Synthesis and Characterization of New Palladium(II) Thiosemicarbazone Complexes and Their Cytotoxic Activity against Various Human Tumor Cell Lines

The palladium(II) bis-chelate complexes of the type [Pd(TSC 1-5 ) 2 ] ( 6–10 ), with their corresponding ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC 1 ( 1 ), 4-phenyl-1-(2′-chloro-benzaldehyde)-thiosemicarbazone, HTSC 2 ( 2 ), 4-phenyl-1-(3′-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC 3 ( 3 ), 4-phenyl-1-(2′-naphthaldehyde)-thiosemicarbazone, HTSC 4 ( 4 ), and 4-phenyl-1-(1′-nitro-2′-naphthaldehyde)-thiosemicarbazone, HTSC 5 ( 5 ), were synthesized and characterized by elemental analysis and spectroscopic techniques (IR and 1 H- and 13 C-NMR). The molecular structure of HTSC 3 , HTSC 4 , and [Pd(TSC 1 ) 2 ] ( 6 ) have been determined by single crystal X-ray crystallography. Complex 6 shows a square planar geometry with two deprotonated ligands coordinated to Pd II through the azomethine nitrogen and thione sulfur atoms in a cis arrangement. The in vitro cytotoxic activity measurements indicate that the palladium(II) complexes (IC 50 = 0.01–9.87  μ M) exhibited higher antiproliferative activity than their free ligands (IC 50 = 23.48–70.86 and >250  μ M) against different types of human tumor cell lines. Among all the studied palladium(II) complexes, the [Pd(TSC 3 ) 2 ] ( 8 ) complex exhibited high antitumor activity on the DU145 prostate carcinoma and K562 chronic myelogenous leukemia cells, with low values of the inhibitory concentration (0.01 and 0.02  μ M, resp.).