THE NUCLEINIO ACIDS. 101 



Their structural relations to each other and to purin are shown 

 below : 



(2)HC (5)C - NI 



Purin = C 5 H 4 N 4 . 



(3)N - C - N 



(4) (9) 



By substituting the group NH 2 for the hydrogen atom at 6, adenin 

 results, and is hence spoken of as a 6-amino-purin : 



HC C NH\ 



I! ^CH Adenin = C 5 H 5 N 5 . 



N C N * 



Hypoxanthin, according to this conception, would be 6-oxypurin, 

 xanthin 2, 6-dioxypurin, and guanin 2-amino-6-oxypurin : 



HN CO HN CO 



HC C NH X CO C NH V 



II II ^CH | || ^)CH 



N C N r HN C N r 



Hypoxanthin = C 5 H 4 N 4 O. Xanthin = C 6 H 4 N 4 O a . 



HN CO 



I 



Guanin = C 5 H 5 N 5 O. 



From these primary bodies the remaining ones then result through 

 a substitution of methyl groups. Heteroxanthin is thus formed 

 from xanthin by replacing the hydrogen atom at 7 with CH 3 , and 

 is therefore 7-methyl-2,6-dioxypurin. Paraxanthin is accordingly 

 l,-7-dimethyl-2,6-dioxypurin, and caffein l,3,7-trimethyl-2,6-dioxy- 

 purin. Theophyllin and theobromin are isomeric with paraxanthin, 

 and structurally l,3-dimethyl-2,6-dioxypurin and 3,7-dimethy 1-2,6- 

 dioxypurin, respectively. Epiguanin is similarly derived from 

 guanin by the replacement of the hydrogen atom at 7 with methyl, 

 and is hence 7-methyl-guanin. 



HN CO CH 3 .N CO 



CO C N.CH 3 , CO C N.CH 3 



H'N I N^ H'N 1-N, 



Heteroxanthin = C 6 H 8 N 4 O 2 . Paraxanthin = C 7 H 8 N 4 O a . 



CH 3 .N CO 



CO C N.CH 3 



CH 3 .N C N- 



Caffein = C 8 H 10 N 4 O 2 . 



