338 



CHEMISTRY OF THE LEUCOMAINS. 



that the xanthin bases possessed essentially the same structure as uric 

 acid. This fact was rendered still more evident when hydroxy-caf- 

 fein not only was recognized to be a tri-methyl uric acid, but on 

 treatment with methyl iodid was shown to form the tetra-methyl 

 uric acid. Fischer therefore abandoned the formulae of caffein and 

 xanthin which he proposed in 1883 and accepted those which Medi- 

 cus had previously suggested. 



The formula which Medicus suggested and which shows best the 

 various decompositions of uric acid is that given below (1). The tauto- 

 meric form (2) has a great deal in its favor, but is not used. Similar 

 tautomeric formulae can be deduced for purin, trichlor purin, adenin 

 and other bases. 



(1) 

 HN— CO 



HO. 



HN— 0— : 



TTric Acid. 



The group C^N^ in the above formulae is designated as the purin 

 nucleus and from it purin itself, CjH^N^, is easily derived. The 

 nomenclature of purin bodies is based upon the order of substitution 

 in the purin nucleus, C^N^. Nine positions are possible as shown in 

 the second formula below : 



=CH 



Hi 



n 



H 



N— C— H 

 PnMH. 



Uric acid becomes 2-6-8 tri-oxypurin. By the introduction of a 

 single methyl group into uric acid a methyl uric acid results. On 

 examining the formula of uric acid it will be seen that theoretically 

 four methyl uric acids are possible. Strange to say there are present 

 six known mono-methyl uric acids ; in other words there are two 

 more than are theoretically possible. 



CH,. 



-NH 



f 



Tt. 



HN— CO HN— CO 



OC C— NCH, 00 C— N-H 



Jo 



HN— C— NH CHs-N— C— NH HN— C— NH HN— C— N.CH, 



1-Methyii Ubio Acid. 3-Methyl Dkic Aoid. 7-Mkthtl Urio Acid. 9-Methyi. Uric Acid. 



By substituting two methyl groups into uric acid a di-methyl uric 

 acid results. Six di-methyl uric acids are possible and all are 

 known, of the tri-methyl uric acids four are possible and are like- 



