Structural, vibrational and quantum chemical investigations for 6,7-dichloro-2-methyl-5,8-quinolinedione. Cytotoxic and molecular docking studies

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6,7-Dichloro-2-methyl-5,8-quinolinedione was investigated using different experimental methods as well as a variety of various quantum chemical calculations in order to characterize its molecular structure as a potential anticancer active compound. We used X-ray diffraction, IR spectrum analysis supplemented by the density functional theory (DFT) calculations, molecular electrostatic potential (MEP) and molecular orbital (HOMO, LUMO) analyses. The analyzes were carried out with respect to 6,7-dichloro-5,8-quinolinedione. It was found that introduction of the methyl group at the C-2 position distinctly affected the crystal structure, formation of H-bonds and the carbonyl stretching IR bands of the title compound. The molecular electrostatic potential map showed how the electrophilic and nucleophilic regions are located in the molecule. The intra- and intermolecular bonding and interaction between bonds were interpreted using the Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis.The title compound was tested for its anticancer activity in vitro against the several human cancer cell lines. 6,7-Dichloro-2-methyl-5,8-quinolinedione showed a higher cytotoxic activity against cancer cell lines containing a higher level of NQO1 enzyme, like melanoma (C-32) and breast (MCF-7) cancer cell lines. The molecular docking was used to examine the probable interaction between the molecule of the tested compound and the NQO1 enzyme. The analysis showed that the 5,8-quinolinedione moiety of the title compound formed a hydrophobic interaction with phenylalanine (Phe 178), tyrosine (Tyr 126 and Tyr 128) and FAD cofactor.