Synthesis and biological evaluation of 1,4-naphthoquinones and quinoline-5,8-diones as antimalarial and schistosomicidal agents

Lewis Acid-Catalyzed Benzannulation of Vinyloxiranes with 3-Formylchromones or 1,4-Quinones for Diversely Functionalized 2-Hydroxybenzophenones, 1,4-Naphthoquinones, and Anthraquinones

A facile and convenient protocol for the regioselective construction of functionalized 2-hydroxybenzophenones is described. This protocol involves the Sc(OTf)3/BF3·OEt2-catalyzed benzannulation of 2-vinyloxirans with 3-formylchromone, which involves cascade in situ diene formation, [4 + 2] cycloaddition, elimination, and ring-opening strategies. Moreover, it provides an expedited synthetic pathway to access biologically intriguing 1,4-naphthoquinones and anthraquinones including vitamin K3 and tectoquinone. The synthesized compounds also hold potential for use as UV filters and show promise as chemosensors for Cu2+ and Mg2+ ions.

Protection Activity of 1,4-Naphthoquinones in Rotenone-Induced Models of Neurotoxicity

The MTS cell viability test was used to screen a mini library of natural and synthetic 1,4-naphthoquinone derivatives (1,4-NQs) from marine sources. This screening identified two highly effective compounds, U-443 and U-573, which showed potential in protecting Neuro-2a neuroblastoma cells from the toxic effects of rotenone in an in vitro model of neurotoxicity. The selected 1,4-NQs demonstrated the capability to reduce oxidative stress by decreasing the levels of reactive oxygen species (ROS) and nitric oxide (NO) in Neuro-2a neuroblastoma cells and RAW 264.7 macrophage cells and displayed significant antioxidant properties in mouse brain homogenate. Normal mitochondrial function was restored and the mitochondrial membrane potential was also regained by 1,4-NQs after exposure to neurotoxins. Furthermore, at low concentrations, these compounds were found to significantly reduce levels of proinflammatory cytokines TNF and IL-1β and notably inhibit the activity of cyclooxygenase-2 (COX-2) in RAW 264.7 macrophages. The results of docking studies showed that the 1,4-NQs were bound to the active site of COX-2, analogically to a known inhibitor of this enzyme, SC-558. Both substances significantly improved the behavioral changes in female CD1 mice with rotenone-induced early stage of Parkinson's disease (PD) in vivo. It is proposed that the 1,4-NQs, U-443 and U-573, can protect neurons and microglia through their potent anti-ROS and anti-inflammatory activities.

Exploring the Therapeutic Marvels: A Comprehensive Review on the Biological Potential of Quinoline-5,8-Dione

Quinoline-5,8-diones, also referred to as 5,8-quinolinediones or quinolinequinones, have been researched extensively for their antiproliferative effects, where they displayed great results. Other than anticancer, they exhibit multiple activities such as antimalarial, antiviral, antibacterial, and antifungal activities. Natural quinolinequinones have also been known for their significant activities. The review highlights the diverse biological activities exhibited by synthetic quinoline- 5,8-diones over the past two decades. Continued research in this field is warranted to fully exploit the therapeutic potential of these intriguing compounds and their derivatives for future drug development. By comprehensively evaluating the therapeutic applications and biological activities of quinoline-5,8-dione derivatives, this review endeavors to provide researchers and practitioners with a valuable resource that will foster informed decision-making and inspire further investigations into harnessing the immense potential of this intriguing scaffold for the benefit of human health.

Synthesis and structure-activity relationship studies of naphthoquinones as STAT3 inhibitors

Based on previous studies, we synthesized a novel class of ortho- and para-naphthoquinones derivatives bearing a phenolic hydroxy or sulfonamide moiety and evaluated their in vitro antiproliferative and signal transducer and activator of transcription-3 (STAT3) phosphorylation inhibitory activities. The biological evaluations of these naphthoquinones revealed that ortho-naphthoquinones containing a phenolic hydroxyl group exhibited greater antiproliferative activity compared to compounds without a phenolic hydroxyl group. Among the synthesized para-naphthoquinones, 21, which has a condensed sulfonamide structure, showed substantially higher antiproliferative activity than that of the parent compound, and was also found to inhibit the phosphorylation of STAT3(Y705) in a dose-dependent manner. A docking simulation using AutoDock Vina suggested that 21 could directly bind to the hinge region of STAT3.

Biological activity of 1,2,3-triazole-2-amino-1,4-naphthoquinone derivatives and their evaluation as therapeutic strategy for malaria control

Malaria can be caused by several Plasmodium species and the development of an effective vaccine is challenging. Currently, the most effective tool to control the disease is the administration of specific chemotherapy; however, resistance to the frontline antimalarials is one of the major problems in malaria control and thus the development of new drugs becomes urgent. The study presented here sought to evaluate the antimalarial activities of compounds derived from 2-amino-1,4-naphthoquinones containing 1,2,3-triazole using in vivo and in vitro models. 1H-1,2,3-Triazole 2-amino-1,4-naphthoquinone derivatives were synthesized and evaluated for antimalarial activity in vitro, using P. falciparum W2 chloroquine (CQ) resistant strain and in vivo using the murine-P. berghei ANKA strain. Acute toxicity was determined as established by the OECD (2001). Cytotoxicity was evaluated against HepG2 and Vero mammalian cell lines. Transmission electron microscopy of the Plasmodium falciparum trophozoite (early and late stages) was used to evaluate the action of compounds derived at ultra-structural level. The compounds displayed low cytotoxicity CC₅₀ > 100 μM, neither did they cause hemolysis at the tested doses and nor the signs of toxicity in the in vivo acute toxicity test. Among the five compounds tested, one showed IC₅₀ values in submicromolar range of 0.8 μM. Compounds 7, 8 and 11 showed IC₅₀ values < 5 μM, and selectivity index (SI) ranging from 6.8 to 343 for HepG2, and from 13.7 to 494.8 for Vero cells. Compounds 8 and 11 were partially active against P. berghei induced parasitemia in vivo. Analysis of the ultrastructural changes associated with the treatment of these two compounds, showed trophozoites with completely degraded cytoplasm, loss of membrane integrity, organelles in the decomposition stage and possible food vacuole deterioration. Our results indicated that compounds 8 and 11 may be considered hit molecules for antimalarial drug discovery platform and deserve further optimization studies.

Toward the Total Synthesis of Alpkinidine: Synthesis of Haloquinone CE Ring System Synthons and Attempted Nucleophilic Bisannulation

Model chemistry involving the bisannulation of 2,3-dichloro-1,4-naphthoquinone with the ester enolate derived from ethyl o-nitrophenylacetic acid, which rapid assembled the ABCD ring system of a pentacyclic pyrroloacridine, has been applied to the attempted synthesis of the marine natural product alpkinidine. The reaction of ethyl o-nitrophenylacetic acid with 6,7-dichloro-2-methylisoquinoline-1,5,8(2H)-trione, required to extend the model strategy to alpkinidine, was unfruitful, giving only complex mixtures. Efforts to direct the regiochemistry of the key Michael substitution step using 6-bromo-2-methylisoquinoline-1,5,8(2H)-trione afforded an adduct sharing the complete carbon skeleton of alpkinidine, but this could not be elaborated to the natural product.

Menadione: a platform and a target to valuable compounds synthesis

Naphthoquinones are important natural or synthetic compounds belonging to the general class of quinones. Many compounds in this class have become drugs that are on the pharmaceutical market for the treatment of various diseases. A special naphthoquinone derivative is menadione, a synthetic naphthoquinone belonging to the vitamin K group. This compound can be synthesized by different methods and it has a broad range of biological and synthetic applications, which will be highlighted in this review.

The Synthesis and Chemistry of Quinolinediones and their Carbocyclic Analogs

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Quinoline-5,8-dione and naphthoquinone nuclei are very important substructures in industrial chemicals and pharmaceuticals. These compounds exhibit a wide variety of activities, including activity as antifungal, antibacterial, antimalarial, antineoplastic, anticoagulant, anticancer, antiviral, radical scavenging, antiplatelet, trypanocidal, cytotoxic and antineoplastic agents. Currently, several research articles about the importance of many natural and synthetic drugs containing quinolinequinone have been reported. This review covers the progress in quinolinequinone and naphthoquinone chemistry over the last five decades.

Structure-Activity Relationship Studies of Antimicrobial Naphthoquinones Derived from Constituents of Tabebuia avellanedae

In this study, based on our previous study, derivatives of naphtho[2,3-b]furan-4,9-diones were synthesized and their antimicrobial activities were evaluated. The screening of these naphthoquinones revealed that the fluorine-containing NQ008 compound exhibited potent and broad antimicrobial activities against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative bacteria, and fungi. The results of the ratio of the minimum bactericidal concentration (MBC) to the minimum inhibitory concentrations (MICs) and time-kill assays suggest that the mode of action of NQ008 is bactericidal. Additionally, the results of a drug resistance study revealed that NQ008 exhibited potent antibacterial activity and may delay the development of bacteria resistance. Furthermore, NQ008 exhibited preliminary antiviral activity against the swine influenza virus and Feline calicivirus.

Bioinspired Photoredox Benzylation of Quinones

3-Benzylmenadiones were obtained in good yield by using a blue-light-induced photoredox process in the presence of Fe(III), oxygen, and γ-terpinene acting as a hydrogen-atom transfer 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 the photogenerated superoxide anion radical.

PfMFR3: A Multidrug-Resistant Modulator in Plasmodium falciparum

In malaria, chemical genetics is a powerful method for assigning function to uncharacterized genes. MMV085203 and GNF-Pf-3600 are two structurally related napthoquinone phenotypic screening hits that kill both blood- and sexual-stage P. falciparum parasites in the low nanomolar to low micromolar range. In order to understand their mechanism of action, parasites from two different genetic backgrounds were exposed to sublethal concentrations of MMV085203 and GNF-Pf-3600 until resistance emerged. Whole genome sequencing revealed all 17 resistant clones acquired nonsynonymous mutations in the gene encoding the orphan apicomplexan transporter PF3D7_0312500 (pfmfr3) predicted to encode a member of the major facilitator superfamily (MFS). Disruption of pfmfr3 and testing against a panel of antimalarial compounds showed decreased sensitivity to MMV085203 and GNF-Pf-3600 as well as other compounds that have a mitochondrial mechanism of action. In contrast, mutations in pfmfr3 provided no protection against compounds that act in the food vacuole or the cytosol. A dihydroorotate dehydrogenase rescue assay using transgenic parasite lines, however, indicated a different mechanism of action for both MMV085203 and GNF-Pf-3600 than the direct inhibition of cytochrome bc1. Green fluorescent protein (GFP) tagging of PfMFR3 revealed that it localizes to the parasite mitochondrion. Our data are consistent with PfMFR3 playing roles in mitochondrial transport as well as drug resistance for clinically relevant antimalarials that target the mitochondria. Furthermore, given that pfmfr3 is naturally polymorphic, naturally occurring mutations may lead to differential sensitivity to clinically relevant compounds such as atovaquone.

Evaluation of the Toxicity on Lung Cells of By-Products Present in Naphthalene Secondary Organic Aerosols

In 2018, seven million people died prematurely due to exposure to pollution. Polycyclic aromatic hydrocarbons (PAHs) are a significant source of secondary organic aerosol (SOA) in urban areas. We investigated the toxic effects of by-products of naphthalene SOA on lung cells. These by-products were 1,4-naphthoquinone (1,4-NQ), 2-hydroxy-1,4-naphthoquinone (2-OH-NQ), phthalic acid (PA) and phthaldialdehyde (OPA). Two different assessment methodologies were used to monitor the toxic effects: real-time cell analysis (RTCA) and the Holomonitor, a quantitative phase contrast microscope. The chemicals were tested in concentrations of 12.5 to 100 µM for 1,4-NQ and 1 to 10 mM for 2-OH-NQ, PA and OPA. We found that 1,4-NQ is toxic to cells from 25 to 100 µM (EC50: 38.7 µM ± 5.2); 2-OH-NQ is toxic from 1 to 10mM (EC50: 5.3 mM ± 0.6); PA is toxic from 5 to 10 mM (EC50: 5.2 mM ± 0.3) and OPA is toxic from 2.5 to 10 mM (EC50: 4.2 mM ± 0.5). Only 1,4-NQ and OPA affected cell parameters (migration, motility, motility speed and optical volume). Furthermore, 1,4-NQ is the most toxic by-product of naphthalene, with an EC50 value that was one hundred times higher than those of the other compounds. RTCA and Holomonitor analysis showed a complementarity when studying the toxicity induced by chemicals.

Antimalarial application of quinones: A recent update

Atovaquone belongs to a naphthoquinone class of drugs and is used in combination with proguanil (Malarone) for the treatment of acute, uncomplicated malaria caused by Plasmodium falciparum (including chloroquine-resistant P. falciparum/P. vivax). Numerous quinone-derived compounds have attracted considerable attention in the last few decades due to their potential in antimalarial drug discovery. Several semi-synthetic derivatives of natural quinones, synthetic quinones (naphtho-/benzo-quinone, anthraquinones, thiazinoquinones), and quinone-based hybrids were explored for their in vitro and in vivo antimalarial activities. A careful literature survey revealed that this topic has not been compiled as a review article so far. Therefore, we herein summarise the recent discovery (the year 2009-2020) of quinone based antimalarial compounds in chronological order. This compilation would be very useful towards the exploration of novel quinone-derived compounds against malarial parasites with promising efficacy and lesser side effects.

Chemotherapy for human schistosomiasis: how far have we come? What's new? Where do we go from here?

Globally, schistosomiasis threatens more than 700 million lives, mostly children, in poor localities of tropical and sub-tropical areas with morbidity due to acute and chronic pathological manifestations of the disease. After a century since the first antimonial-based drugs were introduced to treat the disease, anti-schistosomiasis drug development is again at a bottleneck with only one drug, praziquantel, available for treatment purposes. This review focuses on promising chemotypes as potential starting points in a drug discovery effort to meet the urgent need for new schistosomicides.

Thiazinoquinones as New Promising Multistage Schistosomicidal Compounds Impacting Schistosoma mansoni and Egg Viability

Schistosomiasis is the most significant neglected tropical parasitic disease caused by helminths in terms of morbidity and mortality caused by helminths. In this work, we present the antischistosomal activity against Schistosoma mansoni of a rationally selected small set of thiazinoquinone derivatives, some of which were previously found to be active against Plasmodium falciparum and others synthesized ad hoc. The effects on larvae, juvenile, and adult parasite viability as well as on egg production and development were investigated, resulting in the identification of new multistage antischistosomal hit compounds. The most promising compounds 6, 8, 13, and 14 with a LC₅₀ value on schistosomula from ∼5 to ∼15 μM also induced complete death of juvenile (28 days old) and adult worm pairs (7 weeks old) and a detrimental effect on egg production and development in vitro. Structure-activity relationships (SARs) were analyzed by means of computational studies leading to the hypothesis of a redox-based mechanism of action with a one-electron reduction bioactivation step and the subsequent formation of a toxic semiquinone species, similarly to what was previously observed for the antiplasmodial activity. Our results also evidenced that the selective toxicity against mammalian cells or parasites as well as specific developmental stages of a parasite can be addressed by varying the nature of the introduced substituents.

5,8-Quinolinedione Scaffold as a Promising Moiety of Bioactive Agents

Natural 5,8-quinolinedione antibiotics exhibit a broad spectrum of activities including anticancer, antibacterial, antifungal, and antimalarial activities. The structure-activity research showed that the 5,8-quinolinedione scaffold is responsible for its biological effect. The subject of this review report is a presentation of the pharmacological activity of synthetic 5,8-quinolinedione compounds containing different groups at C-6 and/or C-7 positions. The relationship between the activity and the mechanism of action is included if these data have been included in the original literature. The review mostly covers the period between 2000 and 2019. Previously published literature data were used to present historical points.

Synthesis and Antiplasmodial Activity of 1,2,3-Triazole-Naphthoquinone Conjugates

A series of 34 1,2,3-triazole-naphthoquinone conjugates were synthesized via copper-catalyzed cycloaddition (CuAAC). They were evaluated for their in vitro antimalarial activity against chloroquine-sensitive strains of Plasmodium falciparum and against three different tumor cell lines (SKBr-3, MCF-7, HEL). The most active antimalarial compounds showed a low antiproliferative activity. Simplified analogues were also obtained and some structure–activity relationships were outlined. The best activity was obtained by compounds 3s and 3j, having IC₅₀ of 0.8 and 1.2 μM, respectively. Molecular dockings were also carried on Plasmodium falciparum enzyme dihydroorotate dehydrogenase (PfDHODH) in order to rationalize the results.

Synthesis and Antimicrobial Evaluation of 1,4-Naphthoquinone Derivatives as Potential Antibacterial Agents

1,4-Naphthoquinones are an important class of compounds present in a number of natural products. In this study, a new series of 1,4-naphthoquinone derivatives were synthesized. All the synthesized compounds were tested for in vitro antimicrobial activity. In this present investigation, two Gram-positive and five Gram-negative bacterial strains and one pathogenic yeast strain were used to determine the antibacterial activity. Naphthoquinones tested for its antibacterial potencies, among seven of them displayed better antimicrobial activity against Staphylococcus aureus (S. aureus; 30-70 μg/mL). Some of the tested compounds showed moderate to low antimicrobial activity against Pseudomonas aeruginosa (P. aeruginosa) and Salmonella bongori (S. bongori; 70-150 μg/mL). In addition, most active compounds against S. aureus were evaluated for toxicity to human blood cells using a hemolysis assay. For better understanding, reactive oxygen species (ROS) generation, time-kill kinetic study, and apoptosis, necrosis responses were investigated for three representative compounds.

1,4-Naphthoquinone Analogues: Potent Antibacterial Agents and Mode of Action Evaluation

1,4-Naphthoquinones have antibacterial activity and are a promising new class of compound that can be used to treat bacterial infections. The goal was to improve effective antibacterial agents; therefore, we synthesized a new class of naphthoquinone hybrids, which contain phenylamino-phenylthio moieties as significant counterparts. Compound 4 was modified as a substituted aryl amide moiety, which enhanced the antibacterial activity of earlier compounds 3 and 4. In this study, five bacterial strains Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes), Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Klebsiella pneumoniae (K. pneumoniae) were used to evaluate the antibacterial potency of synthesized naphthoquinones using the minimal inhibitory concentration (MIC) method. Most of the studied naphthoquinones demonstrated major antibacterial activity with a MIC of 15.6 µg/mL–500 µg/mL. Selected compounds (5a, 5f and 5x) were studied for the mode of action, using intracellular ROS generation, determination of apoptosis by the Annexin V-FITC/PI assay, a bactericidal kinetic study and in silico molecular modelling. Additionally, the redox potentials of the specified compounds were confirmed by cyclic voltammetry (CV).

In vitro antiplasmodial activity, pharmacokinetic profiles and interference in isoprenoid pathway of 2-aniline-3-hydroxy-1.4-naphthoquinone derivatives

Background

Plasmodium falciparum has shown multidrug resistance, leading to the necessity for the development of new drugs with novel targets, such as the synthesis of isoprenic precursors, which are excellent targets because the pathway is different in several steps when compared with the human host. Naphthoquinone derivatives have been described as potentially promising for the development of anti-malarial leader molecules. In view of that, the focus in this work is twofold: first, evaluate the in vitro naphthoquinone antiplasmodial activity and cytotoxicity; secondly, investigate one possible action mechanism of two derivatives of hydroxy-naphthoquinones.

Results

The two hydroxy-naphthoquinones derivatives have been tested against P. falciparum in vitro, using strains of parasites chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2), causing 50% inhibition of parasite growth with concentrations that varied from 7 to 44.5 μM. The cell viability in vitro against RAW Cell Line displayed IC₅₀ = 483.5 and 714.9 μM, whereas, in primary culture tests using murine macrophages, IC₅₀ were 315.8 and 532.6 μM for the two selected compounds, causing no haemolysis at the doses tested. The in vivo acute toxicity assays exhibited a significant safety margin indicated by a lack of systemic and behavioural toxicity up to 300 mg/kg. It is suggested that this drug seems to inhibit the biosynthesis of isoprenic compounds, particularly the menaquinone and tocopherol.

Conclusions

These derivatives have a high potential for the development of new anti-malarial drugs since they showed low toxicity associated to a satisfactory antiplasmodial activity and possible inhibition of a metabolic pathway distinct from the pathways found in the mammalian host.

QSAR modeling and chemical space analysis of antimalarial compounds

Generative topographic mapping (GTM) has been used to visualize and analyze the chemical space of antimalarial compounds as well as to build predictive models linking structure of molecules with their antimalarial activity. For this, a database, including ~3000 molecules tested in one or several of 17 anti-Plasmodium activity assessment protocols, has been compiled by assembling experimental data from in-house and ChEMBL databases. GTM classification models built on subsets corresponding to individual bioassays perform similarly to the earlier reported SVM models. Zones preferentially populated by active and inactive molecules, respectively, clearly emerge in the class landscapes supported by the GTM model. Their analysis resulted in identification of privileged structural motifs of potential antimalarial compounds. Projection of marketed antimalarial drugs on this map allowed us to delineate several areas in the chemical space corresponding to different mechanisms of antimalarial activity. This helped us to make a suggestion about the mode of action of the molecules populating these zones.

Antiparasitic activity of menadione (vitamin K3) against Schistosoma mansoni in BABL/c mice

Schistosomiasis is one of the neglected tropical diseases affecting nearly quarter of a billion people in economically challenged tropical and subtropical countries of the world. Praziquantel (PZQ) is the only drug currently available to treat this parasitic disease in spite being ineffective against juvenile worms and concerns about developing resistance to treat reinfections. Our earlier in vitro viability studies demonstrated significant antiparasitic activity of menadione (MEN) (vitamin K₃) against Schistosoma mansoni adult worms. To gain insight into plausible mechanism of antischistosomal activity of MEN, its effect on superoxide anion levels in adult worms were studied in vitro which showed significant increases in both female and male worms. Further confirmation of the deleterious morphological changes in their teguments and organelles were obtained by ultrastructural analysis. Genotoxic and cytotoxic studies in male Swiss mice indicated that MEN was well tolerated at the oral dose of 500mg/kg using the criteria of MNPCE frequency and PCE/RBC ratio in the bone marrow of infected animals. The in vivo antiparasitic activity of MEN was conducted in female BALB/c mice infected with S. mansoni and significant reductions (P<0.001) in total worm burden were observed at single oral doses of 40 and 400mg/kg (48.57 and 61.90%, respectively). Additionally, MEN significantly reduced (P<0.001) the number of eggs in the liver of infected mice by 53.57 and 58.76%, respectively. Similarly, histological analysis of the livers showed a significant reduction (P<0.001) in the diameter of the granulomas. Since MEN is already in use globally as an over-the-counter drug for a variety of common ailments and a dietary supplement with a safety record in par with similar products when used in recommended doses, the above antiparasitic results which compare reasonably well with PZQ, make a compelling case for considering MEN to treat S. mansoni infection in humans.

Pharmacomodulation of the Antimalarial Plasmodione: Synthesis of Biaryl- and N-Arylalkylamine Analogues, Antimalarial Activities and Physicochemical Properties

With the aim of increasing the structural diversity on the early antimalarial drug plasmodione, an efficient and versatile procedure to prepare a series of biaryl- and N-arylalkylamines as plasmodione analogues is described. Using the naturally occurring and commercially available menadione as starting material, a 2-step sequence using a Kochi-Anderson reaction and subsequent Pd-catalyzed Suzuki-Miyaura coupling was developed to prepare three representative biphenyl derivatives in good yields for antimalarial evaluation. In addition, synthetic methodologies to afford 3-benzylmenadione derivatives bearing a terminal -N(Me)₂ or -N(Et)₂ in different positions (ortho, meta and para) on the aryl ring of the benzylic chain of plasmodione were investigated through reductive amination was used as the optimal route to prepare these protonable N-arylalkylamine privileged scaffolds. The antimalarial activities were evaluated and discussed in light of their physicochemical properties. Among the newly synthesized compounds, the para-position of the substituent remains the most favourable position on the benzyl chain and the carbamate -NHBoc was found active both in vitro (42 nM versus 29 nM for plasmodione) and in vivo in Plasmodium berghei-infected mice. The measured acido-basic features of these new molecules support the cytosol-food vacuole shuttling properties of non-protonable plasmodione derivatives essential for redox-cycling. These findings may be useful in antimalarial drug optimization.

Synthesis of functionalized alkyl substituted benzoquinones by Rh-catalyzed additions of boronic acids

An efficient, group tolerant one-pot process has been developed for the synthesis of functionalized-quinones, using a Rh-catalyzed addition as a key step.

Cytotoxicity, hemolysis and in vivo acute toxicity of 2-hydroxy-3-anilino-1,4-naphthoquinone derivatives

The 1,4-naphthoquinones, important members of the family of quinones are used as both crude extracts and as compound manipulated by the pharmaceutical industry. They have gained great emphasis by presenting different pharmacological properties as antibacterial, antiviral, antiprotozoal and anthelmintic, and has antitumor activity. Our aim was to evaluate the cytotoxicity, hemolytic activity and in vivo acute toxicity of three derivatives of 2-hydroxy-1,4-naphthoquinones. The cell viability in vitro against RAW Cell Line displayed IC₅₀ ranging of 483.5–2044.8 μM, whereas in primary culture tests using murine macrophages, IC₅₀ were 315.8–1408.0 μM for naphthoquinones derivatives 4a and 4c respectively, besides no hemolysis was observed at the dose tested. The in vivo acute toxicity assays exhibited a significant safety margin indicated by a lack of systemic and behavioral toxicity up to 300 mg/kg, and at a dose of 1000 mg/kg the derivatives not triggering signs of toxicity although the compound 4a have promoted hepatic steatosis and hyperemia in kidney tissue. Thereby, these modifications decrease the toxicity of the tested derivatives naphthoquinones, providing a high potential for the development of news drugs.

The Redox Cycler Plasmodione Is a Fast-Acting Antimalarial Lead Compound with Pronounced Activity against Sexual and Early Asexual Blood-Stage Parasites

Previously, we presented the chemical design of a promising series of antimalarial agents, 3-[substituted-benzyl]-menadiones, with potent in vitro and in vivo activities. Ongoing studies on the mode of action of antimalarial 3-[substituted-benzyl]-menadiones revealed that these agents disturb the redox balance of the parasitized erythrocyte by acting as redox cyclers-a strategy that is broadly recognized for the development of new antimalarial agents. Here we report a detailed parasitological characterization of the in vitro activity profile of the lead compound 3-[4-(trifluoromethyl)benzyl]-menadione 1c (henceforth called plasmodione) against intraerythrocytic stages of the human malaria parasite Plasmodium falciparum We show that plasmodione acts rapidly against asexual blood stages, thereby disrupting the clinically relevant intraerythrocytic life cycle of the parasite, and furthermore has potent activity against early gametocytes. The lead's antiplasmodial activity was unaffected by the most common mechanisms of resistance to clinically used antimalarials. Moreover, plasmodione has a low potential to induce drug resistance and a high killing speed, as observed by culturing parasites under continuous drug pressure. Drug interactions with licensed antimalarial drugs were also established using the fixed-ratio isobologram method. Initial toxicological profiling suggests that plasmodione is a safe agent for possible human use. Our studies identify plasmodione as a promising antimalarial lead compound and strongly support the future development of redox-active benzylmenadiones as antimalarial agents.

Mappability of drug-like space: towards a polypharmacologically competent map of drug-relevant compounds

Intuitive, visual rendering--mapping--of high-dimensional chemical spaces (CS), is an important topic in chemoinformatics. Such maps were so far dedicated to specific compound collections--either limited series of known activities, or large, even exhaustive enumerations of molecules, but without associated property data. Typically, they were challenged to answer some classification problem with respect to those same molecules, admired for their aesthetical virtues and then forgotten--because they were set-specific constructs. This work wishes to address the question whether a general, compound set-independent map can be generated, and the claim of "universality" quantitatively justified, with respect to all the structure-activity information available so far--or, more realistically, an exploitable but significant fraction thereof. The "universal" CS map is expected to project molecules from the initial CS into a lower-dimensional space that is neighborhood behavior-compliant with respect to a large panel of ligand properties. Such map should be able to discriminate actives from inactives, or even support quantitative neighborhood-based, parameter-free property prediction (regression) models, for a wide panel of targets and target families. It should be polypharmacologically competent, without requiring any target-specific parameter fitting. This work describes an evolutionary growth procedure of such maps, based on generative topographic mapping, followed by the validation of their polypharmacological competence. Validation was achieved with respect to a maximum of exploitable structure-activity information, covering all of Homo sapiens proteins of the ChEMBL database, antiparasitic and antiviral data, etc. Five evolved maps satisfactorily solved hundreds of activity-based ligand classification challenges for targets, and even in vivo properties independent from training data. They also stood chemogenomics-related challenges, as cumulated responsibility vectors obtained by mapping of target-specific ligand collections were shown to represent validated target descriptors, complying with currently accepted target classification in biology. Therefore, they represent, in our opinion, a robust and well documented answer to the key question "What is a good CS map?"

Identification of unusual C–Cl⋯π contacts in 2-(alkylamino)-3-chloro-1,4-naphthoquinones: effect of N-substituents on crystal packing, fluorescence, redox and anti-microbial properties

XRD study demonstrates the opening of unusual C–Cl⋯π synthon in 2-(alkylamino)-3-chloro-1,4-naphthoquinone. Notably, compound holding N-pyridylmethyl exhibits enhanced activity against S. aureus and proved to be more potent than ciprofloxacin.