“The formal analogy between 2: 4-diamino-5-p-chlorophenoxypyrimidine (I) and proguanil (" Paludrine ") (II), and the finding that proguanil was also an antagonist of pteroylglutamic acid , suggested that the pyrimidine compound might have antimalarial activity (Falco, Hitchings, Russell, and VanderWerff, 1949).”