Two novel derivatives of clofazimine [3-(p-chloroanilino)-10-(p-chlorophenyl)-2,10-dihydro-2-isopropylimino)phenazine] and the tetramethylpiperidine (TMP)-substituted phenazines, B4119 [3-(3-chloro-4-fluoroanilino)-10-(3-chloro-4-fluorophenyl)-2,10-dihydro-2(2,2,6,6-tetramethylpiper-4ylimino)phenazine] and B4158 [3-(4-isopropylanilino)-10-(4-isopropylphenyl)-2,10-dihydro-2-(2,2,6,6tetramethylpiper-4-ylimino)phenazine]
(1-8 Β΅M), were evaluated for activity against chloroquin-, quinine-, and sulfadoxine/pyrimethamine-sensitive and -resistant strains of Plasmodium falciparum in vitro, as well as for their effects on polymerisation of haeme to Ξ²-hematin. By using microscopic and flow cytometric methods, it was found that B4119 and B4158, but not clofazimine, inhibited the growth of sensitive, as well as resistant strains of P. falciparum with IC 50 values between 0.22 and 0.7 Β΅M, indicating lack of crossresistance. Augmentation of anti-plasmodial activity was observed when B4119 and B4158 were used in combination with chloroquin or mefloquine. Inhibition of the growth of P. falciparum was associated with interference with haeme polymerisation to Ξ²-hematin in vitro, while administration of B4119 to P. bergheiinfected mice was accompanied by a significant reduction in parasitemia and improved therapeutic activity was observed when this agent was combined with chloroquin. The data presented in this study demonstrate that the TMP-substitution at position 2 on the phenazine nucleus of riminophenazines confers antiplasmodial activity on these compounds. These may prove to be useful forerunners in the design of novel anti-plasmodial pharmacologic agents.