PURINE BASES 



375 



The relationship between purine, xanthine, theobromine 

 and caffeine is best understood from the following considera- 

 tions : — 



Xanthine may be regarded as purine with the addition of 

 two atoms of oxygen attached to the carbon atoms numbered 

 2 and 6 ; and it is accordingly called 2 : 6 dioxypurine, and is 

 given the formula — 



NH— CO 



CO 



C— NH 



\rH 



-N 



NH— C- 

 Xanthine or 2 : 6 dioxypurine 



From this compound theobromine and caffeine are derived 

 by replacing two and three atoms of hydrogen respectively 

 by methyl groups, as may be seen from the following 

 formulae : — 



NH- 



-co 



N{CH3)— CO 



CO C— N(CH3) 



N(CH3)— C— N 

 7 Dimethyl Xanthine or 

 Theobromine 



CO 



-N(CH3) 

 >,CH 



N(CH3)— C— N 

 : 3 : 7 Trimethyl Xanthine 

 or Caffeine 



Xanthine is widely distributed among plants, notably in 

 sprouting seedlings, and occurs also in tea leaves and in the 

 juice of the beetroot. 



Theobromine occurs chiefly in the fruit of Theobroma Cacao 

 (i •5-2-4 per cent), and a small quantity also occurs in kola nut 

 and in tea leaves, but not in coffee ; it acts as a powerful 

 diuretic and has a stimulating effect on the central nervous 

 system, but is less powerful in this respect than caffeine. 



Caffeine occurs to the extent of about 1-2 per cent in kola 

 nuts, 0-I--8 per cent in cocoa beans, from 2-5 per cent in tea 

 leaves, from 0-8-I7 per cent in coffee beans, and from 2-5-3 

 per cent in the fruit of Paullinia cupana ; the latter substance 

 ground up into a paste is consumed in South America under 

 the name of guarana. The so-called Mate or Paraguay tea, 



