Fused Pyrimidines Purines and Pteridines

5-Diaminopyrimidines are frequently the starting framework for the constmction of the second ring in both cyclic systems, as will be shown in the examples that follow, but other methods have also been developed. 

SYNTHETIC METHODS FOR SOME PROMINENT HETEROCYCLIC FAMILIES 

Many biologically active purines have been prepared by the Traube synthesis, where various carboxylic acids provide novelty at the 

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