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Iron(II) and Ru(II) half-sandwich compounds encompass some promising pre-clinical anticancer agents whose efficacy may be tuned by structural modification of the coordinated ligands. Here, we combine two such bioactive metal centres in cationic bis(diphenylphosphino)alkane-bridged heterodinuclear [Fe2+, Ru2+] com-plexes to delineate how ligand structural variations modulate compound cytotoxicity. Specifically, Fe(II) complexes of the type [(eta(5)-C5H5)Fe(CO)(2)(kappa(1)-PPh2(CH2)(n)PPh2)]{PF6} (n = 1-5), compounds 1-5, and heterodinuclear [Fe2+, Ru2+] complexes, [(eta(5)-C5H5)Fe(CO)(2)(mu-PPh2(CH2)nPPh(2)))(eta(6)-p-cymene)RuCl2]{PF6} (n = 2-5) (compounds 7-10), were synthesized and characterised. The mononuclear complexes were moderately cytotoxic against two ovarian cancer cell lines (A2780 and cisplatin resistant A2780cis) with IC50 values ranging from 2.3 +/- 0.5 mu M to 9.0 +/- 1.4 mu M. For 7-10, the cytotoxicity increased with increasing Fe center dot center dot center dot Ru distance, consistent with their DNA affinity. UV-visible spectroscopy suggested the chloride ligands in heterodinuclear 8-10 undergo stepwise substitution by water on the timescale of the DNA interaction experiments, probably affording the species [RuCl(OH2)(eta(6)-p-cymene)(PRPh2)](2+) and [Ru(OH)(OH2)(eta(6)-p-cymene)(PRPh2)](2+) (where PRPh2 has R = [-(CH2)(5)PPh2-Fe(C5H5)(CO)(2)](+)). One interpretation of the combined DNA-interaction and kinetic data is that the mono(aqua) complex may interact with dsDNA through nucleobase coordination. Heterodinuclear 10 reacts with glutathione (GSH) to form stable mono-and bis(thiolate) adducts, 10-SG and 10-SG(2), with no evidence of metal ion reduction (k(1) = 1.07 +/- 0.17 x 10(-1) min(-1) and k(2) = 6.04 +/- 0.59 x 10-3 min(-1) at 37 degrees C). This work highlights the synergistic effect of the Fe2+/Ru2+ centres on both the cytotoxicity and biomolecular interactions of the present heterodinuclear complexes.

A series of bioactive molecules were synthesized from the condensation of aspirin or chlorambucil with terminal alkynes bearing alcohol or amine substituents. Insertion of the resulting alkynes into the iron-carbyne bond of readily accessible diiron bis(cyclopentadienyl) mu-aminocarbyne complexes, [1a,b]CF3SO3, afforded novel diiron complexes with a bridging vinyliminium ligand, [2-10]CF3SO3, functionalized with a bioactive moiety. All compounds were characterized by elemental analysis and IR and multinuclear NMR spectroscopy and in three cases by single-crystal X-ray diffraction. Moreover, the D2O solubility, stability in D2O and cell culture media, and octanol-water partition coefficients of diiron complexes were determined spectroscopically. The cytotoxicity of the complexes was assessed in the tumorigenic A2780 and A2780cisR and the nontumorigenic HEK 293T cell lines. Some complexes exhibit high potency and the ability to overcome resistance in A2780cisR cells (aspirin complexes) or high selectivity relative to HEK 293T cells (chlorambucil complexes). Further studies indicate that the complexes significantly trigger intracellular ROS production, irrespective of the nature of the bioactive fragment. DNA alkylation and protein binding studies were also undertaken.

We have recently reported a series of half-sandwich ruthenium(ii) complexes with curcuminoid ligands showing excellent cytotoxic activities (particularly ionic derivatives containing PTA (PTA = 1,3,5-triaza-7-phosphaadamantane). In the present study, new members of this family of compounds have been prepared with the objective to investigate the effect of a long hydrophobic chain obtained by replacing the OH-groups, present in curcumin and bisdemethoxycurcumin, with the palmitic acid ester. We report the synthesis of ruthenium(ii) and osmium(ii) p-cymene derivatives containing palmitic acid curcumin ester ligands ((1E,3Z,6E)-3-hydroxy-5-oxohepta-1,3,6-triene-1,7-diyl)bis(2-methoxy-4,1-phenylene)dipalmitate (p-curcH) and ((1E,3Z,6E)-3-hydroxy-5-oxohepta-1,3,6-triene-1,7-diyl)bis(4,1-phenylene)dipalmitate (p-bdcurcH). Complexes [M(ii)(cym)(p-curc)/(p-bdcurc)(Cl)] 1-4 (M = Ru or Os) are neutral, whereas [M(ii)(cym)(p-curc)/(p-bdcurc)(PTA)][SO3CF3] 5-8 are salts obtained when the chloride ligand is replaced by the PTA ligand. Stability studies performed on 1-8 in DMSO-PBS under physiological conditions (pH = 7.4) indicate that the complexes remain intact. The complexes exhibit potent and selective cytotoxic activity against an ovarian carcinoma cell line and its cisplatin-resistant form (A2780 and A2780cis), and non-cancerous human embryonic kidney (HEK293T) cells. To define the structure-activity relationships (SAR), the compounds have been compared with other Ru(ii) and Os(ii) complexes with curcuminoid ligands previously reported. SAR data reveal that the bisdemethoxycurcumin complexes are generally more active and selective than analogous curcumin-containing complexes.

The reactions of the dimeric complexes [RuX

Four bipyridine-Type ligands variably derivatized with two bioactive groups (taken from ethacrynic acid, flurbiprofen, biotin, and benzylpenicillin) were prepared via sequential esterification steps from commercial 2,2′-bipyridine-4,4′-dicarboxylic acid and subsequently coordinated to ruthenium(II) p-cymene and iridium(III) pentamethylcyclopentadienyl scaffolds. The resulting complexes were isolated as nitrate salts in high yields and fully characterized by analytical and spectroscopic methods. NMR and MS studies in aqueous solution and in cell culture medium highlighted a substantial stability of ligand coordination and a slow release of the bioactive fragments in the latter case. The complexes were assessed for their antiproliferative activity on four cancer cell lines, showing cytotoxicity to the low micromolar level (equipotent with cisplatin). Additional biological experiments revealed a multimodal mechanism of action of the investigated compounds, involving DNA metalation and enzyme inhibition. Synergic effects provided by specific combinations of metal and bioactive fragments were identified, pointing toward an optimal ethacrynic acid/flurbiprofen combination for both Ru(II) and Ir(III) complexes.

Two pyrazole-based ligands bearing a pyridine moiety, 3-methyl-1-(pyridin-2-yl)-5-pyrazolone (HLpy), and 3-methyl-1-(pyridin-2-yl)-4-trifluoroacetyl-5-pyrazolone (HQpy,CF3), were prepared and fully characterized in the solid-state and the tautomerism of both ligands in solution was also rationalized by using Density Functional Theory. Neutral ruthenium(II) arene complexes of composition [Ru(arene)(Lpy)Cl] and [Ru(arene)(Qpy,CF3)Cl] [arene = p-cymene (cym) or hexamethylbenzene (hmb)]) were synthesized and characterized by IR, 1H, 13C, 15N and 19F NMR spectroscopy, elemental analysis and ESI mass spectrometry. The structures of complexes [Ru(hmb)(Lpy)Cl] and [Ru(hmb)(Qpy,CF3)Cl] were determined by X-ray crystallography, showing κ2-N,N’-coordination not only for Lpy but also for Qpy,CF3 ligand. DFT studies confirm that κ2O,O’-coordination, generally observed in metal complexes with 4-acyl-5-pyrazolone ligands, is not favored in this case. The cytotoxicity of ligands and complexes was evaluated against human ovarian carcinoma cells (A2780 and A2780cisR, cisplatin sensitive and cisplatin-resistant, respectively), and non-tumorous human embryonic kidney SV40 transformed (HEK293T) cells to reveal essentially equivalent activity in the cisplatin sensitive and cisplatin-resistant ovarian carcinoma cells.

Ruthenium(II) complexes with a three-legged piano-stool structure based on an arene ring, an N-heterocyclic carbene (NHC)-carbene ligand with a peracetylated glucose moiety and two chlorides or one bidentate ligand, were prepared and characterized by spectroscopy and crystallography. In one case, the sugar substituent is replaced by an ethyl. The chirality of the sugar results in the formation of two diastereomers that interconvert through rotations around the Ccarbene-Ru and Carene-Ru bonds. In water, the complexes undergo a series of equilibrium hydrolysis steps involving the Ru-Cl bonds. The Ru- arene bond and the sugar acetyls are also partially hydrolyzed, and the selectivity of the process is governed by the nature of the arene and the pH of the solution. The reactivity of the compounds was studied against model nucleophiles and biological macromolecules. In the former case, mass experiments demonstrated a variety of binding modes with a trend reflecting the stability in aqueous environment. In the latter case, protein crystallography was used to characterize the preferential binding sites of one of the complexes. The X-ray structure of the adduct formed upon reaction of one representative complex with hen egg white lysozyme contains a Ru center, which retains the carbene ligand, close to the side chain of Asp119. In the adduct with bovine pancreatic ribonuclease, there are two protein molecules in the asymmetric unit. In one molecule, two Ru centers are located close to the side chains of His105 and of His119, which is the protein active site. In the second molecule, only one Ru center was found in the proximity of the side chain of His105. The Ru complexes also interact with calf-thymus DNA, although without displacing the intercalating probe EB. Finally, the complexes are essentially inactive against the human ovarian carcinoma A2780 cells, the cisplatin-resistant A2780cis cells, and the human embryonic kidney HEK293T cells.