Preparation, physicochemical properties and biological activity of copper(II) complexes with 6-(2-chlorobenzylamino)purine (HL 1) or 6-(3-chlorobenzylamino)purine (HL 2). The single-crystal X-ray structure of [Cu(H +L 2) 2Cl 3]Cl·2H 2O

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Copper(II) complexes of 6-(2-chlorobenzylamino)purine (HL 1) and 6-(3-chlorobenzylamino)purine (HL 2), respectively, were prepared. Depending on the pH of the medium and the molar ratio of reactants the following mononuclear (trigonal-bipyramidal) and dinuclear (octahedral, trigonal-bipyramidal or tetrahedral) complexes were isolated: [Cu 2(μ-HL 1) 2(μ-Cl 2) 2(HL 1) 2Cl 2] ( 1a, b), [Cu 2(μ-Cl) 2(μ-L 1) 2(H 2O) 2] ( 2a), [Cu 2(μ-Cl) 2(μ-L 2) 2(H 2O) 2] ( 2b), [Cu(H +L 2) 2Cl 3]Cl·H 2O ( 3a, b), [Cu 2(μ-Cl) 2(HL 1) 2Cl 2] ( 4a), and [Cu 2(μ-Cl) 2(HL 2) 2Cl 2] ( 4b). The compounds were characterized by elemental analyses, electronic, infrared and mass (FAB+, ES+) spectral data, magnetic susceptibility temperature dependence measurements and molar conductivity data. An X-ray single-crystal structural analysis of [Cu(H +L 2) 2Cl 3]Cl·2H 2O ( 3b) showed that the Cu 2+ ion is penta-coordinated by three chloride ions and by two H +L 2 ligands. Thus, the Cu 2+ ion adopts a distorted trigonal bipyramidal coordination geometry with the protonated H +L 2 ligands coordinated in trans apical positions, while the three chloride ions are situated in an equatorial plane. The cytotoxic activity of the complexes was determined by a calcein AM assay. Mouse melanoma cell line B16-FO, human malignant melanoma cell line G361, human osteogenic sarcoma cell line HOS and human breast adenocarcinoma cell line MCF7 were used. IC 50 values, the drug concentrations lethal to 50% of the tumor cells, were estimated. One of the important mechanisms responsible for the cytotoxicity of cytokinin-derived compounds, the inhibition of cyclin-dependent kinases by the studied complexes, was also determined.