Synthesis and antifolate activity of new diaminopyrimidines and diaminopurines in enzymic and cellular systems

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Abstract
The following new 2,4-diamino-6-methylpyrimidines, 5-cyclohexylmethyl, 5-cyclohexylethyl,and 5-(2-naphthyl), as well as 2,6-diaminopurines, 8-adamantyl and8-adamantylmethyl, were synthesized as potential antifolates. Tese, as well as three known compounds, 2,4-diamino-5-cyclohexyl-6-methylpyrimidine, 2,4-diamino-5-(1-naphthyl) -6- methylpyrimidine, and 2,6-diaminopurine, were compared with respect to the inhibition of growth of mammalian cells in culture (TA 3) and with respect to the inhibition of partially purified dihydrofolate reductase. All of the pyrimidines except for the 5-(1maphthyl) derivative were competitive inhivitors of dihydrofolate reductase, with K values ranging from 0.07 to 0.04 pM. They were 2-5 times better as inhibitors of the isolated dihydrofolate reductase than of the cell growth. 2,4-Diamino-5-(1-naphthyl)-6-methylpyrimidine was a noncomptive inhivitor of the enzyme with a Kvalue of 56 pM. This compound was more potent in inhibiting cell growth than the isolated enzyme. indicating that its biological activity was not related to the inhibition of dihydrofolate reductse. All of the purine derivatives were poor growth inhibitors and although some of them inhibited isolated dihydrofolate reductase, their mode of action in cellular system did not seem to concern folate metabolism, as judged by the inability of hypoxanthine, and glycine to provide protection. The implication of these findings as to the structural requirements for inhibition of dihydrofolate reductase is discussed. The implication of these findings as to the structural requirements for inhibition of dihydrofolate reductase is discussed. The pitfalls of the determinition of ID-50 values instead of a complete kinetic analysis in structure-activity studies are emphasized.

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