Synthesis and characterization of new palladium(II) complexes with ligands derived from furan-2-carbaldehyde and benzaldehyde thiosemicarbazone and their in vitro cytotoxic activities against various human tumor cell lines

With the ligands 4-phenyl-1-(furan-2-carbaldehyde)thiosemicarbazone, HTSC', (1), 4-phenyl-1- (5'-phenyl-furan-2-carbaldehyde)thiosemicarbazone, HTSC ² (2), o-methoxy-benzaldehydethiosemicarbazone, HTSC₃ (3), and o-cyano-benzaldehydethiosemicarbazone, HTSC⁴ (4), the corresponding palladium(II) complexes, Pd(TSC¹)₂ (5), Pd(TSC²)₂ (6), Pd(TSC³)₂ (7), and Pd(TSC⁴)₂ (8) were synthesized and characterized by elemental analysis and spectroscopic techniques. The crystal structure of Pd(TSC³)₂ (7) was determined by single-crystal X-ray diffraction. Complex 7 shows a squareplanar geometry, where two deprotonated ligands are coordinated to the PdII center through the nitrogen and sulfur atoms in a trans arrangement. In vitro antitumor studies against different human tumor cell lines have revealed that the palladium(II) complexes 5- 8 are more cytotoxic (IC50 values in the range of 0.21 - 3.79 μM) than their corresponding ligands (1 - 4) (> 60 μM). These results indicate that the antiproliferative activity is enhanced when thiosemicarbazone ligands are coordinated to the metal. Among the studied palladium(II) complexes, 8 exhibits high antitumor activity on K562 chronic myelogenous leukemia cells with a low value of the inhibitory concentration (IC₅₀ = 0.21 μM).