Abstract
The palladium(II) bis-chelate complexes of the type [Pd(TSC1-5)2] (6–10), with their corresponding ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC1 (1), 4-phenyl-1-(2′-chloro-benzaldehyde)-thiosemicarbazone, HTSC2 (2), 4-phenyl-1-(3′-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC3 (3), 4-phenyl-1-(2′-naphthaldehyde)-thiosemicarbazone, HTSC4 (4), and 4-phenyl-1-(1′-nitro-2′-naphthaldehyde)-thiosemicarbazone, HTSC5 (5), were synthesized and characterized by elemental analysis and spectroscopic techniques (IR and 1H- and 13C-NMR). The molecular structure of HTSC3, HTSC4, and [Pd(TSC1)2] (6) have been determined by single crystal X-ray crystallography. Complex 6 shows a square planar geometry with two deprotonated ligands coordinated to PdII through the azomethine nitrogen and thione sulfur atoms in a cis arrangement. The in vitro cytotoxic activity measurements indicate that the palladium(II) complexes (IC50 = 0.01–9.87 μM) exhibited higher antiproliferative activity than their free ligands (IC50 = 23.48–70.86 and >250 μM) against different types of human tumor cell lines. Among all the studied palladium(II) complexes, the [Pd(TSC3)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 μM, resp.).
Highlights
It has been shown that the α-(N)-heterocyclic carbaldehyde thiosemicarbazones act as chelating agents of the transition metals and some of them exhibit antitumor activity by inhibiting the biosynthesis of DNA, possibly by blocking the enzyme ribonucleotide diphosphate reductase [23,24,25]
We have reported the cytotoxic activity of the ligands derived from benzaldehyde and furaldehyde thiosemicarbazone and their palladium(II) bischelate complexes
Palladium (II) bis(acetylacetonate), potassium tetrachloropalladate, acetone, 4-phenyl-thiosemicarbazide, o-chloro-benzaldehyde, m-hydroxy-benzaldehyde, naphthaldehyde, and 1-nitro-2naphthaldehyde were purchased from Aldrich
Summary
Sulfur containing ligands such as dithiocarbamates and thiosemicarbazones and their transition metal complexes have received more attention in the area of medicinal chemistry, due to their pharmacological properties, such as antiviral [1,2,3], antibacterial [4,5,6,7], antifungal [8,9,10], antiparasitic [11, 12], and antitumor [13,14,15,16,17,18,19] activities. The ligand 6-methylpyridine-2-carbaldehydeN(4)-ethylthiosemicarbazone (HmpETSC) and its complexes [Zn(HmpETSC)Cl2] and [Pd(mpETSC)Cl] exhibit antineoplastic activity against colon cancer human cell lines (HCT 116) with IC50 values of 14.59, 16.96, and 20.65 μM, respectively [26]. We have reported the cytotoxic activity of the ligands derived from benzaldehyde and furaldehyde thiosemicarbazone and their palladium(II) bischelate complexes. In vitro antitumor studies against different human tumor cell lines revealed that these metal complexes (IC50 = 0.21–12.46 μM) were more cytotoxic than their corresponding ligands (IC50 > 60 μM). The present work describes the synthesis, characterization, and antitumor activity of palladium(II) bis-chelate complexes of the type [Pd(TSC1–5)2] (6–10) with the ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC1 (1), 4-phenyl-1-(2-chloro-benzaldehyde)-thiosemicarbazone, HTSC2 (2), 4-phenyl-1-(3-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC3 (3), 4-phenyl-1-(2-naphthaldehyde)-thiosemicarbazone, HTSC4 (4), and 4-phenyl-1-(1-nitro-2-naphthaldehyde)-thiosemicarbazone, HTSC5 (5)
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