Bernard Meunier

100 Years of Baeyer-Villiger Oxidations

In the present review, we report the discovery of the formation of esters and lactones by oxidation of ketones with a peroxide derivative, namely the Baeyer–Villiger reaction. This reaction was first reported by Adolf von Baeyer and Victor Villiger a century ago in 1899, just one year after the oxidant they used (KHSO5) has been described. Furthermore, Baeyer and Villiger established the composition of this new inorganic peroxide and showed that its instability was the reason of a controversy between several European chemists between 1878 and 1893. For the first 50 years the mechanism of the Baeyer–Villiger reaction was a matter of debate. A side product, 1,2,4,5-tetraoxocyclohexane, was ruled out as an intermediate in the ester formation by Dilthey. Criegee postulated a nucleophilic attack of the oxidant on the carbonyl group. This mechanism was confirmed by von E. Doering by a labeling experiment with [18O]benzophenone. The rearrangement step occurs with retention of the stereochemistry at the migrating center. The competitive migration and the rate-determining step are also discussed in this review.

DNA And RNA Cleavage by Metal Complexes

Publisher Summary This chapter discusses DNA and RNA cleavage by metal complexes. DNA and RNA cleavage, a very active field of research, has been developed in two main and complementary directions within the past decade: oxidative cleavage and hydrolysis. In general, the difference between the two different approaches are (1) the preparation of new chemical tools to study genomic DNA. The recognition sites of most of the restriction enzymes are often limited to palindromic sequences, and it is useful to have artificial nucleases able to cleave DNA at any desired sequence, and (2), the synthesis of compounds that cleave nucleic acids should help in the design of potential therapeutic agents for the treatment of cancer and viral diseases. The challenging development of new, efficient DNA and RNA cleavage agents can require a strong cooperation between chemists, biochemists, and molecular biologists.

Efficient Oxidative Dechlorination and Aromatic Ring Cleavage of Chlorinated Phenols Catalyzed by Iron Sulfophthalocyanine

An efficient method has been developed for the catalytic oxidation of pollutants that are not easily degraded. The products of the hydrogen peroxide (H2O2) oxidation of 2,4,6,-trichlorophenol (TCP) catalyzed by the iron complex 2,9,16,23-tetrasulfophthalocyanine (FePcS) were observed to be chloromaleic, chlorofumaric, maleic, and fumaric acids from dechlorination and aromatic cycle cleavage, as well as additional products that resulted from oxidative coupling. Quantitative analysis of the TCP oxidation reaction revealed that up to two chloride ions were released per TCP molecule. This chemical system, consisting of an environmentally safe oxidant (H2O2) and an easily accessible catalyst (FePcS), can perform several key steps in the oxidative mineralization of TCP, a paradigm of recalcitrant pollutants.

Possible modes of action of the artemisinin-type compounds

Artemisinin-type compounds are used for the treatment of uncomplicated and severe forms of malaria. They reduce parasitaemia more rapidly than any other antimalarial compound known, and are effective against multidrug-resistant parasites. However, uncertainties remain as to how they act on the parasite and cause toxicity. In this review, we summarize current ideas.

PREPARATION OF WATER-SOLUBLE CATIONIC PHOSPHORUS-CONTAINING DENDRIMERS AS DNA TRANSFECTING AGENTS

P-dendrimers appear to be excellent candidates as transfecting agents after positively charged functions are grafted at their periphery. Five different generations of protonated dendrimers (1-[G1] to 1-[G5]) and the corresponding methylated series (2-[G1] to 2-[G5]) (two examples are shown here) have been examined as transfecting agents of the luciferase gene within 3T3 cells.

Is alkylation the main mechanism of action of the antimalarial drug artemisinin

Artemisinin is a sesquiterpene lactone with an endoperoxide function essential for its antimalarial activity against chloroquine-resistant strains of Plasmodium falciparum. The mechanism of action of this paradigm molecule for endoperoxide-containing antimalarial drugs is still open to debate. Are the artemisinin derivatives only responsible for oxidative stress or are they able to alkylate heme and parasite proteins? The characterization of a covalent artemisinin-heme model adduct supports the role of C-centered radicals generated by the reductive activation of the peroxidic bond of this class of drugs. Artemether (an artemisinin analogue) and BO7 (a synthetic antimalarial trioxane) are also able to alkylate a porphyrin cycle.

Trioxaquines Are New Antimalarial Agents Active on All Erythrocytic Forms, Including Gametocytes

ABSTRACT Malaria is the third most significant cause of infectious disease in the world. The search for new antimalarial chemotherapy has become increasingly urgent due to parasite resistance to classical drugs. Trioxaquines are synthetic hybrid molecules containing a trioxane motif (which is responsible for the antimalarial activity of artemisinin) linked to an aminoquinoline entity (which is responsible for the antiplasmodial properties of chloroquine). These trioxaquines are highly potent against young erythrocytic stages of Plasmodium falciparum and exhibit efficient activity in vitro against chloroquine-sensitive and -resistant strains of P. falciparum (50% inhibitory concentration, 4 to 32 nM) and are also active in vivo against P. vinckei petteri and P. yoelii nigeriensis in suppressive and curative murine tests. The trioxaquine DU1302 is one of these promising antimalarial agents. The present study confirms the absence of toxicity of this drug on cell lines and in a mice model. Moreover, DU1302 exhibits potent activity against gametocytes, the form transmitted by mosquitoes, as killing of the gametocytes is essential to limit the spread of malaria. The ease of chemical synthesis of this trioxaquine prototype should be considered an additional advantage and would make these drugs affordable without perturbations of the drug supply.

Preparation and Antimalarial Activities of “Trioxaquines”, New Modular Molecules with a Trioxane Skeleton Linked to a 4‐Aminoquinoline

Trioxaquines are new antimalarial drugs which combine two active fragments (an aminoquinoline and a trioxane) with independant modes of action covalently linked within a single molecule. This strategy, which can be characterized as a “covalent bitherapy”, allowed us to obtain modular molecules with high antimalarial activity in vitro either on chloroquine sensitive or on chloroquine resistant Plasmodium falciparum strains.

Selection of a trioxaquine as an antimalarial drug candidate.

Trioxaquines are antimalarial agents based on hybrid structures with a dual mode of action. One of these molecules, PA1103/SAR116242, is highly active in vitro on several sensitive and resistant strains of Plasmodium falciparum at nanomolar concentrations (e.g., IC50 value = 10 nM with FcM29, a chloroquine-resistant strain) and also on multidrug-resistant strains obtained from fresh patient isolates in Gabon. This molecule is very efficient by oral route with a complete cure of mice infected with chloroquine-sensitive or chloroquine-resistant strains of Plasmodia at 26–32 mg/kg. This compound is also highly effective in humanized mice infected with P. falciparum. Combined with a good drug profile (preliminary absorption, metabolism, and safety parameters), these data were favorable for the selection of this particular trioxaquine for development as drug candidate among 120 other active hybrid molecules.

Porphyrin Derivatives for Telomere Binding and Telomerase Inhibition

The capacity of G‐quadruplex ligands to stabilize four‐stranded DNA makes them able to inhibit telomerase, which is involved in tumour cell proliferation. A series of cationic metalloporphyrin derivatives was prepared by making variations on a meso‐tetrakis(4‐N‐methyl‐pyridiniumyl)porphyrin skeleton (TMPyP). The DNA binding properties of nickel(II) and manganese(III) porphyrins were studied by surface plasmon resonance, and the capacity of the nickel porphyrins to inhibit telomerase was tested in a TRAP assay. The nature of the metal influences the kinetics (the process is faster for Ni than for Mn) and the mode of interaction (stacking or external binding). The chemical alterations did not lead to increased telomerase inhibition. The best selectivity for G‐quadruplex DNA was observed for Mn‐TMPyP, which has a tenfold preference for quadruplex over duplex.