The synthesis and study of multimetallic Platinum Group Metal complexes as in vitro phamacological agents

Includes bibliographical references.The success of cisplatin and its analogues for the treatment of different cancers has had a profound effect on establishing the application of metal complexes in medicine. Lately, increasing drug resistance and the emergence of unwanted side effects to currently available therapies have bred a need for novel pharmacological agents. Thus, the design and study of organometallic complexes as potential chemotherapeutics may potentially identify new drug candidates. Apart from platinum based compounds, platinum-like metals such as ruthenium(II), rhodium(III) and iridium(III), have been identified as biologically relevant metals. The purpose of this study is to synthesize three classes of polynuclear complexes containing metals from the Platinum Group Metal (PGM) series and evaluate each class for pharmacological activity in vitro. Each complex class is based on a different ligand type. New mono- and polynuclear organometallic Platinum Group Metal (PGM) complexes based on three ligand classes have been synthesised and characterised using several analytical and spectroscopic techniques including 1H, 13C and 31P NMR, infrared and UV-vis spectroscopy. The first complex series is based on the thiourea containing ligand, 3,4-dichloroacetophenonethiosemicarbazone, which has demonstrated in vitro pharmacological activity. This ligand was reacted with K2[PtCl4] to afford a tetranuclear cycloplatinated thiosemicarbazone complex (2.2). Reaction of 2.2 with different mono- and diphosphanes yielded two mono- and three dinuclear Pt(II) thiosemicarbazone ligands (2.3-2.7). In all of the complexes (2.2-2.7), the thiosemicarbazone ligands act as a dinegative tridentate [C,N,S] donor to each metal centre. Single crystal X-ray analyses of three of the complexes in this series, including the tetraplatinum derivative, confirmed the structural integrity of these complexes. Reactivity studies of the mononuclear platinum(II) complexes revealed that one complex is able to undergo oxidative addition reactions with different aryl iodide substrates. In vitro pharmacological studies of a selection of these complexes as antiparasitic agents have been carried out against the P. falciparum strains, D10 (cisplatin sensitive) and Dd2 (cisplatin resistant)) and Trichomonas vaginalis T1. Their cytotoxic effects on the A2780 (cisplatin sensitive) and A2780cisR (cisplatin resistant) human ovarian carcinoma cell line has also been determined. All of the complexes demonstrated moderate cytotoxic effects as antiparasitics and antitumor agents. No correlation between the number of platinumthiosemicarbazone moieties and pharmacological activity could be discerned. Instead, the type of ancillary ligand used to prepare each complex may influence the lipophilic nature of each complex thus explaining the trend observed

Synthesis, characterization, biological and catalytic studies of tridentate monothiosemicarbazone palladium (II) complexes

Includes abstract.Includes bibliographical references.Nine monothiosemicarbazone ligands were prepared by Schiff-base condensation reactions of thiosemicarbazide and the appropriate aryl aldehyde or ketone. These compounds were isolated as air- and moisture- stable solids and were characterized using NMR and IR spectroscopies, as well as mass spectrometry and elemental analysis in the case of ligand 3-terl.-butyl-2-hydroxy-benzaldehyde thiosemicarbazone, which is a new compound. Four of these ligands were reacted with precursors of type Pd(L)2CI2 yielding eight tridentate thiosemicarbazone Pd(II) complexes with general formula [Pd( 3-0,N,Sthiosemicarbazone)(L)] (L = PPh3 or 4-picoline). Six of these complexes are new compounds and were fully characterized using NMR and IR spectroscopies, mass spectrometry and elemental analysis. In addition, the solid state structures of three complexes were elucidated using single crystal X-ray diffraction methods

The elements of life and medicines

Which elements are essential for human life? Here we make an element-by-element journey through the periodic table and attempt to assess whether elements are essential or not, and if they are, whether there is a relevant code for them in the human genome. There are many difficulties such as the human biochemistry of several so-called essential elements is not well understood, and it is not clear how we should classify elements that are involved in the destruction of invading microorganisms, or elements which are essential for microorganisms with which we live in symbiosis. In general, genes do not code for the elements themselves, but for specific chemical species, i.e. for the element, its oxidation state, type and number of coordinated ligands, and the coordination geometry. Today, the biological periodic table is in a position somewhat similar to Mendeleev's chemical periodic table of 1869: there are gaps and we need to do more research to fill them. The periodic table also offers potential for novel therapeutic and diagnostic agents, based on not only essential elements, but also non-essential elements, and on radionuclides. Although the potential for inorganic chemistry in medicine was realized more than 2000 years ago, this area of research is still in its infancy. Future advances in the design of inorganic drugs require more knowledge of their mechanism of action, including target sites and metabolism. Temporal speciation of elements in their biological environments at the atomic level is a major challenge, for which new methods are urgently needed

Synthesis and evaluation of new polynuclear organometallic Ru(II), Rh(III) and Ir(III) pyridyl ester complexes as in vitro antiparasitic and antitumor agents

New polynuclear organometallic Platinum Group Metal (PGM) complexes containing di- and tripyridyl ester ligands have been synthesised and characterised using analytical and spectroscopic techniques including H-1, C-13 NMR and infrared spectroscopy. Reaction of these polypyridyl ester ligands with either [Ru(p-cymene)Cl-2](2), [Rh(C5Me5)Cl-2](2) or [Ir(C5Me5)Cl-2](2) dimers yielded the corresponding di- or trinuclear organometallic complexes. The polyaromatic ester ligands act as monodentate donors to each metal centre and this coordination mode was confirmed upon elucidation of the molecular structures for two of the dinuclear complexes. The di- and trinuclear PGM complexes synthesized were evaluated for inhibitory effects on the human protozoal parasites Plasmodium falciparum strain NF54 (chloroquine sensitive), Trichomonas vaginalis strain G3 and the human ovarian cancer cell lines, A2780 (cisplatin-sensitive) and A2780cisR (cisplatin-resistant) cell lines. All of the complexes were observed to have moderate to high antiplasmodial activities and the compounds with the best activities were evaluated for their ability to inhibit formation of synthetic hemozoin in a cell free medium. The in vitro antitumor evaluation of these complexes revealed that the trinuclear pyridyl ester complexes demonstrated moderate activities against the two tumor cell lines and were also less toxic to model non-tumorous cells

Recent developments in drug discovery against the protozoal parasites Cryptosporidium and Toxoplasma

Apicomplexan parasites cause some of the most devastating human diseases, including malaria, toxoplasmosis, and cryptosporidiosis. New drug discovery is imperative in light of increased resistance. In this digest article, we briefly explore some of the recent and promising developments in new drug discovery against two apicomplexan parasites, Cryptosporidium and Toxoplasma

Synthesis and structural characterization of binuclear palladium(II) complexes of salicylaldimine dithiosemicarbazones

A series of binuclear palladium(II) salicylaldiminato dithiosemicarbazone complexes have been synthesized and characterized. The palladium complexes were obtained by the reaction of various ethylene- and phenylene-bridged dithiosemicarbazones with Pd(PPh3)2Cl2. The free salicylaldimine ligands and their palladium complexes were characterized by NMR and IR spectroscopies, ESI-mass spectrometry, elemental analyses and for two representative complexes also by X-ray diffraction. In both metal complexes, the solid-state structures show the two palladium centers to be coordinated in a slightly distorted square-planar geometry, which gives rise in each case to five- and six-membered chelate rings. The salicylaldimine thiosemicarbazone ligands coordinate to palladium in a tridentate manner, through the phenolic oxygen, imine nitrogen and thiolate sulfur atoms

Cyclopalladated complexes containing tridentate thiosemicarbazone ligands of biological significance: Synthesis, structure and antimalarial activity

The C-H activation reaction of two aryl-derived thiosemicarbazones with K-2[PdCl4] affords tetranuclear cyclopalladated complexes (3 and 4) where the thiosemicarbazone ligand acts as a tridentate donor [C,N,S] coordinated to palladium via the ortho-carbon of the aryl ring, imine nitrogen and thiolato sulfur. The palladiumesulfur bridging coordination bonds give rise to a Pd4S4 core. These Pd-S-bridging bonds were cleaved with a variety of mono-and bis-phosphines to give a series of mono, di and tetranuclear organopalladium complexes (5-12) where the phosphorus atom coordinates to palladium trans to the imine nitrogen. All of the complexes were fully characterized using various analytical and spectroscopic techniques. These palladium complexes along with their free ligands were evaluated as bioorganometallic antimalarial agents against two Plasmodium falciparum strains, 3D7 (chloroquine sensitive) and K1 (chloroquine and pyrimethamine resistant). Some of the complexes were found to be moderate inhibitors of parasite growth and were more active than the corresponding free ligand. (C) 2010 Elsevier B. V. All rights reserved

Synthesis and structural characterization of binuclear palladium(II) complexes of salicylaldimine dithiosemicarbazones

A series of binuclear palladium(II) salicylaldiminato dithiosemicarbazone complexes have been synthesized and characterized. The palladium complexes were obtained by the reaction of various ethylene- and phenylene-bridged dithiosemicarbazones with Pd(PPh3)2Cl2. The free salicylaldimine ligands and their palladium complexes were characterized by NMR and IR spectroscopies, ESI-mass spectrometry, elemental analyses and for two representative complexes also by X-ray diffraction. In both metal complexes, the solid-state structures show the two palladium centers to be coordinated in a slightly distorted square-planar geometry, which gives rise in each case to five- and six-membered chelate rings. The salicylaldimine thiosemicarbazone ligands coordinate to palladium in a tridentate manner, through the phenolic oxygen, imine nitrogen and thiolate sulfur atoms

Synthesis, characterization, antiplasmodial evaluation and electrochemical studies of water-soluble heterobimetallic ferrocenyl complexes

Three new ferrocenyl-containing heterobimetallic complexes were synthesized using a sodium sulfonate-salicylaldimine mononuclear ferrocenyl complex and various metal precursors. Complexation with ruthenium(II), rhodium(III) and iridium(III) precursors yielded the heterobimetallic complexes, which display good water-solubility. The ferrocenyl ligand acts as a N,O-bidentate chelating ligand, coordinating to the metal center via the imine nitrogen and the deprotonated phenolic oxygen. The complexes were characterized using analytical and spectroscopic techniques. The compounds were evaluated for in vitro antiplasmodial activity against the NF54 chloroquine-sensitive strain of Plasmodium falciparum. The mono- and bimetallic complexes exhibit enhanced activity compared to the salicylaldimine hydrazone. The compounds were evaluated for their ability to inhibit β-haematin formation but were inactive, suggesting an alternative reason for their antiplasmodial activity. Electrochemical studies on the bimetallic complexes revealed a voltammetric wave corresponding to the oxidation of the ferrocenyl group and another at a more positive potential which inhibited the reversibility of the ferrocenyl oxidation

Antiprotozoal activity of palladium(II) salicylaldiminato thiosemicarbazone complexes on metronidazole resistant Trichomonas vaginalis

Clinical cases of metronidazole resistant Trichomonas vaginalis infections have spurred interest in drug discovery against this protozoal parasite. We have carried out structure-activity studies using mononuclear palladium(II) complexes containing salicylaldiminato thiosemicarbazones on a patient isolate of Trichomonas vaginalis highly resistant to the FDA-approved drug metronidazole. A small library of sixteen compounds were analysed on this resistant isolate. Interestingly, compared with our previous analysis of a metronidazole sensitive strain, susceptibility of this resistant isolate to four of the six most potent compounds was observed. Two compounds had similar IC50 values between the resistant strain and a previously analysed sensitive line. Palladium(II) salicylaldiminato thiosemicarbazone complexes may represent, with further development, a new drug discovery direction for treating clinical cases of metronidazole-resistant T. vaginalis. The most potent compound had an IC50 value of 15 μM on parasite growth and showed no effects on common normal flora bacteria and no morphological effects when tested on cultured mammalian cells