Reinvestigation of diphenylmethylpiperazine analogues of pyrazine as new class of Plasmodial cysteine protease inhibitors for the treatment of malaria.

Malaria eradication is still a global challenge due to the lack of a broadly effective vaccine and the emergence of drug resistance to most of the currently available drugs as part of the mainline artemisinin-based combination therapy. A variety of experimental approaches are quite successful in identifying and synthesizing new promising pharmacophore hybrids with distinct mechanisms of action. Based on our recent findings, the current study demonstrates the reinvestigation of a series of diphenylmethylpiperazine and pyrazine-derived molecular hybrids. Pyrazine-derived molecular hybrids were screened to investigate the antiplasmodial activity on drug-susceptible Pf 3D7 and drug-resistant Pf W2 strains. The selected compounds were shown to be potent dual inhibitors of cysteine protease Pf FP2 and Pf FP3. Time-course parasitic development study demonstrated that compounds were able to arrest the growth of the parasite at the early trophozoite stage. The compounds did not show hemolysis of red blood cells and showed selectivity to the parasite compared with the mammalian Vero and A5489 cell lines. The study underlined HR5 and HR15 as a new class of Plasmodial falcipain inhibitors with an IC 50 of 6.2 μM and 5.9 μM for Pf FP2 and 6.8 μM and 6.4 μM for Pf FP3, respectively. Both compounds have antimalarial efficacy with IC 50 values of 3.05 μM and 2.80 μM for the Pf 3D7 strain, and 4.35 μM and 3.39 μM for the Pf W2 strain, respectively. Further structural optimization may turn them into potential Plasmodial falcipain inhibitors for malaria therapeutics.