A Single-Pot Synthesis of Atovaquone: An Antiparasitic Drug of Choice

Regio- and Stereoselective Construction of 1,3,5-Triaroylcyclohexanes via KOtBu-Mediated Cyclotrimerization of Aryl Vinyl Ketones

Herein, we disclose a simple one-pot method for an efficient regio- and stereoselective synthesis of 1,3,5-triaroylcyclohexanes from aryl vinyl ketones using potassium tert-butoxide. The developed protocol allows the construction of various symmetrically substituted cyclohexanes in good to excellent yields. The major product 2 also can be converted to the product 3 (all equatorial) conveniently by acid catalysis. This protocol features a good substrate scope and functional group compatibility.

The Oxidation of Electron-Rich Arenes Using a H2O2-Proline System

This study introduces a novel proline-catalyzed oxidation system employing hydrogen peroxide to synthesize quinones from a diverse range of substrates, including hydroquinones, phenols, resorcinols, aldehydes, and polycyclic aromatics. This approach is well-aligned with green chemistry principles, offering a more environmentally benign approach than earlier studies. Notably, this approach uses cost-effective reagents, proline as a readily available organocatalyst, reduced equivalents of H2O2, metal-free conditions, and notably short reaction times to achieve moderate-to-high yields. This promising approach encourages further exploration of the H2O2-proline system in oxidation reactions. This study's innovative approach and good results set a strong foundation for future research to expand the scope and efficiency of green oxidation processes.

2-hydroxy-1,4-naphthoquinones with 3-alkyldiarylether groups: synthesis and Plasmodium falciparum inhibitory activity

Background: In 1948, the synthesis and Plasmodium lophurae activity of 2-hydroxy-1,4-naphthoquinones containing 3-alkyldiarylether side chains was reported. Method/results: The synthesis of five related compounds, designed to be more metabolically stable, was pursued. The compounds were synthesized using a radical alkylation reaction with naphthoquinones. One compound had a lower IC50 value against various strains of Plasmodium falciparum and assay data indicate that it binds to the Qo site of cytochrome bc1. With a low yield for the radical alkylation of the most active compound, a reductive alkylation method with used to improve reaction yields. Conclusion: Further synthetic knowledge was obtained, and the assay data indicate that there are sensitivity differences between avian and human malarial parasites for these molecules.

1,2,4-Trifunctionalized Cyclohexane Synthesis via a Diastereoselective Reductive Cope Rearrangement and Functional Group Interconversion Strategy

Polyfunctionalized cyclohexanes are privileged scaffolds in drug discovery. Reported herein is a method for synthesizing 1,2,4-trifunctionalized cyclohexanes via diastereoselective reductive Cope rearrangement. The scaffolds obtained can be derivatized by orthogonal functional group interconversion to cyclohexanes bearing a 1-amide, 2-branched arylallyl, and variable 4-functional group.

Antimalarial Inhibitors Targeting Epigenetics or Mitochondria in Plasmodium falciparum: Recent Survey upon Synthesis and Biological Evaluation of Potential Drugs against Malaria

Despite many efforts, malaria remains among the most problematic infectious diseases worldwide, mainly due to the development of drug resistance by P. falciparum. Over the past decade, new essential pathways have been emerged to fight against malaria. Among them, epigenetic processes and mitochondrial metabolism appear to be important targets. This review will focus on recent evolutions concerning worldwide efforts to conceive, synthesize and evaluate new drug candidates interfering selectively and efficiently with these two targets and pathways. The focus will be on compounds/scaffolds that possess biological/pharmacophoric properties on DNA methyltransferases and HDAC’s for epigenetics, and on cytochrome bc1 and dihydroorotate dehydrogenase for mitochondrion.

Repurposing auranofin for treatment of Experimental Cerebral Toxoplasmosis

PURPOSES

Evaluate the effect of auranofin on the early and late stages of chronic infection with Toxoplasma gondii avirulent ME49 strain.

METHODS

Swiss albino mice were orally inoculated with 10 cysts of Toxoplasma gondii, and orally treated with auranofin or septazole in daily doses of 20 mg/kg or 100 mg /kg, respectively, for 30 days. Treatment began either on the same day of infection and mice were sacrificed at the 60th day postinfection or the treatment started after 60 days of infection and mice were sacrificed at the 90th day postinfection.

RESULTS

Auranofin significantly reduced the brain cyst burden and inflammatory reaction at both stages of infection compared to the infected non-treated control. More remarkably, auranofin significant reduced the brain cyst burden in the late stage, while septazole failed. Hydrogen peroxide level was significantly increased in the brain homogenate of mice treated with auranofin only at the early stage of infection. Ultrastructral studies revealed that the anti-Toxoplasma effect of auranofin is achieved by changing the membrane permeability and inducing apoptosis.

CONCLUSIONS

Thus, auranofin could be an alternative for the standard treatment regimen of toxoplasmosis and these results are considered another achievement for the drug against parasitic infection. Being a FDA-approved drug, it can be rapidly evaluated in clinical trials.

Site Selective Chlorination of C(sp3 )-H Bonds Suitable for Late-Stage Functionalization

C(sp³ )-Cl bonds are present in numerous biologically active small molecules, and an ideal route for their preparation is by the chlorination of a C(sp³ )-H bond. However, most current methods for the chlorination of C(sp³ )-H bonds are insufficiently site selective and tolerant of functional groups to be applicable to the late-stage functionalization of complex molecules. We report a method for the highly selective chlorination of tertiary and benzylic C(sp³ )-H bonds to produce the corresponding chlorides, generally in high yields. The reaction occurs with a mixture of an azidoiodinane, which generates a selective H-atom abstractor under mild conditions, and a readily-accessible and inexpensive copper(II) chloride complex, which efficiently transfers a chlorine atom. The reaction's exceptional functional group tolerance is demonstrated by the chlorination of >30 diversely functionalized substrates and the late-stage chlorination of a dozen derivatives of natural products and active pharmaceutical ingredients.

Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes

This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc1 and b6f (Cytbc1/b6f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc1/b6f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc1/b6f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc1/b6f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.

P2X7 receptor inhibition by 2-amino-3-aryl-1,4-naphthoquinones

Extracellular ATP activates purinergic receptors such as P2X7, cationic channels for Ca²⁺, K⁺, and Na⁺. There is robust evidence of the involvement of these receptors in the immune response, so P2X7 receptors (P2X7R) are considered a potential therapeutic target for the development of anti-inflammatory drugs. Although there are many studies of the anti-inflammatory properties of naphthoquinones, these molecules have not yet been explored as P2X7 antagonists. In previous work, our group prepared 3-substituted (halogen or aryl) 2-hydroxy-1,4-naphthoquinones and studied their action on P2X7R. In this paper, eight 2-amino-3-aryl-1,4-naphthoquinones were evaluated to identify the inhibitory activity on P2X7R and the toxicological profile. Three analogues (AD-4CN, AD-4Me, and AD-4F) exhibited reduced toxicity for mammalian cells with CC₅₀ values higher than 500 µM. These three 3-substituted 2-amino-1,4-naphthoquinones inhibited murine P2X7R (mP2X7R) in vitro. However, the analogues AD-4CN and AD-4Me showed low selectivity index values. AD-4F inhibited both mP2X7R and human P2X7R (hP2X7R) with IC₅₀ values of 0.123 and 0.93 µM, respectively. Additionally, this analogue exhibited higher potency than BBG at inhibiting the ATP-induced release of IL-1β in vitro. Carrageenan-induced paw edema in vivo was reversed for AD-4F with an ID₅₀ value of 11.51 ng/kg. Although AD-4F was less potent than previous 3-substituted (halogen or aryl) 2-hydroxy-1,4-naphthoquinones such as AN-04in vitro, this 3-substituted 2-amino-1,4-naphthoquinone revealed higher potency in vivo to reduce the edematogenic response. In silico analysis suggests that the binding site of the novel 2-amino-3-aryl-1,4-naphthoquinone derivatives, including all the tautomeric forms, is located in the pore area of the hP2X7R model. Based on these results, we considered AD-4F to be a satisfactory P2X7R inhibitor. AD-4F might be used as a scaffold structure to design a novel series of inhibitors with potential inhibitory activity on murine (mP2X7R) and human (hP2X7R) P2X7 receptors.

Systematic Identification of Thiosemicarbazides for Inhibition of Toxoplasma gondii Growth In Vitro

One of the key stages in the development of new therapies in the treatment of toxoplasmosis is the identification of new non-toxic small molecules with high specificity to Toxoplasma gondii. In the search for such structures, thiosemicarbazide-based compounds have emerged as a novel and promising leads. Here, a series of imidazole-thiosemicarbazides with suitable properties for CNS penetration was evaluated to determine the structural requirements needed for potent anti-Toxoplasma gondii activity. The best 4-arylthiosemicarbazides 3 and 4 showed much higher potency when compared to sulfadiazine at concentrations that are non-toxic to the host cells, indicating a high selectivity of their anti-toxoplasma activity.

Pd/C-catalyzed dehydrogenation of 2-cinnamoylbenzoic acids to 3-benzylidene-3H-isochroman-1,4-diones

Pd/C, a widely accepted hydrogenation catalyst, is found to catalytically dehydrogenate 2-cinnamoylbenzoic acids to 3-benzylidene-3-H-isochroman-1,4-diones with H₂ as the only byproduct.

Late-Stage C-H Alkylation of Heterocycles and 1,4-Quinones via Oxidative Homolysis of 1,4-Dihydropyridines

Under oxidative conditions, 1,4-dihydropyridines (DHPs) undergo a homolytic cleavage, forming exclusively a Csp3-centered radical that can engage in the C-H alkylation of heterocyclic bases and 1,4-quinones. DHPs are readily prepared from aldehydes, and considering that aldehydes normally require harsh reaction conditions to take part in such transformations, with mixtures of alkylated and acylated products often being obtained, this net decarbonylative alkylation approach becomes particularly useful. The present method takes place under mild reaction conditions and requires only persulfate as a stoichiometric oxidant, making the procedure suitable for the late-stage C-H alkylation of complex molecules. Notably, structurally complex pharmaceutical agents could be functionalized or prepared with this protocol, such as the antimalarial Atovaquone and antitheilerial Parvaquone, thus evidencing its applicability. Mechanistic studies revealed a likely radical chain process via the formation of a dearomatized intermediate, providing a deeper understanding of the factors governing the reactivity of these radical forebears.

Synthesis, characterization and biological activities of 3-aryl-1,4-naphthoquinones – green palladium-catalysed Suzuki cross coupling

Antifungal and trypanocidal aryl-1,4-naphthoquinones were prepared through an aqueous Suzuki protocol with reflux or microwave irradiation.