A series of highly diversified 3‐aroylmenadiones was prepared by a new Friedel–Crafts acylation variant/oxidative demethylation strategy. A mild and versatile acylation was performed between 1,4‐dimethoxy‐2‐methylnaphthalene and various activated/deactivated benzoic and heteroaromatic carboxylic acids, in the presence of mixed trifluoroacetic anhydride and triflic acid, at room temperature and in air. The 1,4‐dimethoxy‐2‐methylnaphthalene‐derived benzophenones were isolated in high yield, and submitted to oxidative demethylation with cerium ammonium nitrate to produce 3‐benzoylmenadiones. All 1,4‐naphthoquinone derivatives were investigated as redox‐active electrophores by cyclic voltammetry. The electrochemical data recorded for 3‐acylated menadiones are characterized by a second redox process, the potentials of which cover a wide range of values (500 mV). These data emphasize the ability of the generated structural diversity at the 3‐aroyl chain of these electrophores to fine‐tune their corresponding redox potentials. These properties are of significance in the context of antimalarial drug development and understanding of the mechanism of bioactivation/action.

1,4-Quinones display unique redox and biological properties and have multiple applications in a wide array of fields, including health. Synthesis of diversely substituted quinonebased compounds remains difficult and usually consists of multiple step sequences. Interest in direct CÀ H radical alkylation of 1,4-quinones has thus continuously grown over this last decade. These reactions involve addition of carbon-centered radicals generated from radical precursors through decarbox-ylative alkylation, hydrogen-atom abstraction, or by carbonhalogen bond reduction. Recent progresses in radical chemistry, including photoredox catalysis, have provided useful tools for quinone functionalization. This Minireview describes the recent progress with these methodologies, including the new promising three-component cascade reactions involving quinones and alkenes, allowing for the preparation of complex substituted 1,4-quinones in a single step.

Plasmodione (PD) is a potent antimalarial redox-active 3-benzyl-menadione acting at low nM range concentrations on different malaria parasite stages. Specific bioactivation of PD was proposed to occur via a cascade of redox reactions starting from one electron-reduction, then benzylic oxidation, leading to generation of several key metabolites including the benzylic alcohol (PD-bzol) and the 3-benzoylmenadione (PDO). In this study, we showed that benzylic oxidation of PD is closely related to the formation of a benzylic semiquinone radical, which can be produced under two conditions: UV-photoirradiation, or catalyzed by P. falciparum apicoplast ferredoxin-NADP + reductase (PfFNR) redox cycling in the presence of oxygen and the parent PD. Electrochemical properties of both PD metabolites were investigated in DMSO and in water. The single-electron reduction potential values of PD, PD-bzol, PDO and a series of 3-benzoylmenadiones were determined according to ascorbate oxidation kinetics. These compounds possess enhanced reactivity towards PfFNR as compared with model quinones. Optimal conditions were set up to obtain the best conversion of the starting PD to corresponding metabolites. UV-irradiation of PD in isopropanol under positive oxygen pressure led to an isolated yield of 31% PDO through the transient semiquinone species formed in a cascade of reactions. In the presence of PfFNR, PDO and PD-bzol could be observed during long lasting redox cycling of PD continuously fueled by NADPH regenerated by an enzymatic system. Finally, we observed and quantified the effect of PD on the production of oxidative stress in the apicoplast of transgenic 3D7 P. falciparum parasites by using the described genetically encoded glutathione redox sensor hGrx1-roGFP2 methodology. The observed fast ROS pulse released in the apicoplast is proposed to be mediated by PD redox cycling catalyzed by PfFNR.

Plasmodione ( PD ) is a potent antimalarial redox-active drug acting at low nM range concentrations on different malaria parasite stages. In this study, in order to determine the precise PD protein interactome in parasites, we developed a class of (pro-)activity-based protein profiling probes (ABPP) as precursors of photoreactive benzophenone-like probes based on the skeleton of PD metabolites ( PDO ) generated in a cascade of redox reactions. Under UV-photoirradiation, we clearly demonstrate that benzylic oxidation of 3-benzylmenadione 11 produces the 3-benzoylmenadione probe 7 , allowing investigation of the proof-of-concept of the ABPP strategy with 3-benzoylmenadiones 7 – 10 . The synthesized 3-benzoylmenadiones, probe 7 with an alkyne group or probe 9 with -NO 2 in para position of the benzoyl chain, were found to be the most efficient photoreactive and clickable probes. In the presence of various H-donor partners, the UV-irradiation of the photoreactive ABPP probes generates different adducts, the expected “benzophenone-like” adducts (pathway 1) in addition to “benzoxanthone” adducts (via two other pathways, 2 and 3). Using both human and Plasmodium falciparum glutathione reductases, three protein ligand binding sites were identified following photolabeling with probes 7 or 9 . The photoreduction of 3-benzoylmenadiones ( PDO and probe 9 ) promoting the formation of both the corresponding benzoxanthone and the derived enone could be replaced by the glutathione reductase-catalyzed reduction step. In particular, the electrophilic character of the benzoxanthone was evidenced by its ability to alkylate heme, as a relevant event supporting the antimalarial mode of action of PD . This work provides a proof-of-principle that (pro-)ABPP probes can generate benzophenone-like metabolites enabling optimized activity-based protein profiling conditions that will be instrumental to analyze the interactome of early lead antiplasmodial 3-benzylmenadiones displaying an original and innovative mode of action.

3-Benzylmenadiones were obtained in good yields by using a blue light-induced photoredox process in the presence of Fe(III), oxygen and γ-terpinene acting as a HAT agent. This methodology is compatible with a wide variety of diversely substituted 1,4-naphthoquinones as well as various cheap, readily available benzyl bromides with excellent functional group tolerance. The benzylation mechanism was investigated and supports a three-step radical cascade with the key involvement of photogenerated superoxide anion radical.