Catalytic Activity of Bis-phosphine Ruthenium(II)−Arene Compounds: Structure−Activity Correlations

Fine-tuning the cytotoxicity of ruthenium(II) arene compounds to enhance selectivity against breast cancers

Ruthenium-based complexes have been suggested as promising anticancer drugs exhibiting reduced general toxicity compared to platinum-based drugs. In particular, Ru(η6-arene)(PTA)Cl2 (PTA = 1,3,5-triaza-7-phosphaadamantane), or RAPTA, complexes have demonstrated efficacy against breast cancer by suppressing metastasis, tumorigenicity, and inhibiting the replication of the human tumor suppressor gene BRCA1. However, RAPTA compounds have limited cytotoxicity, and therefore comparatively high doses are required. This study explores the activity of a series of RAPTA-like ruthenium(II) arene compounds against MCF-7 and MDA-MB-231 breast cancer cell lines and [Ru(η6-toluene)(PPh3)2Cl]+ was identified as a promising candidate. Notably, [Ru(η6-toluene)(PPh3)2Cl]Cl was found to be remarkably stable and highly cytotoxic, and selective to breast cancer cells. The minor groove of DNA was identified as a relevant target.

Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl2(η6-arene)(P)] and cationic [Rh(PP)2]X (X = anion; P and PP = mono- and bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features.

Zinc-catalyzed regioselective C–P coupling of p-quinol ethers with secondary phosphine oxides to afford 2-phosphinylphenols

A highly regioselective C–P coupling reaction of p-quinol ethers with secondary phosphine oxides is developed as a new synthesis method for 2-phosphinylphenols by using Zn(OTf)₂ as the catalyst.

Charge-tagged ligands: useful tools for immobilising complexes and detecting reaction species during catalysis

A critical overview is presented on the use of charged tagged ligands (CTLs) as immobilising agents in organometallic catalysis and as probes for studying mechanisms through electrospray ionisation mass spectrometry (ESI-MS) based on the most recent literature.

In recent years, charge-tagged ligands (CTLs) have become valuable tools in organometallic catalysis. Insertion of an ionic side chain into the molecular skeleton of a known ligand has become a useful protocol for anchoring ligands, and consequently catalysts, in polar and ionic liquid phases. In addition, the insertion of a cationic moiety into a ligand is a powerful tool that can be used to detect reaction intermediates in organometallic catalysis through electrospray ionisation mass spectrometry (ESI-MS) experiments. The insertion of an ionic tag ensures the charge in the intermediates independently of the ESI-MS. For this reason, these ligands have been used as ionic probes in mechanistic studies for several catalytic reactions. Here, we summarise selected examples on the use of CTLs as immobilising agents in organometallic catalysis and as probes for studying mechanisms through ESI-MS.

Somatostatin subtype-2 receptor-targeted metal-based anticancer complexes

Conjugates of a dicarba analogue of octreotide, a potent somatostatin agonist whose receptors are overexpressed on tumor cells, with [PtCl(2)(dap)] (dap = 1-(carboxylic acid)-1,2-diaminoethane) (3), [(η(6)-bip)Os(4-CO(2)-pico)Cl] (bip = biphenyl, pico = picolinate) (4), [(η(6)-p-cym)RuCl(dap)](+) (p-cym = p-cymene) (5), and [(η(6)-p-cym)RuCl(imidazole-CO(2)H)(PPh(3))](+) (6), were synthesized by using a solid-phase approach. Conjugates 3-5 readily underwent hydrolysis and DNA binding, whereas conjugate 6 was inert to ligand substitution. NMR spectroscopy and molecular dynamics calculations showed that conjugate formation does not perturb the overall peptide structure. Only 6 exhibited antiproliferative activity in human tumor cells (IC(50) = 63 ± 2 μM in MCF-7 cells and IC(50) = 26 ± 3 μM in DU-145 cells) with active participation of somatostatin receptors in cellular uptake. Similar cytotoxic activity was found in a normal cell line (IC(50) = 45 ± 2.6 μM in CHO cells), which can be attributed to a similar level of expression of somatostatin subtype-2 receptor. These studies provide new insights into the effect of receptor-binding peptide conjugation on the activity of metal-based anticancer drugs, and demonstrate the potential of such hybrid compounds to target tumor cells specifically.

(R,R(Fc),S(Ru))-Chlorido(η-p-cymene){1-[1-(diphenyl-phosphanyl)ethyl]-2-[2-(diphenyl-phosphanyl)phenyl]ferrocene-κP,P'}ruthenium(II) hexa-fluorido-phosphate

The asymmetric unit of the title compound, [FeRuCl(C₅H₅)(C₁₀H₁₄)(C₃₇H₃₁P₂)]PF₆, contains two independent, geometrically similar Ru^II complexes of a chiral ferrocenyldiphosphane with piano-stool coordination through the η⁶-bound p-cymene ligand, two chelating phospho­rus donor atoms, and an exo-oriented chloride ion. The mean bond lengths of the two Ru complexes are Ru—C = 2.276 Å, Ru—P = 2.3816 Å, and Ru—Cl = 2.3924 Å. Both chloride ligands form only intra­molecular C—H⋯Cl inter­actions. Seven weak inter­molecular C—H⋯F inter­actions involving mainly arene H atoms consolidate the crystal packing, which reveals an approximate c/2 pseudo-translation relating the two independent Ru complex mol­ecules.

The impact of ion pair association upon the 1H NMR spectra of cationic complexes akin to Grubbs catalysts

A reconsideration of the (1)H NMR spectra of cationic transition metal complexes exhibiting the features of cyclophanes on the basis of Mislow's classification of topic groups arrives at the conclusion that the spectral changes triggered by chiral counterions reflect an intracationic diastereotopication of enantiotopic protons rather than the existence of pairs of long-lived diastereomeric ion pairs.

Reactivity and catalytic activity of a robust ruthenium(II)-triphos complex

The ruthenium(II)-triphos acetato complex [RuCl(OAc)(kappa3-triphos)] (triphos = (PPh2CH2)3CMe) has been found to be an active catalyst precursor for the hydrogenation of 1-alkenes under relatively mild conditions (5-50 bar H2, 50 degrees C). In contrast to related triphenylphosphine complexes, [RuCl(OAc)(kappa3-triphos)] is much less air sensitive and high catalytic activities were achieved when catalyst samples were prepared without exclusion of air or moisture. Substitution of the acetato ligand can be effected by treatment of acid, affording [Ru2(mu-Cl)3(kappa3-triphos)2]Cl and [RuCl(kappa3-triphos)]2(BF4)2 with aqueous HCl and [Et2OH]BF4, respectively, or by heating with dmpm in the presence of [NH4]PF6, resulting in formation of [RuCl(kappa2-dmpm)(kappa3-triphos)]PF6 (dmpm = PMe2CH2PMe2). A hydride complex, [RuHCl(kappa3-triphos)], formed by acetato-mediated heterolytic cleavage of dihydrogen is proposed as the active catalytic species. An inner-sphere, monohydride mechanism is suggested for the catalytic cycle, with chloro and triphos ligands playing a spectator role. These mechanistic proposals are consistent with reactivity studies carried out on [RuCl(OAc)(kappa3-triphos)] and [RuH(OAc)(kappa3-triphos)] and supported by a computational analysis. The solid-state structures of [RuCl(OAc)(kappa3-triphos)], [RuCl(kappa3-triphos)]2(BF4)2, and [RuCl(kappa2-dmpm)(kappa3-triphos)]PF6 have been established by X-ray diffraction.

Tuning the hydrophobicity of ruthenium(II)-arene (RAPTA) drugs to modify uptake, biomolecular interactions and efficacy

The antitumour activity of the organometallic ruthenium(ii)-arene mixed phosphine complexes, [Ru(eta(6)-p-cymene)Cl(PTA)(PPh(3))]BF(4) and [Ru(eta(6)-C(6)H(5)CH(2)CH(2)OH)Cl(PTA)(PPh(3))]BF(4) (PTA = 1,3,5-triaza-7-phosphaadamantane), have been evaluated in vitro and compared to their RAPTA analogues, [Ru(eta(6)-p-cymene)Cl(2)(PTA)] and [Ru(eta(6)-C(6)H(5)CH(2)CH(2)OH)Cl(2)(PTA)] . The results show that the addition of the PPh(3) ligand to increases the cytotoxicity towards the TS/A adenocarcinoma cancer cells, which correlates with increased uptake, but also increases cytotoxicity to non-tumourigenic HBL-100 cells, thus decreasing selectivity. The decrease in selectivity has been correlated to increased DNA interactions relative to proteins, demonstrated by reactivity of the compounds with a 14-mer oligonucleotide and the model proteins ubiquitin and cytochrome-c.