Novel 8-nitroquinolin-2(1H)-ones as NTR-bioactivated antikinetoplastid molecules: Synthesis, electrochemical and SAR study

Synthesis of Nitrostyrylthiazolidine-2,4-dione Derivatives Displaying Antileishmanial Potential

A series of 61 thiazolidine-2,4-diones bearing a styryl group at position 5 was synthesized in 2-5 steps and their structure was proved by elemental and spectral analyses. The compounds obtained were evaluated in vitro against the promastigote stage of the kinetoplastid parasite Leishmania infantum and the human HepG2 cell line, to determine selectivity indices and to compare their activities with those of antileishmanial reference drugs. The study of structure-activity relationships indicated the potential of some derivatives bearing a nitro group on the phenyl ring, especially when located at the meta position. Thus, among the tested series, compound 14c appeared as a hit compound with good antileishmanial activity (EC50 = 7 µM) and low cytotoxicity against both the hepatic HepG2 and macrophage THP-1 human cell lines (CC50 = 101 and 121 µM, respectively), leading to good selectivity indices (respectively, 14 and 17), in comparison with the reference antileishmanial drug compound miltefosine (EC50 = 3.3 µM, CC50 = 85 and 30 µM, SI = 26 and 9). Regarding its mechanism of action, among several possibilities, it was demonstrated that compound 14c is a prodrug bioactivated, predominantly by L. donovani nitroreductase 1, likely leading to the formation of cytotoxic metabolites that form covalent adducts in the parasite. Finally, compound 14c is lipophilic (measured CHI LogD7.7 = 2.85) but remains soluble in water (measured PBS solubility at pH7.4 = 16 µM), highlighting the antileishmanial potential of the nitrostyrylthiazolidine-2,4-dione scaffold.

Intramolecular Hydrogen Bonding Effect on the Electron-Transfer Thermodynamics of a Series of o-Nitrobenzyl Alcohol Derivatives

From thermoelectrochemical experiments and electronic structure calculations of a series of nitrobenzyl alcohol derivatives, the effect of intramolecular hydrogen bonding (IHB) on the electron transfer thermodynamics is discussed on a molecular basis. A linear correlation between formal reduction potential (E1/2) values and temperature was obtained for the temperature range from 300 to 350 K. Estimated electron transfer entropy values (ΔS)─determined from this dependence─and the enthalpy (ΔΔH) changes relative to o-nitrobenzyl alcohol confirmed that the effect of the formation of IHB proved to be decisive in the charge-transfer thermodynamics. The possibility of intermolecular hydrogen bonding is further discussed upon comparing thermodynamic data among three different solvents.

Measuring DNA modifications with the comet assay: a compendium of protocols

The comet assay is a versatile method to detect nuclear DNA damage in individual eukaryotic cells, from yeast to human. The types of damage detected encompass DNA strand breaks and alkali-labile sites (e.g., apurinic/apyrimidinic sites), alkylated and oxidized nucleobases, DNA-DNA crosslinks, UV-induced cyclobutane pyrimidine dimers and some chemically induced DNA adducts. Depending on the specimen type, there are important modifications to the comet assay protocol to avoid the formation of additional DNA damage during the processing of samples and to ensure sufficient sensitivity to detect differences in damage levels between sample groups. Various applications of the comet assay have been validated by research groups in academia, industry and regulatory agencies, and its strengths are highlighted by the adoption of the comet assay as an in vivo test for genotoxicity in animal organs by the Organisation for Economic Co-operation and Development. The present document includes a series of consensus protocols that describe the application of the comet assay to a wide variety of cell types, species and types of DNA damage, thereby demonstrating its versatility.

Nitro compounds against trypanosomatidae parasites: Heroes or villains?

Chagas disease and Human African trypanosomiasis (HAT) are caused by Trypanosoma cruzi, T. brucei rhodesiense or T. b. gambiense parasites, respectively; while Leishmania is caused by parasites from the Leishmania genus. In recent years, many efforts have been addressed to develop inhibitors against these parasites, especially nitro-containing derivatives, which can interfere with essential enzymes from the protozoa. In this review, all anti-trypanosomatidae nitrocompounds reported so far are shown herein, highlighting their activities and SAR analyses, providing all the benefits and problems associated with this ambiguous chemical group. Finally, this review paper will be useful for many research teams around the world, which are searching for novel trypanocidal and leishmanicidal agents.

The Potential of 2-Substituted Quinolines as Antileishmanial Drug Candidates

There is a need for new, cost-effective drugs to treat leishmaniasis. A strategy based on traditional medicine practiced in Bolivia led to the discovery of the 2-substituted quinoline series as a source of molecules with antileishmanial activity and low toxicity. This review documents the development of the series from the first isolated natural compounds through several hundred synthetized molecules to an optimized compound exhibiting an in vitro IC₅₀ value of 0.2 µM against Leishmania donovani, and a selectivity index value of 187, together with in vivo activity on the L. donovani/hamster model. Attempts to establish structure–activity relationships are described, as well as studies that have attempted to determine the mechanism of action. For the latter, it appears that molecules of this series act on multiple targets, possibly including the immune system, which could explain the observed lack of drug resistance after in vitro drug pressure. We also show how nanotechnology strategies could valorize these drugs through adapted formulations and how a mechanistic targeting approach could generate new compounds with increased activity.

N-(4-acetamidophenyl)-5-acetylfuran-2-carboxamide as a novel orally available diuretic that targets urea transporters with improved PD and PK properties

Urea transporters (UTs) have been identified as new targets for diuretics. Functional deletion of UTs led to urea-selective urinary concentrating defects with relative salt sparing. In our previous study, a UT inhibitor with a diarylamide scaffold, which is denoted as 11a, was demonstrated as the first orally available UT inhibitor. However, the oral bioavailability of 11a was only 4.38%, which obstructed its clinical application. In this work, by replacing the nitro group of 11a with an acetyl group, 25a was obtained. Compared with 11a, 25a showed a 10 times stronger inhibitory effect on UT-B (0.14 μM vs. 1.41 μM in rats, and 0.48 μM vs. 5.82 μM in mice) and a much higher inhibition rate on UT-A1. Moreover, the metabolic stability both in vitro and in vivo and the drug-like properties (permeability and solubility) of 25a were obviously improved compared with those of 11a. Moreover, the bioavailability of 25a was 15.18%, which was 3 times higher than that of 11a, thereby resulting in significant enhancement of the diuretic activities in rats and mice. 25a showed excellent potential for development as a promising clinical diuretic candidate for targeting UTs to treat diseases that require long-term usage of diuretics, such as hyponatremia.

Monocyclic Nitro-heteroaryl Nitrones with Dual Mechanism of Activation: Synthesis and Antileishmanial Activity

5-Nitro-furan nitrones (1) and 5-nitro-thiophene nitrones (2) were synthesized in one step. Compounds 1a-c had the most potent leishmanicidal activity against intracellular amastigote forms of Leishmania amazonensis and L. infantum (from 0.019 to 2.76 μM), with excellent selectivity (from 39 to 5673). The comparison of the leishmanicidal activity in promastigotes of wild type L. donovani with those overexpressing nitroreductases NRT1 or NRT2 shows that 1a,b are activated by both, which could slow the development of resistance. Their redox potential (E _redox) obtained by cyclic voltammetry (-0.67 and -0.62 V) shows that the reduction of the nitro group is modulated by the nitrone group. Oral administration of 1b to mice infected by L. infantum reduced the parasite load on the spleen by 76.6 and 95.0% with doses of 50 and 100 mg/kg, respectively, administered twice a day, for 5 days. In the liver, the parasite load suppression was above 75% with either treatment.

Single- and Two-Electron Reduction of Nitroaromatic Compounds by Flavoenzymes: Mechanisms and Implications for Cytotoxicity

Nitroaromatic compounds (ArNO₂) maintain their importance in relation to industrial processes, environmental pollution, and pharmaceutical application. The manifestation of toxicity/therapeutic action of nitroaromatics may involve their single- or two-electron reduction performed by various flavoenzymes and/or their physiological redox partners, metalloproteins. The pivotal and still incompletely resolved questions in this area are the identification and characterization of the specific enzymes that are involved in the bioreduction of ArNO₂ and the establishment of their contribution to cytotoxic/therapeutic action of nitroaromatics. This review addresses the following topics: (i) the intrinsic redox properties of ArNO₂, in particular, the energetics of their single- and two-electron reduction in aqueous medium; (ii) the mechanisms and structure-activity relationships of reduction in ArNO₂ by flavoenzymes of different groups, dehydrogenases-electrontransferases (NADPH:cytochrome P-450 reductase, ferredoxin:NADP(H) oxidoreductase and their analogs), mammalian NAD(P)H:quinone oxidoreductase, bacterial nitroreductases, and disulfide reductases of different origin (glutathione, trypanothione, and thioredoxin reductases, lipoamide dehydrogenase), and (iii) the relationships between the enzymatic reactivity of compounds and their activity in mammalian cells, bacteria, and parasites.

Recent Advances in One-Pot Modular Synthesis of 2-Quinolones

It is known that 2-quinolones are broadly applicable chemical structures in medicinal and agrochemical research as well as various functional materials. A number of current publications about their synthesis and their applications emphasize the importance of these small molecules. The early synthetic chemistry originated from the same principle of the classical Friedländer and Knorr procedures for the preparation of quinolines. The analogous processes were developed by applying new synthetic tools such as novel catalysts, the microwave irradiation method, etc., whereas recent innovations in new bond forming reactions have allowed for novel strategies to construct the core structures of 2-quinolones beyond the bond disconnections based on two classical reactions. Over the last few decades, some reviews on structure-based, catalyst-based, and bioactivity-based studies have been released. In this focused review, we extensively surveyed recent examples of one-pot reactions, particularly in view of modular approaches. Thus, the contents are categorized as three major sections (two-, three-, and four-component reactions) according to the number of reagents that ultimately compose atoms of the core structures of 2-quinolones. The collected synthetic methods are discussed from the perspectives of strategy, efficiency, selectivity, and reaction mechanism.

Effects of the Distance between Radical Sites on the Reactivities of Aromatic Biradicals

Coupling of the radical sites in isomeric benzynes is known to hinder their radical reactivity. In order to determine how far apart the radical sites must be for them not to interact, the gas-phase reactivity of several isomeric protonated (iso)quinoline- and acridine-based biradicals was examined. All the (iso)quinolinium-based biradicals were found to react slower than the related monoradicals with similar vertical electron affinities (i.e., similar polar effects). In sharp contrast, the acridinium-based biradicals, most with the radical sites farther apart than in the (iso)quinolinium-based systems, showed greater reactivities than the relevant monoradicals with similar vertical electron affinities. The greater distances between the two radical sites in these biradicals lead to very little or no spin-spin coupling, and no suppression of radical reactivity was observed. Therefore, the radical sites can still interact if they are located on adjacent benzene rings and only after being separated further than that does no coupling occur. The most reactive radical site of each biradical was experimentally determined to be the one predicted to be more reactive based on the monoradical reactivity data. Therefore, the calculated vertical electron affinities of relevant monoradicals can be used to predict which radical site is most reactive in the biradicals.

New 8-Nitroquinolinone Derivative Displaying Submicromolar in Vitro Activities against Both Trypanosoma brucei and cruzi

An antikinetoplastid pharmacomodulation study was conducted at position 6 of the 8-nitroquinolin-2(1H)-one pharmacophore. Fifteen new derivatives were synthesized and evaluated in vitro against L. infantum, T. brucei brucei, and T. cruzi, in parallel with a cytotoxicity assay on the human HepG2 cell line. A potent and selective 6-bromo-substituted antitrypanosomal derivative 12 was revealed, presenting EC₅₀ values of 12 and 500 nM on T. b. brucei trypomastigotes and T. cruzi amastigotes respectively, in comparison with four reference drugs (30 nM ≤ EC₅₀ ≤ 13 μM). Moreover, compound 12 was not genotoxic in the comet assay and showed high in vitro microsomal stability (half life >40 min) as well as favorable pharmacokinetic behavior in the mouse after oral administration. Finally, molecule 12 (E° = -0.37 V/NHE) was shown to be bioactivated by type 1 nitroreductases, in both Leishmania and Trypanosoma, and appears to be a good candidate to search for novel antitrypanosomal lead compounds.

Selective synthesis of substituted amino-quinoline derivatives by C-H activation and fluorescence evaluation of their lipophilicity-responsive properties

Push-pull type fluorescent amino-quinoline derivatives (TFMAQ) bearing phenyl aromatic groups in the 8-position (TFMAQ-8Ar series) were synthesized via palladium-catalyzed C-H activation reaction in short steps. The N-arylation or C-H activation reactions were selectively controlled with high yield by combinations of palladium and phosphine ligands. The TFMAQ-8Ar analogues exhibited fluorescent solvatochromism in non-polar and polar solvents. In non-polar solvent, the absolute fluorescence quantum yield was high, wheareas the fluorescence was almost quenched in polar solvent. The TFMAQ-8Ar derivatives also showed high fluorescence emission at solid state owing to the planar structure between the quinoline ring and phenyl ring at the 7-amino group, as demonstrated by X-ray crystal structure analysis. The fluorescence imaging of 3T3-L1 cell using TFMAQ-8Ar derivatives was performed by confocal laser microscopy. Strong and specific emissions at lipid droplets were observed owing to the accumulation of TFMAQ-8Ar derivatives. Therefore, we propose that the TFMAQ-8Ar derivatives should become a versatile fluorescence probe for the live imaging of lipid droplets.

Synthesis and antileishmanial activity of fluorinated rhodacyanine analogues: The 'fluorine-walk' analysis

In a search for potent antileishmanial drug candidates, eighteen rhodacyanine analogues bearing fluorine or perfluoroalkyl substituents at various positions were synthesized. These compounds were tested for their inhibitory activities against Leishmania martiniquensis and L. orientalis. This 'fluorine-walk' analysis revealed that the introduction of fluorine atom at C-5, 6, 5', or 6' on the benzothiazole units led to significant enhancement of the activity, correlating with the less negative reduction potentials of the fluorinated analogues confirmed by the electrochemical study. On the other hand, CF₃ and OCF₃ groups were found to have detrimental effects, which agreed with the poor aqueous solubility predicted by the in silico ADMET analysis. In addition, some of the analogues including the difluorinated species showed exceptional potency against the promastigote and axenic amastigote stages (IC₅₀ = 40-85 nM), with the activities surpassing both amphotericin B and miltefosine.

Oxidative Aromatization of 3,4-Dihydroquinolin-2(1 H)-ones to Quinolin-2(1 H)-ones Using Transition-Metal-Activated Persulfate Salts

Inorganic persulfate salts were identified as efficient reagents for the oxidative aromatization of 3,4-dihydroquinolin-2(1 H)-ones through the activation of readily available transition metals, such as iron and copper. The feasible protocol conforming to the requirement of green chemistry was utilized in the preparation of the key intermediate (7-(4-chlorobutoxy)quinolin-2(1 H)-one 2) of brexpiprazole in 80% isolated yield on a 100 g scale, and different quinolin-2(1 H)-one derivatives with various functional groups were demonstrated in 52-89% yields.

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.