According to guarana.com (who should know:) it is: 3,7-Dihydro-1,3,7-trimethyl-1H-purine-2,6-dione. In case you don't recognise this, purine-2,6-dione is xanthine (like guanine, a nucleoside base) so this is 1,3,7-trimethyl xanthine or....(drum roll)...Caffeine! Yes, people, that's right it is the same as cafeine - the moral? Always believe what Webster 1913 tells you. :-)

Gua"ra*nine` (?), n. Chem.

An alkaloid extracted from guarana. Same as Caffeine.

 

© Webster 1913.