Synthesis of copper(II) complexes of isatin thiosemicarbazone derivatives: In vitro anti-cancer, DNA binding, and cleavage activities

Abstract

Six new Cu(II) complexes of thiosemicarbazone Schiff base with isatin moiety were synthesized through the reaction of Cu(II) with (Z)-2-(2-oxoindolin- 3-ylidene)-N-phenylhydrazinecarbothioamide (CuL1), (Z)-2-(5-methyl-2-oxoindolin- 3-ylidene)-N-phenylhydrazinecarbothioamide (CuL2), (Z)-2-(5-fluoro-2-oxoindolin- 3-ylidene)-N-phenylhydrazinecarbothioamide (CuL3), (Z)-N-methyl-2-(5-nitro-2- oxoindolin-3-ylidene)hydrazinecarbothioamide (CuL4), (Z)-N-methyl-2-(5-methyl-2- oxoindolin-3-ylidene)hydrazinecarbothioamide (CuL5), and (Z)-N-ethyl-2-(5- methyl-2-oxoindolin-3-ylidene)hydrazinecarbothioamide (CuL6). The structures of the Schiff bases and their copper complexes were characterized based on the elemental analysis, and on the infrared, UV-Vis, 1H and 13C NMR and ESI-mass spectral data. The structures of the CuL2 and CuL3 complexes were further characterized by single-crystal X-ray diffraction. The interaction of these complexes with calf thymus (CT)-DNA exhibited high intrinsic binding constant (Kb = 1.6 × 105-14.6 × 105 M-1), which reflected intercalative activity of these complexes toward CT-DNA. This result was also confirmed by the viscosity data. Electrophoresis studies revealed that the CuL1 and CuL2 complexes were able to cleave the DNA via oxidative pathway, whereas CuL3, CuL4, CuL5, and CuL6 induced DNA cleavage via oxidative and hydrolytic pathways. The in vitro anti-proliferative study establishes the anticancer potency of these compounds against the human colorectal carcinoma cell line.