Design, synthesis and mechanistic exploration of anti-plasmodial Indolo[2,3-b]quinoxaline-7-chloroquinoline hybrids

Aim: The aim of this study is to synthesize indolo[2,3-b]quinoxaline-4-aminoquinoline-based hybrids and evaluate their effectiveness against chloroquine-susceptible (3D7) and resistant (W2) Plasmodium falciparum strains, with expected inhibition of P. falciparum chloroquine resistance transporter (PfCRT) and heme. Methods: The hybrids were synthesized and in vitro evaluated against both susceptible and resistant strains. Molecular docking and studies were conducted to assess the binding affinities for the PfCRT protein. Additionally, heme-inhibition studies using hemin chloride provided valuable insights into the interaction between the ligand and heme. The binding constant (logK) was calculated, providing quantitative details about the strength of this interaction. Conclusion: The synthesized hybrids showed reasonable potency against both P. falciparum strains. The most potent hybrid 10d, with fluorine-substitution exhibited good activity. Molecular docking studies indicated strong binding affinities for the PfCRT protein. Heme inhibition studies further supported the potential of 10d as an effective anti-plasmodial agent. A series of indolo[2,3-b]quinoxaline-7-chloroquinoline based hybrids were designed and synthesized and evaluated for their anti-plasmodial activity. The hybrids were tested against both chloroquine-sensitive (3D7) and chloroquine-resistant (W2) strains of Plasmodium falciparum. The results demonstrated that the compounds exhibited reasonable potency, suggesting that these hybrids could serve as potential candidates for overcoming chloroquine resistance in malaria treatment. Among the series, compound 10d, featuring a fluorine substitution, displayed notably superior activity against the chloroquine-resistant W2 strain. Molecular docking studies were conducted to investigate the binding interactions between the synthesized compounds and the PfCRT protein, a key target in chloroquine resistance. The results indicated that 10d, in particular, exhibited strong binding affinities for the PfCRT protein. Further validation of the anti-plasmodial potential of compound 10d was obtained through heme inhibition studies. These studies confirmed that compound 10d effectively inhibits heme detoxification within the parasite, thereby enhancing its activity. This dual mode of action underscores the compound's promise as an effective treatment option. Molecular modeling shows that both 10d and 10f bind strongly to PfCRT, with 10d exhibiting better interaction retention and 10f showing promising binding despite lower stability, highlighting their potential as effective PfCRT inhibitors.