Design, synthesis and antimalarial activity of novel bis{N-[(pyrrolo[1,2-a]quinoxalin-4-yl)benzyl]-3-aminopropyl}amine derivatives

DNA G-quadruplexes in the genome of Trypanosoma cruzi as potential therapeutic targets for Chagas disease: Dithienylethene ligands as effective antiparasitic agents

Chagas disease is caused by the parasite Trypanosoma cruzi and affects over 7 million people worldwide. The two actual treatments, Benznidazole (Bzn) and Nifurtimox, cause serious side effects due to their high toxicity leading to treatment abandonment by the patients. In this work, we propose DNA G-quadruplexes (G4) as potential therapeutic targets for this infectious disease. We have found 174 PQS per 100,000 nucleotides in the genome of T. cruzi and confirmed G4 formation of three frequent motifs. We synthesized a family of 14 quadruplex ligands based in the dithienylethene (DTE) scaffold and demonstrated their binding to these identified G4 sequences. Several DTE derivatives exhibited micromolar activity against epimastigotes of four different strains of T. cruzi, in the same concentration range as Bzn. Compounds L3 and L4 presented remarkable activity against trypomastigotes, the active form in blood, of T. cruzi SOL strain (IC50 = 1.5-3.3 μM, SI = 25-40.9), being around 40 times more active than Bzn and displaying much better selectivity indexes.

Crafting mono- and novel bis-methylated pyrroloquinoxaline derivatives from a shared precursor and its application in the total synthesis of marinoquinoline A

The synthesis of mono- and novel bis-methylated pyrrolo[1,2-a]quinoxalines through the addition of unstable methyl radicals to aryl isocyanides is described contingent upon the reaction conditions employed. The strategy has been effectively employed in the total synthesis of the natural product marinoquinoline A.

G-Quadruplexes as Key Transcriptional Regulators in Neglected Trypanosomatid Parasites

G-quadruplexes (G4s) are nucleic acid secondary structures that have been linked to the functional regulation of eukaryotic organisms. G4s have been extensively characterised in humans and emerging evidence suggests that they might also be biologically relevant for human pathogens. This indicates that G4s might represent a novel class of therapeutic targets for tackling infectious diseases. Bioinformatic studies revealed a high prevalence of putative quadruplex-forming sequences (PQSs) in the genome of protozoans, which highlights their potential roles in regulating vital processes of these parasites, including DNA transcription and replication. In this work, we focus on the neglected trypanosomatid parasites, Trypanosoma and Leishmania spp., which cause debilitating and deadly diseases across the poorest populations worldwide. We review three examples where G4-formation might be key to modulate transcriptional activity in trypanosomatids, providing an overview of experimental approaches that can be used to exploit the regulatory roles and relevance of these structures to fight parasitic infections.

Synthesis, molecular docking and dynamics studies of pyridazino[4,5-b]quinoxalin-1(2H)-ones as targeting main protease of COVID-19

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a crisis in public health. Because, the 3CLpro, the main protease of SARS-CoV-2, possesses a critical role in coronavirus replication, many efforts have been devoted to developing various inhibitors to prevent the fast spread of COVID-19. In the current work, a number of various pyridazino[4,5-b]quinoxalin-1(2H)-one derivatives bearing thiadiazine and thiadiazole fragments has been prepared via a straightforward and practical strategy involving the reaction of 2-(ethoxycarbonyl)-3-formylquinoxaline 1,4-dioxide with thiocarbohydrazide under reflux conditions. To determine the bioavailability of pyridazino[4,5-b]quinoxalin-1(2H)-one derivatives, Lipinski's rule of five has been carried out. Regarding this rule, none of the synthesized compounds exhibit any deviation from Lipinski's rule of five. Furthermore, molecular docking and molecular dynamics approaches have been implemented to figure out the potential interactions of products with SARS-CoV-2 main protease. The outcomes of molecular docking studies demonstrate that the phenyl and nitrophenyl substituted pyridazino[4,5-b]quinoxalin-1(2H)-one show the lowest binding affinity among the other compounds, indicating a favorable orientation in the active site of the chymotrypsin-like cysteine protease. In addition, the MD simulation performed to evaluate the stability of the protein-ligand complex represents that the average binding energy of the nitrophenyl complex is less than that of the phenyl complex. Therefore, according to the in silico results, the inhibitory effect of the nitrophenyl complex is more significant than the phenyl complex.Communicated by Ramaswamy H. Sarma.

Design, Synthesis, and Antiprotozoal Evaluation of New Promising 2,9-Bis[(substituted-aminomethyl)]-4,7-phenyl-1,10-phenanthroline Derivatives, a Potential Alternative Scaffold to Drug Efflux

A series of novel 2,9-bis[(substituted-aminomethyl)]-4,7-phenyl-1,10-phenanthroline derivatives was designed, synthesized, and evaluated in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani and Trypanosoma brucei brucei). Pharmacological results showed antiprotozoal activity with IC50 values in the sub and μM range. In addition, the in vitro cytotoxicity of these original molecules was assessed with human HepG2 cells. The substituted diphenylphenanthroline 1l was identified as the most potent antimalarial derivative with a ratio of cytotoxic to antiparasitic activities of 505.7 against the P. falciparum CQ-resistant strain W2. Against the promastigote forms of L. donovani, the phenanthrolines 1h, 1j, 1n and 1o were the most active with IC50 from 2.52 to 4.50 μM. The phenanthroline derivative 1o was also identified as the most potent trypanosomal candidate with a selectivity index (SI) of 91 on T. brucei brucei strain. FRET melting and native mass spectrometry experiments evidenced that the nitrogen heterocyclic derivatives bind the telomeric G-quadruplexes of P. falciparum and Trypanosoma. Moreover, as the telomeres of the parasites P. falciparum and Trypanosoma could be considered to be possible targets of this kind of nitrogen heterocyclic derivatives, their potential ability to stabilize the parasitic telomeric G-quadruplexes have been determined through the FRET melting assay and by native mass spectrometry.

Application of N,N-Dimethylethanolamine as a One-Carbon Synthon for the Synthesis of Pyrrolo[1,2-a]quinoxalines, Quinazolin-4-ones, and Benzo[4,5]imidazoquinazolines via [5 + 1] Annulation

The synthesis of N-heterocycles composes a significant part of synthetic chemistry. In this report, a Cu(II)-catalyzed green and efficient synthesis of pyrrolo[1,2-a]quinoxaline, quinazolin-4-one, and benzo[4,5]imidazoquinazoline derivatives was developed, employing N,N-dimethylethanolamine (DMEA) as a C1 synthon. Green oxidant O₂ is critical in these transformations, facilitating the formation of a key intermediate─a reactive iminium ion. The method conducted under mild conditions is compatible with a diversity of functional groups, providing an appealing alternative to the previously developed protocols.

New structural classes of antimalarials

Malaria remains a major vector borne disease claiming millions of lives worldwide due to infections caused by Plasmodium sp. Discovery and development of antimalarial drugs have previously been dominated majorly by single drug therapy. The malaria parasite has developed resistance against first line and second line antimalarial drugs used in the single drug therapy. This has drawn attention to find ways to alleviate the disease burden supplanted by combination therapy with multiple drugs to overcome drug resistance. Emergence of resistant strains even against the combination therapy has now mandated the revision of the current antimalarial pharmacotherapy. Research efforts of the past decade led to the discovery and identification of several new structural classes of antimalarial agents with improved biological attributes over the older ones. The following is a comprehensive review, addressed to the new structural classes of heterocyclic and natural compounds that have been identified during the last decade as antimalarial agents. Some of the classes included herein contain one or more pharmacophores amalgamated into a single bioactive scaffold as antimalarial agents, which act upon the conventional and novel targets.

Synthesis of Hydroxylated Polycyclic Pyrrolo/Indolo[1,2-a]quinoxaline-Fused Lactam Derivatives via PhI(OAc)2-Promoted 1,2-Bond Migration and Solvent Insertion

PhI(OAc)₂-mediated ring expansion via 1,2-bond migration and concurrent solvent insertion generate hydroxylated polycyclic pyrrolo/indolo[1,2-a]quinoxaline-fused lactam derivatives in a highly diastereoselective fashion from spiro-fused quinoxalines in good-to-excellent yield. X-ray crystal structure analysis reveals that the polycyclic lactams are nonplanar molecules devoid of any symmetry as they possess one or two axially chiral biaryl or N-arylindolyl bridges along with one chiral center at the bridgehead carbon.

Synthesis, Crystal Structure and Anti-Leukemic Activity of 1,3-Dihydro-1-{1-[4-(4-phenylpyrrolo[1,2-a]quinoxalin-3-yl)benzyl]piperidin-4-yl}-2H-benzimidazol-2-one

1,3-Dihydro-1-{1-[4-(4-phenylpyrrolo[1,2-a]quinoxalin-3-yl)benzyl]piperidin-4-yl}-2H-benzimidazol-2-one has been synthesized through a multi-step pathway starting from commercially available 2-nitroaniline. A structure characterization of this new substituted pyrrolo[1,2-a]quinoxaline compound was achieved by using FT-IR, 1H-NMR, 13C-NMR, X-Ray and HRMS spectral analysis. This new pyrroloquinoxaline derivative shows an interesting cytotoxic potential against several human leukemia cell lines (HL60, K562 and U937 cells).

Pd-Catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines

An efficient Pd-catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines with aryl iodides is described, providing a selective route toward a series of 1-arylated and 1,3-diarylated pyrrolo[1,2-a]quinoxalines in good yields. This method features a broad substrate scope, good functional group tolerance and gram-scale synthesis. Furthermore, the C3-thiocyanation of the arylated product is also achieved. We believe that these novel aryl-substituted pyrrolo [1,2-a]quinoxalines will have a variety of applications in organic synthesis and medicinal chemistry.

A theoretical investigation on the degradation reactions of CH3CH2CH2NH and (CH3CH2CH2)2N radicals in the presence of NO, NO2 and O2

The degradation reactions of propylamino and dipropylamino radicals in the presence of NO, NO₂ and O₂ were investigated at the CCSD(T)/6-311++G (2d, 2p)//B3LYP/6-311++G (d,p) levels of theory. Result indicates that nitrosamines, nitramines, nitroso-oxy compounds and imines can be formed at atmosphere. Time dependent density functional theory (TDDFT) calculation shows that nitrosamines and nitroso-oxy compounds can photolyze under sunlight, while nitramines cannot undergo photolysis in the daytime. Moreover, the ecotoxicity assessment result implies that the degradation of propyl-substituted amines by OH radicals, NO and NO₂ will reduce their toxicity to fish, daphnia and green algae in the aquatic environment.

Design, synthesis, and characterization of novel aminoalcohol quinolines with strong in vitro antimalarial activity

Malaria is the fifth most lethal parasitic infections in the world. Herein, five new series of aminoalcohol quinolines including fifty-two compounds were designed, synthesized and evaluated in vitro against Pf3D7 and PfW2 strains. Among them, fourteen displayed IC₅₀ values below or near of 50.0 nM whatever the strain with selectivity index often superior to 100.17b was found as a promising antimalarial candidate with IC₅₀ values of 14.9 nM and 11.0 nM against respectively Pf3D7 and PfW2 and a selectivity index higher than 770 whatever the cell line is. Further experiments were achieved to confirm the safety and to establish the preliminary ADMET profile of compound 17b before the in vivo study performed on a mouse model of P. berghei ANKA infection. The overall data of this study allowed to establish new structure-activity relationships and the development of novel agents with improved pharmacokinetic properties.

Antiplasmodial 2-thiophenoxy-3-trichloromethyl quinoxalines target the apicoplast of Plasmodium falciparum

The identification of a plant-like Achille's Heel relict, i.e. the apicoplast, that is essential for Plasmodium spp., the causative agent of malaria lead to an attractive drug target for new antimalarials with original mechanism of action. Although it is not photosynthetic, the apicoplast retains several anabolic pathways that are indispensable for the parasite. Based on previously identified antiplasmodial hit-molecules belonging to the 2-trichloromethylquinazoline and 3-trichloromethylquinoxaline series, we report herein an antiplasmodial Structure-Activity Relationships (SAR) study at position two of the quinoxaline ring of 16 newly synthesized compounds. Evaluation of their activity toward the multi-resistant K1 Plasmodium falciparum strain and cytotoxicity on the human hepatocyte HepG2 cell line revealed a hit compound (3k) with a PfK1 EC₅₀ value of 0.3 μM and a HepG2 CC₅₀ value of 56.0 μM (selectivity index = 175). Moreover, hit-compound 3k was not cytotoxic on VERO or CHO cell lines and was not genotoxic in the in vitro comet assay. Activity cliffs were observed when the trichloromethyl group was replaced by CH₃, CF₃ or H, showing that this group played a key role in the antiplasmodial activity. Biological investigations performed to determine the target and mechanism of action of the compound 3k strongly suggest that the apicoplast is the putative target as showed by severe alteration of apicoplaste biogenesis and delayed death response. Considering that there are very few molecules that affect the Plasmodium apicoplast, our work provides, for the first time, evidence of the biological target of trichloromethylated derivatives.

Current status of quinoxaline and quinoxaline 1,4-di-N-oxides derivatives as potential antiparasitic agents

Parasitic diseases are a public health problem, especially in developing countries where millions of people are affected every year. Current treatments have several drawbacks: emerging resistance to the existing drugs, lack of efficacy, and toxic side effects. Therefore, new antiparasitic drugs are urgently needed to treat and control diseases that affect human health, such as malaria, Chagas disease, leishmaniasis, amebiasis, giardiasis schistosomiasis, and filariasis, among others. Quinoxaline is a compound containing a benzene ring and a pyrazine ring. The oxidation of both pyrazine ring nitrogens allows the obtention of quinoxaline 1,4-di-N-oxides (QdNOs) derivatives. By modifying the chemical structure of these compounds, it is possible to obtain a wide variety of biological properties. This review investigated the activity of quinoxaline derivatives and QdNOs against different protozoan parasites and helminths. We also cover the structure-activity relationship (SAR) and summarize the main findings related to their mechanisms of action from published works in recent years. However, further studies are needed to determine specific molecular targets. This review aims to highlight the new development of antiparasitic drugs with better pharmacological profiles than current treatments.

Recent Updates on the Synthesis of Bioactive Quinoxaline-Containing Sulfonamides

Quinoxaline is a privileged pharmacophore that has broad-spectrum applications in the fields of medicine, pharmacology and pharmaceutics. Similarly, the sulfonamide moiety is of considerable interest in medicinal chemistry, as it exhibits a wide range of pharmacological activities. Therefore, the therapeutic potential and biomedical applications of quinoxalines have been enhanced by incorporation of the sulfonamide group into their chemical framework. The present review surveyed the literature on the preparation, biological activities and structure-activity relationship (SAR) of quinoxaline sulfonamide derivatives due to their broad range of biomedical activities, such as diuretic, antibacterial, antifungal, neuropharmacological, antileishmanial, anti-inflammatory, anti-tumor and anticancer action. The current biological diagnostic findings in this literature review suggest that quinoxaline-linked sulfonamide hybrids are capable of being established as lead compounds; modifications on quinoxaline sulfonamide derivatives may give rise to advanced therapeutic agents against a wide variety of diseases.

Highly selective C3-H iodination of pyrrolo[1,2-a]quinoxalines

We report a C3-H direct iodination of pyrrolo[1,2-a]quinoxalines with TBAI or I2; a series of novel 3-iodopyrrolo[1,2-a]quinoxaline derivatives were obtained with excellent regioselectivity and broad substrate scope. Mechanism studies show that a catalytic amount of p-toluenesulfonic acid significantly promotes the selectivity and conversion of the reaction. Notably, the reaction can be performed on a gram scale, and the iodinated products can be further transformed into potentially biologically active pyrrolo[1,2-a]quinoxaline derivatives by palladium-catalyzed coupling reactions.

Synthesis of 4-Aryl Pyrrolo[1,2-α]quinoxalines via Iron-Catalyzed Oxidative Coupling from an Unactivated Methyl Arene

Herein, we describe the direct synthesis of pyrrolo[1,2-α]quinoxaline via oxidative coupling between methyl arene and 1-(2-aminophenyl) pyrroles. Oxidation of the benzylic carbon of the methyl arene was achieved by di-t-butyl peroxide in the presence of an iron catalyst, followed by conversion to an activated aldehyde in situ. Oxygen played a crucial role in the oxidation process to accelerate benzaldehyde formation. Subsequent Pictet-Spengler-type annulation completed the quinoxaline structure. The protocol tolerated various kinds of functional groups and provided 22 4-aryl pyrrolo[1,2-α]quinoxalines when various methyl arene derivatives were used. The developed method proceeded in air, and all catalysts, reagents, and solvents were easily accessible.

Design, synthesis, and antiprotozoal evaluation of new 2,4-bis[(substituted-aminomethyl)phenyl]quinoline, 1,3-bis[(substituted-aminomethyl)phenyl]isoquinoline and 2,4-bis[(substituted-aminomethyl)phenyl]quinazoline derivatives

A series of new 2,4-bis[(substituted-aminomethyl)phenyl]quinoline, 1,3-bis[(substituted-aminomethyl)phenyl]isoquinoline, and 2,4-bis[(substituted-aminomethyl)phenyl]quinazoline derivatives was designed, synthesised, and evaluated in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani, and Trypanosoma brucei brucei). Biological results showed antiprotozoal activity with IC₅₀ values in the µM range. In addition, the in vitro cytotoxicity of these original molecules was assessed with human HepG2 cells. The quinoline 1c was identified as the most potent antimalarial candidate with a ratio of cytotoxic to antiparasitic activities of 97 against the P. falciparum CQ-sensitive strain 3D7. The quinazoline 3h was also identified as the most potent trypanosomal candidate with a selectivity index (SI) of 43 on T. brucei brucei strain. Moreover, as the telomeres of the parasites P. falciparum and Trypanosoma are possible targets of this kind of nitrogen heterocyclic compounds, we have also investigated stabilisation of the Plasmodium and Trypanosoma telomeric G-quadruplexes by our best compounds through FRET melting assays.

1-Phenyl-8-[[4-(pyrrolo[1,2-a]quinoxalin-4-yl)phenyl]methyl]-1,3,8-triazaspiro[4.5]decan-4-one: Synthesis, Crystal Structure and Anti-Leukemic Activity

1-Phenyl-8-[[4-(pyrrolo[1,2-a]quinoxalin-4-yl)phenyl]methyl]-1,3,8-triazaspiro[4.5]decan-4-one has been successfully synthesized via a multi-step pathway starting from 2-nitroaniline. Structure characterization of this original pyrrolo[1,2-a]quinoxaline derivative was achieved by FT-IR, 1H-NMR, 13C-NMR, X-Ray and HRMS spectral analysis. This title compound shows interesting cytotoxic potential against several human leukemia cell lines (K562, HL60, and U937 cells).

Iron-catalyzed [3 + 2]-cycloaddition of in situ generated N-ylides with alkynes or olefins: access to multi-substituted/polycyclic pyrrole derivatives

An iron-catalyzed one-pot three-component reaction of 1-substituted benzimidazoles with diazoacetates and electron-deficient alkynes or alkenes has been reported. Mechanistically, the reaction goes through a 1,3-dipolar cycloaddition of catalytically generated benzimidazolium N-ylides with various activated alkynes or alkenes, leading to multi-substituted and polycyclic fused pyrrole derivatives, respectively.

Synthesis of new piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives as inhibitors of Candida albicans multidrug transporters by a Buchwald-Hartwig cross-coupling reaction

Two series of piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives were prepared via a Buchwald–Hartwig cross-coupling reaction and then evaluated for their ability to inhibit the drug efflux activity of CaCdr1p and CaMdr1p transporters of Candida albicans overexpressed in a Saccharomyces cerevisiae strain. In the initial screening of twenty-nine piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives, twenty-three compounds behaved as dual inhibitors of CaCdr1p and CaMdr1p. Only four compounds showed exclusive inhibition of CaCdr1p or CaMdr1p. Further biological investigations were developed and for example, their antifungal potential was evaluated by measuring the growth of control yeast cells (AD1-8u⁻) and efflux pump-overexpressing cells (AD-CDR1 and AD-MDR1) after exposition to variable concentrations of the tested compounds. The MIC₈₀ values of nineteen compounds ranging from 100 to 901 μM for AD-CDR1 demonstrated that relative resistance index (RI) values were between 8 and 274. In comparison, only seven compounds had RI values superior to 4 in cells overexpressing Mdr1p. These results indicated substrate behavior for nineteen compounds for CaCdr1p and seven compounds for CaMdr1p, as these compounds were transported via MDR transporter overexpressing cells and not by the AD1-8u⁻ cells. Finally, in a combination assay with fluconazole, two compounds (1d and 1f) have shown a synergistic effect (fractional inhibitory concentration index (FICI) values ≤ 0.5) at micromolar concentrations in the AD-MDR1 yeast strain overexpressing CaMdr1p-protein, indicating an excellent potency toward chemosensitization.

Two series of piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives were prepared via a Buchwald–Hartwig cross-coupling reaction and then evaluated for their ability to inhibit the drug efflux activity of two Candida albicans transporters.

NCS-promoted thiocyanation and selenocyanation of pyrrolo[1,2-a]quinoxalines

An efficient NCS-promoted thiocyanation of pyrrolo[1,2-a]quinoxalines with NH₄SCN or KSCN was developed. Moreover, in the presence of KSeCN, the selenocyanation of pyrrolo[1,2-a]quinoxalines was also achieved.

KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones

A series of diverse fused [1,2,4]triazolo[3,4-c]quinoxalines was obtained by an efficient KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones.

G4-iM Grinder: when size and frequency matter. G-Quadruplex, i-Motif and higher order structure search and analysis tool

We present G4-iM Grinder, a system for the localization, characterization and selection of potential G4s, i-Motifs and higher order structures. A robust and highly adaptable search engine identifies all structures that fit the user’s quadruplex definitions. Their biological relevance, in vitro formation probability and presence of known-to-form structures are then used as filters. The outcome is an efficient methodology that helps select the best candidates for a subsequent in vitro analysis or a macroscopic genomic quadruplex assessment. As proof of the analytical capabilities of G4-iM Grinder, the human genome was analyzed for potential G4s and i-Motifs. Many known-to-form structures were identified. New candidates were selected considering their score and appearance frequency. We also focused on locating Potential Higher Order Quadruplex Sequences (PHOQS). We developed a new methodology to predict the most probable subunits of these assemblies and applied it to a PHOQS candidate. Taking the human average density as reference, we examined the genomes of several etiological causes of disease. This first of its class comparative study found many organisms to be very dense in these potential quadruplexes. Many presented already known-to-form-G4s and i-Motifs. These findings suggest the potential quadruplexes have as therapeutic targets for these diseases that currently kill millions worldwide.

Synthesis of 1H-3-{4-[(3-Dimethylaminopropyl)aminomethyl]phenyl}-2-phenylindole and Evaluation of Its Antiprotozoal Activity

1H-3-{4-[(3-Dimethylaminopropyl)aminomethyl]phenyl}-2-phenylindole was synthesized via a multi-step pathway starting from 2-iodoaniline. Structure characterization of this new indole compound was achieved by 1H-NMR, 13C-NMR and ESI-MS spectral analysis. The title compound was screened in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani and Trypanosoma brucei brucei). Biological results showed antiparasitic activity with IC50 values in the μM range.

Unimolecular Decomposition Reactions of Propylamine and Protonated Propylamine

A detailed computational study of the decomposition reaction mechanisms of cis-propylamine (cis-PA), trans-propylamine (trans-PA), and the cis-isomer of its protonated form (cis-HPA) has been carried out. Fourteen major pathways with their kinetic and thermodynamic parameters are reported. All reported reactions have been located with a concerted transition state, leading to significant products that agree with previous theoretical and experimental studies. Among six decomposition pathways of trans-PA, the formation of propene and NH₃ is the significant one, kinetically and thermodynamically, with an activation energy barrier of 281 kJ mol^-1. The production of two carbenes is found via two different transition states, where the reactions are thermodynamically controlled and reversible. Furthermore, five decomposition pathways of cis-PA have been considered where the formation of ethene, methylimine, and H₂ is the most plausible one with an activation energy barrier of 334 kJ mol^-1. The results show that the formation of propene and NH₄ ⁺ from the decomposition of cis-HPA is the most favorable reaction with an activation barrier of 184 kJ mol^-1, that is, the lowest activation energy calculated for all decomposition pathways.

G-Quadruplex Identification in the Genome of Protozoan Parasites Points to Naphthalene Diimide Ligands as New Antiparasitic Agents

G-quadruplexes (G4) are DNA secondary structures that take part in the regulation of gene expression. Putative G4 forming sequences (PQS) have been reported in mammals, yeast, bacteria, and viruses. Here, we present PQS searches on the genomes of T. brucei, L. major, and P. falciparum. We found telomeric sequences and new PQS motifs. Biophysical experiments showed that EBR1, a 29 nucleotide long highly repeated PQS in T. brucei, forms a stable G4 structure. G4 ligands based on carbohydrate conjugated naphthalene diimides (carb-NDIs) that bind G4’s including hTel could bind EBR1 with selectivity versus dsDNA. These ligands showed important antiparasitic activity. IC₅₀ values were in the nanomolar range against T. brucei with high selectivity against MRC-5 human cells. Confocal microscopy confirmed these ligands localize in the nucleus and kinetoplast of T. brucei suggesting they can reach their potential G4 targets. Cytotoxicity and zebrafish toxicity studies revealed sugar conjugation reduces intrinsic toxicity of NDIs.

Design, synthesis, and antiprotozoal evaluation of new 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline derivatives

A series of new 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline derivatives was synthesized, and the compounds were screened in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani, and Trypanosoma brucei brucei). Biological results showed antiparasitic activity with IC₅₀ values in the μm range. The in vitro cytotoxicity of these molecules was assessed by incubation with human HepG2 cells; for some derivatives, cytotoxicity was observed at significantly higher concentrations than antiparasitic activity. The 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline 1h was identified as the most potent antimalarial candidate with ratios of cytotoxic-to-antiparasitic activities of 107 and 39 against a chloroquine-sensitive and a chloroquine-resistant strain of P. falciparum, respectively. As the telomeres of the parasite P. falciparum are the likely target of this compound, we investigated stabilization of the Plasmodium telomeric G-quadruplexes by our phenanthroline derivatives through a FRET melting assay. The ligands 1f and 1m were noticed to be more specific for FPf8T with higher stabilization for FPf8T than for the human F21T sequence.