Purine bases are heterocyclic compounds consisting of a pyrimidine ring and an imidazole ring fused together. The ring system was named by Emil Fischer, a German chemist.

      

Two purines that are constituents of nucleic acids are adenine (6-aminopurine) (2-amino-6-hydroxypurine). Other purines of metabolic importance are hypoxanthine, xanthine and uric acid. Hypoxanthine is derived from adenine by the replacement of the amino group by the hydroxyl group. Some purines also act as diuretic drugs.