Pierre Le Gendre

Caffeine-Based Gold(I) N-Heterocyclic Carbenes as Possible Anticancer Agents: Synthesis and Biological Properties

A new series of gold(I) N-heterocyclic carbene (NHC) complexes based on xanthine ligands have been synthesized and characterized by mass spectrometry, NMR, and X-ray diffraction. The compounds have been tested for their antiproliferative properties in human cancer cells and nontumorigenic cells in vitro, as well as for their toxicity in healthy tissues ex vivo. The bis-carbene complex [Au(caffein-2-ylidene)2][BF4] (complex 4) appeared to be selective for human ovarian cancer cell lines and poorly toxic in healthy organs. To gain preliminary insights into their actual mechanism of action, two biologically relevant in cellulo targets were studied, namely, DNA (more precisely a higher-order DNA structure termed G-quadruplex DNA that plays key roles in oncogenetic regulation) and a pivotal enzyme of the DNA damage response (DDR) machinery (poly-(adenosine diphosphate (ADP)-ribose) polymerase 1 (PARP-1), strongly involved in the cancer resistance mechanism). Our results indicate that complex 4 acts as an efficient and selective G-quadruplex ligand while being a modest PARP-1 inhibitor (i.e., poor DDR impairing agent) and thus provide preliminary insights into the molecular mechanism that underlies its antiproliferative behavior.

Multinuclear Cytotoxic Metallodrugs: Physicochemical Characterization and Biological Properties of Novel Heteronuclear Gold-Titanium Complexes

An unprecedented series of titanocene-gold bi- and trimetallic complexes of the general formula [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)(CH(2))(n)PPh(2))TiCl(2)](m)AuCl(x)](q+) (n = 0, 2, or 4; m = 1, x = 1, q = 0 or m = 2, x = 0, q = 1) have been prepared and characterized spectroscopically. The luminescence spectroscopy and photophysics of one of the compounds, [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)PPh(2))TiCl(2)](2)Au]PF(6), have been investigated in 2MeTHF solution and in the solid state at 77 and 298 K. Evidence for interfragment interactions based on the comparison of electronic band positions and emission lifetimes, namely, triplet energy transfer (ET) from the Au- to the Ti-containing chromophores, is provided. The cytotoxicity of the complexes was evaluated on A2780 ovarian cancer cells and on their cisplatin-resistant cell line A2780cisR; the compounds showed activity in the low micromolar range that was markedly more active than the corresponding titanocene-phosphine precursors [(η(5)-C(5)H(5))(η(5)-C(5)H(4)(CH(2))(n)PPh(2))TiCl(2)], cisplatin, and, for some of them, the gold analogue [(PPh(3))AuCl]. In an attempt to draw preliminary structure-activity relationships, cell uptake measurements and interaction studies with plasmid DNA and the model protein ubiquitin (Ub) have been undertaken on some of the compounds.

Gold(I) NHC-based homo- and heterobimetallic complexes: synthesis, characterization and evaluation as potential anticancer agents

While N-heterocyclic carbenes (NHC) are ubiquitous ligands in catalysis for organic or industrial syntheses, their potential to form transition metal complexes for medicinal applications has still to be exploited. Within this frame, we synthesized new homo- and heterobimetallic complexes based on the Au(I)–NHC scaffold. The compounds were synthesized via a microwave-assisted method developed in our laboratories using Au(I)–NHC complexes carrying a pentafluorophenol ester moiety and another Au(I) phosphane complex or a bipyridine ligand bearing a pendant amine function. Thus, we developed two different methods to prepare homo- and heterobimetallic complexes (Au(I)/Au(I) or Au(I)/Cu(II), Au(I)/Ru(II), respectively). All the compounds were fully characterized by several spectroscopic techniques including far infrared, and were tested for their antiproliferative effects in a series of human cancer cells. They showed moderate anticancer properties. Their toxic effects were also studied ex vivo using the precision-cut tissue slices (PCTS) technique and initial results concerning their reactivity with the seleno-enzyme thioredoxin reductase were obtained.

Assessing the Differential Affinity of Small Molecules for Noncanonical DNA Structures

The targeting of higher‐order DNA structures has been thoroughly developed with G‐quadruplex DNA but not with other structures like branched DNA (also known as DNA junctions). Because these alternative higher‐order DNA architectures might be of high biological relevance, we implemented a high‐throughput version of the FRET melting assay that enabled us to map the interactions of a candidate with four different DNA structures (duplex‐ and quadruplex DNA, three‐ and four‐way junctions) in a rapid and reliable manner. We also introduce a novel index, the BONDS (branched and other noncanonical DNA selectivity) index, to conveniently quantify this differential affinity.

Ti–Ru bimetallic complexes: catalysts for ring-closing metathesis

The reaction of the titanocene monophosphanes ( 1 – 4 ) with the dimer [( p -cymene)RuCl 2 ] 2 gives the heterobimetallic compounds ( p -cymene)[(η 5 -C 5 H 5 )(μ-η 5 :η 1 -C 5 H 4 (CR 2 ) n PR′ 2 )TiCl 2 ]RuCl 2 ( 5 – 8 ). The structure of 8 , determined by X-ray diffraction, is reported here. A preliminary assessment of the performance of these complexes in ring-closing metathesis (RCM) revealed an excellent Ti–Ru–allenylidene pre-catalyst 12 .

Anticancer Agents: Does a Phosphonium Behave Like a Gold(I) Phosphine Complex? Let a “Smart” Probe Answer!

Gold phosphine complexes, such as auranofin, have been recognized for decades as antirheumatic agents. Clinical trials are now underway to validate their use in anticancer or anti-HIV treatments. However, their mechanisms of action remain unclear. A challenging question is whether the gold phosphine complex is a prodrug that is administered in an inactive precursor form or rather that the gold atom remains attached to the phosphine ligand during treatment. In this study, we present two novel gold complexes, which we compared to auranofin and to their phosphonium analogue. The chosen ligand is a phosphine-based smart probe, whose strong fluorescence depends on the presence of the gold atom. The in vitro biological action of the gold complexes and the phosphonium derivative were investigated, and a preliminary in vivo study in healthy zebrafish larvae allowed us to evaluate gold complex biodistribution and toxicity. The different analyses carried out showed that these gold complexes were stable and behaved differently from phosphonium and auranofin, both in vitro and in vivo. Two-photon microscopy experiments demonstrated that the cellular targets of these gold complexes are not the same as those of the phosphonium analogue. Moreover, despite similar IC50 values in some cancer cell lines, gold complexes displayed a low toxicity in vivo, in contrast to the phosphonium salt. They are therefore suitable for future in vivo investigations.

Synthesis of enol esters catalysed by ‘early–late’ Ti–Ru complexes

Abstract The titane–ruthenium heterobimetallic compounds ( p -cymene)[(η 5 -C 5 H 5 )(μ-η 5 :η 1 -C 5 H 4 (CH 2 ) m PR 2 )TiCl 2 ]RuCl 2 4 – 6 have been revealed to be quite good catalysts for the addition of formic acid to 1-hexyne and phenylacetylene. These preliminary results led us to synthesize new tetrametallic complexes 10 – 12 via the reaction of the titanocene phosphanes 1 – 3 with the polymer [Ru(CO) 2 (μ-O 2 CH)] n . Their catalytic ability for the enol esters formation has been studied.

Synthesis and structural studies of TiRu polymetallic systems

The reaction of the titanocene monophosphines 1 and 2 with the dimer [(p-cymene)RuCl2]2 give the heterobimetallic compounds (p-cymene)[(h-C5H4)(m-h:h-C5H4PPh2)TiCl2]RuCl2 and (p-cymene)[(h-C5H4)(m-h:h-C5H4CH2CH2PPh2)TiCl2]RuCl2, respectively. Both structures have been confirmed by X-ray diffraction. By using same procedure, the synthesis of a trimetallic complex Ru Ti Ru has been achieved.

First catalytic allyltitanation reactions

Catalytic allyltitanation reactions were accomplished from dienes and aldehydes with only 5% of titanocene complexes at the expense of employing stoichiometric amounts of PMHS.

A Simple Phosphine–Diolefin‐Promoted Copper‐Catalysed N‐Arylation of Pyrazoles with (Hetero)aromatic Bromides: The Case of Chloroarenes Revisited

A molecularly defined new phosphine–diolefin cubane copper pre‐catalyst used at 1.25 mol % under mild conditions promotes the coupling of pyrazoles to functionalised aryl and heteroaryl bromides, which hold a variety of functional groups. This versatile phosphorus‐based system was thus successfully used, under identical conditions, for the coupling of a large scope of heteroaromatics to selectively produce pyridinyl‐ and pyrimidinyl‐pyrazoles, as well as several novel furyl‐, thienyl‐ and thiazolyl‐substituted pyrazoles. The careful investigation of coupling with the analogous aryl and heteroaryl chlorides clearly indicated that for specifically activated chloroarenes a direct nucleophilic aromatic substitution (SNAr) is easily achieved in the absence of any copper and ligand. These results are pertinent with regards to the reported protocols in which copper–ligand systems have been claimed as useful for coupling activated chloroarenes.