CHEMISTRY OF PURINES AND PYRIMIDINES 



97 



an animal product. The prediction appeared to have been borne out by the 

 reported isolation of isoguanine from pig blood, '^* although this finding could 

 not be confirmed'^'' (see also Schiitz"^). However, isoguanine occurs in the 

 wings of butterflies'^^ and was once'^^ thought to be a pterin ("guano- 

 pterin"). Isoguanine is also found as the aglycone of the riboside, crotono- 

 side, in the croton bean {Croton figlium L.)-"^''^^ The structure of crotono- 

 side as a 9-riboside of isoguanine was inferred from ultraviolet absorption 

 spectra, ^^° and established as 9-jS-D-ribofuranosylisoguanine by synthesis.^*' 

 A total synthesis of isoguanine has been accomplished. '^- 



N 



OH 



NH, 



OH 



HO I 



H 



XXIII 



2,8-Dihydroxyadenine 



HO 



/-^N/^N 



Reference to xanthine (XXVI) '^^ and hypoxanthine or "sarkin" 

 (XXVII)^*^ has been made a number of times above. These substances are 

 frequently present in animal sources as a result of the action of the enzymes 

 guanase and adenase on the parent purines or of nucleosidases on the cor- 



" M. V. Buell and M. E. Perkins, J. Biol. Chem. 72, 745 (1927). 



'^ S. Bergstrom, P. Edman, and O. Hail, Acta Chem. Scand. 3, 1128 (1949). 



'^ F. A. Sciiiitz, Biochem. Z. 273, 52 (1934). 



'«R. Punmann, Ann. 544, 182 (1940). 



" C. 8ch6pf and E. Becker, Ann. 524, 49 (1936). 



"* E. Ciierbuliez and K. Bernhard, Heh. Chim. Acta 15, 464, 978 (1932). 



^9 J. R. Spies, ./. Am. Chem. Soc. 61, 350 (1939). 



8» R. Falconer, J. M. Gulland, and L. F. Story, J. Chem. Soc. 1939, 1784. 



s' J. Davoll, J. Am. Chem. Soc. 73, 3174 (1951). 



"2 A. Bendich, J. F. Tinker, and G. B. Brown, ./. .4///. Chem. Soc. 70, 3109 (1948). 



" Beilstein, 26, 447 (1937). 



8^ Beilstein, 26, 416 (1937). 



