GLYOXALINE OR IMINAZOLE DERIVATIVES. 



Histidine, histamine and urocanic acid are compounds which 

 contain the heterocyclic glyoxaline or iminazole ring made up of 

 2 nitrogen atoms and 3 carbon atoms : 



C-N X 



II ^C 

 /*** 



C N/ 



This ring structure is also present in the purine ring which is a 

 combination of the pyrimi dine and iminazole rings. 



Histidine is y3-iminazole-a-aminopropionic acid. 



Histamine is /3-iminazole-ethylamine. 



Urocanic acid is /3-iminazole-acrylic acid. 



HC NH HC NH HC NH 



CH CH 



C N C N 



CH 



CH.NH 2 



CH 2 CH 



CH 2 .NH 2 CH 



COOH COOH 



Histidine. Histamine. Urocanic acid. 



Histidine is a constituent of proteins and is contained in greatest 

 amount in the protein haemoglobin. 



Histamine is a product of the putrefaction of histidine (or proteins). 

 It is a constituent of ergot and is present in putrified meat, etc. It 

 has a marked physiological action upon the sympathetic nervous 

 system. 



Urocanic acid has been isolated twice from the urine of dogs and 

 also from a trypsin digest of protein. 



Histidine. 



Preparation. 



Histidine can be readily prepared from blood as follows : 

 2 parts of ox blood are added in portions to i part of concentrated 

 hydrochloric acid contained in a large round-bottom flask and heated to boil- 

 ing for 10 hours. The solution is evaporated to remove most of the hydro- 

 chloric acid, nearly neutralised and filtered. The yellow filtrate is made 

 alkaline with sodium carbonate and boiled until ammonia is no longer evolved, 

 again filtered and precipitated with mercuric chloride solution, the reaction 



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