78 THE NITROGENOUS DERIVATIVES OF THE ALBUMINS. 



They Comprise xantliin, hypoxuntliin (or sarcin), episarcin, hetero- 

 xaiithin, paraxanthin, theophyllin, thcobromin, catfein, guaiiin, epi- 

 guanin, adcnin, and carnin. Of these, i>araxanthin, heteroxanthin, 

 epiguanin, and episarcin have thus far been found only in the urine. 

 Tlicophyllin, theobroniin, and caflein arc confined to* the vegetable 

 world, while the remaining members of the group are common con- 

 stituents of both animal and vegetable cells. All these bodies are 

 closely related to each other and to uric acid, which, as we shall see 

 later, constitutes one of the most important end-products of animal 

 metabolism. According to Emil Fischer, they are derived from a 

 hypothetical substance, which has been termed purin, and it has 

 previously been pointed out that in this manner a further relation- 

 ship is established between the micleinic bases and thymin, as it is 

 probable that this substance, or allied bodies, constitute the ante- 

 cedents of the purin radicle. Behrend, in fact, has pointed out that 

 through the condensation of urea and isodialuric acid, which is 

 closely related to uracil, uric acid results. These relations are shown 

 below^ : 



(6) 



(l) N=CH 



(2)HC (5)0 - NH V 



II >CH(8) Purin = C 5 H 4 N 4 . 



(3) N - C - N ^ 



(4) (9) 



By substituting the group NH 2 for the hydrogen atom at 6, adenin 

 results, and is hence spoken of as a 6-amino-purin : 



HC C - NH X 



>CH Adenin = C 5 H 5 N 5 . 



N - c - N ^ 



Hypoxanthin, according to this conception, would be 6-oxypurin, 

 xanthin 2, 6-dioxypurin, and guanin 2-amino-6-oxypurin : 



HN 



I 

 H 



C C - NH, CO C - NH N 



ii i >CH i yes. 



N -- C -- JS* HN - C - N^ 



Hypoxanthin = C 5 H 4 N 4 O. Xanthin = CsH^NiOg. 



HN - CO 



I I 



HN=C C - NH V 



I >CH 



HN -- C --- N ^ 

 Guanin = C 5 H 5 N 5 O. 



From these primary bodies the remaining ones then result through 

 a substitution of methyl groups. Heteroxanthin is thus formed 

 from xanthin by replacing the hydrogen atom at 7 with CH 3 , and 

 is therefore 7-methyl-2,6-dioxypurin. Paraxanthin is accordingly 



