Carbonyl Derivatives of Chloride-Dimethyl Sulfoxide-Ruthenium(II) Complexes: Synthesis, Structural Characterization, and Reactivity of Ru(CO)x(DMSO)4-xCl2 Complexes (x = 1-3)

Precise Identification of the Dimethyl Sulfoxide Triggered Tricarbonyldichlororuthenium(II) Dimer for Releasing CO

Low concentrations of carbon monoxide (CO) can play vital roles in pharmacological and physiological functions in the human body. The transition-metal carbonyl complexes of the tricarbonyldichlororuthenium(II) dimer [Ru₂(CO)₆Cl₄ (CORM-2)] were proposed as CO-releasing molecules (CORMs) to improve the delivery efficiency of CO for therapeutic effects. The accurate identification of final products for CORMs in solution and the detailed mechanisms of the release of CO were the essential prerequisite for its effective physiological application, which have been deficient. In this study, utilizing the cutting-edge two-dimensional (2D) IR spectroscopy, with the intrinsic vibrational modes and the coupling information on dynamics of intramolecular vibrational energy redistribution (IVR), the final products of A, B, C, and E are accurately identified when CORM-2 is dissolved in dimethyl sulfoxide (DMSO). Furthermore, with the clues on intermolecular interaction and chemical exchange dynamics between different products, the transformations between different products are also directly characterized for the first time. These findings challenge the results from the classic 1D spectroscopic pattern, and they evidently demonstrated that the release of CO from CORM-2 in DMSO was slow and complicated with multiple reaction pathways. Combining with DFT simulations, the detailed mechanisms of release of CO for CORM-2 dissolved in DMSO are schematically proposed, which can significantly contribute to its drug optimization and pharmacological as well as physiological applications.

Rare Example of Stereoisomeric 2 + 2 Metallacycles of Porphyrins Featuring Chiral-at-Metal Octahedral Ruthenium Corners

In this paper, we describe three new stereoisomers of the already known 2 + 2 metallacycle of porphyrins [ trans, cis, cis-RuCl₂(CO)₂(4' cisDPyP)]₂ (2, 4' cisDPyP = 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin), namely [{ trans,cis,cis-RuCl₂(CO)₂}(4' cisDPyP)₂{ cis,cis,cis-RuCl₂(CO)₂}] (14) and [ cis,cis,cis-RuCl₂(CO)₂(4' cisDPyP)]₂ (15), in which the chiral { cis,cis,cis-RuCl₂(CO)₂} fragment has either a C or A handedness. The least abundant 15 exists as a mixture of two stereoisomers defined as alternate (15_alt, both porphyrins are trans to a Cl and a CO) and pairwise (15_pw, one porphyrin is trans to two chlorides and the other to two carbonyls), each one as a statistical mixture of meso ( AC) and racemic ( AA and CC) diastereomers. Remarkably, both 14 and 15 are-to the best of our knowledge-unprecedented examples of 2D metallacycles with octahedral chiral-at-metal connectors, and 14 is the first example of a 2 + 2 molecular square with stereoisomeric Ru(II) corners. Whereas 2 is selectively obtained by treatment of trans,cis,cis-RuCl₂(CO)₂(dmso-O)₂ (1) with 4' cisDPyP, 14 and 15 were obtained, together with 2 (major product), using stereoisomers of 1, either cis,cis,trans-RuCl₂(CO)₂(dmso-S)₂ (5) or cis,cis,cis-RuCl₂(CO)₂(dmso)₂ (6), as precursors. From a general point of view, this work demonstrates that-even for the smallest 2 + 2 metallacycle and using a symmetric organic linker-several stereoisomers can be generated when using octahedral metal connectors of the type {MA₂B₂} that are not stereochemically rigid. As a proof-of-concept, it also opens the way to new-even though challenging-opportunities: unprecedented and yet unexplored chiral metallosupramolecular assemblies can be obtained and eventually exploited (e.g., for supramolecular catalysis) by using stereogenic octahedral metal connectors amenable to become chiral centers.

Ru(ii)-Peptide bioconjugates with the cppH linker (cppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid): synthesis, structural characterization, and different stereochemical features between organic and aqueous solvents

Three new Ru(ii) bioconjugates with the C-terminal hexapeptide sequence of neurotensin, RRPYIL, namely trans,cis-RuCl2(CO)2(cppH-RRPYIL-κNp) (7), [Ru([9]aneS3)(cppH-RRPYIL-κNp)(PTA)](Cl)2 (8), and [Ru([9]aneS3)Cl(cppH-RRPYIL-κNp)]Cl (11), where cppH is the asymmetric linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid, were prepared in pure form and structurally characterized in solution. The cppH linker is capable of forming stereoisomers (i.e. linkage isomers), depending on whether the nitrogen atom ortho (No) or para (Np) to the carboxylate on C4 in the pyrimidine ring binds the metal ion. Thus, one of the aims of this work was to obtain pairs of stereoisomeric conjugates and investigate their biological (anticancer, antibacterial) activity. A thorough NMR characterization clearly indicated that in all cases exclusively Np conjugates were obtained in pure form. In addition, the NMR studies showed that, whereas in DMSO-d6 each conjugate exists as a single species, in D2O two (7) or even three if not four (8 and 11) very similar stable species form (each one corresponding to an individual compound). Similar results were observed for the cppH-RRPYIL ligand alone. Overall, the NMR findings are consistent with the occurrence of a strong intramolecular stacking interaction between the phenol ring of tyrosine and the pyridyl ring of cppH. Such stacking interactions between aromatic rings are expected to be stronger in water. This interaction leads to two stereoisomeric species in the free cppH-RRPYIL ligand and in the bioconjugate 7, and is somehow modulated by the less symmetrical Ru coordination environments in 8 and 11, affording three to four very similar species.

A contribution to the rational design of Ru(CO)3Cl2L complexes for in vivo delivery of CO

A few ruthenium based metal carbonyl complexes, e.g. CORM-2 and CORM-3, have therapeutic activity attributed to their ability to deliver CO to biological targets. In this work, a series of related complexes with the formula [Ru(CO)3Cl2L] (L = DMSO (3), L-H3CSO(CH2)2CH(NH2)CO2H) (6a); D,L-H3CSO(CH2)2CH(NH2)CO2H (6b); 3-NC5H4(CH2)2SO3Na (7); 4-NC5H4(CH2)2SO3Na (8); PTA (9); DAPTA (10); H3CS(CH2)2CH(OH)CO2H (11); CNCMe2CO2Me (12); CNCMeEtCO2Me (13); CN(c-C3H4)CO2Et) (14)) were designed, synthesized and studied. The effects of L on their stability, CO release profile, cytotoxicity and anti-inflammatory properties are described. The stability in aqueous solution depends on the nature of L as shown using HPLC and LC-MS studies. The isocyanide derivatives are the least stable complexes, and the S-bound methionine oxide derivative is the more stable one. The complexes do not release CO gas to the headspace, but release CO2 instead. X-ray diffraction of crystals of the model protein Hen Egg White Lysozyme soaked with 6b (4UWN) and 8 (4UWN) shows the addition of Ru(II)(CO)(H2O)4 at the His15 binding site. Soakings with 7(4UWN) produced the metallacarboxylate [Ru(COOH)(CO)(H2O)3](+) bound to the His15 site. The aqueous chemistry of these complexes is governed by the water-gas shift reaction initiated with the nucleophilic attack of HO(-) on coordinated CO. DFT calculations show this addition to be essentially barrierless. The complexes have low cytotoxicity and low hemolytic indices. Following i.v. administration of CORM-3, the in vivo bio-distribution of CO differs from that obtained with CO inhalation or with heme oxygenase stimulation. A mechanism for CO transport and delivery from these complexes is proposed.

(15)N NMR spectroscopy unambiguously establishes the coordination mode of the diimine linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH) in Ru(ii) complexes

We investigated the reactivity of three Ru(ii) precursors -trans,cis,cis-[RuCl2(CO)2(dmso-O)2], cis,fac-[RuCl2(dmso-O)(dmso-S)3], and trans-[RuCl2(dmso-S)4] - towards the diimine linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH) or its parent compound 4-methyl-2-(2'-pyridyl)pyrimidine ligand (mpp), in which a methyl group replaces the carboxylic group on the pyrimidine ring. In principle, both cppH and mpp can originate linkage isomers, depending on how the pyrimidine ring binds to ruthenium through the nitrogen atom ortho (N(o)) or para (N(p)) to the group in position 4. The principal aim of this work was to establish a spectroscopic fingerprint for distinguishing the coordination mode of cppH/mpp also in the absence of an X-ray structural characterization. By virtue of the new complexes described here, together with the others previously reported by us, we successfully recorded {(1)H,(15)N}-HMBC NMR spectra at natural abundance of the (15)N isotope on a consistent number of fully characterized Ru(ii)-cppH/mpp compounds, most of them being stereoisomers and/or linkage isomers. Thus, we found that (15)N NMR chemical shifts unambiguously establish the binding mode of cppH and mpp - either through N(o) or N(p)- and can be conveniently applied also in the absence of the X-ray structure. In fact, coordination of cppH to Ru(ii) induces a marked upfield shift for the resonance of the N atoms directly bound to the metal, with coordination induced shifts (CIS) ranging from ca.-45 to -75 ppm, depending on the complex, whereas the unbound N atom resonates at a frequency similar to that of the free ligand. Similar results were found for the complexes of mpp. This work confirmed our previous finding that cppH has no binding preference, whereas mpp binds exclusively through N(p). Interestingly, the two cppH linkage isomers trans,cis-[RuCl2(CO)2(cppH-κN(p))] (5) and trans,cis-[RuCl2(CO)2(cppH-κN(o))] (6) were easily obtained in pure form by exploiting their different solubility properties.

The emergence of sulfoxides as efficient ligands in transition metal catalysis

Sulfoxides are capable of forming stable complexes with transition metals and there have been many comprehensive studies into their binding properties. However, the use of sulfoxides, particularly chiral sulfoxides, as ligands in transition metal catalysis is rather less well developed. This review aims to describe these catalytic studies and covers new developments that are showing very promising results and that have led to a renewed interest in this field.

Uncoupling charge movement from channel opening in voltage-gated potassium channels by ruthenium complexes

The Kv2.1 channel generates a delayed-rectifier current in neurons and is responsible for modulation of neuronal spike frequency and membrane repolarization in pancreatic β-cells and cardiomyocytes. As with other tetrameric voltage-activated K(+)-channels, it has been proposed that each of the four Kv2.1 voltage-sensing domains activates independently upon depolarization, leading to a final concerted transition that causes channel opening. The mechanism by which voltage-sensor activation is coupled to the gating of the pore is still not understood. Here we show that the carbon-monoxide releasing molecule 2 (CORM-2) is an allosteric inhibitor of the Kv2.1 channel and that its inhibitory properties derive from the CORM-2 ability to largely reduce the voltage dependence of the opening transition, uncoupling voltage-sensor activation from the concerted opening transition. We additionally demonstrate that CORM-2 modulates Shaker K(+)-channels in a similar manner. Our data suggest that the mechanism of inhibition by CORM-2 may be common to voltage-activated channels and that this compound should be a useful tool for understanding the mechanisms of electromechanical coupling.

Exploring the antimicrobial action of a carbon monoxide-releasing compound through whole-genome transcription profiling of Escherichia coli

We recently reported that carbon monoxide (CO) has bactericidal activity. To understand its mode of action we analysed the gene expression changes occurring when Escherichia coli, grown aerobically and anaerobically, is treated with the CO-releasing molecule CORM-2 (tricarbonyldichlororuthenium(II) dimer). Microarray analysis shows that the E. coli CORM-2 response is multifaceted, with a high number of differentially regulated genes spread through several functional categories, namely genes involved in inorganic ion transport and metabolism, regulators, and genes implicated in post-translational modification, such as chaperones. CORM-2 has a higher impact in E. coli cells grown anaerobically, as judged by the repression of genes belonging to eight functional classes which are not seen in the response of aerobically CORM-2-treated cells. The biological relevance of the variations caused by CORM-2 was substantiated by studying the CORM-2 sensitivity of selected E. coli mutants. The results show that the deletion of redox-sensing regulators SoxS and OxyR increased the sensitivity to CORM-2 and suggest that while SoxS plays an important role in protection against CORM-2 under both growth conditions, OxyR seems to participate only in the aerobic CORM-2 response. Under anaerobic conditions, we found that the heat-shock proteins IbpA and IbpB contribute to CORM-2 defence since the deletion of these genes increases the sensitivity of the strain. The induction of several met genes and the hypersensitivity to CORM-2 of the ΔmetR, ΔmetI and ΔmetN mutant strains suggest that CO has effects on the methionine metabolism of E. coli. CORM-2 also affects the transcription of several E. coli biofilm-related genes and increases biofilm formation in E. coli. In particular, the absence of tqsA or bhsA increases the resistance of E. coli to CORM-2, and deletion of tsqA leads to a strain that has lost its capacity to form biofilm upon treatment with CORM-2. In spite of the relatively stable nature of the CO molecule, our results show that CO is able to trigger a significant alteration in the transcriptome of E. coli which necessarily has effects in several key metabolic pathways.

Sulfoxide as a ligand in iron(II) porphyrinates: S- or O-bound?

In order to study the bonding of sulfoxides to iron(II) porphyrinates, an equilibrium study of Fe(TPP) with tetramethylenesulfoxide (TMSO) has been performed. UV-vis spectra at different concentrations of TMSO have shown distinct character belonging to three species: four-coordinate Fe(II)(TPP), five-coordinate [Fe(II)(TPP)(TMSO)], and six-coordinate [Fe(II)(TPP)(TMSO)2]. The isosbestic points for the low TMSO concentrations suggest that the equilibrium constant K1 is much larger than K2. Analysis of spectral data by the nonlinear least-squares program SQUAD gives K1 = 267 and K2 approximately 1. Even though the five-coordinate species is the dominant species under the synthetic conditions, only the six-coordinate species was crystallized and characterized by an X-ray diffraction study. [Fe(TPP)(TMSO)2] (C52H44Fe-N4O2S2): monoclinic, P2(1)/c, a = 11.2580(3) A, b = 15.9262(5) A, c = 12.3930(4) A, beta = 116.246(1) degrees , V = 1992.95(10) A3, Z = 2. X-ray crystallography demonstrates the complex is a low-spin bis-TMSO ligated species. The average Fe-Np distance is 1.999(4) A. The most important feature is that TMSO is coordinated to iron(II) by the sulfur donors, not oxygen. The Fe-S distance is 2.2220(3) A.

fac-{Ru(CO)3}2+-Core Complexes and Design of Metal-Based Drugs. Synthesis, Structure, and Reactivity of Ru−Thiazole Derivative with Serum Proteins and Absorption−Release Studies with Acryloyl and Silica Hydrogels as Carriers in Physiological Media

The reaction of [Ru2(CO)6Cl4], 1, with excess THZ (1,3-thiazole) in absolute ethanol at 55 degrees C produces fac-[Ru(CO)3Cl2(THZ)], 2, in high yield. [Ru(CO)2Cl2(THZ)2], 3, is formed at higher temperature (ca 70 degrees C) and higher concentration of THZ. The X-ray structures of the new compounds have been determined, and density functional studies performed at the hybrid B3LYP/(Lanl2DZ, Ru; 6-311+G**, CHClNOS) level allowed the estimation of the structures of several conformers as well as that of their relative total electronic energies. Compound 2 is soluble (slowly) in aqueous media, where it reacts with the transport proteins bovine serum albumin (BSA) and human apotransferrin (HTF), and at a lower extent with calf thymus DNA (CT-DNA) and with guanosine-5'-monophosphate (GMP). The complex molecule is adsorbed by certain synthetic acryloyl polymers that have terminal carboxylate functions and is embedded in silica gels when these latter are prepared in the presence of a solution of 2. Ruthenium species are slowly released from the loaded gels into physiological solutions at pH 7.4. The reactivity of 2 with biomolecules and synthetic hydrogels makes it a compound of interest for anticancer and antimetastases tests.

Therapeutic applications of carbon monoxide-releasing molecules

Carbon monoxide (CO), which is formed in mammalian cells through the oxidation of haem by the enzyme haem oxygenase, actively participates in the regulation of key intracellular functions. Emerging evidence reveals that an increased generation of haem oxygenase-derived CO plays a critical role in the resolution of inflammatory processes and alleviation of cardiovascular disorders. The authors have identified a novel class of substances, CO-releasing molecules (CO-RMs), which are capable of exerting a variety of pharmacological activities via the liberation of controlled amounts of CO in biological systems. A wide range of CO carriers containing manganese (CORM-1), ruthenium (CORM-2 and -3), boron (CORM-A1) and iron (CORM-F3) are currently being investigated to tailor therapeutic approaches for the prevention of vascular dysfunction, inflammation, tissue ischaemia and organ rejection.

Carbon monoxide inhibits endothelin-1 release by human pulmonary artery smooth muscle cells

Endothelin-1 is a potent vasoconstrictor with mitogenic properties. This 21-amino-acid protein, released in the vasculature by endothelial and smooth muscle cells, has been implicated in pulmonary hypertension. More recently, evidence has accumulated for a role of the heme oxygenase system in pulmonary hypertension. Heme oxygenase catalyses the breakdown of heme to produce carbon monoxide, biliverdin and free iron. Here we show that a carbon monoxide-releasing molecule, but not biliverdin, inhibits endothelin-1 release from serum-stimulated human pulmonary artery smooth muscle cells. Under certain conditions, carbon monoxide appears to act as an endogenous break on endothelin-1 release.

Heme oxygenase is expressed in human pulmonary artery smooth muscle where carbon monoxide has an anti-proliferative role

Heme oxygenase is the rate-limiting enzyme in the catabolism of heme to carbon monoxide, bilirubin and free iron. Many cell types express heme oxygenase-2 constitutively while heme oxygenase-1 is induced at sites of inflammation and oxidative stress. In systemic blood vessels, carbon monoxide may have an important homeostatic role where, like its better-studied counterpart nitric oxide, it is emerging as a vasodilator and an inhibitor of proliferation. However, much less is known regarding the role of heme oxygenase and carbon monoxide in the pulmonary circulation where vascular responses are very different. Here, using primary cultures of human pulmonary artery smooth muscle cells, we present novel data showing that this cell type expresses heme oxygenase-2 constitutively and, in the presence of oxidants, can induce heme oxygenase-1. We also show that the carbon monoxide-releasing molecule, tricarbonyldichlororuthenium (II) dimer, potently and profoundly inhibits proliferation of human pulmonary artery smooth muscle cells. Pulmonary hypertension is a disease characterised by abnormal vascular smooth muscle cell growth and remodelling of the pulmonary vasculature. Our observations support the growing evidence that the heme oxygenase/carbon monoxide system may play a role in the pathology of pulmonary hypertension.

Carbon monoxide-releasing molecules: characterization of biochemical and vascular activities

Carbon monoxide (CO) is generated in living organisms during the degradation of heme by the enzyme heme oxygenase, which exists in constitutive (HO-2 and HO-3) and inducible (HO-1) isoforms. Carbon monoxide gas is known to dilate blood vessels in a manner similar to nitric oxide and has been recently shown to possess antiinflammatory and antiapoptotic properties. We report that a series of transition metal carbonyls, termed here carbon monoxide-releasing molecules (CO-RMs), liberate CO to elicit direct biological activities. Specifically, spectrophotometric and NMR analysis revealed that dimanganese decacarbonyl and tricarbonyldichlororuthenium (II) dimer release CO in a concentration-dependent manner. Moreover, CO-RMs caused sustained vasodilation in precontracted rat aortic rings, attenuated coronary vasoconstriction in hearts ex vivo, and significantly reduced acute hypertension in vivo. These vascular effects were mimicked by induction of HO-1 after treatment of animals with hemin, which increases endogenously generated CO. Thus, we have identified a novel class of compounds that are useful as prototypes for studying the bioactivity of CO. In the long term, transition metal carbonyls could be utilized for the therapeutic delivery of CO to alleviate vascular- and immuno-related dysfunctions. The full text of this article is available at http://www.circresaha.org.