The synthesis and characterization of a new water-soluble N,N-chelating iminophosphorane ligand TPA=N-C(O)-2-NC5H4 (N,N-IM) (1) and its d8 (AuIII, PdII and PtII) coordination complexes are reported. The structures of cationic [AuCl2(N,N-IM)] ClO4 (2) and neutral [MCl2(N,N-IM)] M = Pd (3), Pt(4) complexes were determined by X-ray diffraction studies or by means of density-functional calculations. While the Pd and Pt compounds are stable in mixtures of DMSO/H2O over 4 days, the gold derivative (2) decomposes quickly to TPA=O and previously reported neutral gold(III) compound [AuCl2(N,N-H)] 5 (containing the chelating N,N- fragment HN-C(O)-2-NC5H4). The cytotoxicities of complexes 2–5 were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells and DU-145 human prostate cancer cells. Pt (4) and Au compounds (2 and 5) are more cytotoxic than cisplatin to these cell lines and to cisplatin-resistant Jurkat sh-Bak cell lines and their cell death mechanism is different from that of cisplatin. All the compounds show higher toxicity against leukemia cells when compared to normal human T-lymphocytes (PBMC). The interaction of the Pd and Pt compounds with calf thymus and plasmid (pBR322) DNA is different from that of cisplatin. All compounds bind to human serum albumin (HSA) faster than cisplatin (measured by fluorescence spectroscopy). Weak and stronger binding interactions were found for the Pd (3) and Pt (4) derivatives by isothermal titration calorimetry. Importantly, for the Pt (4) compounds the binding to HSA was reversed by addition of a chelating agent (citric acid) and by a decrease in pH.
The synthesis and characterization of a new water-soluble iminophosphorane ligand TPAN-C(O)-2BrC6H4 (1, C,N-IM; TPA = 1,3,5-triaza-7-phosphaadamantane) is reported. Oxidative addition of 1 to Pd2(dba)3 affords the orthopalladated dimer [Pd(μ-Br){C6H4(C(O)NTPA-kC,N)-2}]2 (2) as a mixture of cis and trans isomers (1:1 molar ratio) where the iminophosphorane moeity behaves as a C,N-pincer ligand. By addition of different neutral or monoanionic ligands to 2, the bridging chlorides can be cleaved and a variety of hydrophilic or water-soluble mononuclear organometallic palladium(II) complexes of the type [Pd{C6H4(C(O)NTPA-kC,N)-2}(L-L)] (L-L = acac (3); S2CNMe2 (4); 4,7-diphenyl-1,10-phenanthrolinedisulfonic acid disodium salt C12H6N2(C6H4SO3Na)2 (5)), [Pd{C6H4(C(O)NTPA-kC,N)-2}(L)Br] (L = P(mC6H4SO3Na)3 (6); P(3-pyridyl)3 (7)), and [Pd(C6H4(C(O)NTPA)-2}(TPA)2Br] (8) are obtained as single isomers. All new complexes were tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells, normal T-lymphocytes (PBMC), and DU-145 human prostate cancer cells. Compounds [Pd(μ-Br){C6H4(C(O)NTPA-kC,N)-2}]2 (2) and [Pd{C6H4(C(O)NTPA-kC,N)-2}(acac)] (3) (which has been crystallographically characterized) display higher cytotoxicity against the above-mentioned cancer cell lines while being less toxic to normal T-lymphocytes (peripheral blood mononuclear cells: PBMC). In addition, 3 is very toxic to cisplatin-resistant Jurkat shBak, indicating a cell death pathway that may be different from that of cisplatin. The interaction of 2 and 3 with plasmid (pBR322) DNA is much weaker than that of cisplatin, pointing to an alternative biomolecular target for these cytotoxic compounds. All the compounds show an interaction with human serum albumin faster than that of cisplatin.
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