176 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



when a purple or violet precipitate appears. The Purine Bases are 

 formed by the union of a pyrimidine nucleus with an Iminazolyl radical : 



N=CH N=CH 



HC NHx 



HC CH 



N CH 



Purine. Pyrimidine. 



The purine bases which are obtained from the nucleic acids repre- 

 sent only two members of a large group of substances which includes 

 Uric Acid, Caffeine and Theobromine. For convenience of reference 

 the carbon and nitrogen atoms in the central complex are often num- 

 bered as follows: 



> 



r/ 



N 3 



The purine substances which are most important from a physio- 

 logical point of view are Uric Acid, Xanthine, Guanine, Hypoxanthine 

 and Adenine, while Caffeine, Theobromine and Theophylline are also of 

 importance from a medical and dietetic point of view. Their structure 

 is as follows: 



Uric acid is 2, 6, 8, trioxypurine 



Xanthine " 2, 6, dioxypurine 



Guanine " 2, amino, 6, oxypurine 



Hypoxanthine " 6, oxypurine 



Adenine " 6, aminopurine 



Caffeine " 1, 3, 7, trimethyl, 2, 6, dioxypurine 



Theobromine " 3, 7, dimethyl, 2, 6, dioxypurine 



Theophylline " 1, 3, dimethyl, 2, 6, dioxypurine 



Thus the formula for Guanine may be graphically represented: 

 HN co 



H 2 NC 



N 



Guanine 



while that of Adenine is as follows: 



N=CNH 2 



HC 



