Chalcone Mannich base derivatives: synthesis, antimalarial activities against Plasmodium knowlesi, and molecular...

Development and discovery of new antimalarial drugs are needed to overcome the multi-resistance of Plasmodium parasites to commercially available drugs. Modifying the substitutions on the amine groups has been shown to increase antimalarial activities and decrease cross-resistance with chloroquine. In this study, we have synthesized several chalcone derivatives via the substitution of aminoalkyl groups into the aromatic chalcone ring using the Mannich-type reaction. The chalcone derivatives were evaluated for their antimalarial properties against Plasmodium knowlesi A1H1 and P. falciparum 3D7, as well as their molecular docking on Plasmodium falciparum dihydrofolate reductases-thymidylate synthase (PfDHFR-TS). Data from in vitro evaluation showed that chalcone Mannich-type base derivatives 2a, 2e, and 2h displayed potential antimalarial activities against P. knowlesi with EC₅₀ of 2.64, 2.98, and 0.10 μM, respectively, and P. falciparum 3D7 with EC₅₀ of 0.08, 2.69, and 0.15 μM, respectively. The synthesized compounds 2a, 2e, and 2h exerted high selectivity index (SI > 10) values on the A1H1 and 3D7 strains. The molecular docking analysis on PfDHFR-TS supported the in vitro assay of 2a, 2e, and 2h by displaying CDOCKER energy of -48.224, -43.292, and -45.851 kcal mol^-1. Therefore, the evidence obtained here supports that PfDHFR-TS is a putative molecular target for the synthesized compound.