PURIN BASES. 341 



xanthin and guanin is seen in the difficulty of preparing alkyl deriva- 

 tives of guanin, whereas with xanthin the result is easily obtained. 

 Fischer and Eeese failed in preparing alkyl derivatives, and Wulff 

 succeeded only with ethyl guanin. Recently, however, Fischer has 

 succeeded in effecting the synthesis of two methyl derivatives and of 

 guanin itself. The structural formulse, thus deduced, for guanin 

 and epiguanin are given on p. 339. It will be seen that guanin is 

 2-amino-6-oxypurin, while epiguanin is 7-methyl guanin. 



Two of the five possible isomers of guanin have been prepared 

 synthetically by Fischer. One of these, 6-amino-2-oxypurin, very 

 closely resembles guanin, so much so that it can be easily mistaken 

 for this base. 



Hypoxanthin. — This is 6-oxypurin and inasmuch as it can be 

 readily prepared from adenin by the action of nitrous acid, it follows 

 that the latter is 6-aminopurin. Of the four possible formulse for 

 adenin Fischer selects the one given below. Two isomers of adenin 

 are possible. 



HN— CO N=CI.NH, 



Hg P— ][fH :hc o— nh 



CH II I (in 



Htpoxahthih. Asbhih. 



It should be remembered that there are isomers of both of these 

 bases and that tautomeric forms may exist as in the case of uric acid. 



The relation of adenin and hypoxanthin to uric acid and xanthin 

 was clearly shown by Kriiger in 1891 and 1893, although the struc- 

 ture of these bases was not fixed by Fischer until 1897. Thus, the 

 bromin derivatives of adenin and hypoxanthin correspond to those of 

 xanthin, guanin and caffein, and on oxidation with chlorin yield alloxan 

 and urea. The bromin derivatives of hypoxanthin, adenin, xanthin, 

 guanin, and caffein result by the substitution of bromin in the CH 

 group of xanthin, i. e., in position 8. The analogy to the other 

 members of the uric acid group is seen from the following equations : 



C^H^Np, + O + H,0 = C,H,Np, + CON,H,. 



ITbic Acid. 



C,H,Np, + 20 + H,0 = C,H,N,0, + CON,H,. 



XAHTHIir. 



C,H,Np + 30 + H,0 = C,H,Np, + CON^,. 



Htpoxahthin. 



CjHjNp + 30 + H,0 = CgH^NjOj + C.NH.N,H, + CO,. 



Guanin. Pabaeanic Acid. Gdanidih. 



C^H^N + 30 + 2HP = C,H^,0, + CON,H, + NH,. (?) 



Adbnin. 



