Experimental

disorder in main residue; R factor = 0.053; wR factor = 0.130; data-to-parameter ratio = 15.6. In the title compound, C13H13NO4, the asymmetric unit contains four independent molecules, each exhibiting an intramolecular N—H O hydrogen bond. The ethyl group in one of the four molecules is disordered, with a refined occupancy ratio of 0.295 (16):0.705 (16). A face-to-face stacking interaction is found between the benzene rings of the quinoline units of two of the molecules [centroid–centroid distance = 3.541 (2) Å], which are sandwiched by the other two molecules through N—H O hydrogen bonding. In the crystal, the sandwiched molecules are assembled via stacking interactions along the b-axis direction with their translation-symmetry equivalents [centroid–centroid distance = 3.529 (2) Å], and are further linked through N—H O hydrogen bonding. The other two molecules are linked via stacking interactions with their inversion-symmetry equiva-lents [centroid–centroid distances = 3.512 (3) and 3.716 (4) Å] and via N—H O hydrogen bonding. Related literature For the background of this study, see: Ishikawa & Fujii (2011). For the synthesis of the title compound, see: Ozeki et al