Diaminopyrimidines are a class of organic chemical compounds that include two amine groups on a pyrimidine ring. Diaminopyrimidines are a class of organic chemical compounds that include two amine groups on a pyrimidine ring. They include many dihydrofolate reductase inhibitor drugs (such as pyrimethamine, trimetrexate, and piritrexim and the antibiotics Iclaprim and trimethoprim). Some have been patented as anti-cancer drugs.