160 CHEMISTRY OF PLANT LIFE 



to mean an oxygen atom attached by both its bonds to one of the 

 carbons in the nucleus, instead of its customary use to mean the 

 monovalent OH group replacing a hydrogen, as in the case of all 

 other nomenclature of organic compounds. With this under- 

 standing, reference to the numbered nucleus formula above 

 will make plain the structure of all of the purine bases which are 

 included in the following list: 



Hypoxanthine, CsEUN-iO, = 6-monoxypurine. 



Xanthine, CsH4N402 = 2, 6-dioxypurine. 



Uric acid, C5H4N4CJ3, = 2, 6, 8-trioxypurine. 



Adenine, CsHs^NH^, = 6-aminopurine. 



Guanine, CsHs^ONH^, = 2-amino-6-oxypurine. 



Theobromine, C 5 H 2 N402(CH3)2 = 3, 7-dimethyl-2, 6-dioxy- 

 purine, or dimethyl xanthine. 



Theophylline, C 5^^02(^3)2 = !, 3-dimethyl-2, 6-dioxypu- 

 rine. 



Caffeine, C 5 HN 4 02(CH3)3 = 1, 3, 7-trimethyl-2, 6-dioxypurine, 

 or triniethyl xanthine. 



In order to make these structural relationships quite clear, 

 the following formulas for uric acid and for caffeine are presented 

 as typical examples: 



HN C=O CH 3 N C=0 



=C C N\-H O=C C N^ 



I II >C=0 I || \ CH 



HN C N/H CH 3 N C N^ 



Uric acid Caffeine 



Uric acid is found in the excrement of all animals; in the urine 

 of mammals, and in the solid excrement of birds and reptiles. 

 It is not known to occur in plants. 



Xanthine and hypoxanthine occur in animal urine, and also in 

 the tissues of both plants and animals. 



Adenine and gaunine are constituents of all nucleic acids (see 

 below) and, hence, are found in all plant and animal tissues. 

 Guanine is the chief constituent of the excrement of spiders, and 

 is found also in Peruvian guano. It is also a constituent of the 

 scales of fishes. 



Caffeine, theophylline, and theobromine are not found in animal 

 tissues, but are fairly widely distributed in plants. Caffeine and 

 theobromine are the active constituents of tea leaves and coffee 



