Structural Diversity of Copper(II) Complexes with N-(2-Pyridyl)Imidazolidin-2-Ones(Thiones) and Their in Vitro Antitumor Activity

Six series of structurally different mono- and binuclear copper(II) complexes 5–10 were obtained by reacting N-(2-pyridyl)imidazolidin-2-ones (1a–l), N,N'-bis(2-pyridyl)imidazolidin-2-ones (2a,b), N-acyl-N'(2-pyridyl)imidazolodin-2-ones (3a–j) and N-(2-pyridyl)imidazolidine-2-thiones (4a–g) with copper(II) chloride at an ambient temperature. The coordination modes of the complexes obtained were established by elemental analysis, IR spectroscopic data and single crystal X-ray diffraction studies. The in vitro cytotoxic activities of both the free ligands and copper(II) complexes were evaluated using a crystal violet microtiter plate assay on five human tumor cell lines: LCLC-103H, A-427, SISO, RT-4 and DAN-G. The free ligands 1–4 at concentration attainable in cancer cells of 20 μM showed no meaningful cytotoxic effect with cell viability in the range of 88%–100%. The most potent copper(II) complex of 1-(6-ethoxy-2-pyridyl)imidazolidin-2-one (6b) exhibited selective cytotoxicity against A-427 lung cancer cell line, while the complexes of 1-(5-methyl-2-pyridyl)imidazolidine-2-thione (5h) and 1-(4-tert-butyl-2-pyridyl)imidazolidine-2-thione (5j) showed cytostatic effect against a whole panel of five human tumor cell lines. In conclusion, the only complexes that showed remarkably increased activity in comparison to the free ligands were those obtained from N-(2-pyridyl)imidazolidine-2-thiones 4c and 4e substituted with alkyl group at position 4 or 5 of pyridine ring.