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.

New Strategies for Novel Drugs: Antimicrobial Peptides Containing Ferrocene with Improved Antifungal and Antiplasmodial Biological Activity.

BACKGROUND: Fungal and parasitic diseases are global health problems, and the available treatments are becoming ineffective, mainly due to the emergence of resistant strains of pathogens. Furthermore, the drugs currently in use exhibit high toxicity and side effects. The scarcity of efficient treatments for fungal and parasitic diseases has motivated the search for new drug candidates, including antimicrobial peptides. The chemokine class RP1 peptide shows inhibitory activity against bacteria, viruses, cancer cells and parasites. In addition, the organometallic compound ferrocene showed antiparasitic activity. OBJECTIVE: Study aimed to assess the effect of conjugation of the RP1 peptide with ferrocene in terms of its structure, biological activity against fungi and parasites and toxicity. METHODS: Peptides and conjugates were synthesized using solid phase peptide synthesis (SPPS). The Fc-RP1 peptide showed antifungal and antimalarial activities with low toxicity in the U87 and HepG2 cell lines. RESULTS: The mechanism of action of these peptides, analyzed by flow cytometry in the fungus Cryptococcus neoformans, was through membrane permeabilization, with an emphasis on the Fc-RP1 peptide that presented the highest rate of PI-positive cell marking. CONCLUSION: In conclusion, ferrocene conjugated to antimicrobial peptide RP1 is an attractive biomolecule for drug discovery against fungal and parasitic diseases.

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.

Synthesis, Profiling, and in Vivo Evaluation of Cyclopeptides Containing N-Methyl Amino Acids as Antiplasmodial Agents.

Malaria is a major tropical disease where important needs are to mitigate symptoms and to prevent the establishment of infection. Cyclopeptides containing N-methyl amino acids with in vitro activity against erythrocytic forms as well as liver stage are presented. The synthesis, parasitological characterization, physicochemical properties, in vivo evaluation, and mice pharmacokinetics are described.