Xanthine is also a precursor in the synthesis of a range of biorelevant molecules . Its derivatives include theophylline (widely used in the treatment of respiratory conditions ), caffeine (a well-known central nervous system stimulant ), and theobromine (the primary alkaloid found in cocoa ). As such, xanthine's use as a scaffold in the synthesis of its biologically active derivatives has also been highlighted to be of interest . Aside from biorelevant applications, the role of synthetic xanthine as an effective nucleator in the epitaxial nucleation of polyhydroxyalkanoate (PHA) polymers has also been investigated. PHA polymers are of interest because they are known to degrade in every natural environment on earth: knowledge of the crystal structure of xanthine could provide further insight into its role as a naturally occurring nucleating agent for this purpose .