Synthesis and biological activity of 8-oxadihydropteridines

A series of 6-substituted and 6,7-disubstituted pyrimido[4,5-b][1,4]oxazines (8-oxadihydropteridines) was synthesized through the condensation of an alpha-halo ketone and 2,5-diamino-4,6-pyrimidinediol. The resulting 8-oxadihydropteridines were assayed as potential antifolates in a dihydrofolate reductase enzyme system. The 2-amino-4-hydroxyoxa-dihydropteridines were found to possess greater biological activity than the corresponding 2,4-diamino compounds. The pteroic acid homeostere 2-amino-4-hydroxy-6-phenethyl-8-oxadihydropteridine was the most potent of the compounds tested.