CHEMISTRY OF PURINES AND PYRIMIDINES 



83 



in III.-" Both systems, I and II, have been used in a single work.-' Con- 

 fusion also arises from nomenclature inconsistency. For example, in Chemi- 



N 



.N/4 

 3 

 I 



IN- 

 2C 



-C6 



I 

 C5 



3N— C4 

 II 



cal Abstracts, IV is called 2,4,6(l//,3//,5//)-pyrimidinetrione, whereas V 

 is called 6-methyl-2,4-pyrimidinediol,'* and isobarbituric acid is listed as 

 5-hydroxy -2,4(1//, 3f/)-pyrimidinedione.^- 



CH3 



H 



H 



6 



2 3 4 



H 



o I o 



H 

 IV 



N 



An/ 



HO 



OH 



Since the pyrimidine nucleus is symmetrical about a plane including 

 C-2 and C-5, alternative numbering is possible (see II and III above). 



Fischer^ -^ introduced the term purine which he derived from purum and 

 uricum, and employed the widely used construction (VI) based upon the 

 Medicus formula now ascribed to uric acid. This heterocycle (VI) consists 



IN— C6 



I I 7 

 2C 5C— N 



C8 



3N- 



-N 



VI 



of a fused pyrimidine and imidazole nucleus in which carbon atoms 4 and 

 5 are shared by both rings. 



The ring and numbering system employed by Chemical Abstracts^^ and 



^^ V. Meyer and P. Jacobson, "Lehrbuch der organischen Chemie," Vol. II, p. 1172. 



De Gruyter, Berlin and Leipzig, 1920. 

 *' A. A. Morton, "The Chemistry of Heterocyclic Compounds," p. 483. McGraw-Hill, 



New York, 1946. 

 ^^Chem. Ahstr. 44, 12451, 12845 (1950). 

 " E. Fischer, Ber. 31, 2550 (1898); 32, 435 (1899). 



