PURINES. 



Uric acid, xanthine, hypoxanthine, guanine, adenine, caffeine, theo- 

 bromine and others are classed together in the special group of com- 

 pounds known as the purines. Not only are these compounds found 

 associated in nature in both animals and plants, but also they are 

 chemically very closely related. They yield alloxan, or dimethyl- 

 alloxan, on oxidation, and have many other similar reactions. 



All these compounds have been synthesised by Emil Fischer and 

 their exact chemical relationship to one another established. The result 

 of these investigations has shown that they are all derived from the 

 compound purine, which stands in the same kind of relationship to 

 them as a hydrocarbon does to an alcohol, an amine, etc. Thus : 



Purine C 6 H 4 N 4 



Hypoxanthine = monoxypurine C 5 H 4 N 4 O 



Xanthine = dioxypurine C 5 H 4 N 4 O 2 



Uric acid * trioxypurine C 5 H 4 N 4 O 3 



Adenine = aminopurine C 6 H 3 N 4 .NH 2 



Guanine = amino-oxypurine C 5 H 3 N 4 . . NH a 



Theobomine = dimethyl dioxypurine C 5 H 2 N 4 O 2 (CH 3 ) 2 



Theophyllin = dimethyl dioxypurine C 5 H 2 N 4 O 2 (CH 3 ) 2 



Caffeine = trimethyl dioxypurine C S HN 4 O 2 (CH 3 ) 3 . 



The compounds have the hetero:yclic ring structure in which the 

 atoms are numbered in the following order : 



IN c 



2C 8 C 7 N 



I 



N_ 



> 



The formulae for the var'ous compounds are ; 



N=CH HN C=O HN C=O 



HC C NH HC C NH O=C C NH 



CH 



C N 

 Purine. 



CH 



HN C = 

 \ = C C 



NH 



HN-C NH 



Uric acid, 



or 



2, 6, 8-trioxypurine. 



6-monoxypurine. 



N=C NH 2 



HC C NH 



N CH 



N-C N 

 Adenine, 



or 



6-aminopurine. 

 286 



2, 6-dioxypurine. 

 CH 3 .N C^O 



O=C C NH 



II \ 



CH 



CH 3 .N C N 

 Theophylline, 



or 

 i, ^-dimethylxanthine. 



