 Other notable purines are hypoxanthine (4), xanthine (5), theobromine (6), caffeine (7), uric acid (8) and isoguanine (9).Aside from the crucial roles of purines (adenine and guanine) in DNA and RNA, purines are also significant components in a number of other important biomolecules, such as ATP, GTP, cyclic AMP, NADH, and coenzyme A. Purine (1) itself, has not been found in nature, but it can be produced by organic synthesis.They may also function directly as neurotransmitters, acting upon purinergic receptors.