URIC ACID AND THE PURINE BODIES 635 



The first oxidation product of purine is hypoxanthine, which has 

 long been known as a constituent of meat extract. Adenine, the amino 

 derivative of hypoxanthine, occurs in combination with other substances 

 in the nuclear material. The second oxidation product is xanthine and 

 its amino derivative, guanine. They occur in the same places as hypo- 

 xanthine and adenine. The highest oxidation product of all is the well- 

 known urinary constituent, uric acid, which may therefore be chemically 

 designated as trioxypurine. In addition to the purines of animal origin, 

 there are also certain ones of vegetable origin the methyl purines, which 

 exist as the alkaloids of tea and coffee namely, caffeine, theobromine, 

 and theine. 



To understand the chemical structure of this group of substances, 

 it is perhaps simplest to start with that of uric acid. This consists 

 essentially of two urea molecules linked together by a central chain of 

 three carbon atoms, as will be evident from the accompanying structural 

 formula : 



HN-CO 



OC C-NH 



! I! \ 

 . co 



I II / 



HN-C-NH 

 (urea) (urea) 



\ 



(central chain) 



This structure can be shown by methods both of decomposition and 

 of synthesis. When uric acid is decomposed by oxidizing it with nitric 

 acid, it yields urea and a residue called alloxan ; or it can be synthesized 

 from urea and trichlorlactamide, a derivative of lactic acid, which it 

 will be remembered contains three carbon atoms. The changes involved 

 in this synthesis will be made clear by examination of the accompanying 

 structural formula, in which the manner of production of the by- 

 products of the reaction (NH 3 , H 2 and HC1) are shown by dotted lines: 





NH. ! H NH.. ; - C = O 



/ I 



CO 



\ 



H J-C ! OH H ! NH 



Cl i || CO 



\ C- i~~Cl~H~~i NH . (urea) 



(urea) NH. j ~ II Cl j 



( trichlorlactamide ) 



