6-Hydrophobic aromatic substituent pyrimethamine analogues as potential antimalarials for pyrimethamine-resistant Plasmodium falciparum

Novel hybrids of quinoline with pyrazolylchalcones as potential antimalarial agents: Synthesis, biological evaluation, molecular docking and ADME prediction

A novel series of pyrazolyl chalcones containing quinoline scaffold, 5 a-v has been synthesized by Claisen Schimdt condensation of aromatic acetophenone with 1-(4-methylquinolin-2-yl)-3-aryl-1H-pyrazole-4-carbaldehyde in quantitative yield. The compounds were characterized using IR, NMR, MS and elemental analysis. An E-configuration about CC ethylenic bond was determined using ¹H NMR spectroscopy. These compounds exhibited significant antimalarial potential against CQ-sensitive and CQ-resistant strain of Plasmodium falciparum. Structure activity relationship has also been established based on outcomes of in vitro schizont inhibition assay. Compound 5u, (Z)-3-(1-(4-methylquinolin-2-yl)-3-p-tolyl-1H-pyrazol-4-yl)-1-p-tolylprop-2-en-1-one, was found to be the most potent among the series of synthetic analogues. In vivo, it demonstrated significant parasitemia suppression of 78.01% at a dose of 200 mg/kg against P. berghei in infected mice without any mortality in 7 days. In silico molecular docking study revealed that this compound 5u bound to the active site of cysteine protease falcipain-2 enzyme. Furthermore, in silico ADME studies, were also performed and physicochemical qualifications of the title compounds were determined. The biological outcomes of newer heterocyclic compounds may pave the new paths for researchers in development of potential antimalarial agents.

Discovery of new non-pyrimidine scaffolds as Plasmodium falciparum DHFR inhibitors by fragment-based screening

In various malaria-endemic regions, the appearance of resistance has precluded the use of pyrimidine-based antifolate drugs. Here, a three-step fragment screening was used to identify new non-pyrimidine Plasmodium falciparum dihydrofolate reductase (PfDHFR) inhibitors. Starting from a 1163-fragment commercial library, a two-step differential scanning fluorimetry screen identified 75 primary fragment hits. Subsequent enzyme inhibition assay identified 11 fragments displaying IC₅₀ in the 28-695 μM range and selectivity for PfDHFR. In addition to the known pyrimidine, three new anti-PfDHFR chemotypes were identified. Fragments from each chemotype were successfully co-crystallized with PfDHFR, revealing a binding in the active site, in the vicinity of catalytic residues, which was confirmed by molecular docking on all fragment hits. Finally, comparison with similar non-hit fragments provides preliminary input on available growth vectors for future drug development.

Driving antimalarial design through understanding of target mechanism

Malaria continues to be a global health threat, affecting approximately 219 million people in 2018 alone. The recurrent development of resistance to existing antimalarials means that the design of new drug candidates must be carefully considered. Understanding of drug target mechanism can dramatically accelerate early-stage target-based development of novel antimalarials and allows for structural modifications even during late-stage preclinical development. Here, we have provided an overview of three promising antimalarial molecular targets, PfDHFR, PfDHODH and PfA-M1, and their associated inhibitors which demonstrate how mechanism can inform drug design and be effectively utilised to generate compounds with potent inhibitory activity.

An insight into the recent development of the clinical candidates for the treatment of malaria and their target proteins

Malaria is an endemic disease, prevalent in tropical and subtropical regions which cost half of million deaths annually. The eradication of malaria is one of the global health priority nevertheless, current therapeutic efforts seem to be insufficient due to the emergence of drug resistance towards most of the available drugs, even first-line treatment ACT, unavailability of the vaccine, and lack of drugs with a new mechanism of action. Intensification of antimalarial research in recent years has resulted into the development of single dose multistage therapeutic agents which has advantage of overcoming the antimalarial drug resistance. The present review explored the current progress in the development of new promising antimalarials against prominent target proteins that have the potential to be a clinical candidate. Here, we also reviewed different aspects of drug resistance and highlighted new drug candidates that are currently in a clinical trial or clinical development, along with a few other molecules with excellent antimalarial activity overs ACTs. The summarized scientific value of previous approaches and structural features of antimalarials related to the activity are highlighted that will be helpful for the development of next-generation antimalarials.