The Collaborative International Dictionary of English v.0.48:

Xanthinine \Xan"thi*nine\, n. [Gr. xanqo`s yellow + quinine.]
   (Chem.)
   A complex nitrogenous substance related to urea and uric
   acid, produced as a white powder; -- so called because it
   forms yellow salts, and because its solution forms a blue
   fluorescence like quinine.
   [1913 Webster]