reported coordinates to likely represent the correct absolute structure of the crystal studied, and the pairs were kept separate in the refinement.

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.