Michel Pfeffer

A Ruthenium-Containing Organometallic Compound Reduces Tumor Growth through Induction of the Endoplasmic Reticulum Stress Gene CHOP

Cisplatin-derived anticancer therapy has been used for three decades despite its side effects. Other types of organometallic complexes, namely, some ruthenium-derived compounds (RDC), which would display cytotoxicity through different modes of action, might represent alternative therapeutic agents. We have studied both in vitro and in vivo the biological properties of RDC11, one of the most active compounds of a new class of RDCs that contain a covalent bond between the ruthenium atom and a carbon. We showed that RDC11 inhibited the growth of various tumors implanted in mice more efficiently than cisplatin. Importantly, in striking contrast with cisplatin, RDC11 did not cause severe side effects on the liver, kidneys, or the neuronal sensory system. We analyzed the mode of action of RDC11 and showed that RDC11 interacted poorly with DNA and induced only limited DNA damages compared with cisplatin, suggesting alternative transduction pathways. Indeed, we found that target genes of the endoplasmic reticulum stress pathway, such as Bip, XBP1, PDI, and CHOP, were activated in RDC11-treated cells. Induction of the transcription factor CHOP, a crucial mediator of endoplasmic reticulum stress apoptosis, was also confirmed in tumors treated with RDC11. Activation of CHOP led to the expression of several of its target genes, including proapoptotic genes. In addition, the silencing of CHOP by RNA interference significantly reduced the cytotoxicity of RDC11. Altogether, our results led us to conclude that RDC11 acts by an atypical pathway involving CHOP and endoplasmic reticulum stress, and thus might provide an interesting alternative for anticancer therapy.

Selected applications to organic synthesis of intramolecular C-H activation reactions by transition metals

Cyclometallated compounds obtained via the well-known intramolecular C-H activation by transition metals of N- or S- containing ligands may lead to organic heterocycles through reaction with alkynes. The mechanistic implications of the formation of both C-C and C-Y bonds are discussed. A reaction pathway involving insertion of the alkyne into the metal- carbon bond of the starting material followed by intramolecular addition of the Y atom to the resulting metallated-vinyl unit is proposed based on both the regioselectivity of the insertion and the existence of genuine isolated intermediates for the formation of the heterocyclic compounds.

Dynamic Kinetic Resolution of Racemic β-Haloalcohols : Direct Access to Enantioenriched Epoxides

The direct chemo-enzymatic DKR of racemic beta-haloalcohols is reported, yielding the corresponding optically active epoxides in a single step. The mutant haloalcohol dehalogenase HheC Cys153Ser Trp249Phe is used for the asymmetric ring closure, whereas racemization of the remaining enantiomer of the haloalcohol is achieved using the new iridacycle 3, one of the most effective racemization catalysts to date for beta-haloalcohols.

Further insight into the mechanism of the palladium induced carbocyclisation of aryl rings.

Abstract The depalladation of several cyclopalladated compounds, containing two inserted diphenlacetylenes in the PdC bond has been acheived by treatment with either a neutral coordinating ligand such as pyridine, triphenylphosphine or maleic anhydride. This has afforded carbocyclic compounds where one or two of the aryl groups of the butadienyl chain have been annulated as a result of CC bond formation. These demetallation reactions could be performed under rather mild conditions which enabled the characterisation of an intermediate which in turn provided valuable information about the mechanism of the palladium mediated carbocyclisation reaction.

Fast racemisation of chiral amines and alcohols by using cationic half-sandwich ruthena- and iridacycle catalysts

The lipase-catalysed resolution of alcohols and amines yields only 50 % of the desired enantiopure product. However, addition of a racemisation catalyst leads to 100 % yield in what is called a dynamic kinetic resolution (DKR). There is a need for new racemisation catalysts that are fast and compatible with the conditions of the enzymatic reaction. We show that cationic half-sandwich ruthena- and iridacycle complexes are highly active and efficient in the racemisation of chiral alcohols and amines. Upon activation with base, these complexes are able to selectively racemise alcohols, whereas the non-activated complexes are selective catalysts for the racemisation of amines. We have applied the iridacycles in the DKR of racemic beta-chloroalcohols to produce chiral epoxides in a biphasic system in good yields and high ee (ee=enantiomeric excess).

Library of second-generation cycloruthenated compounds and evaluation of their biological properties as potential anticancer drugs: Passing the nanomolar barrier

A library of 32 organoruthenium compounds has been synthesised. Known and novel C-N cyclometalated compounds as well as N-C-N and N-N-C pincer derivatives of this metal have been used in this purpose. Most of the compounds have been tested for their in vitro antitumoral behaviours, good to excellent activities have thus been found. Several of the newly synthesized compounds pass the symbolic barrier of the nanomolar range for their IC(50) indicating a critical improvement. The level of activity is tentatively correlated to physicochemical properties of the compounds such as their Ru(III/II) redox potential and their lipophilicity (log P).

Induction of caspase 8 and reactive oxygen species by ruthenium-derived anticancer compounds with improved water solubility and cytotoxicity

Organometallic compounds which contain metals, such as ruthenium or gold, have been investigated as a replacement for platinum-derived anticancer drugs. They often show good antitumor effects, but the identification of their precise mode of action or their pharmacological optimization is still challenging. We have previously described a class of ruthenium(II) compounds with interesting anticancer properties. In comparison to cisplatin, these molecules have lower side effects, a reduced ability to interact with DNA, and they induce cell death in absence of p53 through CHOP/DDIT3. We have now optimized these molecules by improving their cytotoxicity and their water solubility. In this article, we demonstrate that by changing the ligands around the ruthenium we modify the ability of the compounds to interact with DNA. We show that these optimized molecules reduce tumor growth in different mouse models and retain their ability to induce CHOP/DDIT3. However, they are more potent inducers of cancer cell death and trigger the production of reactive oxygen species and the activation of caspase 8. More importantly, we show that blocking reactive oxygen species production or caspase 8 activity reduces significantly the activity of the compounds. Altogether our data suggest that water-soluble ruthenium(II)-derived compounds represent an interesting class of molecules that, depending on their structures, can target several pro-apoptotic signaling pathways leading to reactive oxygen species production and caspase 8 activation.

Selective hetero- and carbo-cycle syntheses via masked cyclopalladated secondary amine and ketone functions

Abstract The iodo-bridged or cationic cyclopalladated complexes 1b and 1c derived from N -phenyl-2-pyridylamine and 4b derived from phenyl-2-pyridylketone reacted with internal alkynes to yield five-membered heterocyclic 3 and carbocyclic products 6 with high chemoselectivity. The indoles 3b – 3f , formed from 1b or 1c and disymmetric alkynes, were obtained regioselectively, suggesting that this reaction might be under both electronic and steric control. Analysis of the regiochemistry of this reaction has led us to propose a pathway involving a nucleophilic addition of the secondary amine function to an alkyne activated by η 2 - coordination to palladium. The indenol derivatives 6 , obtained as stable bis( O , N )-palladated chelates, result from the insertion of the alkyne into the Pd-C bond of 4b followed by attack of the palladated vinyl carbon atom on the electrophilic carbonyl function. In so far as their reactivities towards alkynes are concerned, 1b and 1c behave as masked cyclopalladated secondary amine functions and 4b as masked cyclopalladated ketone functions.

Reactivity of cyclopalladated compounds. Part 18. Compared reactivity of the Pd–C bonds of two closely related six-membered palladocyclic rings with substituted alkynes. X-Ray and molecular structures of [Pd{C(Ph)C(R)C(Ph)C(R)(o-C6H4NCMeNHPh)}Cl](R = CO2Et) and [Pd{C(R)[C(CO2Me)C(R)C(R)C(R)C(R)][o-C6H4NCMe(OH)]}Cl](R = CO2Me)

The reactions between alkynes and the chloride-bridged cyclopalladated dimers derived from orthopalladation of acetanilide, [{P[graphic omitted])}2(µ-Cl)2](1), and amidine, [{P[graphic omitted]Ph)}2(µ-Cl)2](2), afforded organometallic products in which one, two, or three alkynes had been inserted into the Pd–C bonds of (1) and (2), the ratio of alkyne : palladium in the final products being independent of the stoicheiometry of the reaction. Compound (1) gave with hexafluorobut-2-yne the mono-inserted product [{P[graphic omitted])](µ-Cl)}2]. With diphenylacetylene it gave an unstable product (7) in which two alkynes had been added per palladium atom forming with the acetanilide unit a spirocyclic ligand η3-bonded to the palladium centre. Compound (7) decomposed on heating to afford quantitatively the pentasubstituted naphthalene derivative C10H3Ph4(NHCMeO). Compound (2) reacted with diphenylacetylene and ethyl 3-phenylpropionate to give the di-inserted products [P[graphic omitted]CMeNHPh)}Cl](11, R = Ph; 12, R = CO2Et). The structure of (12) was ascertained by an X-ray structure determination, which confirmed the regioselectivity of the insertion reaction and that (12) is an eight-membered palladocyclic ring through the co-ordination to the metal of the nitrogen atom immediately adjacent to the phenyl ring. Triple insertion of alkynes was observed when reacting (1) and (2) with dimethyl acetylenedicarboxylate affording [P[graphic omitted]CMeYH)]}Cl](9, Y = O; 13, Y = NPh). The structure of (9) has been confirmed by an X-ray diffraction study. A related triple insertion occured when treating (1) with but-2-yne affording a thermally unstable intermediate; its depalladation led to trans-o-C6H4(NHCMeO)CHCH(C5Me5).

Reactivity of cyclopallatated compounds. III. Reaction with group V donor atoms ligands

Abstract In organic solvents, ligands such as pyridine, trialkyl and triarylphosphines, Triphenylarsine and stibine react quantitatively with cyclopalladated dimers of the type (Pd(CN)X) 2 (where CN = acetophenone hydazone) to give monomeric compounds of the type Pd(C-N)LX(X = Cl, Br, I). The presence of an excess of phosphine leads to Pd(C-N)L 2 X, in which the nitrogen is no longer coordinated. With bidentate ligands a new type of complexes is obtained: in which AA represents 1,2-bis(diphenylphosphino)ethane and 1,2-bis(diphenylarsino)ethane. With ethylenediamine (en), only the ionic complex [Pd(CN) en] + X − is formed. In aqueous solutions, cationic compounds of palladium can be isolated with pyridine or bidentate ligands. The stereochemistry of these complexes is discussed on the basis of v(PdX) infrared frequencies; N.M.R. data for the CN ligand are given.