Structural Biochemistry/Nucleic Acid/Nitrogenous Bases/Purines/Xanthine
Xanthine is a purine base that’s an antecedent of uric acid and is generally found in muscle tissue, blood, urine and some plants. It is a water insoluble toxic yellowish white powder and acids that’s soluble in caustic soda; it sublimes when heated. It is involved in purine degradation and is converted from hypoxanthine and converted to uric acid by xanthine oxidase. Some of its derivatives are widely known as mild stimulants, which include caffeine, a sleep-inhibiting methylated xanthine found in coffee, and theobromine, a bitter alkaloid found in cacao.
There is a genetic disease of xanthine metabolism, xanthinuria, due to deficiency of an enzyme, xanthine oxidase. Xanthinuria is a rare genetic disorder where individuals are unable to convert xanthine into uric acid because of the lack of enzyme xanthine oxidase resulting in an accumulation of xanthine. Symptoms include renal failure and kidney stones. There is currently no treatment available to cure this disease.
Clinical Use 
Xanthine derivatives are collectively known as xanthines, which are a group of alkaloids used as stimulants and bronchodilators. As a result of widespread side effects, many of these derivatives have been treated as second-rate asthma treatment medication.
Berg, et al. Biochemistry, 6th Ed. 2007.