Novel Schiff bases based on the quinolinone skeleton: syntheses, X-ray structures and fluorescent properties

A series of a new type of Schiff bases 1-7, derived from 2-phenyl-3-amino-4(1H)-quinolinone and R-salicyladehyde derivatives wherein R = 3-hydroxy (1), 3,4-dihydroxy (2), 3-methoxy (3), 3-carboxy (4), 3-allyl (5), 5-chloro (6), and 5-nitro (7), was synthesized and structurally characterized. Each of the molecules 1, 3 and 7 consists of three planar moieties (i.e., a quinolinone and two phenyl rings), which are mutually oriented differently depending on the appropriate substituent R and the extent of non-covalent contacts stabilizing the crystal structures. The compounds were studied for their fluorescence properties, where compound 6 yielded the strongest intensity both in the solid phase and in 100 μM ethanol solution with a quantum yield of φ = 3.6% as compared to quinine sulfate used as a standard. The in vitro cytotoxicity of these compounds was tested against the human osteosarcoma (HOS) and breast adenocarcinoma (MCF7) cell lines, revealing no activity up to the concentration of 50 µM.