Methyl 1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylate monohydrate

In the structure of the title compound, C13H14N2O3·H2O, all atoms of the organic molecule except the terminal methyl group of the ethyl group attached to the N atom of the pyridinone ring are roughly coplanar, with an r.m.s. deviation of 0.0897 Å. In the crystal, C—H⋯O contacts link pairs of naphthyridine molecules into head-to-tail dimers. These are joined by strong O—H⋯O hydrogen bonds from the water molecules into infinite chains along the a axis.

In the structure of the title compound, C 13 H 14 N 2 O 3 ÁH 2 O, all atoms of the organic molecule except the terminal methyl group of the ethyl group attached to the N atom of the pyridinone ring are roughly coplanar, with an r.m.s. deviation of 0.0897 Å . In the crystal, C-HÁ Á ÁO contacts link pairs of naphthyridine molecules into head-to-tail dimers. These are joined by strong O-HÁ Á ÁO hydrogen bonds from the water molecules into infinite chains along the a axis.
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); 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, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON.  (Gavrilova & Bosnich, 2004;Mintert & Sheldrick, 1995). These compounds are also biologically active with anti-bacterial (Chen et al., 2001), anti-hypertensive (Ferrarini et al., 2000) and anti-inflammatory (Roma et al., 2000) properties. In a continuation of our work on the synthesis, biological activity and crystal structures of various  (15)° with respect to the pyridinone and pyridine rings respectively. In addition, a solvent water molecule is also present and stabilizes the crystal structure through intermolecular hydrogen bonding interactions. The molecule exhibits C-H···O type weak intermolecular hydrogen bonding and forms dimers through the formation of ten membered ring motif R 2 2 (10) (Bernstein, et al., 1995). These are further connected via water molecules along the a axis to form infinite chains. On the other hand, one of the hydrogen atoms of water molecule is also involved in the formation of six membered ring motif with O atoms of pyridinone ring and the ester (Fig. 2, Table. 1).

Experimental
A mixture of 1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid (100.0 mmol; 23.22 g) and thionyl chloride (50 ml) was refluxed for a period of 4 h followed by distillation (under reduced pressure) of the excess thionyl chloride. After complete removal of thionyl chloride, methanol (100 ml) was slowly added and stirred for two hours followed by the addition of ice cooled water (300 ml). The contents were washed with aqueous sodium carbonate (0.5 M) and water respectively followed by crystallization from methanol to give suitable crystals. Yield: 92%.

Refinement
All C-bonded H-atoms were positioned in an idealized geometry, with C-H = 0.95Å for aromatic CH and C-H =0.98Å for the methyl group. U(H) was set to 1.2U eq for all C aromatic and 1.5U eq for the C methyl & oxygen atoms. The H atoms of the water molecule were located in a difference Fourier map and refined freely with U(H) = 1.5U eq (O).

Figure 1
The structure of (I) with 50% displacement ellipsoids.

Figure 2
A crystal packing plot parallel to a with hydrogen bonds drawn as dashed lines. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.