Alix Sournia-Saquet

Redox Chemistry of Copper–Amyloid-β: The Generation of Hydroxyl Radical in the Presence of Ascorbate is Linked to Redox-Potentials and Aggregation State

Aggregation of the β‐amyloid peptide (Aβ) to amyloid plaques is a key event in Alzheimers disease. According to the amyloid‐cascade hypothesis, Aβ aggregates are toxic to neurons through the production of reactive oxygen species (ROS). Copper ions play an important role, because they are able to bind to Aβ and influence its aggregation properties. Moreover, Cu–Aβ is supposed to be directly involved in ROS production. To get a better understanding of these reactions, we measured the production of HO. and the redox potential of Cu–Aβ. The results were compared to other biological copper–peptide complexes in order to get an insight into the biological relevance. Cu–Aβ produced more HO. than the complex of copper with Asp‐Ala‐His‐Lys (Cu–DAHK), but less than with Gly‐His‐Lys (Cu–GHK). Cyclic voltammetry revealed that the order for reduction potential is Cu–GHK>Cu–Aβ>Cu–DAHK, but for the oxidation potential the order is reversed. Thus, easier copper redox cycling correlated to higher HO. production. The copper complex of the form Aβ1–42 showed a HO. production five‐times higher than that of the form Aβ1–40. Time‐dependence and aggregation studies suggest that an aggregation intermediate is responsible for this increased HO. production.

Characterization of new specific copper chelators as potential drugs for the treatment of Alzheimer's disease.

The non-controlled redox-active metal ions, especially copper, in the brain of patients with Alzheimer disease (AD) should be considered at the origin of the intense oxidative damage in the AD brain. Several bis(8-aminoquinoline) ligands, such as 1 and PA1637, are able to chelate Cu(2+) with high affinity, and are specific chelators of copper with respect to iron and zinc. They are able to efficiently extract Cu(2+) from a metal-loaded amyloid. In addition, these tetradentate ligands are specific for the chelation of Cu(2+) compared with Cu(+). Consequently, the copper ion is easily released from the bis(8-aminoquinoline) ligand under reductive conditions, and can be trapped again by a protein having some affinity for copper such as human serum albumin (HSA) proteins. In addition, the copper is not efficiently released from [Cu(CQ)2] in reductive conditions. The catalytic production of H2O2 by [Cu(2+)-Aβ(1-28)]/ascorbate is inhibited in vitro by the bis(8-aminoquinoline) 1, suggesting that 1 should be able to play a protective role against oxidative damages induced by copper-loaded amyloids.

Ruthenium Complexes with Dendritic Ferrocenyl Phosphanes: Synthesis, Characterization, and Application in the Catalytic Redox Isomerization of Allylic Alcohols

An efficient system for the catalytic redox isomerization of the allylic alcohol 1-octen-3-ol to 3-octanone is presented. The homogeneous ruthenium(II) catalyst contains a monodentate phosphane ligand with a ferrocene moiety in the backbone and provides 3-octanone in quantitative yields. The activity is increased by nearly 90 % with respect to the corresponding triphenyl phosphane ruthenium(II) complex. By grafting the catalyst at the surface of a dendrimer, the catalytic activity is further increased. By introducing different spacers between ferrocene and phosphorus, the influence on the electronic properties of the complexes is shown by evaluating the electrochemical behavior of the compounds.

Ordered Layered Dendrimers Constructed from Two Known Dendrimer Families: Inheritance and Emergence of Properties

A new concept is presented, namely the synthesis of dendrimers intrinsically composed in alternation of building blocks pertaining to two known families of dendrimers: phosphorhydrazone dendrimers and triazine-piperazine dendrimers. These mixed dendrimers with layered controlled architecture inherit their easy (31) P NMR characterization and their thermal stability from the phosphorhydrazone family, and their decreased solubility from the triazine-piperazine family. However, they have also their own and original characteristics. Both parent families are white powders, whereas the mixed dendrimers are yellow, orange, or red powders, depending on the generation. DFT calculations were carried out on model dendrons to understand these special color features. Remarkably, these dendrimers incorporating redox-active organic entities allow for the first time the monitoring of the growth of an organic dendrimer by electrochemistry while highlighting an even-odd generation behavior.

Heteroleptic Bis(cis-1,2-disubstituted ethylene-1,2-dithiolato)nickel Complexes Obtained by Ligand-Exchange Reaction: Synthesis and Properties

The ligand-exchange reaction has been investigated to synthesize nickel bis(dithiolene) complexes bearing one hydroxyl functional group aimed at being grafted thereafter onto polymer materials. This reaction leads easily to heteroleptic complexes with the ethylene-1,2-dithiolato core substituted by either alkyl or aryl moieties. Details on synthetic parameters are given. A direct link between the electronic properties of the obtained molecules and those of the parent complexes involved in the ligand-exchange reaction is highlighted and also demonstrates that this reaction is a powerful method for preparing nickel complexes with tailor-made frontier orbital energies.

Synthesis and mechanistic investigation of iron(II) complexes of isoniazid and derivatives as a redox-mediated activation strategy for anti-tuberculosis therapy

The emergence of multidrug-resistant strains of Mycobacterium tuberculosis (MTB) represents a major threat to global health. Isoniazid (INH) is a prodrug used in the first-line treatment of tuberculosis. It undergoes oxidation by a catalase-peroxidase KatG, leading to generation of an isonicotinoyl radical that reacts with NAD(H) forming the INH-NADH adduct as the active metabolite. A redox-mediated activation of isoniazid using an iron metal complex was previously proposed as a strategy to overcome isoniazid resistance due to KatG mutations. Here, we have prepared a series of iron metal complexes with isoniazid and analogues, containing alkyl substituents at the hydrazide moiety, and also with pyrazinamide derivatives. These complexes were activated by H2O2 and studied by ESR and LC-MS. For the first time, the formation of the oxidized INH-NAD adduct from the pentacyano(isoniazid)ferrate(II) complex was detected by LC-MS, supporting a redox-mediated activation, for which a mechanistic proposition is reported. ESR data showed all alkylated hydrazides, in contrast to non-substituted hydrazides, only generated alkyl-based radicals. The structural modifications did not improve minimal inhibitory concentration (MIC) against MTB in comparison to isoniazid iron complex, providing support to isonicotinoyl radical formation as a requirement for activity. Nonetheless, the pyrazinoic acid hydrazide iron complex showed redox-mediated activation using H2O2 with generation of a pyrazinoyl radical intermediate and production of pyrazinoic acid, which is in fact the active metabolite of pyrazinamide prodrug. Thereby, this strategy can also unveil new opportunities for activation of this type of drug.

Synthesis, X-ray crystal structures, optical properties and modelling data of neutral bis(1,2-dithiolene) nickel complexes of the “non-cyclic SR” family

Three nickel-bisdithiolene-based compounds were synthesized and characterized by X-ray single crystal (for two of them), electrochemical and spectroscopic analyses. A minor change in the alkyl chain structure surrounding the nickel-bisdithiolene core induces dramatic changes in molecular packing: complex 1 crystallizes in a triclinic (P) space group while complex 3 crystallizes in a monoclinic (C2/c) space group. No such differences are to be noted concerning electrochemical or spectroscopic characteristics, the alkyl chains induce no influence on electronic parameters. Furthermore, theoretical calculations were conducted to obtain theoretical insight of the behaviour of the complexes. The three complexes were investigated by DFT calculations using the PBE0 functional.

Efficient analoging around ethionamide to explore thioamides bioactivation pathways triggered by boosters in Mycobacterium tuberculosis

Ethionamide is a key antibiotic prodrug of the second-line chemotherapy regimen to treat tuberculosis. It targets the biosynthesis of mycolic acids thanks to a mycobacterial bioactivation carried out by the Baeyer-Villiger monooxygenase EthA, under the control of a transcriptional repressor called EthR. Recently, the drug-like molecule SMARt-420, which triggers a new transcriptional regulator called EthR2, allowed the derepression a cryptic alternative bioactivation pathway of ethionamide. In order to study the bioactivation of a collection of thioisonicotinamides through the two bioactivation pathways, we developed a new two-step chemical pathway that led to the efficient synthesis of eighteen ethionamide analogues. Measurements of the antimycobacterial activity of these derivatives, used alone and in combination with boosters BDM41906 or SMARt-420, suggest that the two different bioactivation pathways proceed via the same mechanism, which implies the formation of similar metabolites. In addition, an electrochemical study of the aliphatic thioisonicotinamide analogues was undertaken to see whether their oxidation potential correlates with their antitubercular activity measured in the presence or in the absence of the two boosters.

Antitrypanosomatid Pharmacomodulation at Position 3 of the 8-Nitroquinolin-2(1H)-one Scaffold Using Palladium-Catalysed Cross-Coupling Reactions

An antikinetoplastid pharmacomodulation study at position 3 of the recently described hit molecule 3‐bromo‐8‐nitroquinolin‐2(1H)‐one was conducted. Twenty‐four derivatives were synthesised using the Suzuki–Miyaura cross‐coupling reaction and evaluated in vitro on both Leishmania infantum axenic amastigotes and Trypanosoma brucei brucei trypomastigotes. Introduction of a para‐carboxyphenyl group at position 3 of the scaffold led to the selective antitrypanosomal hit molecule 3‐(4‐carboxyphenyl)‐8‐nitroquinolin‐2(1H)‐one (21) with a lower reduction potential (−0.56 V) than the initial hit (−0.45 V). Compound 21 displays micromolar antitrypanosomal activity (IC50=1.5 μm) and low cytotoxicity on the human HepG2 cell line (CC50=120 μm), having a higher selectivity index (SI=80) than the reference drug eflornithine. Contrary to results previously obtained in this series, hit compound 21 is inactive toward L. infantum and is not efficiently bioactivated by T. brucei brucei type I nitroreductase, which suggests the existence of an alternative mechanism of action.