Xanthines

[Greek: xanthos yellow: named from the yellow color of its nitrate] a white, amorphous base, 2,6-dioxypurine, C₅H₄N₄O₂, from most of the body tissues and fluids, urinary calculi, and certain plants. It is formed by the oxidation of hypoxanthine and may be oxidized to uric acid. It is insoluble in cold water, but freely soluble in dilute acid and alkaline solutions. It possesses stimulant properties to muscle tissue, especially that of the heart. Dimethyl x., theobromine. trimethyl x., caffeine.

Source: Dorland's illustrated Medical Dictionary