Synthesis, Antimalarial Activity, and Structure–Activity Relationship of 7-(2-Phenoxyethoxy)-4(1H)-quinolones

ICI 56,780 (5) displayed causal prophylactic and blood schizonticidal activity (ED50 = 0.05 mg/kg) in rodent malaria models but produced rapid acquisition of parasitological resistance in P. berghei infected mice. Herein we describe the synthesis of analogues of 5 with EC50 as low as 0.15 nM against multidrug resistant P. falciparum. Optimal activity with low cross-resistance indexes (RI) to atovaquone was achieved by introducing ortho-substituted aryl moieties at the 3-position of the 7-(2-phenoxyethoxy)-4(1H)-quinolone core.