Purine

Purine is a heterocyclicaromaticorganic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines and their tautomers. They are the most widely occurring nitrogen-containing heterocycles in nature.

In nucleic acids, two types of nucleobases are purine derivatives: adenine (A) and guanine (G).