Carboxamides purine analogues

Azaguanine was the first purine analogue shown to be incorporated into polynucleotides [337] and, since its primary metabolic effect is on protein synthesis, the incorporation into RNA is considered the basis for its biologic activity [338]. In microbial systems 8-aza-adenine, 8-azahypoxanthine, 8-azaxanthine, and 5(4)-amino-l/f-l, 2, 3-triazole-4(5)-carboxamide are all incorporated into RNA as 8-azaguanylic acid [336]. 

Pyrazolo[3,4-d]pyrimidines are of considerable chemical and pharmacological importance as purine analogues [75], Various compounds with related structures also possess antitumor and antileukemia activities [76]. Therefore, the investigation about new methods and synthesis of new derivatives of these compounds attracted considerable amount of interest. Reaction of 5-amino-l-phenyl-l/7-pyrazolo-4-carboxamide with aromatic aldehyde in the presence of HPAs, HjPWjjO q and Hj [NaP5W29MoO,jJ, gave derivatives of 6-aryl-l//-pyrazolo[3,4-r ]pyrimidin-4[5//]-ones. It was confirmed that HPA with Preyssler structure shows higher activity and yields due to the higher number of acidic protons (Scheme 3.29) [77]. 

Some pyrrolo 2,1 -/] [ 1,2,4]triazines which are analogues of purines have been obtained from l-aminopyrrole-2-carbonitrile (or carboxamide) (Scheme 4)[94JHC781]. 

Ribavirin, USP. Ribavirin is l-j3-o-ribofuranosyl-l.2.4-thiazole-3-carboxamide. The compound is a purine nucleoside analogue with a modified base and a D-riho.se sugar moiety. The. structure of ribavirin is show n below. 

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