Discovery of new piperaquine hybrid analogs linked by triazolopyrimidine and pyrazolopyrimidine scaffolds with antiplasmodial and transmission blocking activities.

The World Health Organization (WHO) estimated that there were 247 million malaria cases in 2021 worldwide, representing an increase in 2 million cases compared to 2020. The urgent need for the development of new antimalarials is underscored by specific criteria, including the requirement of new modes of action that avoid cross-drug resistance, the ability to provide single-dose cures, and efficacy against both assexual and sexual blood stages. Motivated by the promising results obtained from our research group with [1,2,4]triazolo[1,5-a]pyrimidine and pyrazolo[1,5-a]pyrimidine derivatives, we selected these molecular scaffolds as the foundation for designing two new series of piperaquine analogs as potential antimalarial candidates. The initial series of hybrids was designed by substituting one quinolinic ring of piperaquine with the 1,2,4-triazolo[1,5-a]pyrimidine or pyrazolo[1,5-a]pyrimidine nucleus. To connect the heterocyclic systems, spacers with 3, 4, or 7 methylene carbons were introduced at the 4 position of the quinoline. In the second series, we used piperazine as a spacer to link the 1,2,4-triazolo[1,5-a]pyrimidine or pyrazolo[1,5-a]pyrimidine group to the quinoline core, effectively merging both pharmacophoric groups via a rigid spacer. Our research efforts yielded promising compounds characterized by low cytotoxicity and selectivity indices exceeding 1570. These compounds displayed potent in vitro inhibitory activity in the low nanomolar range against the erythrocytic form of the parasite, encompassing both susceptible and resistant strains. Notably, these compounds did not show cross-resistance with either chloroquine or established P. falciparum inhibitors. Even though they share a pyrazolo- or triazolo-pyrimidine core, enzymatic inhibition assays revealed that these compounds had minimal inhibitory effects on PfDHODH, indicating a distinct mode of action unrelated to targeting this enzyme. We further assessed the compounds' potential to interfere with gametocyte and ookinete infectivity using mature P. falciparum gametocytes cultured in vitro. Four compounds demonstrated significant gametocyte inhibition ranging from 58 % to 86 %, suggesting potential transmission blocking activity. Finally, we evaluated the druggability of these new compounds using in silico methods, and the results indicated that these analogs had favorable physicochemical and ADME (absorption, distribution, metabolism, and excretion) properties. In summary, our research has successfully identified and characterized new piperaquine analogs based on [1,2,4]triazolo[1,5-a]pyrimidine and pyrazolo[1,5-a]pyrimidine scaffolds and has demonstrated their potential as promising candidates for the development of antimalarial drugs with distinct mechanisms of action, considerable selectivity, and P. falciparum transmission blocking activity.

A Short Review of Antimalarial Compounds with Sulfonamide Moiety.

Malaria is a public health problem that causes thousands of deaths, primarily in children in African regions. Artemisinin-based combination therapies (ACTs) have helped to save thousands of lives; however, due to Plasmodium's resistance to available treatments, there is a need to search for new low-cost drugs that act through different mechanisms of action to contain this disease. This review shows that compounds with sulfonamide moiety, possibly, act as inhibitors of P. falciparum carbonic anhydrases, moreover, when linked to a variety of heterocycles potentiate the activities of these compounds and may be used in the design of new antimalarial drugs.

An Overview of Treatment Guidelines and Methods of Synthesis of Drugs Used in Leprosy Chemotherapy.

Leprosy is a Neglected Tropical Disease (NTDs) caused by Mycobacterium leprae (M. leprae). The treatment is considered effective, however, the high dose Multidrug Therapy (MDT) for a long period and its adverse effects result in the abandonment of the treatment by patients. Indeed, antimicrobial resistance is still an obstacle that must be overcome in the treatment of leprosy. In the present article, we reviewed the WHO guidelines for the chemotherapy of leprosy and the methods of synthesis of these drugs.

Comparative study between the anti-P. falciparum activity of triazolopyrimidine, pyrazolopyrimidine and quinoline derivatives and the identification of new PfDHODH inhibitors.

In this work, we designed and synthesized 35 new triazolopyrimidine, pyrazolopyrimidine and quinoline derivatives as P. falciparum inhibitors (3D7 strain). Thirty compounds exhibited anti-P. falciparum activity, with IC50 values ranging from 0.030 to 9.1 µM. The [1,2,4]triazolo[1,5-a]pyrimidine derivatives were more potent than the pyrazolo[1,5-a]pyrimidine and quinoline analogues. Compounds 20, 21, 23 and 24 were the most potent inhibitors, with IC50 values in the range of 0.030-0.086 µM and were equipotent to chloroquine. In addition, the compounds were selective, showing no cytotoxic activity against the human hepatoma cell line HepG2. All [1,2,4]triazolo[1,5-a]pyrimidine derivatives inhibited PfDHODH activity in the low micromolar to low nanomolar range (IC50 values of 0.08-1.3 µM) and did not show significant inhibition against the HsDHODH homologue (0-30% at 50 µM). Molecular docking studies indicated the binding mode of [1,2,4]triazolo[1,5-a]pyrimidine derivatives to PfDHODH, and the highest interaction affinities for the PfDHODH enzyme were in agreement with the in vitro experimental evaluation. Thus, the most active compounds against P. falciparum parasites 20 (R = CF3, R1 = F; IC50 = 0.086 µM), 21 (R = CF3; R1 = CH3; IC50 = 0.032 µM), 23, (R = CF3, R1 = CF3; IC50 = 0.030 µM) and 24 (R = CF3, 2-naphthyl; IC50 = 0.050 µM) and the most active inhibitor against PfDHODH 19 (R = CF3, R1 = Cl; IC50 = 0.08 µM - PfDHODH) stood out as new lead compounds for antimalarial drug discovery. Their potent in vitro activity against P. falciparum and the selective inhibition of the PfDHODH enzyme strongly suggest that this is the mechanism of action underlying this series of new [1,2,4]triazolo[1,5-a]pyrimidine derivatives.

Antimalarial and anti-inflammatory activities of new chloroquine and primaquine hybrids: Targeting the blockade of malaria parasite transmission.

Malaria is a disease that requires new drugs not only to fight Plasmodium but also to reduce symptoms of infection such as fever and inflammation. A series of 21 hybrid compounds were designed from chloroquine (CQ) and primaquine (PQ) linked to the pharmacophoric group present in phenylacetic anti-inflammatory drugs. These compounds were designed to have dual activity: namely, to be capable of killing Plasmodium and still act on the inflammatory process caused by malaria infection. The compounds were assayed with nine different biological methods. The carbonylated CQ derivative 6 (n = 3; R1 = Cl) was more potent than CQ in vitro, and 8 (n = 4; R1 = H) reduced P. berghei parasitemia up to 37% on day 7. The carbonylated PQ derivative 17 (R = Br) was slightly less potent than PQ. The gem-difluoro PQ derivative 20 (R = Cl) exhibited high transmission blockade of the malaria sporogonic cycle in mosquitoes. Compounds 6 and 20 dose-dependently reduced nitric oxide (NO) production and inhibited TNFα production by LPS-stimulated J774A.1 macrophages. Our results indicate a viable and interesting approach in planning new chemical entities that act as transmission-blocking drugs for treating malaria caused by P. falciparum and P. vivax and the anti-inflammatory process related to this disease.

New pyrazolopyrimidine derivatives as Leishmania amazonensis arginase inhibitors.

Arginase performs the first enzymatic step in polyamine biosynthesis in Leishmania and represents a promising target for drug development. Polyamines in Leishmania are involved in trypanothione synthesis, which neutralize the oxidative burst of reactive oxygen species (ROS) and nitric oxide (NO) that are produced by host macrophages to kill the parasite. In an attempt to synthesize arginase inhibitors, six 1-phenyl-1H-pyrazolo[3,4-d]pyrimidine derivatives with different substituents at the 4-position of the phenyl group were synthesized. All compounds were initially tested at 100 µM concentration against Leishmania amazonensis ARG (LaARG), showing inhibitory activity ranging from 36 to 74%. Two compounds, 1 (R=H) and 6 (R=CF3), showed arginase inhibition >70% and IC50 values of 12 µM and 47 µM, respectively. Thus, the kinetics of LaARG inhibition were analyzed for compounds 1 and 6 and revealed that these compounds inhibit the enzyme by an uncompetitive mechanism, showing Kis values, and dissociation constants for ternary complex enzyme-substrate-inhibitor, of 8.5 ±â€¯0.9 µM and 29 ±â€¯5 µM, respectively. Additionally, the molecular docking studies proposed that these two uncompetitive inhibitors interact with different LaARG binding sites, where compound 1 forms more H-bond interactions with the enzyme than compound 6. These compounds showed low activity against L. amazonensis free amastigotes obtained from mice lesions when assayed with as much as 30 µM. The maximum growth inhibition reached was between 20 and 30% after 48 h of incubation. These results suggest that this system can be promising for the design of potential antileishmanial compounds.

Synthesis, Biological Evaluation, and Molecular Modeling Studies of New Thiadiazole Derivatives as Potent P2X7 Receptor Inhibitors.

Twenty new 2-(1H-pyrazol-1-yl)-1,3,4-thiadiazole analogs were synthetized to develop P2X7 receptor (P2X7R) inhibitors. P2X7R inhibition in vitro was evaluated in mouse peritoneal macrophages, HEK-293 cells transfected with hP2X7R (dye uptake assay), and THP-1 cells (IL-1ß release assay). The 1-(5-phenyl-1,3,4-thiadiazol-2-yl)-1H-pyrazol-5-amine derivatives 9b, 9c, and 9f, and 2-(3,5-dimethyl-1H-pyrazol-1-yl)-5-(4-fluorophenyl)-1,3,4-thiadiazole (11c) showed inhibitory effects with IC50 values ranging from 16 to 122 nM for reduced P2X7R-mediated dye uptake and 20 to 300 nM for IL-1ß release. In addition, the in vitro ADMET profile of the four most potent derivatives was determined to be in acceptable ranges concerning metabolic stability and cytotoxicity. Molecular docking and molecular dynamics simulation studies of the molecular complexes human P2X7R/9f and murine P2X7R/9f indicated the putative intermolecular interactions. Compound 9f showed affinity mainly for the Arg268, Lys377, and Asn266 residues. These results suggest that 2-(1H-pyrazol-1-yl)-1,3,4-thiadiazole analogs may be promising novel P2X7R inhibitors with therapeutic potential.

Current Antimalarial Therapies and Advances in the Development of Semi-Synthetic Artemisinin Derivatives.

According to the World Health Organization, malaria remains one of the biggest public health problems in the world. The development of resistance is a current concern, mainly because the number of safe drugs for this disease is limited. Artemisinin-based combination therapy is recommended by the World Health Organization to prevent or delay the onset of resistance. Thus, the need to obtain new drugs makes artemisinin the most widely used scaffold to obtain synthetic compounds. This review describes the drugs based on artemisinin and its derivatives, including hybrid derivatives and dimers, trimers and tetramers that contain an endoperoxide bridge. This class of compounds is of extreme importance for the discovery of new drugs to treat malaria.

Design, synthesis and anti-P. falciparum activity of pyrazolopyridine-sulfonamide derivatives.

Ten 1-phenyl-1H-pyrazolo[3,4-b]pyridine derivatives connected by a linker group to benzenesulfonamide moieties with different substituents in the 4-position were synthesized and assayed against Plasmodium falciparum. These ten compounds exhibited activity in vitro against the chloroquine-resistant clone W2 with IC50 values ranging from 3.46 to 9.30µM. The most active derivatives with substituent R2=Cl or CH3 at the benzenesulfonamide moiety exhibited the lowest IC50. Compounds with an R1=CO2Et substituent at the 5-position of the 1H-pyrazolo[3,4-b]pyridine ring presented lower activity than those with a CN substituent. The 1H-pyrazolo[3,4-b]pyridine system appears to be promising for further studies as an antimalarial for overcoming the burden of resistance in P. falciparum.

New pentasubstituted pyrrole hybrid atorvastatin-quinoline derivatives with antiplasmodial activity.

Cerebral malaria is caused by Plasmodium falciparum. Atorvastatin (AVA) is a pentasubstituted pyrrole, which has been tested as an adjuvant in the treatment of cerebral malaria. Herein, a new class of hybrids of AVA and aminoquinolines (primaquine and chloroquine derivatives) has been synthesized. The quinolinic moiety was connected to the pentasubstituted pyrrole from AVA by a linker group (CH2)n=2-4 units. The activity of the compounds increased with the size of the carbons chain. Compound with n=4 and 7-chloroquinolinyl has displayed better activity (IC50=0.40 µM) than chloroquine. The primaquine derivative showed IC50=1.41 µM, being less toxic and more active than primaquine.

Anti-Plasmodium falciparum activity of quinoline-sulfonamide hybrids.

Fifteen quinoline-sulfonamide hybrids, with a 7-chloroquinoline moiety connected by a linker group to arylsulfonamide moieties with different substituents in the 4-position were synthesized and assayed against Plasmodium falciparum. The compounds displayed high schizonticidal blood activity in vitro, with IC50 values ranging from 0.05 to 1.63 µM, in the anti-HPR2 assay against clone W2-chloroquine-resistant; ten of them showed an IC50 (ranging from 0.05 to 0.40 µM) lower than that of chloroquine and sulfadoxine. Among them, two compounds inhibited Plasmodium berghei parasitemia by 47% and 49% on day 5 after mice inoculation. The most active, in vivo, hybrid 13 is considered to be a new prototype for the development of an antimalarial drug against chloroquine-resistant parasites.

Novel selective inhibitor of Leishmania (Leishmania) amazonensis arginase.

Arginase is a glycosomal enzyme in Leishmania that is involved in polyamine and trypanothione biosynthesis. The central role of arginase in Leishmania (Leishmania) amazonensis was demonstrated by the generation of two mutants: one with an arginase lacking the glycosomal addressing signal and one in which the arginase-coding gene was knocked out. Both of these mutants exhibited decreased infectivity. Thus, arginase seems to be a potential drug target for Leishmania treatment. In an attempt to search for arginase inhibitors, 29 derivatives of the [1,2,4]triazolo[1,5-a]pyrimidine system were tested against Leishmania (Leishmania) amazonensis arginase in vitro. The [1,2,4]triazolo[1,5-a]pyrimidine scaffold containing R1  = CF3 exhibited greater activity against the arginase rather than when the substituent R1  = CH3 in the 2-position. The novel compound 2-(5-methyl-2-(trifluoromethyl)-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)hydrazinecarbothioamide (30) was the most potent, inhibiting arginase by a non-competitive mechanism, with the Ki and IC50 values for arginase inhibition estimated to be 17 ± 1 µm and 16.5 ± 0.5 µm, respectively. These results can guide the development of new drugs against leishmaniasis based on [1,2,4]triazolo[1,5-a]pyrimidine derivatives targeting the arginase enzyme.

New compounds hybrids 1h-1,2,3-triazole-quinoline against Plasmodium falciparum.

Malaria is one of the most prevalent parasitic diseases in the world. The global importance of this disease, current vector control limitations, and the absence of an effective vaccine make the use of therapeutic antimalarial drugs the main strategy to control malaria. Chloroquine is a cost-effective antimalarial drug with a relatively robust safety profile, or therapeutic index. However, chloroquine is no longer used alone to treat patients with Plasmodium falciparum due to the emergence and spread of chloroquine-resistant strains, which have also been reported for Plasmodium vivax. However, the activity of 1,2,3-triazole derivatives against chloroquine-sensitive and chloroquine-resistant strains of P. falciparum has been reported in the literature. To enhance the anti-P. falciparum activity of quinoline derivatives, we synthesized 11 new quinoline-1H-1,2,3-triazole hybrids with different substituents in the 4-positions of the 1H-1,2,3-triazole ring, which were assayed against the W2-chloroquine-resistant P. falciparum clone. Six compounds exhibited activity against the P. falciparum W2 clone, chloroquine-resistant, with IC50 values ranging from 1.4 to 46 µm. None of these compounds was toxic to a normal monkey kidney cell line, thus exhibiting good selectivity indexes, as high 351 for one compound (11).

New trifluoromethyl triazolopyrimidines as anti-Plasmodium falciparum agents.

According to the World Health Organization, half of the World's population, approximately 3.3 billion people, is at risk for developing malaria. Nearly 700,000 deaths each year are associated with the disease. Control of the disease in humans still relies on chemotherapy. Drug resistance is a limiting factor, and the search for new drugs is important. We have designed and synthesized new 2-(trifluoromethyl)[1,2,4]triazolo[1,5-a]pyrimidine derivatives based on bioisosteric replacement of functional groups on the anti-malarial compounds mefloquine and amodiaquine. This approach enabled us to investigate the impact of: (i) ring bioisosteric replacement; (ii) a CF3 group substituted at the 2-position of the [1,2,4]triazolo[1,5-a]pyrimidine scaffold and (iii) a range of amines as substituents at the 7-position of the of heterocyclic ring; on in vitro activity against Plasmodium falciparum. P. falciparum dihydroorotate dehydrogenase (PfDHODH) through strong hydrogen bonds. The presence of a trifluoromethyl group at the 2-position of the [1,2,4]triazolo[1,5-a]pyrimidine ring led to increased drug activity. Thirteen compounds were found to be active, with IC50 values ranging from 0.023 to 20 µM in the anti-HRP2 and hypoxanthine assays. The selectivity index (SI) of the most active derivatives 5, 8, 11 and 16 was found to vary from 1,003 to 18,478.

N-(4-Chloro-phen-yl)-5-(4,5-dihydro-1H-imidazol-2-yl)thieno[2,3-b]pyridin-4-amine.

In the title compound, C(16)H(13)ClN(4)S, the thienopyridine fused-ring system is nearly planar (r.m.s. deviation = 0.0333 Å) and forms a dihedral angle of 4.4 (3)° with the attached dihydro-imidazole ring (r.m.s. deviation = 0.0429 Å) allowing for the formation of an intra-molecular (exocyclic amine)N-H⋯N(imine) hydrogen bond. The benzene rings of the disordered (50:50) -N(H)-C(6)H(4)Cl residue form dihedral angles of 59.1 (3) and 50.59 (15)° with the fused ring system. In the crystal, (imidazole amine)N-H⋯N(pyridine) hydrogen bonds lead to a supra-molecular helical chain along the b axis. The chains assemble into layers (ab plane) with inter-digitation of the chloro-benzene rings which results in weak C-H⋯Cl inter-actions in the c-axis direction.

4-(3-Fluoro-anilino)thieno[2,3-b]pyridine-6-carb-oxy-lic acid.

In the title compound, C(14)H(9)FN(2)O(2)S, the thieno[2,3-b]pyridine residue is almost planar (r.m.s. deviation = 0.0194 Å), with the carb-oxy-lic acid group [dihedral angle = 11.9 (3)°] and the benzene ring [71.1 (4)°] being twisted out of this plane to different extents. An intra-molecular N-H⋯O(carbon-yl) hydrogen bond closes an S(6) ring. Supra-molecular chains along [01-1] mediated by O-H⋯N(pyridine) hydrogen bonds feature in the crystal. A three-dimensional architecture is completed by π-π inter-actions occurring between the benzene ring and the two rings of the thieno[2,3-b]pyridine residue [centroid-centroid distances = 3.6963 (13) and 3.3812 (13) Å]. The F atom is disordered over the two meta sites in a near statistical ratio [0.545 (5):0.455 (5)].

Design and synthesis of new N-(5-trifluoromethyl)-1H-1,2,4-triazol-3-yl benzenesulfonamides as possible antimalarial prototypes.

A rational approach was used to synthesize a new set of 15 1H-1,2,4-triazol-3-yl benzenesulfonamide derivatives with the aim of developing new antimalarial lead compounds. These derivatives were prepared in yields between 50% and 62%, and their structures were elucidated using IR, ¹H-, ¹³C-, ¹9F-NMR, MS and elemental analysis. A docking study based on sulfonamides previously used against malaria identified trifluoromethyl-substituted derivatives to be the best lead compounds for new antimalarial drug development.

Identification of a potential lead structure for designing new antimicrobials to treat infections caused by Staphylococcus epidermidis-resistant strains.

Bacterial infections are a significant cause of morbidity and mortality among critically ill patients. The increase of antibiotic resistance in bacteria from human microbiota-such as Staphylococcus epidermidis, an important nosocomial pathogen that affects immunocompromised patients or those with indwelling devices-increased the desire for new antibiotics. In this study we designed, synthesized, and determined the antimicrobial activity of 27 thieno[2,3-b]pyridines (1, 2, 2a-2m, 3, 3a-3m) derivatives against a drug-resistant clinical S. epidermidis strain. In addition, we performed a structure-activity relationship analysis using a molecular modeling approach, and discuss the drug absorption, distribution, metabolism, excretion, and toxicity profile and Lipinski's "rule of five," which are tools to assess the relationship between structures and drug-like properties of active compounds. Our results showed that compound 3b (5-(1H-tetrazol-5-yl)-4-(3;-methylphenylamino)thieno[2,3-b]pyridine) was as active as oxacillin and chloramphenicol but with lower theoretical toxicity risks and a better drug likeness and drug score potential than chloramphenicol. All molecular modeling and biological results reinforced the promising profile of 3b for further experimental investigation and development of new antibacterial drugs.

SAR of a series of anti-HSV-1 acridone derivatives, and a rational acridone-based design of a new anti-HSV-1 3H-benzo[b]pyrazolo[3,4-h]-1,6-naphthyridine series.

Herpes Simplex Virus (HSV) infections are among the most common human diseases. In this work, we assess the structural features and electronic properties of a series of ten 1-hydroxyacridone derivatives (1a-j) recently described as a new class of non-nucleoside inhibitors of Herpes Simplex Virus-1 (HSV-1). Based on these molecules, we applied rigid analogue and isosteric replacement approaches to design and synthesize nine new 3H-benzo[b]pyrazolo[3,4-h]-1,6-naphthyridine derivatives (2a-i). The biological and computational results of these new molecules were compared with 1-hydroxyacridones. An inhibitory profile was observed in 10-Cl substituted 3H-benzo[b]pyrazolo[3,4-h]-1,6-naphthyridine derivative (2f), which presents the same substituent at the analogous position of 1-hydroxyacridone derivative (1b). The structure-activity relationship (SAR) studies pointed out the 10-position next to nitrogen atom as important for the anti-HSV-1 profile in the pyrazolo-naphthyridine derivatives tested, which reinforced the promising profile for further experimental investigation. The most potent acridone and pyrazolo-naphthridine derivatives were also submitted to an in silico ADMET screening in order to determine their overall drug-score, which confirmed their potential antiviral profile.