6-Substituted 2,4-Diamino-5-(4-earbethoxyphenylazo)pyrimidines as Potential Precursors of Tetrahydropteridine Antimetabolites

2,4-Diamino-5(4-carbet.hoxyphenylazo)pyrimidines bearing the 3-anilino-2-liydroxypropylamino or 3-amlino-2-chloropropylamino substituents in the 6 position have been synthesized and compared in biological systems with 2,4,6-triamino-5-(4-carbethoxyphenylazo)pyrimidine to test the hypothesis that the former compounds might undergo an in vivo conversion to a tetrahydropteridine. Xo evidence to support this hypothesis could be found, and it was demonstrated that azopyrimidines are inhibitors, rather than substrates, of rat azo reductases.