Synthesis, structure and in vitro anticancer, DNA binding and cleavage activity of palladium (II) complexes based on isatin thiosemicarbazone derivatives

Six novel palladium(II) complexes of a thiosemicarbazone Schiff base with isatin moiety (PdL1 to PdL6) were synthesized by the reaction of palladium(II) with the following: (Z)‐2‐(2‐oxoindolin‐3‐ylidene)‐N‐phenylhydrazinecarbothioamide (L1H), (Z)‐2‐(5‐methyl‐2‐oxoindolin‐3‐ylidene)‐N‐phenylhydrazinecarbothioamide (L2H), (Z)‐2‐(5‐fluoro‐2‐oxoindolin‐3‐ylidene)‐N‐phenylhydrazinecarbothioamide (L3H), (Z)‐N‐methyl‐2‐(5‐nitro‐2‐oxoindolin‐3‐ylidene)hydrazinecarbothioamide (L4H), (Z)‐N‐methyl‐2‐(5‐methyl‐2‐oxoindolin‐3‐ylidene)hydrazinecarbothioamide (L5H) and (Z)‐N‐ethyl‐2‐(5‐methyl‐2‐oxoindolin‐3‐ylidene)hydrazinecarbothioamide (L6H). The structures of these complexes were characterized using elemental analysis and infrared, UV–visible, 1H NMR and mass spectroscopies. The structure of PdL5 was further characterized using single‐crystal X‐ray diffraction. The interaction of these complexes with calf thymus DNA was characterized with a high intrinsic binding constant (Kb = 5.78 × 104 to 1.79 × 106 M−1), which reflected the intercalative activity of these complexes towards calf thymus DNA. This result was also confirmed from viscosity data. Electrophoresis studies revealed that complexes PdL1 to PdL6 could cleave DNA via an oxidative pathway in the presence of an external agent. Data obtained from an in vitro anti‐proliferative study clearly established the anticancer potency of these compounds against the human colorectal carcinoma cell line HCT 116. Pd(II) complexes of isatin thiosemicarbazone derivatives were prepared and examined for their anticancer activity against human colorectal (HCT 116) cell line as well as for their binding and cleavage activities. All the complexes exhibited a clear anticancer potency. The complexes exhibited a high intrinsic binding constant and could cleave DNA via an oxidative pathway.