2-Hydroxy-7-methoxy-9H-carbazole-3-carbaldehyde

The title compound, C14H11NO3, was isolated from the roots of Clausena wallichii. The carbazole ring system is approximately planar (r.m.s. deviation = 0.039 Å) and the dihedral angle between the two benzene rings is 4.63 (7)°. An intramolecular O—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, molecules are linked into a zigzag network extending parallel to the ac plane by O—H⋯N and N—H⋯O hydrogen bonds.

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 Sripisut & Laphookhieo 2010;Kongkathip & Kongkathip 2009;Ito et al., 1997;Li et al., 1991;Tangyuenyongwatthana et al., 1992) and some of these compounds show interesting pharmacological activities Yenjai et al. 2000). Although Clausena wallichii is one of the Rutaceae plants, however phytochemical reports on the chemical constituents from this plant are rare. As part of our continuing study of chemical constituents and bioactive compounds from Thai medicinal plants, we report herein the crystal structure of the title compound, which was isolated from the roots of C.
wallichii collected from Phrae province in the northern region of Thailand.
The crystal packing of the title compound is stabilized by intermolecular O-H···N and N-H···O hydrogen bonds (Table   1) which link the molecules into a zigzag network extending parallel to the ac plane.

Experimental
The roots of C. wallichii (1.02 Kg) were successively extracted with CH 2 Cl 2 over the period of 3 days each at room temperature to provide the crude CH 2 Cl 2 extract which subjected to quick column chromatography (QCC) over silica gel eluted with a gradient of hexane-EtOAc (100% hexane to 100% EtOAc) to provide nine fractions (A-I). Fraction G (3.12 g) was further separated by QCC with a gradient of 10% EtOAc-hexane to 100% EtOAc to give seven subfractions (G1-G7). Subfraction G4 (118.9 mg) was subjected to repeated column chromatography using 30% EtOAc-hexane to yield the yellow solid of the title compound (12.8 mg). Yellow plate-shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from CH 2 Cl 2 /acetone (1:1 v/v) by the slow evaporation of the solvent at room temperature after several days; m.p. 496.7-498.8 K (decomposition).

Refinement
Atom H1N1 was located in a difference map and refined isotropically. The remaining H atoms were placed in calculated positions with O-H = 0.81, C-H = 0.93 for aromatic and CH, and 0.96 Å for CH 3 atoms. The U iso values were constrained supplementary materials sup-2 to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 1.81 Å from C9 and the deepest hole is located at 1.29 Å from C3. 851 Friedel pairs were used to determine the absolute structure. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. The O-H···O hydrogen bond is shown as a dashed line.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.