2,9-Dimethyl-7-phenyl-N-(4-methylphenyl)dibenzo[b,h][1,6]naphthyridin-6-amine

The title compound, C31H25N3, was synthesized from 6,4′,4′′-trimethyl-2,4-bis(N-phenylamino)quinoline and is the first structural example containing a phenyl and phenylamino fragment attached to a fused dibenzo[1,6]naphthyridine moiety. The fused tetracyclic ring system is essentially planar [r.m.s. deviation = 0.08 (3) Å]. The phenyl ring and the phenylamino group are inclined by 82.68 (6) and 35.31 (5)°, respectively, to the mean plane of the fused tetracyclic ring system. A weak intramolecular N—H⋯π(arene) interaction may in part influence the conformation of the molecule. In the crystal, molecules are linked by weak intermolecular C—H⋯N hydrogen bonds into centrosymmetric dimers. Additional stabilization is provided by weak C—H⋯π and π–π stacking interactions [centroid–centroid distances = 3.834 (2) and 3.898 (1) Å].

Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 and SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009). DV acknowledges the Department of Science and Technology (DST) for providing data collection facilities under major research projects and is also thankful for financial support to the Department under the UGC-SAP and DST-FIST programs.   Sivakumar et al. 2003;Seebacher et al., 2010). [1,6]Naphthyridine compounds are known to have biological activities (Ruchelman et al. 2005;Hinschberger et al. 2003;Feng et al., 2008). Dibenzo [1,6]naphthyridines are reported to have potent Topomerase I targeting, cytotoxic (Ruchelman et al., 2003) and are also proven anti-tumour agents. A series of [1,6] naphthyridine compounds were shown to exhibit potent activity against human cytomegalovirus (Bedard et al. , 2000). We are focused on preparing heterocyclic naphthyridine derivatives with potential biological properties. The crystal structure of the title compound is presented herein.

2,
The molecular structure of the title compound is shown in Fig. 1 The fused tetracyclic ring system is essentially planar (r.m.s. deviation = 0.08 (3)Å) as was reported for a previously determined structure (Vennila et al., 2010). The phenyl ring and the phenyl amino group are inclined by 82.68 (6)° and 35.31 (5)°, respectively to the mean plane of the fused tetracyclic ring system. The bond lengths (Allen et al., 1987) and angles are in the normal ranges. In the crystal structure (Fig. 2), molecules are linked by weak intermolecular C-H···N hydrogen bonds into centrosymmetric dimers. Additional stabilization is provided by weak C-H···π and π-π stacking interactions.

Experimental
The synthesis follows the procedure of Manoj & Rajendra Prasad (2009). Preparation of 6,4',quinoline: A mixture of appropriate 2,4-dichloro-6-methylquinoline (0.010 mol) and p-toluidine (0.010 mol) was heated at 433K for half an hour. The product obtained was washed with water, dried and purified by column chromatography over silica gel and eluted with ethyl acetate : methanol mixture (95 : 5) to yield a white solid. The product was recrytallized from methanol. Preparation of 2,9,h] [1,6] naphthyridine: An mixture of 6,4',4''-trimethyl-2,4-bis-(N-phenylamino) quinoline (0.0010 mol) and benzoic acid (0.0011 mol) was added to polyphosphoric acid (3 g of P 2 O 5 in 1.5 mL of H 3 PO 4 ) and kept at 323-328 K for 5 hours. The reaction was monitored by TLC. After the completion of the reaction, the reaction mixture was poured into ice water and neutralised with saturated NaHCO 3 solution to remove the excess benzoic acid. The precipitate was filtered, dried and purified by column chromatography over silica gel using petroleum ether : ethyl acetate (99 : 1) mixture to obtain yellow solid. The yellow solid was dissolved in ethylacetate and left to crystallize at 277K for about 6 months. Only few crystals were obtained and the best available was used for the X-ray structure analysis.

Refinement
The H-atoms were positioned geometrically and treated as riding atoms: C-H =0.93 Å H-aromatic, C-H = 0.96 Å Hmethyl, and N-H = 0.86 Å, with U iso = k×U eq (parent C or N-atom), where k = 1.5 for methyl H-atoms, and = 1.2 for all other H-atoms. The low percentage of data used (because of low theta cut-off) may affect the precision of the structure. Fig. 1. The molecular structure of the title compound showing the thermal ellipsoids drawn at the 50% probability level.

Special details
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.