Xanthine

Xanthine is a naturally occurring substance found in blood, muscles, liver and urine, as well as in many plants (coffee beans, tea leaves, potatoes). Xanthine is an intermediate product of purine degradation and is converted into uric acid by the enzyme xanthine oxidase.
Xanthine is the lead substance of the N-methyl derivatives of xanthine, which are important in nature and are formed by methylation. These include the purine alkaloids caffeine, theobromine and theophylline, which are found in tea leaves, coffee beans, cocoa and cola nuts.