PURIN BASES. 337 



by Fischer, who failed to chauge xanthin into uric acid or uric acid 

 into xanthin. While therefore uric acid, xanthin, and hypoxanthin 

 contain three, two, and one atoms of oxygen, respectively, and are 

 structurally closely allied, nevertheless thus far it has not been pos- 

 sible to convert directly any one of those compounds into the others. 



Only very recently Sundwik has attempted the reduction of uric 

 acid by boiling it with sodium hydrate and chloroform. By this 

 procedure he believes that he has prepared xanthin and hypoxanthin, 

 but a confirmation of these results is necessary. 



By electrolytic reduction of uric acid Tafel ^ obtained a substance 

 which he has designated as puron, CgHgN^O^. This body is neither 

 acid nor basic in character and is therefore a fully saturated com- 

 pound. It readily changes into an unsaturated isomer — iso-puron. A 

 tetrahydrouric acid, C^HgN^Oj, was also obtained which with baryta 

 gave a — ^ diamino-propionic acid, CgH^NjOj ; and with nitrous 

 acid a base C^HyNjO^. 



The classical investigations of Fischer, however, have shown that 

 indirectly uric acid may be changed to xanthin or to hypoxanthin 

 and these bases in turn by a similar indirect process can be converted 

 into uric acid. Thusj on treating 1-3 di-methyl uric acid with phos- 

 phorus pentachlorid Fischer obtained chlor-theophyllin, which on 

 reduction with hydriodic acid gave theophyllin or di-methyl xan- 

 thin. By introducing a methyl group into the latter caffein or tri- 

 methyl xanthin results. In a similar way caffein may be prepared 

 from 1-3-7 tri-methyl uric acid. Inasmuch as the di- and tri-methyl 

 uric acids can be prepared artificially it follows that the complete 

 synthesis of theophyllin and of caffein was effected by this trans- 

 formation. 



Subsequently (1897) Fischer converted potassium urate by means 

 of phosphorus oxychlorid into an oxy-di-chlor purin and this into 

 tri-chlor purin. The latter by a series of transformations which it 

 is unnecessary to detail was -changed into xanthin, hypoxanthin, 

 adenin, guanin, heteroxanthin and paraxanthin. With the exception 

 of methyl xanthin all of the known purin bases found in the urine 

 have been therefore not only made from uric acid but their complete 

 synthesis has also been effected. 



The starting point in the consideration of the structure of the 

 purin bodies is uric acid, which is not only the earliest known, but 

 also the most easily obtainable and best studied member of this 

 group. The structure of uric acid as given by Medicus in 1876 

 was verified and fully established by the studies of Fischer in 1884. 

 On the other hand, these early investigations of Fischer on the xan- 

 thin bases led him to ascribe to these somewhat different formulae 

 than did Medicus. When, however, Fischer in 1895 succeeded in 

 convertiug di-methyl uric acid into chlor-theophyllin it was evident 



^Berichte, 34, 258, 1181 (1901). 

 22 



