AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 1 03 



Several well-known and commonly occurring substances have 

 been shown to be derivatives of this same hypothetical com- 

 pound purine. The simplest of these is xanthine, which is a 

 di-hydroxy-purine. It is present in urine and in animal tissues. 

 Theobromine^ the active constituent of the cocoa bean and pres- 

 ent in chocolate and cocoa, is the di-methyl derivative of xan- 

 thine, i.e. di-methyi-di-hydroxy-purine. Cafeine, or thein, the 

 active constituent of coffee and tea, is a tri-methyl derivative of 

 xanthine or tri-methyl-di-hydroxy-purine. Writing the formu- 

 las all together will show their relationship. 



N=CH 



HC C-NK 



II \CH 



Purine 



N = C(OH) /NH-CO 



(HO)C C-NHv or OC C-NH. 



^CH \ II XH 



N-C-N^ \HN-C-N' 



Xanthine, Di-hydroxy-purine 



N = C(OH) /NH-CO 



I / I 

 (HO)C C-NH. or OC C-NHv 



II ^C(OH) \ II >C0 



Uric acid, Tri-h^'droxy-purine 



NH-CO • CH3 



I /CH3 I 

 OC C-N< /N-CO ,CH3 



II >CH / I / 

 N-C-N^ OC C-N( 



I \ II \CH 



CH3 \n-c-n^ 



CH3 



^ Theobromine Caffeine 



Di-methyl xanthine Tri-methyl xanthine 



