Synthesis, crystal structures, antiproliferative activities and reverse docking studies of eight novel Schiff bases derived from benzil

Eight novel Schiff bases derived from benzil dihydrazone (BDH) or benzil monohydrazone (BMH) and four fused-ring carbonyl compounds (3-formylindole, FI; 3-acetylindole, AI; 3-formyl-1-methylindole, MFI; 1-formylnaphthalene, FN) were synthesized and characterized by elemental analysis, ESI-QTOF-MS, ¹H and ¹³C NMR spectroscopy, as well as single-crystal X-ray diffraction. They are (1Z,2Z)-1,2-bis{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFI), C₃₂H₂₄N₆, (1Z,2Z)-1,2-bis{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethane (BDHAI), C₃₄H₂₈N₆, (1Z,2Z)-1,2-bis{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BMHMFI) acetonitrile hemisolvate, C₃₄H₂₈N₆·0.5CH₃CN, (1Z,2Z)-1,2-bis{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFN), C₃₆H₂₆N₄, (Z)-2-{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFI), C₂₃H₁₇N₃O, (Z)-2-{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethanone (BMHAI), C₂₄H₁₉N₃O, (Z)-2-{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHMFI), C₂₄H₁₉N₃O, and (Z)-2-{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFN) C₂₅H₁₈N₂O. Moreover, the in vitro cytotoxicity of the eight title compounds was evaluated against two tumour cell lines (A549 human lung cancer and 4T₁ mouse breast cancer) and two normal cell lines (MRC-5 normal lung cells and NIH 3T3 fibroblasts) by MTT assay. The results indicate that four (BDHMFI, BDHFN, BMHMFI and BMHFN) are inactive and the other four (BDHFI, BDHAI, BMHFI and BMHAI) show severe toxicities against human A549 and mouse 4T₁ cells, similar to the standard cisplatin. All the compounds exhibited weaker cytotoxicity against normal cells than cancer cells. The Swiss Target Prediction web server was applied for the prediction of protein targets. After analyzing the differences in frequency hits between these active and inactive Schiff bases, 18 probable targets were selected for reverse docking with the Surflex-dock function in SYBYL-X 2.0 software. Three target proteins, i.e. human ether-á-go-go-related (hERG) potassium channel, the inhibitor of apoptosis protein 3 and serine/threonine-protein kinase PIM1, were chosen as the targets. Finally, the ligand-based structure-activity relationships were analyzed based on the putative protein target (hERG) docking results, which will be used to design and synthesize novel hERG ion channel inhibitors.

Theoretical investigation on the interaction of benzazaborole derivatives with iodide ion: Structural, binding and fluorescence properties analysis

The structural, fluorescence properties and binding interaction of benzazaborole derivatives 1-hydroxy-2-(α-methyl) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADE) and 1-hydroxy-2-(2-chloro) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADC) with iodide ion have been investigated utilizing density functional theory (DFT) and Time-dependent density functional theory (TD-DFT) method, in which the PADE and PADC showed strong emission in aqueous solution and fluorescence quenching was observed upon addition of iodide ion. The theoretical study indicates that the strong hydrogen-bond (O-H…I) between benzazaborole derivatives and iodide ion leads to the formation of the benzazaborole-iodide ion complexes. The excited state properties have been explored by theoretical calculation to understand the fluorescent quenching upon introduction of iodide ion. The strong fluorescent emission is originated by the electron transfer from benzyl and phosphate moieties to benzo boron nitrogen fused heterocycle moiety, while the fluorescence quenching is attributed to the electron transfer between the PADE (PADC) and iodide ion. The density difference (EDD) maps and the frontier molecular orbitals diagrams during excitation and de-excitation process demonstrate that the photoinduced electron transfer process between PADE (PADC) and iodide ion leads to fluorescence quenching after a significant internal conversion.