20 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Combinations of Amino Acids with Ammonia. 

 The amides of amino acids, such as glycinamide, 



NH 2 .CH 2 .CO NH 2 , 



the compounds prepared by Curtius, and the polypeptides (later) of 

 Emil Fischer, such as glycyl-glycine, 



NH 2 . CH 2 . CO NH CH 2 . COOH, 



are combinations of amino acids in which one carboxyl group only is 

 attached to the ammonia residue. 



A compound, in which two carboxyl groups of amino acids are 

 attached to ammonia, namely, diglycinimide, 



NH 2 .CH 2 .CO NH OC. CH 2 .NH 2 , 



was prepared in 1907 by Bergell. Starting from chloracetamide he 

 obtained chloracetonitrile by heating it with phosphoric anhydride : 

 Cl . CH 2 . CO . NH 2 = H 2 O + Cl . CH 2 . CN. 



From this compound dichlorodiacetamide resulted in its interaction with 

 chloracetic acid, 



Cl . CH 2 . CN + HOOC . CH 2 C1 = Cl . CH 2 . CO NH OC . CH 2 C1, 



and on treating it with ammonia, diglycinimide hydrochloride was 

 obtained, 



C1.CH 2 .CO NH OC.CH 2 

 NH 4 C1 + NH 2 .CH 2 .CO NH OC. CH 2 . NH 2 + HC1, 



from which the free base was prepared by means of silver oxide as a 

 crystalline substance of a basic character. 



Bergell continued his work on this substance in conjunction with 

 Feigl. Diglycinimide was stable to acids and to the weak alkalies, 

 magnesia and sodium bicarbonate, but it was converted by caustic 

 alkalies and by baryta into ammonia and an acid of the constitution 



/CH.J.COOH 

 NH/ 



\CH 2 .COOH 



which was identical with " diglykolamidsaure " prepared in 1862 by 

 Heintz. Its formation probably took place through the intermediate 



ring compound, 



/CO CH 2V 



NH/ \NH. 



\CO CH 2 / 



It did not give rise to ammonia and glycine as was expected ; its 

 benzoyl derivative, however, on hydrolysis was converted into hippuric 

 acid, ammonia and glycine : 



C 6 H B . CO . NH . CH 2 . CO NH OC . CH 2 . NH 2 + aH 2 O = 

 C 8 H 5 . CO . NH . CH 2 . COOH + NH 3 + HOOC . CH 2 . NH 2 . 



