Design and Synthesis of Novel Hybrid Molecules against Malaria

Microwave synthesis and antimalarial screening of novel 4-amino benzoic acid (PABA)-substituted pyrimidine derivatives as Plasmodium falciparum dihydrofolate reductase inhibitors

Antimalarial drug resistance is a major threat due to the emerging resistance to all the available drugs in the market. In an approach to develop alternative drugs, a novel class of Pf-DHFR inhibitors was developed using pyrimidine as the core nucleus and substituting the 4- and 6- positions with amines and 4-amino benzoic acid (PABA) to avoid the problem of drug resistance. The resultant compounds 3(a-j) after primary in silico screening and filtering were synthesized using microwave efficiently in high yield and reduced time period compared to conventional synthesis. The antimalarial assay was performed in vitro, against chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2) strains of Plasmodium falciparum using chloroquine as a reference standard. The IC₅₀ values were in the range of 5.26-106.76 µg/ml for 3D7 and in Dd2 the value ranges from 4.71 to 112.98 µg/ml. Compounds 3d, 3e, 3f and 3h showed significant antimalarial activity against both the strains of P. falciparum with no cytotoxicity against fibroblast cell line and 3f was found to be the most potent among them. The hemolysis assay of all the compounds in fresh erythrocytes showed insignificant hemolysis below 5% at a higher dose level. Hence, the present study suggests the possible utility of PABA-substituted pyrimidine scaffold for further development of new Pf-DHFR inhibitors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03236-w.

Quantitative Analysis of the Potency of Equimolar Two-Drug Combinations and Combi-Molecules Involving Kinase Inhibitors In Vitro: The Concept of Balanced Targeting

The median-effect principle proposed by Chou and Talalay is the most effective approach to parameterize interactions between several agents in combination. However, this method cannot be used to evaluate the effectiveness of equimolar drug combinations, which are comparative references for dual-targeting molecular design. Here, using data acquired through the development of “combi-molecules” blocking two kinases (e.g., EGFR-c-Src and EGFR-c-Met), we established potency indices for equimolar and dual-targeted inhibitors. If the fold difference (κ) between the IC50 of the two individual kinase inhibitors was >6, the IC50 of their equimolar combination resembled that of the more potent inhibitor. Hence, the “combi-targeting” of the two kinases was considered “imbalanced” and the combination ineffective. However, if κ ≤ 6, the IC50 of the combination fell below that of each individual drug and the combi-targeting was considered “balanced” and the combination effective. We also showed that combi-molecules should be compared with equimolar combinations only under balanced conditions and propose a new parameter Ω for validating their effectiveness. A multi-targeted drug is effective if Ω < 1, where Ω is defined as the IC50 of the drug divided by that of the corresponding equimolar combination. Our study provides a methodology to determine the in vitro potency of equimolar two-drug combinations as well as combi-/hybrid molecules inhibiting two different kinase targets.

Kravtsov V, Melnic E, Petrou A, Glamočlija J, Soković M, Carazo A, Mladěnka P, Poroikov V, Geronikaki A, Macaev FZ. Chromenol Derivatives as Novel Antifungal Agents: Synthesis, In Silico and In Vitro Evaluation

Herein we report the synthesis of some new 1H-1,2,4-triazole functionalized chromenols (3a-3n) via tandem reactions of 1-(alkyl/aryl)-2-(1H-1,2,4-triazole-1-yl) with salicylic aldehydes and the evaluation of their antifungal activity. In silico prediction of biological activity with computer program PASS indicate that the compounds have a high novelty compared to the known antifungal agents. We did not find any close analog among the over 580,000 pharmaceutical agents in the Cortellis Drug Discovery Intelligence database at the similarity cutoff of 70%. The evaluation of antifungal activity in vitro revealed that the highest activity was exhibited by compound 3k, followed by 3n. Their MIC values for different fungi were 22.1-184.2 and 71.3-199.8 µM, respectively. Twelve from fourteen tested compounds were more active than the reference drugs ketoconazole and bifonazole. The most sensitive fungus appeared to be Trichoderma viride, while Aspergillus fumigatus was the most resistant one. It was found that the presence of the 2-(tert-butyl)-2H-chromen-2-ol substituent on the 4th position of the triazole ring is very beneficial for antifungal activity. Molecular docking studies on C. albicans sterol 14α-demethylase (CYP51) and DNA topoisomerase IV were used to predict the mechanism of antifungal activities. According to the docking results, the inhibition of CYP51 is a putative mechanism of antifungal activity of the novel chromenol derivatives. We also showed that most active compounds have a low cytotoxicity, which allows us to consider them promising antifungal agents for the subsequent testing activity in in vivo assays.

4-Aminosalicylic Acid-based Hybrid Compounds: Synthesis and In vitro Antiplasmodial Evaluation

Background:

Malaria is a deadly and infectious disease responsible for millions of death worldwide, mostly in the African region. The malaria parasite has developed resistance to the currently used antimalarial drugs, and it has urged researchers to develop new strategies to overcome this challenge by designing different classes of antimalarials.

Objectives:

A class of hybrid compounds containing 4-aminosalicylic acid moiety was prepared via esterification and amidation reactions and characterized using FTIR, NMR and LC-MS. In vitro antiplasmodial evaluation was performed against the asexual NF54 strain of P. falciparum parasites.

Methods:

In this research, known 4-aminoquinoline derivatives were hybridized with 4- aminosalicylic acid to afford hybrid compounds via esterification and amidation reactions. 4- aminosalicylic acid, a dihydrofolate compound inhibits DNA synthesis in the folate pathway and is a potential pharmacophore for the development of antimalarials.

Results:

The LC-MS, FTIR, and NMR analysis confirmed the successful synthesis of the compounds. The compounds were obtained in yields in the range of 63-80%. The hybrid compounds displayed significant antimalarial activity when compared to 4-aminosalicylic acid, which exhibited poor antimalarial activity. The IC50 value of the most potent hybrid compound, 9 was 9.54±0.57 nm.

Conclusion:

4-aminosalicylic has different functionalities, which can be used for hybridization with a wide range of compounds. It is a potential pharmacophore that can be utilized for the design of potent antimalarial drugs. It was found to be a good potentiating agent when hybridized with 4- aminoquinoline derivatives suggesting that they can be utilized for the synthesis of a new class of antimalarials.

A Novel Hybrid of Chloroquine and Primaquine Linked by Gold(I): Multitarget and Multiphase Antiplasmodial Agent

Plasmodium parasites kill 435 000 people around the world every year due to unavailable vaccines, a limited arsenal of antimalarial drugs, delayed treatment, and the reduced clinical effectiveness of current practices caused by drug resistance. Therefore, there is an urgent need to discover and develop new antiplasmodial candidates. In this work, we present a novel strategy to develop a multitarget metallic hybrid antimalarial agent with possible dual efficacy in both sexual and asexual erythrocytic stages. A hybrid of antimalarial drugs (chloroquine and primaquine) linked by gold(I) was synthesized and characterized by spectroscopic and analytical techniques. The CQPQ-gold(I) hybrid molecule affects essential parasite targets, it inhibits β-hematin formation and interacts moderately with the DNA minor groove. Its interaction with PfTrxR was also examined in computational modeling studies. The CQPQ-gold(I) hybrid displayed an excellent in vitro antimalarial activity against the blood-stage of Plasmodium falciparum and liver-stage of Plasmodium berghei and efficacy in vivo against P. berghei, thereby demonstrating its multiple-stage antiplasmodial activity. This metallic hybrid is a promising chemotherapeutic agent that could act in the treatment, prevention, and transmission of malaria.

Primaquine-quinoxaline 1,4-di-N-oxide hybrids with action on the exo-erythrocytic forms of Plasmodium induce their effect by the production of reactive oxygen species

Background

The challenge in anti-malarial chemotherapy is based on the emergence of resistance to drugs and the search for medicines against all stages of the life cycle of Plasmodium spp. as a therapeutic target. Nowadays, many molecules with anti-malarial activity are reported. However, few studies about the cellular and molecular mechanisms to understand their mode of action have been explored. Recently, new primaquine-based hybrids as new molecules with potential multi-acting anti-malarial activity were reported and two hybrids of primaquine linked to quinoxaline 1,4-di-N-oxide (PQ–QdNO) were identified as the most active against erythrocytic, exoerythrocytic and sporogonic stages.

Methods

To further understand the anti-malarial mode of action (MA) of these hybrids, hepg2-CD81 were infected with Plasmodium yoelii 17XNL and treated with PQ–QdNO hybrids during 48 h. After were evaluated the production of ROS, the mitochondrial depolarization, the total glutathione content, the DNA damage and proteins related to oxidative stress and death cell.

Results

In a preliminary analysis as tissue schizonticidals, these hybrids showed a mode of action dependent on peroxides production, but independent of the activation of transcription factor p53, mitochondrial depolarization and arrest cell cycle.

Conclusions

Primaquine–quinoxaline 1,4-di-N-oxide hybrids exert their antiplasmodial activity in the exoerythrocytic phase by generating high levels of oxidative stress which promotes the increase of total glutathione levels, through oxidation stress sensor protein DJ-1. In addition, the role of HIF1a in the mode of action of quinoxaline 1,4-di-N-oxide is independent of biological activity.

Hybrid Molecules Composed of 2,4-Diamino-1,3,5-triazines and 2-Imino-Coumarins and Coumarins. Synthesis and Cytotoxic Properties

A series of 2-imino-2H-chromen-3-yl-1,3,5-triazine compounds 5⁻12, which are namely hybrids of 2,4-diamino-1,3,5-triazines and 2-imino-coumarins, was synthesized by reacting 2-(4,6-diamine-1,3,5-triazin-2-yl)acetonitriles 1⁻4 with 2-hydroxybenzaldehydes. After this, upon heating in aqueous DMF, 2-imino-2H-chromen-3-yl-1,3,5-triazines 10 and 12 were converted into the corresponding 2H-chromen-3-yl-1,3,5-triazines 13 and 14, which are essentially hybrids of 2,4-diamino-1,3,5-triazines and coumarins. The in vitro anticancer activity of the newly prepared compounds was evaluated against five human cancer cell lines: DAN-G, A-427, LCLC-103H, SISO and RT-4. The greatest cytotoxic activity displayed 4-[7-(diethylamino)-2-imino-2H-chromen-3-yl]-6-(4-phenylpiperazin-1-yl)-1,3,5-triazin-2-amine (11, IC₅₀ in the range of 1.51⁻2.60 μM).

Quinoline-Based Hybrid Compounds with Antimalarial Activity

The application of quinoline-based compounds for the treatment of malaria infections is hampered by drug resistance. Drug resistance has led to the combination of quinolines with other classes of antimalarials resulting in enhanced therapeutic outcomes. However, the combination of antimalarials is limited by drug-drug interactions. In order to overcome the aforementioned factors, several researchers have reported hybrid compounds prepared by reacting quinoline-based compounds with other compounds via selected functionalities. This review will focus on the currently reported quinoline-based hybrid compounds and their preclinical studies.

Are Antimalarial Hybrid Molecules a Close Reality or a Distant Dream?

Emergence of drug-resistant Plasmodium falciparum strains has led to a situation of haste in the scientific and pharmaceutical communities. Hence, all their efforts are redirected toward finding alternative chemotherapeutic agents that are capable of combating multidrug-resistant parasite strains. In light of this situation, scientists have come up with the concept of hybridization of two or more active pharmacophores into a single chemical entity, resulting in "antimalarial hybrids." The approach has been applied widely for generation of lead compounds against deadly diseases such as cancer and AIDS, with a proven potential for use as novel drugs, but is comparatively new in the sphere of antimalarial drug discovery. A sudden surge has been evidenced in the number of studies on the design and synthesis of hybrids for treating malaria and may be regarded as proof of their potential advantages over artemisinin-based combination therapy (ACT). However, it is evident from recent studies that most of the potential advantages of antimalarial hybrids, such as lower toxicity, better pharmacokinetics, and easier formulation, have yet to be realized. A number of questions left unaddressed at present need to be answered before this approach can progress to the late stages of clinical development and prove their worth in the clinic. To the best of our knowledge, this compilation is the first attempt to shed light on the shortcomings that are surfacing as more and more studies on molecular hybridization of the active pharmacophores of known antimalarials are being published.

Introducing New Antimalarial Analogues of Chloroquine and Amodiaquine: A Narrative Review

Antimalarial drugs with the 4-aminoquinoline scaffold such as the important drugs, chloroquine (CQ) and amodiaquine (AQ), have been used to prevent and treat malaria for many years. The importance of these drugs is related to their simple usage, high efficacy, affordability, and cost-effectiveness of their synthesis. In recent years, with the spread of parasite resistance to CQ and cross-resistance to its other analogues have decreased their consumption in many geographical areas. On the other hand, AQ is an effective antimalarial drug which its usage has been restricted due to hepatic and hematological toxicities. The significance of the quinoline ring at quinoline-based antimalarial drugs has prompted research centers and pharmaceutical companies to focus on the design and synthesis of new analogues of these drugs, especially CQ and AQ analogues. Accordingly, various derivatives have been synthesized and evaluated in vitro and in vivo against the resistant strains of the malaria parasite to solve the problem of drug resistance. Also, the pharmacokinetic properties of these compounds have been evaluated to augment their efficacy and diminish their toxicity. Some of these analogues are currently in clinical and preclinical development. Consequently, the recent researches showed yet 4-aminoquinoline scaffold is active moiety in new compounds with antiplasmodial activity. Hence, the aim of this review article is to introduce of the novel synthetic analogues of CQ and AQ, which may constitute the next generation of antimalarial drugs with the 4-aminoquinoline scaffold.