NUCLEIN OR PURINE METABOLISM 875 



products of the examination and oxidation of guanine and adenine. 

 Fischer has shown that all these bodies are derivatives of a base 

 purine. They contain a central chain of three carbon atoms to 

 which is attached on each side a urea group, so that they may be 

 regarded as diureides. Purine itself has the formula 



HC C NH 



II II >CH 



N C N/ 



Purine 



The relation of the purine bases obtained from disintegration of nucleic 

 acid to purine itself has been given on p. 114. From these formulae 

 we see that adenine and hypoxanthine are related to one another, 

 adenine being 6-aminopurine, while hypoxanthine is 6-oxypurine. 

 In the same way guanine and xanthine are related, guanine being 

 2-amino-6-oxypurine, while xanthine is 2-G-oxypurine. The investiga- 

 tion of the relationships of these bases was of interest to physiologists 

 since it brought to light the close relation which they have to uric 

 acid, a substance which has been known as a constituent of urine 

 and urinary calculi for a long time, having been discovered in 1776 by 

 Scheele. Uric acid is a 2-6-8-trioxypurine and has the formula 



HN CO 



CO C NH 



HN C--NH X 



Uric acid = 2-6-8-trioxypurine 



In uric acid the two urea groups are attached to a central 3-carbon 

 chain, and it is interesting to note that one of the first syntheses of 

 uric acid, namely, that by Horbaczewski, was accomplished by 

 melting together trichlorlactamide and urea in a sealed tube. 



Belonging to the same group of purines are the two bases which 

 form the essential constituents of tea, coffee,, and cocoa. In tea and 

 coffee is found caffeine, which is l-3-7-trimethyl-2-6-dioxypurine, and 

 in cocoa occurs the closely allied theobromine, which is 3-7-dimethyl- 

 2-6-dioxypurine. Caffeine is thus methyltheobromine. 



CH 3 N CO HN CO 



CO C N CO C N 



II >H || \CH 



CH 3 N C N^ CH 3 N C N^ 



Caffeine = l-3-7-trimethyl- Theobromine =3-7-dimethyI- 



2-6-dioxypurine 2-6-dioxypurine 



