Amino derivatives of indolone-N-oxide: Preparation and antiplasmodial properties

Abstract There is an urgent need for new antimalarial drugs with novel mechanisms of action on novel targets. Indolone- N -oxides (INODs) display antimalarial properties in vitro and in vivo , but identified leads such as 6-(4-chloro-phenyl)-5-oxy-[1,3]dioxolo[4,5- f ]indol-7-one 1 , suffer from very poor aqueous solubility. In this study, structural modifications have been made by introducing various amino and bulky groups to produce sufficiently water soluble and active compounds for further pharmacological and pharmacokinetic studies. We report here the preparation of twelve novel amino derivatives and their antiplasmodial activities including those of two other structurally known compounds. The 5-methoxy-2-(4-morpholin-4-yl-phenyl)-1-oxy-indol-3-one, 9 , has the highest antiplasmodial activity in vitro (IC 50  = 6.5 nM; FcB1 strain) and selectivity index (SI (CC 50 MCF7/IC 50 FcB1) = 4538.5). The 6-amino-2-(4-chloro-phenyl)-1-oxy-indol-3-one, 14 , (IC 50  = 183 nM; SI = 60), is an excellent candidate for further mechanistic studies. Indeed, this is structurally the closest analogue to the current lead, 1 , bearing an NH 2 group at R 2 offering possibilities for functionalization and labeling.