N-[p-[[(2, 4-Diaminopyrido [2, 3-d] pyrimidin-6-yl) methyl] amino] benzoyl]-~-glutamic acid (la, 5-deazaaminopterin) and the 5-methyl analogue (lb) were synthesized in 14 steps from 5- cyanouracil (4a) and 5-cyano-6-methyluracil (4b), respectively, by exploitation of the novel pyrimidine to pyrido [2, 3-d] pyrimidine ring transformation reaction. The 5-cyanouracils 4 were treated with chloromethyl methyl ether to the 1, 3-bis (methoxymethyl) uracils (5, ...