AbstractA group of fifty‐five 2‐[(4‐11[(dialkylamino)alkyI]amino11‐6‐methyl‐2‐pyrimidinyl)amino]‐benzimidazoles (VII) was synthesized in 3‐88% yield by the condensation of the requisite 2‐[(2‐benzimidazolyl)amino]‐4‐chloro‐6‐methylpyrimidine (VI) with the appropriate polyamine in ethanol‐hydrochloric acid or neat with excess amine containing potassium iodide. The 2‐[(2‐benzimidazolyl)amino]‐6‐methyl‐4‐pyrirnidinol precursors (V), obtained in 11‐51% yield by cyclization of 2‐(cyanoamino)‐4‐hydroxy‐6‐methylpyrimidine with a suitably substitutedo‐phenylenediamine, were chlorinated with phosphorus oxychloride to give the intermediate 2‐[(2‐benzimidazolyl)amino]‐4‐chloro‐6‐rnethylpyrimidines (VI) (27‐99%). Oxidation of 5,6‐dichloro‐2‐[(4‐11[4‐(diethylamino)‐l‐methylbutyl]amino 11‐6‐methyl‐2‐pyrimidinyl) amino ]benzimidazole (29) withm‐chloroperbenzoic acid gave the distalN4'‐oxide (31) (19%). Fusion of 2,3‐uiaminopyridine with 2‐(cyanoamino)‐4‐hydroxy‐6‐methylpyrimidine provided 2‐[(4‐hydroxy‐6‐tnethyl‐2‐pyrimidinyl)amino]‐lH‐imitlazo[4,5‐b]pyrimidine (VIII) (30%), which upon chlori‐nation with phosphorus oxychloride (63%) followed by amination with iN, N‐diethylethylene‐diamine afforded 2‐(4‐11[2‐(diethylamino)ethyl] amino 11‐6‐methyl‐2‐pyrimidinyl)‐lH‐imidazo [4,5‐b]pyridine (X) (8%). Thirty‐eight of the novel 2‐[(4‐amino‐6‐methyl‐2‐pyrimidinyl)amino]‐benzimidazoles possessed “curative” activity againstPlasmodium bergheiat single subcutaneous doses ranging from 20.640 mg./kg. Orally, thirty‐one compounds exhibited suppressive activity againstP. bergheicomparable with or superior to the reference drugs 1‐(p‐chlorophenyl)‐3‐(4‐11[2‐(diethylarnino)ethyl]amino 11‐6‐methyl‐2‐pyrimidinyl)guanidine (I) and quinine hydrochloride, while twelve of them were 5 to 28 times as potent as I and quinine hydrochloride. Eight compounds also displayed strong suppressive activity againstP. gallinaceumin chicks. 5,6‐Dichloro‐2‐[(4‐112‐(diethylamino)ethyl]amino11‐6‐methyl‐2‐pyrimidinyl]benzimidazole (18) showed marked activity against a cycloguanil‐resistant line ofP. berghei, and the most promising member of the series, namely 5,6‐dichloro‐2‐[(4