86 AARON BENDICH 



to the purine system (uric acid) was elucidated by Fischer. ^^ These reac- 

 tions are summarized below: 



H 



ii^l^'-^ NH2 I c=o 



c \ 



1 

 c 



H2N I / \ o ^ 



H2N NH I 



xi 



Guanidine Parabanic acid 



2,6,8-trichloropurine > 6-hydroxy-2,8-dichloropurine ^ 2-amino-6- 



CjHsONa 



hydroxy-8- 

 chloropurine 



HI 



2,6-diethoxy-8-chloropurine > Xanthine < Guanine 



Total syntheses of guanine and xanthine were first described by Traube.'^ 

 Five pyrimidines have been isolated to date from nucleic acid sources. 

 The first to be discovered, thymine (2,6-dihydroxy-5-methylpyTimidine or 

 5-methyluracil, XI)," was isolated in 1893 by Kossel and Neumann^^'^^ 

 from acid hydrolysates of the nucleic acids of calf thymus and beef spleen. 

 These investigators, as well as Jones'*" and Steudel and Kossel,^' found that 

 thymine was not identical with the isomeric 2 , 6-dihydroxy-4-methylpyrim- 

 idine which had been synthesized and named 4-methyluracil by Behrend''^ 

 in 1884. The studies of Steudel,^^ in which urea was obtained following 

 permanganate oxidation of thymine, led him to conclude that XI expressed 

 the proper structure. This conclusion was soon confirmed by a number of 



3« W. Traube, Ber. 33, 1371, 3035 (1900). 



" Beilstein, 24, 353 (1936). 



38 A. Kossel and A. Neumann, Ber. 26, 2753 (1893). 



" A. Kossel and A. Neumann, Ber. 27, 2215 (1894). 



" W. Jones, Z. physwl. Chem. 29, 20 (1899). 



*' H. Steudel and A. Kossel, Z. physiol. Chem. 29, 303 (1899). 



*^ R. Behrend, Ann. 229, 1 (1885). 



" H. Steudel, Z. physiol. Chem. 30, 539 (1900). 



