Synthesis, in silico analyses, antiplasmodial, heme detoxification and cytotoxic activities of pyrano[2,3-c]pyrazole-4-aminoquinoline hybrids as antimalarial agents

Abstract

Malaria, an infectious disease that spreads widely and can kill people, is still a problem for global health. It is known that the Plasmodium falciparum is the major and dangerous protozoan parasite in the Plasmodium genus. This study adds to the list of possible solutions by making a group of new pyrano[2,3-c]pyrazole-4-aminoquinoline hybrids. Here, nineteen novel hybrids were synthesized with a percentage yield of 10 to 49% by covalently linking the scaffolds of 4-aminoquinoline and pyrano[2,3-c]pyrazoles via an ethyl linker and characterized using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Among all, high yields were observed for hybrids containing electron-withdrawing groups, such as –CN (24n, 49%), –COOH (24p, 42%), and –NO2 (24j, 38%) at the para position of the phenyl ring attached to the pyranopyrazole moiety. All the nineteen hybrid compounds were subjected to in silico studies prior to molecular docking, including physicochemical and absorption, distribution, metabolism, excretion, and toxicity (ADMET) predictions, such as protein plasma binding (PPB), inhibition of CYP2C19, blood-brain barrier (BBB), and inhibition of P-glycoprotein (PgP), to pre-screen the drug-like properties of the hybrid compounds. Molecular docking was used to test each hybrid's and standard chloroquine's ability to bind to Plasmodium falciparum lactate dehydrogenase enzyme (PfLDH), an important enzyme in the parasite's glycolytic pathway. The hybrid compounds had a stronger binding affinity than the standard chloroquine (CQ). Additionally, the study explored the interaction between five hybrids and hemin, a pivotal component in the heme detoxification pathway of malaria parasites. The isothermal titration calorimetry (ITC) showed that the hybrids had different strengths when binding to hemin. This was because their structures were different. Hybrids 24a and 24g showed a strong affinity for hemin with Ka values of (1.43±0.60)×106 M-1 and (1.64±0.97)×106 M-1, respectively, indicating that they might be able to stop the disruption process. This study provides insights into the promising antimalarial properties of pyrano[2,3-c]pyrazole-4-aminoquinoline hybrids. It details their interactions with PfLDH and hemin and offers potential avenues for developing novel therapeutic strategies against malaria. The schizontical antimalarial test of pyrano[2,3-c]pyrazole-4-aminoquinoline hybrid compound shows that all nineteen hybrid compounds were potent with the IC50 values ranging from 0.0151 to 0.301 μM against the CQ-sensitive 3D7 P. falciparum strain, and were found to be active against the CQ-resistant K1 P. falciparum strain with the IC50 values ranging from 0.01895 to 2.746 μM. All the tested hybrid compounds were less potent than the standard drug Chloroquine dipaspate (CQDP) against the CQ-sensitive 3D7 strain. In contrast, nine of the nineteen hybrids (24d, 24g, 24h, 24i, 24l, 24n, 24o, 24r and 24s) displayed superior antimalarial activity than the CQDP against the CQ-resistant K1 P. falciparum strain. Among all the tested hybrids, 24c against the 3D7 strain and 24h against the K1 strain were the most promising antimalarial agents with 0.0151 and 0.01895 μM of IC50 values, respectively. In conclusion, the synthesis of pyrano[2,3-c]pyrazole-4-aminoquinoline hybrids introduces new chemical entities that have the potential to exhibit potent antimalarial activity. This could address the ongoing challenge of drug resistance in malaria treatment.