Purines, general

Purines, like alkaloids, are nitrogenous compounds, but are not included among the alkaloids because they are soluble in warm water. Well-known purines are adenine, guanine, thymine and cytosine, the building blocks of DNA. Thymine is replaced by uracil in the RNA. Other known purines are caffeine, hypoxanthine, isoguanine, theobromine, theophylline.