High Quality Content by WIKIPEDIA articles! Xanthopterin is a yellow, crystalline solid, that occurs mainly in the wings of butterflies and in the urine of mammals. Small microorganisms convert it into folic acid. It is the end product of a non-conjugated pteridine compound, and inhibits the growth of lymphocytes produced by concanovalin. High levels of the chemical were found in patients with liver disease and hemolysis, the latter increasing levels by 35%.