.GLUCURONIC ACIDS. 221 



On account of this tendency to ring-formation the amino-acetalde- 

 hyde as well as the amino-aldehydes as a group, stand, according to NEU- 

 BERG, in close relationship to many ring systems, such as imidazole, 

 piperazine, pyrazine, pyridine and others, and also to the alkaloids. 



The amino-sugars, like the amino-aldehydes, can also unite, form- 

 ing ring compounds, and this seems to be the case on the decomposi- 

 tion of free glucosamine in aqueous solution, which occurs with access 

 of air (LOBRY DE BRUYN). As found by STOLTE 1 2,5-ditetraoxybutyl 

 pyrazine (= fructosazine) is hereby produced according to the following 

 equation : 



NH 2 N 



O 4 H 9 C 4 .CH+CHO O 4 H 9 C 4 .C CH 



I +0= | || +3H 2 



HO CH.C 4 H 9 4 HC C.C 4 H 9 4 



. 



I 

 C 



NH 2 N 



Fructosazine 



The 2,5-ditetraoxybutyl pyrazine, which STOLTE obtained by LOBRY 

 DE BRUYN's 2 method from fructose in methyl alcohol solution and 

 ammonia, and which he calls fructosazine, can be oxidized outside of the 

 body into 2,5-pyrazine dicarboxylic acid. 



The same acid can be formed in the animal body (rabbits), although not 

 constantly, after introducing fructosazine. It also passes into the urine of 

 rabbits after intravenous injection of d-fructose and glycocoll (SPIRO), a behavior 

 which SPIRO claims indicates that carbohydrates in metabolism react with the 

 cleavage products of proteins. STOLTE'S experiments to decide the question 

 whether in the animal body the glucosamine in its decomposition passes into 

 fructosazine did not at first yield conclusive results. His more recent investiga- 

 tions 3 show on the contrary that in rabbits 2-oxymethylpyrazine-5-carboxylic 

 acid is formed as an oxidation product, and this can be oxidized outside of the 

 body into pyrazine-2, 5-dicarboxylic acid. 



b. Glucuronic Acids. 



The glucuronic acids occurring in the animal body either physiolog- 

 ically or pathologically, are conjugated acids which will be described in 

 detail in a subsequent chapter (XIV). We will here describe only the 

 d-glucuronic acid in connection with the carbohydrates. 



CHO 

 d-Glucuronic acid (glycuronic acid), CeHioO? = (CH.OH) 4 , is a deriva- 



COOH 

 tive of glucose, and has been synthetically prepared by E. FISCHER and 



1 Hofmeister's Beitrage, 11. 



2 Cited by Stolte, Hofmeister's Beitrage, 11. 



3 Spiro, Hofmeister's Beitrage, 10, p. 283; Stolte, Biochem. Zeitschr., 12. 



