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Bernard Meunier

Publications and source records attributed to Bernard Meunier.

52 records · Page 3Linked to original sources
PubMed2002

A minor groove binding copper-phenanthroline conjugate produces direct strand breaks via beta-elimination of 2-deoxyribonolactone.

Copper-phenanthroline complexes and their conjugates are useful reagents for studying nucleic acid interactions. Although DNA cleavage by such complexes was discovered more than 20 years ago, significant questions remain unanswered regarding the chemical mechanism(s) by which DNA is damaged. Kinetic evidence is provided, which demonstrates that the major pathway for DNA damage by a minor groove binding molecule conjugated to copper phenanthroline (6) involves C1'-oxidation. Additional experiments using 6 and a DNA substrate containing 2-deoxyribonolactone (1) show that direct strand breaks are produced via beta-elimination from 1. These studies support the original mechanism for DNA damage by copper phenanthroline put forth by Sigman and a more recent proposal concerning the mechanism for direct strand break formation.

Chromatography, High Pressure Liquid↗
PubMed2002

Alkylation of heme by the antimalarial drug artemisinin.

The peroxide function of artemisinin has been activated by iron(II)-heme generated in situ from iron(III)-protoporphyrin-IX and glutathione, a biologically relevant reductant. In mild conditions, this reaction produced a high yield (85%) of heme derivatives alkylated at alpha-, beta-, and delta-meso positions by a C4-centered radical derived from artemisinin.

Alkylation↗
PubMed2002

Alkylating capacity and reaction products of antimalarial trioxanes after activation by a heme model.

The reactivity of 1,2,4-trioxane molecules 2-5, structurally related to the antimalarial drug artemisinin, with a heme model, manganese(II) tetraphenylporphyrin, is reported. With the pharmacologically active drugs 2-4, covalent adducts were obtained by addition of a drug-derived radical onto the porphyrin macrocycle, whereas no reaction was obtained with the nonactive compound 5. This confirms that alkylation is probably one of the key factors of the pharmacological activity of endoperoxide-based antimalarial drugs.

Alkylation↗
PubMed2002

From mechanistic studies on artemisinin derivatives to new modular antimalarial drugs.

In the first part of this account, the antimalarial drug artemisinin is presented, and the current hypotheses on the mechanism of action of this endoperoxide-based drug are reviewed. The alkylating ability of artemisinin and synthetic analogues toward heme related to their antimalarial efficacy are underlined. Some possible ways for discovery of new drugs, especially the design of trioxaquines, new active molecules recently patented that have been prepared by covalent attachment of a trioxane residue having alkylating ability to a quinoline moiety known to easily penetrate within infected erythrocytes, are presented.

Alkylating Agents↗
PubMed2002

Characterization of the dehydro-guanidinohydantoin oxidation product of guanine in a dinucleotide.

The study of the biological consequences of oxidative damage to DNA requires the characterization of DNA lesions at a molecular level. The oxidation of guanine in the dinucleoside monophosphate, d(GpT), by a metal-oxo porphyrin produces a dehydro-guanidinohydantoin derivative. The (1)H NMR spectrum of this oxidized guanine derivative is reported. The structure was confirmed by the chemical transformation of the dehydro-guanidinohydantoin derivative into a linear oxaluric acid derivative upon hydrolysis at ambient temperature. The proposed mechanism of formation of the dehydro-guanidinohydantoin derivative is in agreement with the labeling experiments performed with H(2)(18)O.

DNA↗
PubMed2002

Mn(III) pyrophosphate as an efficient tool for studying the mode of action of isoniazid on the InhA protein of Mycobacterium tuberculosis.

The antituberculosis drug isoniazid (INH) is quickly oxidized by stoichiometric amounts of manganese(III) pyrophosphate. In the presence of nicotinamide coenzymes (NAD+, NADH, nicotinamide mononucleotide [NMN+]) and nicotinic acid adenine dinucleotide (DNAD+), INH oxidation produced the formation of INH-coenzyme adducts in addition to known biologically inactive products (isonicotinic acid, isonicotinamide, and isonicotinaldehyde). A pool of INH-NAD(H) adducts preformed in solution allowed the rapid and strong inhibition of in vitro activity of the enoyl-acyl carrier protein reductase InhA, an INH target in the biosynthetic pathway of mycolic acids: the inhibition was 90 or 60% when the adducts were formed in the presence of NAD+ or NADH, respectively. Under similar conditions, no inhibitory activity of INH-NMN(H) and INH-DNAD(H) adducts was detected. When an isolated pool of 100 nM INH-NAD(H) adducts was first incubated with InhA, the enzyme activity was inhibited by 80%; when present in excess, both NADH and decenoyl-coenzyme A are able to prevent this phenomenon. InhA inhibition by several types of INH-coenzyme adducts coexisting in solution is discussed in relation with the structure of the coenzyme, the stereochemistry of the adducts, and their existence as both open and cyclic forms. Thus, manganese(III) pyrophosphate appears to be an efficient and convenient alternative oxidant to mimic the activity of the Mycobacterium tuberculosis KatG catalase-peroxidase and will be useful for further mechanistic studies of INH activation and for structural investigations of reactive INH species in order to promote the design of new inhibitors of InhA as potential antituberculous drugs.

Antitubercular Agents↗
PubMed1999

Characterization of the Main Radical and Products Resulting from a Reductive Activation of the Antimalarial Arteflene (Ro 42-1611).

The peroxide-containing antimalarial drug arteflene (Ro 42-1611) generates an alkyl radical after the reductive homolytic cleavage of the peroxide bond in the presence of a heme model Mn(II)(TPP). This alkyl radical has been trapped by TEMPO, and the different products of the reduction activation of arteflene have been characterized. These data suggest that, in these experimental conditions, arteflene is not a significant alkylating agent compared to artemisinin, a trioxane-containing antimalarial drug.

Journal Article↗
PubMed1999

Structures of Fe(II) Complexes with N,N,N'-Tris(2-pyridylmethyl)ethane-1,2-diamine Type Ligands. Bleomycin-like DNA Cleavage and Enhancement by an Alkylammonium Substituent on the N' Atom of the Ligand.

The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) = N,N,N'-tris(2-pyridylmethyl)-N'-methyl-ethane-1,2-diamine) have been isolated. Bernal et al. (Bernal, J.; et al. J. Chem. Soc., Dalton Trans. 1995, 3667-3675) have prepared this ligand and the corresponding complex [L(5)Fe(II)Cl]PF(6). We obtained the structural data of [L(5)Fe(II)Cl]BPh(4) by X-ray diffraction. It crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 17.645(7) Å, b = 16.077(6) Å, c = 13.934(5) Å, V = 3953(3) Å(3), and Z = 4. It presents Fe(II)-N bond lengths close to 2.2 Å, typical of high-spin Fe(II). In solution the [L(5)Fe(II)(H(2)O)](BPh(4))(2) complex showed a dependence of spin state upon the nature of the solvent. It was high spin in acetone and changed to low spin in acetonitrile. This was detected by UV-vis spectroscopy and by (1)H NMR. Bernal et al. (ibidem) showed that these complexes in the presence of an excess of H(2)O(2) give a purple species, very likely the [L(5)Fe(III)(OOH)](2+) derivative, with spectroscopic signatures analogous to those of "activated bleomycin". The formation of [L(5)Fe(III)(OOH)](2+) is confirmed here by electrospray ionization mass spectrometry. We found that a L(5)/Fe system gave single-strand breaks on plasmid DNA in the presence of either a reducing agent (ascorbate) and air or oxidants (H(2)O(2), KHSO(5), MMPP) at 0.1 &mgr;M concentration. The methyl group in L(5) was substituted by a (CH(2))(5)N(CH(3))(3)(+) group in order to get higher affinity with DNA. The corresponding ligand L(5)(+) was used to prepare the complexes [L(5)(+)Fe(II)Cl]Y(2) (Y = BPh(4)(-), PF(6)(-), ClO(4)(-)) and [L(5)(+)Fe(II)Br](PF(6))(2). The crystal structure of [L(5)(+)Fe(II)Cl](ClO(4))(2) was solved. It crystallizes in the monoclinic space group P2(1)/a with a = 14.691(2) Å, b = 13.545(2) Å, c = 17.430(2) Å, beta = 93.43(1) degrees, V = 3462(1) Å(3), and Z = 4. The Fe(II)-ligand distances are similar to those of [L(5)Fe(II)Cl]BPh(4). At the relatively low concentration of 0.01 &mgr;M, [L(5)(+)Fe(II)Br](2+) promoted DNA breaks. The reaction was not inhibited by hydroxyl radical scavengers. The reaction might involve a nondiffusible oxygen reactive species, either a coordinated hydroperoxide or a high-valent metal-oxo entity.

Journal Article↗
PubMed1998

Preparation of the New Bis(phenanthroline) Ligand "Clip-Phen" and Evaluation of the Nuclease Activity of the Corresponding Copper Complex.

The best nuclease activities of 1,10-phenanthroline-copper complexes have been observed for a chelate/metal stoichiometry of 2/1. To favor this stoichiometry, the "Clip-Phen" ligand was synthesized with two 1,10-phenanthroline units linked via their C2-carbons by a short flexible arm. An exogenous amine function was present to allow future vectorization of this new chelating ligand. X-ray analysis of monocrystals of Clip-Phen confirmed its structure. An EPR study of (Clip-Phen)CuCl(2) showed that the cupric ion was pentacoordinated with a water molecule as the possible fifth ligand. The Cu(I/II) redox couple was found to be near 85 mV vs SCE, close to the redox couple of (Phen)(2)CuCl(2). A comparison of the nuclease activity of copper complexes of Clip-Phen and 1,10-phenanthroline indicated that (Clip-Phen)Cu was the more active.

Journal Article↗
PubMed1997

Origin of the Oxygen Atom in C-H Bond Oxidations Catalyzed by a Water-Soluble Metalloporphyrin.

The monopersulfate oxidation of 4-isopropylbenzoic acid performed in H(2)(18)O and catalyzed by a water-soluble metalloporphyrin indicated that half of the oxygen atoms incorporated in 4-(1-hydroxy-1-methylethyl)benzoic acid, the primary hydroxylation product, came from water. A redox tautomerism of the active high-valent hydroxo-metal-oxo porphyrin intermediate coupled with an oxygen rebound mechanism explained this result. Under similar conditions, ketoprofen was directly oxidized to 3-benzoylacetophenone, via at least two different reaction pathways. Trapping of radical intermediates by molecular oxygen competed with the oxygen rebound mechanism.

Journal Article↗
PubMed1997

Metalloporphyrin-Catalyzed Oxidation of 2-Methylnaphthalene to Vitamin K(3) and 6-Methyl-1,4-naphthoquinone by Potassium Monopersulfate in Aqueous Solution.

The metalloporphyrin-catalyzed oxidation of 2-methynaphthalene (1) by potassium monopersulfate produced mainly two naphthoquinones: 2-methyl-1,4-naphthoquinone (2) (menadione or vitamin K(3)) and 6-methyl-1,4-naphthoquinone (3). In aqueous solution and at room temperature in the presence of 5 mol % of the water-soluble metalloporphyrins MnTPPS or FeTMPS, 2-methylnaphthalene was quantitatively oxidized to quinones 2 and 3. Based on experiments performed in(18)O-labeled water and according to the "redox tautomerism" mechanism previously described for such catalysts, the oxidation to quinones is proposed to be mainly due to a cytochrome P-450-type oxygenation reaction (oxygen atom transfer), rather than a peroxidase-type oxidation (electron transfer).

Journal Article↗
PubMed1996

Synthesis and Characterization of New Chiral Schiff Base Complexes with Diiminobinaphthyl or Diiminocyclohexyl Moieties as Potential Enantioselective Epoxidation Catalysts.

New chiral Schiff base complexes have been obtained by condensation of 2,2'-diamino-1,1'-binaphthalene or 1,2-diaminocyclohexane and various salicylaldehydes and by subsequent metalation with manganese, iron, cobalt, nickel, copper, or zinc. The complete (1)H and (13)C NMR characterization of the ligands is reported, as are the X-ray crystal structures of (1R,2R)-(-)-N,N'-bis[3-(N,N-dimethylamino)salicylidene]-trans-1,2-cyclohexanediimine and [(1R,2R)-(-)-N,N'-bis(salicylidene)-trans-1,2-cyclohexanediiminato]copper(II). The new chiral manganese complexes have been evaluated in the oxygenation of prochiral olefins and sulfides using sodium hypochlorite, hydrogen peroxide, or N-methylmorpholine N-oxide/m-chloroperbenzoic acid as oxidant.

Journal Article↗
PubMedDate not supplied

Acridine conjugates of 3-clip-phen: influence of the linker on the synthesis and the DNA cleavage activity of their copper complexes.

To increase the DNA cleavage activity and the cell delivery of the bis(phenanthroline) DNA cleaver "3-Clip-Phen", conjugates between 3-Clip-Phen and the intercalators acridine and 6-chloro-2-methoxyacridine, through amino acid linkers of various length, were prepared. After complexation with CuCl(2), the ability of these conjugates to cleave phiX 174 DNA in the presence of a reductant and air was compared. The results indicated that (i) the coupling of 3-Clip-Phen to an acridine derivative increased the DNA cleavage efficiency of the copper complexes, (ii) the acridine derivatives were more active than 6-chloro-2-methoxyacridine derivatives, (iii) the linker length influenced cleavage efficiency, the highest DNA cleavage activity being obtained for an aminocaproic spacer.

Acridines↗
PubMedDate not supplied

Microstructured liposome array.

Conversion of a DNA chip to a nanocapsule array was performed by grafting on a liposome an oligonucleotide complementary to an oligonucleotide bound to the array. Each liposome may be loaded by a soluble molecule or may present a hydrophobic or amphiphilic molecule inserted in its wall. To detect liposomes on the chip, we used fluorescent dyes encapsulated in the liposome internal volume or fluorescent lipids. We observed that an oligonucleotide-grafted liposome containing a defined dye specifically accumulated on the area where its complementary oligonucleotide had been spotted on the array. The virtually unlimited amount of addresses allows the specific binding of large amounts of liposomes in one single batch.

Liposomes↗