CHEMISTRY OF PURINES AND PYRIMIDINES 



85 



the correct cyclic structure for hypoxanthine, it was not until 1897 that 

 concrete chemical evidence for the stiiicture of adenine (IX) was made 

 available by Fischer in his partial synthesis of both adenine and hypoxan- 

 thine from 2,6,8-trichloropurine-^ obtained from uric acid: 



POCh NH3 



Uric acid -> 2,6,8-tnchloropuiine — > 6-amino-2,8-dichloropurine 



HI 



Adenine 



HO NO 



> 6-hydroxy-2,8-dichloropurine ^ Hypoxanthine 



Total s>aitheses of adenine and hypoxanthine were accomplished in 1904 

 by Traube.^" (The Traube syntheses are discussed on page 131.) Certain 

 of the chemical and physical properties of adenine and other purines and 

 pyrimidines are listed in Table I and are discussed below. 



NH 



OH 



HoN 



Guanine (2-amino-6-hydroxypurine, X)^^ was found in 1844 in the ex- 

 creta (guano) of birds^- "^^ before it was recognized as a nucleic acid con- 

 stituent.^'* The accepted cyclic structure for guanine, postulated by Medi- 

 cus,® received considerable support from its conversion by nitrous acid to 

 xanthine (2,6-dih3droxypurine) and the chloric acid oxidation of guanine 

 to guanidine and parabanic acid by Strecker.^^ The relationship of guanine 



" E. Fischer, Ber. 30, 2226 (1897) . 

 30 W. Traube, Ann. 331, 64 (1904). 

 'I Beilstein, 26, 449 (1937). 



32 Magnus, Ann. 51, 395 (1844). 



33 B. Unger, Ann. 58, 18 (1846); 59, 58 (1846). 



34 A. Kossel, Z. physiol. Chem. 8, 404 (1883-1884); see also Z. physiol. Chem. 3, 284 

 (1879); 5, 152, 267 (1881). 



3^ A. Strecker, Ann. 108, 129, 141 (1858); 118, 151 (1861). 



