From Eterna Wiki
A purine is an organic compound consisting of the fusion of two aromatic rings, a hexagonal one (pyrimidine) and a pentagonal one (imidazole).
There are many naturally occurring purines. Two of the five bases in nucleic acids - adenine and guanine - are purines. In RNA, these bases form hydrogen bonds with their complementary pyrimidines uracil and cytosine.
Other notable purines are hypoxanthine, xanthine, theobromine, caffeine, uric acid and isoguanine.