Search

The pharmacological profile of medicinally relevant Ru(III) coordination compounds has been ascribed to their interactions with proteins, as several studies have provided evidence that DNA is not the primary target. In this regard, numerous spectroscopic and crystallographic studies have indicated that the Ru(III) ligands play an important role in determining the metal binding site, acting as the recognition element in the early stages of the protein-complex formation. Herein, we present a series of near-atomic-resolution X-ray crystal structures of the adducts formed between the antimetastatic metallodrug imidazolium trans-[tetrachlorido(S-dimethyl sufoxide)(1H-imidazole)ruthenate(III)] (NAMI-A) and hen egg-white lysozyme (HEWL). These structures elucidate a series of binding events starting from the noncovalent interaction of intact NAMI-A ions with HEWL (1.5 h), followed by the stepwise exchange of all Ru ligands except for 1H-imidazole (26 h) to the final "ruthenated" protein comprising one aquated Ru ion coordinated to histidine-15 of HEWL (98 h). Our structural data clearly support a two-step mechanism of protein ruthenation, illustrating the ligand-mediated recognition step of the process.

The pharmacological profile of medicinally relevant Ru(III) coordination compounds has been ascribed to their interactions with proteins, as several studies have provided evidence that DNA is not the primary target. In this regard, numerous spectroscopic and crystallographic studies have indicated that the Ru(III) ligands play an important role in determining the metal binding site, acting as the recognition element in the early stages of the protein-complex formation. Herein, we present a series of near-atomic-resolution X-ray crystal structures of the adducts formed between the antimetastatic metallodrug imidazolium

The targeted synthesis of metal–organic frameworks (MOFs) with open metal sites, following reticular chemistry rules, provides a straightforward methodology toward the development of advanced porous materials especially for gas storage/separation applications. Using a palladated tetracarboxylate metalloligand as a 4-connected node, we succeeded in synthesizing the first heterobimetallic In(III)/Pd(II)-based MOF with square-octahedron (soc) topology. The new MOF, formulated as [In3O(L)1.5(H2O)2Cl]·n(solv) (1), features the oxo-centered trinuclear clusters, [In3(μ3-O)(−COO)6], acting as trigonal-prismatic 6-connected nodes that linked together with the metalloligand trans-[PdCl2(PDC)2] (L4–) (PDC: pyridine-3,5-dicarboxylate) to form a 3D network. After successful activation of 1 using supercritical CO2, high-resolution microporous analysis revealed the presence of small micropores (5.8 A) with BET area of 795 m2 g–1 and total pore volume of 0.35 cm3 g–1. The activated solid shows high gravimetric (92.3 cm3 ...

With the aim of assessing how the aromaticity of the inert chelating ligand can influence the activity of ruthenium(II) polypyridyl complexes, two new monofunctional ruthenium(II) complexes, [Ru(Cl-Ph-tpy)(phen)Cl]Cl (1) and [Ru(Cl-Ph-tpy)(o-bqdi)Cl]Cl (2) (where Cl-Ph-tpy = 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine, phen = 1,10-phenanthroline, o-bqdi = o-benzoquinonediimine), were synthesized. All complexes were fully characterized by elemental analysis and spectroscopic techniques (IR, UV–Vis, 1D and 2D NMR, XRD). Their chemical behavior in aqueous solution was studied by UV–Vis and NMR spectroscopy showing that both compounds are relatively labile leading to the formation of the corresponding aqua species 1a and 2a. 1H NMR spectroscopy studies performed on complexes 1 and 2 demonstrated that after the hydrolysis of the Cl ligand, they are capable to interact with guanine derivatives (i.e., 9-methylguanine (9MeG) and 5′-GMP) through the N7, forming monofunctional adduct. The kinetics and the mechanism of the reaction of complexes 1 and 2 with the biologically more relevant 5′-GMP ligand were studied by UV–Vis spectroscopy. DNA/protein interactions of the complexes have been examined by photophysical studies, which demonstrated a bifunctional binding mode of the complexes with DNA and the complexes strongly quench the fluorescence intensity of bovine serum albumin (BSA) through the mechanism of both static and dynamic quenching. Complexes 1 and 2 strongly induced apoptosis of treated cancer cells with high percentages of apoptotic cells and negligible percentage of necrotic cells. In addition, both ruthenium complexes decreased Bcl-2/Bax ratio causing cytochrome c mitochondrial release, the activation of caspase-3 and induction of apoptosis.

In this study, we have developed a series of new monofunctional Ru(II) complexes of the general formula mer-[Ru(Cl-Ph-tpy)(N-N)Cl]Cl in which Cl-Ph-tpy is 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine, N-N is a bidentate chelating ligand (1,2-diaminoethane (en, 1), 1,2-diaminocyclohexane (dach, 2) or 2,2′-bipyridine (bpy, 3)). All complexes were fully characterized by elemental analysis and spectroscopic techniques (IR, UV–Vis, 1D and 2D NMR). Their chemical behavior in aqueous solution was studied by UV–Vis and NMR spectroscopy showing that all compounds are relatively labile leading to the formation of the corresponding aqua species 1aq–3aq. Their DNA binding ability was evaluated by UV–Vis spectroscopy, fluorescence quenching measurements and viscosity measurements. Competitive studies with ethidium bromide (EB) showed that the complexes can displace DNA-bound EB, suggesting strong competition with EB (Ksv=1.1–2.7×104M−1). These experiments show that the ruthenium complexes interact with DNA via intercalation. The complexes bind to serum protein albumin displaying relatively high binding constants (Ksv=104–105M−1). Compound 3 displayed from high to moderate cytotoxicity against two cancer cell lines HeLa and A549 (with IC50 ca. 12.7μM and 53.8μM, respectively), while complexes 1 and 2 showed only moderate cytotoxicity (with IC50 ca. 84.8μM and 96.3μM, respectively) against HeLa cells. The cell cycle analysis (by flow cytometry) of HeLa and A549 cells treated with complex 3 shows minor changes on the cell cycle phase distribution.

Journal of biological inorganic chemistry 25(4), 635 - 645 (2020). doi:10.1007/s00775-020-01786-z, The high-resolution X-ray crystal structures of the adducts formed between the “half sandwich”-type Ru(II) coordination compound [Ru$^{II}$(1,4,7-trithiacyclononane)(ethane-1,2-diamine)Cl]$^+$ and two proteins, namely hen egg-white lysozyme and proteinase K, are presented. The structures unveil that upon reaction with both enzymes the Ru(II) compound is coordinated by solvent-exposed aspartate residues after releasing the chloride ligand (Asp101 in lysozyme, Asp200 and Asp260 in proteinase K), while retaining the two chelating ligands. The adduct with Asp101 residue at the catalytic cleft of lysozyme is accompanied by residue-specific conformational changes to accommodate the Ru(II) fragment, whereas the complexes bound at the two calcium-binding sites of proteinase K revealed minimal structural perturbation of the enzyme. To the best of our knowledge, proteinase K is used here for the first time as a model system of protein metalation and these are the first X-ray crystal structures of protein adducts of a Ru(II) coordination compound that maintains its coordination sphere almost intact upon binding. Our data demonstrate the role of ligands in stabilizing the protein adducts via hydrophobic/aromatic or hydrogen-bonding interactions, as well as their underlying role in the selection of specific sites on the electrostatic potential surface of the enzymes., Published by Springer, New York

A novel NbO-type MOF is reported based on a palladated organic linker, showing a remarkable gravimetric and volumetric CO2 uptake, reaching 201.8 cm(3) g(-1) (9.0 mmol g(-1), 39.7 wt%) and 187.8 cm(3) cm(-3) at 273 K and 1 bar, respectively. Accurate theoretical calculations revealed that the exceptional CO2 uptake is due to the combination of Lewis base Pd(ii)-CO2 (24.3 kJ mol(-1)) and Lewis acid Cu(ii)-CO2 (30.3 kJ mol(-1)) interactions, as well as synergistic pore size effects.

This paper is a tribute to the rich chemistry and great versatility of ruthenium-dmso precursors: over the years, from a handful of complexes we prepared literally hundreds of derivatives with all types of ligands, from mono- to poly-dentate, from pure sigma-donors (e.g. NH3) to phosphines and strong pi-acceptors such as CO and NO. This systematic and extensive investigation had a red thread running through it: the identification of compounds that might have functional roles, either because they possess peculiar physical-chemical properties or because they undergo predictable and stereo-controlled substitution reactions, i.e. are well-behaved precursors. From a more fundamental point of view, this systematic investigation led us to get a deeper understanding of the subtle differences in the soft nature of ruthenium and osmium, as well as in the delicate balance between electronic and steric preferences of the dmso ligand and of its remarkable adaptability to the coordination environment.

© 2018 The Royal Society of Chemistry. With the aim of assessing whether Au(iii) compounds with pincer type ligands might be utilized as potential antitumor agents, three new monofunctional Au(iii) complexes of the general formula [Au(N-N'-N)Cl]Cl2, where N-N'-N = 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine (H2LtBu, 1), 2,6-bis(5-tert-butyl-1-methyl-1H-pyrazol-3-yl)pyridine (Me2LtBu, 2) or 2,6-bis((4S,7R)-1,7,8,8-tetramethyl-4,5,6,7-tetrahydro-1H-4,7-methanoindazol-3-yl)pyridine (Me2∗L, 3) were synthesized. All complexes were characterized by elemental analysis, spectroscopic techniques (IR, UV-Vis, 1D and 2D NMR) and mass spectrometry (MALDI TOF MS). The chemical behavior of the complexes under physiological conditions was studied by UV-Vis spectroscopy, which showed that all compounds were remarkably stable and that the gold center remained in the 3+ oxidation state. The kinetics and the mechanism of the reaction of complexes 1-3 with guanine derivatives (i.e. guanosine (Guo) and guanosine-5′-monophosphate (5′-GMP)) and calf thymus DNA (CT DNA) were studied by stopped-flow spectroscopy. The three complexes displayed moderately different rate constants in their reactions with Guo, 5′-GMP and CT DNA, which can be explained by the steric hindrance and σ-donicity of the methyl substituent on the bis-pyrazolylpyridine fragment in complexes 2 and 3. The measured enthalpies and entropies of activation (ΔH≠ > 0, ΔS≠ < 0) supported an associative mechanism for the substitution process. The interaction of the newly synthesized complexes 1-3 with CT DNA was investigated by UV-Vis and fluorescence spectroscopy, and also by viscosity measurements, which all indicated that complexes 1-3 bound to CT DNA with moderate binding affinity (Kb = 1.6-5.7 × 103 M-1) and stabilized the duplex of CT DNA. Molecular docking indicated that complexes 1-3 interacted with DNA via intercalation. Complex 1 reduced the cell survival of all the investigated cell lines (A549, A375, and LS-174) with IC50 values being up to 20 μM. We have shown that 1 induced perturbations of the cell cycle and led to apoptosis in human melanoma A375 cells. Complex 1 also affected the level of reactive oxygen species (ROS) in the same cells. However, pre-treatment of A375 cells with NAC (ROS scavenger) reversed the effect of 1 on their survival.

In this review we summarize our work on development of Ru complexes with potential antitumor activity, which was performed over the last few years. In order to establish the structure-activity relationship for Ru(II) compounds, we have designed, synthesized and thoroughly studied several Ru(II) complexes, which were divided in three main groups: i) organometallic Ru(II)-arene complexes, ii) Ru(II) half-sandwich coordination complexes bearing neutral face-capping macrocyclic ligands, such as 1,4,7-trithiacyclononane ([9]aneS3) and 1,4,7-triazacyclononane ([9]aneN3), and iii) Ru(II)-polypyridyl complexes. Our most recent experiments moved toward synthesis, chemistry and reactivity of the heteronuclear ruthenium(II)/ferrocene complexes. The first part of the present review gives a brief overview of the structural features and anticancer activity of ruthenium complexes. The second part is focused mainly on the results obtained from the kinetic and mechanistic studies of the reactions between Ru(II) complexes and guanine derivatives, such as 9-methylguanine (9MeG), guanosine (Guo) and guanosine-5′-monophosphate (5′-GMP), as well as on structural characterization of the final products of these reactions. In the final part we deal with the reactions of Ru(II) complexes with DNA, which is widely accepted as a potential target for cytotoxic ruthenium compounds. We have also described the interactions of Ru(II) compounds with the most abundant transport proteins from human serum: human serum albumin (HSA) and transferrin (Tf). We believe that a systematic review of the aforementioned studies will not only contribute to the future development of ruthenium complexes as potential antitumor agents, but will also help to understand the potential toxicity of ruthenium-based drugs. © 2019 Elsevier B.V.

Continuing the study of the physicochemical and biological properties of ruthenium-quinolone adducts, four novel complexes with the general formula [Ru([9]aneS3)(dmso-κS)(quinolonato-κ2O,O)](PF6), containing the quinolones levo fl oxacin (1), nalidixic acid (2), oxolinic acid (3), and cinoxacin (4), were prepared and characterized in solid state as well as in solution. Contrary to their organoruthenium analogues, these complexes are generally relatively stable in aqueous solution as substitution of the dimethylsulfoxide (dmso) ligand is slow and not quantitative, and a minor release of the quinolonato ligand is observed only in the case of 4. The complexes bind to serum proteins displaying relatively high binding constants. DNA binding was studied using UV − vis spectroscopy, cyclic voltammetry, and performing viscosity measurements of CT DNA solutions in the presence of complexes 1 − 4. These experiments show that the ruthenium complexes interact with DNA via intercalation. Possible electrostatic interactions occur in the case of compound 4, which also shows the most pronounced rate of hydrolysis. Compounds 2 and 4 also exhibit a weak inhibition of cathepsins B and S, which are involved in the progression of a number of diseases, including cancer. Furthermore, complex 2 displayed moderate cytotoxicity when tested on the HeLa cell line.

In this study, we investigated the ability of Ru(ii) polypyridyl complexes to act as DNA binders. The substitution reactions of three Ru(ii) chlorophenyl terpyridine complexes, i.e. [Ru(Cl-Ph-tpy)(en)Cl]Cl (1), [Ru(Cl-Ph-tpy)(dach)Cl]Cl (2) and [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) (Cl-Ph-tpy = 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, en = 1,2-diaminoethane, dach = 1,2-diaminocyclohexane, bpy = 2,2'-bipyridine), with a mononucleotide guanosine-5'-monophosphate (5'-GMP) and oligonucleotides such as fully complementary 15-mer and 22-mer duplexes with a centrally located GG-binding site for DNA, and fully complementary 13-mer duplexes with a centrally located GG-binding site for RNA were studied quantitatively by UV-Vis spectroscopy. Duplex RNA reacts faster with complexes 1-3 than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. The measured enthalpies and entropies of activation (ΔH≠ > 0, ΔS≠ < 0) support an associative mechanism for the substitution process. 1H NMR spectroscopy studies performed on complex 3 demonstrated that after the hydrolysis of the Cl ligand, it is capable to interact with guanine derivatives (i.e., 9-methylguanine (9MeG) and 5'-GMP) through N7, forming monofunctional adducts. The molecular structure of the cationic compound [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) was determined in the solid state by X-ray crystallography. The interactions of 1-3 with calf thymus (CT) and herring testes (HT) DNA were examined by stopped-flow spectroscopy, in which HT DNA was sensibly more reactive than CT DNA. The reactivity towards the formation of Ru-DNA adducts was also revealed by a gel mobility shift assay, showing that complexes 1 and 2 have a stronger DNA unwinding ability compared to complex 3. Overall, the complexes with bidentate aliphatic diamines proved to be superior to those with bpy in terms of capability to bind to the here studied biomolecules.

We report here two novel "extended-arms" porphyrins, TetbpyPP and TedabpyPP, in which four peripheral bpy fragments are connected to the meso positions of the macrocycle through flexible linkers of different length and hydrophilicity. We describe also the new, water-soluble, tetracationic conjugate [TedabpyPP{Ru([9]aneS3)Cl}(4)][Cl](4) (6). Compound 6 belongs to the series of cationic Ru-porphyrin conjugates 1-5, each bearing four peripheral Ru(II) half-sandwich coordination compounds, that we recently prepared as potential photosensitizing chemotherapeutic agents. The in vitro cell growth inhibition of conjugates 1-6 toward MDA-MB-231 human breast cancer cells and HBL-100 human nontumorigenic epithelial cells are reported, together with the phototoxic effects of 1, 4, and 6 on MDA-MB-231 cells. All conjugates have IC(50) values in the low micromolar range that decrease by 1 order of magnitude upon irradiation of cell cultures with visible light. The most promising compounds 1 and 6 are phototoxic at low light and drug doses.

The preparation and structural characterization of several new Ru(II) complexes in which four coordination positions are occupied by the sulfur atoms of a macrocycle, either 1,4,7,10-tetrathiacyclododecane ([12]aneS4) or 1,5,9,13-tetrathiacyclohexadecane ([16]aneS4), and the two others by relatively labile ligands (Cl−, NO 3 - , H2O, dmso-S), are described:cis-[Ru([12]aneS4)(dmso-S)(H2O)](CF3SO3)2 (2a), cis-[Ru([12]aneS4)(dmso-S)(ONO2)](NO3) (2b), cis-[Ru([16]aneS4)Cl2] (4), and trans-[Ru([16]aneS4)(dmso-S)(H2O)](CF3SO3)2 (5).The complexes of the larger [16]aneS4 macrocycle have a flexible coordination geometry, either cis or trans, that makes them unsuited for being used as precursors in metal-driven self-assembly processes.On the contrary, the [12]aneS4 complexes cis-[Ru([12]aneS4)(dmso-S)Cl]Cl (1) and, above all, its chlorido free derivatives cis-[Ru([12]aneS4)(dmso-S)(H2O)](CF3SO3)2 (2a) and cis-[Ru([12]aneS4)(dmso-S)(ONO2)](NO3) (2b) are potential precursors of the geometrically stable 90° bis-acceptor fragment cis-[Ru([12]aneS4)]2+.Preliminary results of their reactivity towards the linear linker pyrazine (pyz) showed that the nature of the isolated product depends on that of the counter-anion.When treated with pyz 2b afforded the dinuclear complex [{Ru([12]aneS4)(ONO2)}2(μ-pyz)](NO3)2 (8), while 2a gave the molecular triangle [{cis-Ru([12]aneS4)(μ-pyz)}3](CF3SO3)6 (9), both in low yields.The X-ray structures of compounds 2a, 2b, 4, 5, [{Ru([12]aneS4)Cl}2(μ-pyz)]Cl2 (7), 9, and of the sandwich complex[Ru([12]aneS3-S)2](CF3SO3)2 (3), in which only three sulfur atoms of each macrocycle are bound to ruthenium, are also described.

The condensation of pyrrole with 4-pyridylcarboxyaldehyde and methyl 4-formyl benzoate under Adler–Longo conditions yielded the series of meso-(4′-pyridyl)/(4′-carboxymethylphenyl)porphyrins as a mixture. Careful column chromatography afforded each isomer in pure form. In this paper we focus on the two bis-substituted isomeric meso-porphyrins, 5,10-bis(4′-pyridyl)-15,20-bis(4′-carboxymethylphenyl)porphyrin and 5,15-bis(4′-pyridyl)-10,20-bis(4′-carboxymethylphenyl)porphyrin, respectively, 4′-cis and 4′-transDPyDMeP. The assignment of the geometry of the two isomers was performed by 1H NMR spectroscopy on the trinuclear adducts [(4′-cisDPyDMeP){Ru(TPP)(CO)}2] and [(4′-transDPyDMeP){Ru(TPP)(CO)}2], obtained by selective coordination of [Ru(TPP)(CO)(EtOH)] (TPP=tetraphenylporphyrin) to the peripheral nitrogen atoms. The axially bound ruthenium porphyrins act as chemical shift reagents on the central porphyrin, allowing a clear distinction of the pyrrole proton resonances and consequent unambiguous assignment of the geometry of each isomer based upon symmetry considerations.

A series of new Ru(II)-DMSO complexes containing dicarboxylate ligands (dicarb), namely, oxalate (ox), malonate (mal), methylmalonate (mmal), dimethylmalonate (dmmal), and succinate (suc), have been synthesized and structurally characterized. These compounds were prepared from the known Ru(II)-Cl-DMSO anticancer complexes cis,fac-[RuCl2(DMSO-S)3(DMSO-O)] (1) and trans-[RuCl2(DMSO-S)4] (2) and from the chloride-free precursor fac-[Ru(DMSO-S)3(DMSO-O)3][CF3SO3]2 (3), with the aim of assessing how the nature of the anionic ligands influences the biological activity of these species. Basically, the investigated ligands can be divided into two groups. The reaction of either 1 or 2 with K2(dicarb) (dicarb = ox, mal, mmal) yielded preferentially the mononuclear species [K]fac-[RuCl(DMSO-S)3(eta2-dicarb)] (dicarb = mal, 6; mmal, 9; ox, 14) that contains a chelating dicarboxylate unit and a residual chloride. Likewise, when 3 was used as a precursor, the neutral mononuclear species fac-[Ru(DMSO-O)(DMSO-S)3(eta2-dicarb)] (dicarb = mal, 7; mmal, 10; ox, 16), which contains a DMSO-O ligand in the place of Cl-, was obtained. On the contrary, K2(suc) and K2(dmmal) yielded preferentially the dinuclear species [fac-Ru(DMSO-S)3(H2O)(mu-dicarb)]2 (dicarb = dmmal, 11; suc, 13), with two bridging dicarboxylate moieties. The two water molecules in anti geometry have strong intramolecular H-bonding with the non-coordinated oxygen atoms of the carboxylate groups. The solid-state X-ray structural data showed that the preferential binding mode of the investigated dicarboxylates, either bridging (mu) or chelating (eta2), is dictated mainly by steric reasons. Oxalate, unlike the other dicarboxylates, has also the bridging bis-chelate (eta4,mu) coordination mode available: this was found in the dinuclear species [{fac-RuCl(DMSO-S)3}2(eta4,mu-ox)] (15) and [{fac-Ru(DMSO-O)(DMSO-S)3}2(eta4,mu-ox)][CF3SO3]2 (17). We also isolated the unprecedented neutral metallacycle, [fac-Ru(DMSO-S)3(eta3,mu-ox)]4 (18), in which each oxalate unit has one unbound oxygen atom. The new complexes were thoroughly characterized by 1-D (1H and 13C) and 2-D (H-H- COSY and HMQC) NMR spectroscopy in solution and by IR spectroscopy in the solid state. The molecular structures of 10 compounds, 6-11, 13, 15, 17, and 18, were determined by X-ray crystallography. The behavior of selected complexes in aqueous solution was investigated by 1H NMR spectroscopy.

The solution structure of the PdII·bleomycin A2 complex was resolved by NMR spectroscopy in combination with molecular modelling. The preparation of the complex in 1.0 M NaCl aqueous solutions leads to the formation of a major compound, which is very stable at ambient temperature. Our NMR spectroscopic data demonstrate that bleomycin is coordinated through the β-aminoalanine secondary amine, the pyrimidine ring N1, the deprotonated histidyl amide and the imidazole N1, in contrast to an earlier study that proposed coordination of the valerate amide. 2D NMR spectroscopic data were used as distance constraints in simulated annealing molecular-dynamics calculations and the first solution structure of a square-planar metallo-bleomycin is reported. In order to assess the toxicity of PdII·bleomycin, cytotoxicity measurements were performed in U937 and K562 leukemia cell lines using two methods. In both cell lines the free drug and the complex exhibit similar toxicity as a function of time. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Two of the most successful chemotherapeutic agents used in the treatment of several neoplasias are bleomycin and cisplatin. Both drugs attack the DNA leading to the cancer cells death via different mechanisms. In view of the fact that the combination with each other leads to enhanced activity with less sever side effects, we have undertaken NMR studies on the complexes formed between bleomycin and PtII, PdII, cisplatin and transplatin. Herein we present a brief review of the studies on metallobleomycins which were carried out by our lab and others, as an outline of the results obtained using NMR in combination to circular dichroism spectroscopy. Our data indicate that in most cases and under several conditions studied, both metal ions form similar complexes with BLM while more than one species are present in the solution. Structural implications and comparisons with other metallobleomycins are being discussed. .

Στη παρούσα διατριβή περιγράφεται η σύνθεση, ο χαρακτηρισμός και διάφορες μελέτες βιολογικού ενδιαφέροντος νέων συμπλόκων του λευκοχρύσου(ΙΙ) και του ρουθηνίου(ΙΙ) που περιέχουν δικαρβοξυλικούς υποκαταστάτες, ως ενδεχόμενα αντικαρκινικά και αντιμεταστατικά μέσα. Για τη σύνθεση των συμπλόκων λευκοχρύσου χρησιμοποιήθηκε μια καινούργια και πολύ ελπιδοφόρα τεχνική, η σύνθεση μέσω στερεάς φάσης. Σύμφωνα με αυτή δύο αμινοξέα προσκολλούνται διαδοχικά σε μια ρητίνη, στη συνέχεια προσκολλάται ένας «σύνδεσμος» και μετά γίνεται η σύμπλεξη του λευκοχρύσου. Εναλλακτικά, πρώτα γίνεται η σύνθεση του συμπλόκου «σύνδεσμος»-Pt και στη συνέχεια αυτό προσκολλάται στο διπεπτίδιο. Το τελικό στάδιο και στις δύο πορείες είναι η αποκοπή της ρητίνης και η παραλαβή του ελεύθερου συμπλόκου. Απομονώθηκαν δύο νέα σύμπλοκα, το Β614 και Β617, στα οποία το διπεπτίδιο ήταν το διπεπτίδιο γλυκίνη-γλυκίνη. Στο Β614 το άκρο του «συνδέσμου» ήταν ένα δικαρβοξύλιο στο οποίο ο PtII ήταν δεσμευμένος χηλικά ενώ οι άλλες δύο θέσεις στη σφαίρα σύνταξης του μετάλλου ήταν κατειλημμένες από δύο μόρια ΝΗ3. Στο Β617 το άκρο ήταν ένα τμήμα αιθυλενοδιαμίνης (en) στην οποία ο PtII ήταν και πάλι δεσμευμένος χηλικά ενώ οι άλλες δύο θέσεις ήταν κατειλημμένες από τον δισθενή χηλικό υποκαταστάτη 1,1- κυκλοβούτανο δικαρβοξυλικό ιόν (1,1-cyclobutane dicarboxylate, cbdc). Τα αρχικά αντιδραστήρια, τα ενδιάμεσα προϊόντα και τα τελικά σύμπλοκα χαρακτηρίσθηκαν με φασματοσκοπία NMR (1H, 195Pt) και φασματομετρία μάζας (MS). Τα σύμπλοκα του ρουθηνίου συντέθηκαν με τους παραδοσιακούς τρόπους (σε διάλυμα) καθώς πολύ λίγα είναι γνωστά για την αλληλεπίδραση δικαρβοξυλίων με ιόντα RuΙΙ. Οι δικαρβοξυλικοί υποκαταστάτες που χρησιμοποιήθηκαν ήταν: τα οξαλικά (oxalate, ox), τα μηλονικά (malonate, mal), τα ηλεκτρικά (succinate, suc) και τα 1,1-κυκλοβούτανοδιικά (cbdc) ιόντα. Τα σύμπλοκα που απομονώθηκαν, ανάλογα με τις συνθήκες, ήταν 1) μονομερή (στα οποία ο υποκαταστάτης δρα δισχιδως/χηλικά): K[fac-RuCl(dmso-S)3(η2-ox-O,O/)] (B71), fac-[Ru(dmso-S)3(dmso-O)(η2-ox-O,O/)] (B73), K[fac-RuCl(dmso-S)3(η2-mal-O,O/)]·2H2O (B81), fac-[Ru(dmso-S)3(dmso-O)(η2-mal-O,O/)] (Β82), K[fac- RuCl(dmso-S)3(η2-cbdc-O,O/)]·2H2O (B91), 2) διμερή (στα οποία ο υποκαταστάτης δρα ως γέφυρα, με το κάθε καρβοξύλιο να συμπλέκεται μονοσχιδώς): {fac-Ru(dmso-S)3(H2O)(μ-mal-O,O/)}2 (Β83), {fac-Ru(dmso- S)3(H2O)(μ-cbdc-O,O/)}2 (Β92), {fac-Ru(dmso-S)3(NH3)(μ-cbdc-O,O/)}2 (Β93), {fac-Ru(dmso-S)3(H2O)(μ-suc- O,O/)}2 (Β101), 3) διμερή (στα οποία ο υποκαταστάτης δρα δισ-δισχιδώς): [{fac-Ru(dmso-S)3(Cl)}2(η4,μ-ox)] (B72), [{fac-Ru(dmso-S)3(dmso-O)}2(η4,μ-ox)](CF3SO3)2 (B74) και 4) τετραμερές (στο οποίο ο υποκαταστάτης δρα χηλικά και συγχρόνως γέφυρα μέσω του ενός από τα δύο ελεύθερα άτομα οξυγόνου): {fac-Ru(dmso- S)3(η3,μ-ox)}4 (Β75). Όλα τα σύμπλοκα χαρακτηρίσθηκαν πλήρως με στοιχειακή ανάλυση και διάφορες φασματοσκοπικές μεθόδους όπως NMR (1H, 13C, COSY, HMQC), IR, UV-Vis. Επίσης οι μοριακές δομές των συμπλόκων Β72, Β74, Β75, Β81, Β82, Β83, Β92, Β93 και Β101 προσδιορίσθηκαν με κρυσταλλογραφία ακτίνων-Χ. Μελετήθηκε εκτενώς η χημική συμπεριφορά αυτών των συμπλόκων εντός υδατικών διαλυμάτων και πραγματοποιήθηκαν in vitro βιολογικές δοκιμασίες για να εκτιμηθεί η ενδεχόμενη αντικαρκινική τους δράση.

With the aim of assessing whether ruthenium(II) compounds with meridional geometry might be utilized as potential antitumor agents, a series of new, water-soluble, monofunctional ruthenium(II) complexes of the general formula mer-[Ru(L3)(N-N)X][Y]n (where L3 = 2,2′:6′,2 ″-terpyridine (tpy) or 4 ′-chloro-2,2′:6′,2″-terpyridine (Cl-tpy), N-N = 1,2-diaminoethane (en), 1,2-diaminocyclohexane (dach), or 2,2′ -bipyridine (bpy); X = Cl or dmso-S; Y = Cl, PF6 , or CF3SO3 ; n = 1 or 2, depending on the nature of X) were synthesized. All complexes were fully characterized by elemental analysis and spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), and for three of them, i.e., [Ru(Cl-tpy)(bpy)Cl][Cl] (3Cl), [Ru(Cl-tpy)(en)(dmso-S)][Y]2 [Y = PF6 (6PF6), CF3SO3 (6OTf )] and [Ru(Cl-tpy)(bpy)(dmso-S)][CF3SO3 ]2 (8OTf ), the X-ray structure was also determined. The new terpyridine complexes, with the exception of 8, are well soluble in water (>25 mg/mL). 1H and 31P NMR spectroscopy studies performed on the three selected complexes [Ru(Cl-tpy)(N-N)Cl]+ [N-N = en (1), dach (2), and bpy (3)] demonstrated that, after hydrolysis of the Cl ligand, they are capable of interacting with guanine derivatives [i.e., 9-methylguanine (9MeG) or guanosine-5 ′ -monophosphate (5′-GMP)] through N7, forming monofunctional adducts with rates and extents that depend strongly on the nature of N-N: 1 ≈ 2 ≫ 3. In addition, compound 1 shows high selectivity toward 5′ -GMP compared to adenosine-5′-monophosphate (5′ -AMP), in a competition experiment. Quantitative kinetic investigations on 1 and 2 were performed by means of UV/visible spectroscopy. Overall, the complexes with bidentate aliphatic diamines proved to be superior to those with bpy in terms of solubility and reactivity (i.e., release of Cl− and capability to bind guanine derivatives). Contrary to the chlorido compounds, the corresponding dmso derivatives proved to be inert (viz., they do not release the monodentate ligand) in aqueous media.

Six half-sandwich RuII coordination compounds of the general formula [Ru([9]aneS3)(L–L)(L′)][PF6]n {2–7; [9]aneS3 = 1,4,7-trithiacyclononane, L–L = 2,2′-bipyridine (bpy), 1,2-diaminoethane (en), (±)-trans-1,2-diaminocyclohexane (dach), picolinate (pic); L′ = pyridine (py), 3-acetylpyridine (3-acpy), imidazole (im); n = 1 or 2, depending on the nature of L–L} were prepared and characterized. If irradiated with blue light (λ = 400–490 nm) in aqueous solution, they readily dissociate the monodentate L′ ligand to generate selectively the corresponding aqua species. The extent and rate of photoinduced ligand release depend primarily on the nature of the chelating ligand (bpy >> en ≈ dach > pic) and, to a minor extent, on that of the leaving ligand (py > im > 3-acpy). Photolabile compounds 2–5 showed no significant antiproliferative activity against the MDA-MB-231 human mammary carcinoma cell line, both in the dark and upon irradiation with blue light. The clean photodissociation process that characterizes this class of half-sandwich RuII compounds, and the substantial lack of toxicity of the photogenerated Ru aqua species, suggest that they might be suitable for the preparation of “caged” RuII compounds. In the frame of this work, two unexpected dinuclear compounds, namely, [{Ru([9]aneS3)(en)}2(μ-en)][CF3SO3]4 (9) and [{Ru([9]aneS3)}2(μ-dach)(μ-CH3O)2][CF3SO3]2·2CH3OH (10)―both containing rare examples of bridging en and dach ligands―were also isolated and structurally characterized.

The preparation and structural characterization of three cationic Ru(II)-dmso carbonyls and of four neutral mono- and dicarbonyl Os(II)-dmso derivatives is reported. The two monocarbonyl species fac-[Ru(CO)(dmso-O)3 (dmso-S)2][PF6]2 (11) and cis,cis,cis-[RuCl(CO)(dmso-O)2(dmso-S)2][PF6] (12) were obtained from the neutral monocarbonyl precursor cis,trans,cis-[RuCl2(CO)(dmso-O)(dmso-S)2] (3) upon stepwise replacement of the chlorides with dmso, that binds in each case through the oxygen atom. The dicarbonyl cationic complex cis,cis,trans-[Ru(CO)2(dmso-O)2(dmso-S)Cl][PF6] (13) was instead obtained upon treatment of the neutral tricarbonyl precursor fac-[RuCl2(CO)3(dmso-O)] (8) with AgPF6 in the presence of DMSO: replacement of a Cl− with a dmso-O impliedalso the substitution of one CO ligand by another dmso (that binds through S trans to Cl). The Os(II) carbonyls trans,trans,trans-[OsCl2(CO)(dmso-O)(dmso-S)2] (17), trans,cis,cis-[OsCl2(CO)2(dmso-O)2] (18), cis,mer-[OsCl2(CO)(dmso-S)3] (19), and cis,trans,cis-[OsCl2(CO)(dmso-O)(dmso-S)2] (20) were obtained by treatment of the Os(II)-dmso precursors trans-[OsCl2(dmso-S)4] (14) and cis,fac-[OsCl2(dmso-O)(dmso-S)3] (15) with CO. Each one of them is structurally similar to an already known Ru(II) analog, even though - in agreement with the expected greater inertness of Os(II) - more forcing reaction conditions were required for their preparation. Interestingly, compound 20 could not be isolated in pure form, but only as a 1:1 cocrystallized mixture with its precursor 15. The dmso ligand is always bound through the oxygen atom when trans to CO. We are con fi dent that the new Ru(II)- and Os(II)-dmso carbonyl species described here represent a contribution to expand the pool of complexes bearing some easily replaceable dmso ligands to be used as well-behaved precursors in inorganic synthesis.

The synthesis of the inert Ru(II) half-sandwich coordination compounds, [Ru([9]aneS 3 )(bpy)(py)][PF 6 ] 2 (1, [9]aneS 3 = 1,4,7-trithiacyclononane, bpy = 2,2 0 -bipyridine, py = pyridine), [Ru([9]aneS 3 )(en)(py)][PF 6 ] 2 (2, en = 1,2-diaminoethane), and [Ru([9]aneN 3 )(en)(dmso-S)][PF 6 ] 2 (3, [9]aneN 3 = 1,4,7-triazacyclo- nonane), is reported along with the X-ray crystal structure of 1. We investigated whether these com- plexes have photochemical properties which might make them suitable for use as pro-drugs in photochemotherapy. Complexes 1 and 2 underwent rapid (minutes) aquation with dissociation of the pyridine ligand in aqueous solution when irradiated with blue light (k = 420 or 467 nm). The photode- composition of 3 was much slower. All complexes readily formed adducts with 9-ethylguanine (9-EtG) when this model nucleobase was present in the photolysis solution. Similarly, complex 1 formed adducts with the tripeptide glutathione (GSH), but only when photoactivated. HPLC and MS studies of 1 showed that irradiation promoted rapid formation of 1:1 (major) and 1:2 (minor) adducts of the oligonucleotide d(ATACATGCTACATA) with the fragment {Ru([9]aneS 3 )(bpy)} 2+ . Density functional theory (DFT) calcula- tions and time-dependent DFT reproduced the major features of the absorption spectra and suggested that the lowest-lying triplet state with 3 MLCT character, which is readily accessible via intersystem cross- ing, might be responsible for the observed dissociative behavior of the excited states. These complexes are promising for further study as potential photochemotherapeutic agents.

With the aim of expanding the structure-activity relationship investigation, the series of Ru(II) half sandwich coordination compounds of the type [Ru([9]aneS3)(chel)(L)](n+) previously described by us (where [9]aneS3 is the neutral face-capping ligand 1,4,7-trithiacyclononane, chel is a neutral or anonic chelating ligand, L = Cl(-) or dmso-S, n = 0-2) was extended to 1,4,7-triazacyclononane ([9]aneN3). In addition, new neutral N-N, and anionic N-O and O-O chelating ligands, i.e. dach (trans-1,2-diaminocyclohexane), pic(-) (picolinate), and acac(-) (acetylacetonate), were investigated in combination with both [9]aneS3 and [9]aneN3. Overall, ten new half-sandwich complexes were prepared and fully characterized and their chemical behaviour in aqueous solution was established. The single-crystal X-ray structures of eight of them, including the versatile precursor [Ru([9]aneN3)(dmso-S)(2)Cl]Cl (9), were also determined. The results of in vitro antiproliferative tests performed on selected compounds against MDA-MB-231 human mammary carcinoma cells confirmed that, in this series, only compounds that hydrolyse the monodentate ligand at a reasonable rate show moderate activity, provided that the chelate ligand is a hydrogen bond donor.

The Ru(II) complex fac-[RuCl(dmso-S)(3)(dmso-O)(2)][PF(6)] (P2) was found to be an excellent precursor for the facile preparation in high yield of half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N)(2)][PF(6)] (e.g. (N)(2) = 1,2-diaminoethane (en, 4), trans-1,2-diaminocyclohexane (dach, 5), or 2 NH(3) (6)). Neutral half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N-O)] where N-O is an anionic chelating ligand (e.g. N-O = picolinate (pic, 7)) are best prepared from the universal Ru(II)-dmso precursor cis-[RuCl(2)(dmso)(4)] (P1). These complexes, that were fully characterized in solution and in the solid state, are structurally similar to the anticancer organometallic compounds [Ru(η(6)-arene)(chel)Cl][PF(6)](n) but, in place of a face-capping arene, have the fac-Ru(dmso-S)(3) fragment. In contrast to what observed for the corresponding arene compounds, that rapidly hydrolyze the Cl ligand upon dissolution in water, compounds 4-6 are very stable and inert in aqueous solution. Probably their inertness is the reason why they showed no significant cytotoxicity against the MDA-MB-231 cancer cell line.

The 1,4-disubstituted 1,2,3-triazole ligand prepared by click chemistry 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole (ppt) was investigated as novel chelating ligand for Ru(II) complexes with potential antitumor activity. The preparation and structural characterization, mainly by NMR spectroscopy in solution and by X-ray crystallography in the solid state, of four new Ru(II) complexes is reported: two isomeric Ru-dmso compounds, trans,cis-[RuCl(2)(dmso-S)(2)(ppt)] (1) and cis,cis-[RuCl(2)(dmso-S)(2)(ppt)] (2), and two half-sandwich Ru-[9]aneS(3) coordination compounds, [Ru([9]aneS(3))(dmso-S)(ppt)][CF(3)SO(3)](2) (3) and [Ru([9]aneS(3))Cl(ppt)][CF(3)SO(3)] (4). In all compounds ppt firmly binds to ruthenium in a bidentate fashion through the pyridyl nitrogen atom and the triazole N2, thus forming a puckered six-membered ring. The chemical behavior in aqueous solution of the water-soluble complexes 3 and 4 was studied by UV-Vis and NMR spectroscopy and compared to that of the previously described organometallic analogue [Ru(η(6)-p-cymene)Cl(ppt)][Cl] (5) in view of their potential antitumor activity. Compounds 3-5 were tested also in vitro for cytotoxic activity against two human cancer cell lines, one sensitive and one resistant to cisplatin, in comparison with cisplatin. Compound 4, the one that aquates faster, was found to be more cytotoxic than cisplatin against human lung squamose carcinoma cell line (A-549).

The conjugation of porphyrins to metal fragments is a strategy for making new compounds that are expected to combine the phototoxicity and the tumour-localization properties of the porphyrin chromophore with the cytotoxicity of the metal fragment for additive antitumour effect. We report here the preparation of new classes of porphyrin-ruthenium conjugates with potential bio-medical applications. Ruthenium was chosen because several Ru compounds have shown promising anticancer activity. The conjugation with the porphyrin moiety was accomplished either through peripheral pyridyl rings (e.g.meso-4'-tetrapyridylporphyrin, 4'TPyP) or through bpy units (e.g.meso-(p-bpy-phenyl)porphyrins, bpy(n)-PPs, n = 1-4). The number of Ru fragments attached to the porphyrins ranges from 1 to 4 and the total charge of the conjugates from -4 to +8. Different types of peripheral fragments, both Ru(III) and Ru(II), have been used: in some cases they are structurally similar to established anticancer compounds. Examples are [Na](4)[4'TPyP{trans-RuCl(4)(dmso-S)}(4)] (2), that bears four NAMI-type Ru(III) fragments, or [4'TPyP{Ru([9]aneS3)(en)}(4)][CF(3)SO(3)](8) (3) and [bpy(4)-PP{Ru([9]aneS3)(dmso-S)}(4)][CF(3)SO(3)](8) (9) (en = ethane-1,2-diamine, [9]aneS3 = 1,4,7-trithiacyclononane) that have four half-sandwich Ru(II) compounds. The Ru fragments may either contain one or more labile ligands, such as in 2 or in 9, or be coordinatively saturated and substitutionally inert, such as in 3 or in [bpy(4)-PP{Ru([12]aneS4)}(4)][CF(3)SO(3)](8) (11) ([12]aneS4 = 1,4,7,10-tetrathiacyclododecane). Most of the ruthenium-porphyrin conjugates described in this work are soluble--at least moderately--in aqueous solution and are thus suitable for biological investigations, in particular for cytotoxicity and photo-cytotoxicity tests.

The preparation, structural characterization, and chemical behavior in aqueous solution of a series of new Ru [9]aneS 3 half-sandwich complexes of the type [Ru([9]aneS 3 )Cl(N N)][CF 3 SO 3 ] and [Ru([9]aneS 3 )(dmso-S)(N N)][CF 3 SO 3 ] 2 ( 5 – 15 , N N = substituted bpy or 2 × 1-methylimidazole) are described. The X-ray structures of [Ru([9]aneS 3 )Cl(3,3′-H 2 dcbpy)][CF 3 SO 3 ] ( 9 ) (3,3′-H 2 dcbpy = 3,3′-dicarboxy-2,2′-bipyridine), [Ru([9]aneS 3 )Cl(4,4′-dmobpy)][CF 3 SO 3 ] ( 13 ) (4,4′-dmobpy = 4,4′-dimethoxy-2,2′-bipyridine), and [Ru([9]aneS 3 )Cl(1-MeIm) 2 ][CF 3 SO 3 ] ( 15 ) (1-MeIm = 1-methylimidazole) were also determined. The new compounds are structurally similar to anticancer-active organometallic half-sandwich complexes of formula [Ru(η 6 -arene)Cl(N N)][PF 6 ]. Three chloro compounds ( 5 , 9 , 15 ) were tested in vitro for cytotoxic activity against two human cancer cell lines in comparison with the previously described [Ru([9]aneS 3 )Cl(en)][CF 3 SO 3 ] ( 1 , en = ethylenediamine), [Ru([9]aneS 3 )Cl(bpy)][CF 3 SO 3 ] ( 2 ), and with their common dmso precursor [Ru([9]aneS 3 )Cl(dmso-S) 2 ][CF 3 SO 3 ] ( 3 ). Only the ethylenediamine complex 1 showed some antiproliferative activity, ca. one order of magnitude lower than the reference organometallic half-sandwich compound RM175 that contains biphenyl instead of [9]aneS 3 . This compound was further tested against a panel of human cancer cell lines (including one resistant to cisplatin).

We performed extensive studies on the kinetics of hydrolysis of a series of Ru(II)–dmso complexes containing dicarboxylate ligands, such as oxalate, malonate, succinate and 1,1-cyclobutane dicarboxylate (cbdc), derived from anticancer-active Ru(II)–dmso–Cl precursors. The in vitro antitumor activity of those compounds in comparison with their chloride precursors was evaluated against two tumor cell lines, the human KB oral carcinoma and the murine B16-F10 melanoma. The aim of this study was to assess how the nature of the anionic ligands (i.e. dicarboxylates vs. chlorides) affects the chemical behavior and the in vitro antitumor activity of Ru(II)–dmso complexes. Among the tested compounds only one complex, the dimer [fac-Ru(dmso-S)3(H2O)(μ-cbdc)]2 (5), exhibited moderate activity against both cell lines. Interestingly, this compound is the most kinetically stable in aqueous solution among those investigated. Despite the moderate in vitro activity, in an in vivo test, complex 5 exhibited no activity against both the primary tumor growth and the formation of spontaneous metastases on the MCa mammary carcinoma model.

Two ruthenium compounds, namely [ImH]trans-[RuCl4(Im)(dmso-S)] (NAMI-A, Im = imidazole) and [IndH] trans-[RuCl4(Ind)2] (KP1019, Ind = indazole) have already completed phase I clinical trials as anticancer agents. They both have properties different from platinum anticancer drugs: for example, NAMI-A is selectively active against metastases of solid tumors. They show that in the field of anticancer metal drugs a new approach, based on targeted therapies, is possible. After a concise history of ruthenium anticancer compounds, this contribution will focus on ruthenium-dmso complexes and, in particular, on NAMI-A. Particular emphasis is given on the challenges that are inherent to this field: how to develop new anticancer ruthenium compounds and how to select new active compounds that manifest their anticancer activity through non-conventional mechanisms.

With the aim of further developing the structure-activity relationship in biologically active half-sandwich Ru(ii)-[9]aneS(3) complexes ([9]aneS(3)=1,4,7-trithiacyclononane), a series of new mono- and dinuclear complexes bearing the chelating dicarboxylate ligands oxalate (ox), malonate (mal) and methylmalonate (mmal), have been synthesized and studied. Treatment of the precursor [Ru([9]aneS(3))(dmso)(3)][CF(3)SO(3)](2) (7) with equivalent amounts of K(2)(dicarb) afforded the corresponding neutral complexes with the general formula [Ru([9]aneS(3))(dmso-S)(eta(2)-dicarb)] (where dicarb=ox (1), mal (2) and mmal (3)), while using half an equivalent of K(2)(ox), the symmetric dimer [{Ru([9]aneS(3))(dmso-S)}(2)(mu-eta(4)-ox)][CF(3)SO(3)](2) (4) was isolated. The reaction of with the oxalato complex fac-[Ru(dmso-S)(3)(dmso-O)(eta(2)-ox)] (9) yielded two asymmetric dimers, namely [{Ru([9]aneS(3))(dmso-S)}(mu-eta(4)-ox){fac-Ru(dmso-S)(3)(CF(3)SO(3))}][CF(3)SO(3)] (5) and [{Ru([9]aneS(3))(dmso-S)}(mu-eta(4)-ox){fac-Ru(dmso-S)(3)(dmso-O)}][CF(3)SO(3)](2) (6), depending on the reaction conditions. All new complexes were structurally characterized, both in solution (by NMR spectroscopy) and in the solid state (by X-ray crystallography). The chemical behavior of the complexes in aqueous solution was studied by UV-Vis and NMR spectroscopy in view of their potential antitumor activity: the monomers partially release a dmso ligand to yield the monofunctional aqua adduct [Ru([9]aneS(3))(eta(2)-dicarb)(H(2)O)], while the dimers rapidly open up the oxalato bridge to give two mononuclear fragments. Splitting of the asymmetric dimers 5 and 6 occurs selectively and the ox moiety remains bonded to the fac-Ru(dmso-S)(3) fragment. A detailed comparison of the structural and chemical features of 1-6 with those of similar dicarboxylate complexes possessing the fac-Ru(dmso-S)(3) fragment in place of Ru([9]aneS(3)) allows us to draw a number of general conclusions on the binding preferences of dicarb ligands on the octahedral Ru(II) center.

The development of new metal anticancer compounds is a challenge for inorganic chemists. We have to face the fact that four decades of research in this field have only produced a small number of clinically used compounds, most often developed through serendipity rather than through rational chemical design. Nevertheless, by virtue of the wealth of knowledge acquired in these years, medicinal inorganic chemistry is probably mature for making significant steps forward and there are great expectations for future developments. With the aim of contributing to the rationalization of this field, we suggest here a categorization of metal anticancer compounds into five classes based on their mode of action: (i) the metal has a functional role, i.e. it must bind to the biological target; (ii) the metal has a structural role, i.e. it is instrumental in determining the shape of the compound and binding to the biological target occurs through non-covalent interactions; (iii) the metal is a carrier for active ligands that are delivered in vivo; (iv) the metal compound is a catalyst; and (v) the metal compound is photoactive and behaves as a photo-sensitizer. Selected examples for each category are given. The few metal anticancer drugs that are in clinical use are all believed to be functional compounds. Our classification, that is clearly focused on the metal compound and is independent from the nature of its bio-target(s)-most often still unknown-has the purpose of providing an intellectual tool that might be helpful in the rational development of new drugs.

The 1,1-cyclobutane dicarboxylate ligand (cbdc), that normally binds to metal centres as a chelate (eta(2)-cbdc-O,O'), prefers to bind in an unprecedented bridging fashion (micro-cbdc-O,O') on cationic Ru(ii) centres bearing ancillary ligands (e.g. H(2)O, NH(3)) capable of making intramolecular H-bonds with the non-coordinated oxygen atoms of the carboxylate groups. Thus, the thermodynamic product of the reaction between cis,fac-[RuCl(2)(dmso-S)(3)(dmso-O)]() and cbdc in a number of different reaction conditions is the dinuclear species with two bridging cbdc units fac-[Ru(micro-cbdc-O,O')(dmso-S)(3)(H(2)O)](2) (2). Similarly, reaction of cis,fac-[RuCl(2)(dmso-S)(3)(NH(3))] (3) with cbdc yielded the corresponding dinuclear species fac-[Ru(micro-cbdc-O,O')(dmso-S)(3)(NH(3))](2) (4), in which ammonia occupies the position of the water molecule in 2. Both dinuclear species 2 and 4 were characterized by X-ray crystallography and have an anti geometry with respect to the H(2)O or NH(3) ligands. The results from the X-ray studies are consistent with the NMR spectroscopic data, indicating that the dinuclear structures observed in the solid state are maintained in solution. The mononuclear anionic complex with a chelating cbdc unit, K{fac-[RuCl(eta(2)-cbdc-O,O')(dmso-S)(3)]}(5), was isolated under appropriate conditions form the reaction of 1 with K(2)(cbdc) and was demonstrated to be an intermediate in the formation of 2.