60 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Amides and Imides of Amino Acids and Polypeptides. 



The occurrence of asparagine and glutamine in plants and the for- 

 mation of ammonia by the hydrolysis of proteins points to the 

 presence of amide groups in the protein molecule. This combination 

 may be only with these aminodicarboxylic acids, but there is the 

 possibility that the amide groups may be attached to other units. 



Amides of amino acids have therefore been prepared. The earlier 

 investigators only obtained the hydrochlorides of these compounds. 

 Fischer and Koenigs prepared the diamide of aspartic acid. Koenigs 

 and Mylo prepared the amides of glycine, alanine, aminobutyric acid, 

 valine, leucine, phenylalanine and tyrosine by the action of liquid 

 ammonia upon the esters. The reaction took place readily except 

 with valine ; in the preparation of glycine amide glycyl-glycine amide 

 was also formed but it was not isolated in a pure state. 



Bergell and Wiilfing in 1910 found that these amides could be 

 readily obtained by the action of aqueous ammonia upon the esters and 

 that glycine amide was best prepared from chloracetyl amide. Glycine 

 amide hydrochloride was formed by the action of ammonia and the 

 compound itself was obtained by treatment with the calculated 

 quantity of sodium hydrate. The corresponding derivatives hippur- 

 amide and chloracetyl-glycine amide were obtained when these amides 

 were treated with benzoyl chloride and chloracetyl chloride. 



By treating chloracetyl-glycine amide with ammonia they obtained 

 glycyl-glycine amide, and by similar reactions they prepared glycyl- 

 leucine amide and alanyl-leucine amide. Continuing the process of 

 adding on the halogen derivative Bergell and Brugsch have pro- 

 ceeded as far as obtaining chloracetyl-glycyl-leucine amide and chlor- 

 acetyl-diglycyl-leucine amide. In all these compounds the leucine 

 radicle is at the end of the chain. 



Leucine amide was of particular interest : as it gave with copper 

 sulphate and caustic soda a red crystalline compound and it was hydro- 

 lysed by trypsin asymmetrically. 



The other amides were not hydrolysed by trypsin ; leucine 

 amide and alanine amide were hydrolysed by extracts of the liver, 

 spleen and kidney ; it seemed that the hydrolysis of leucine amide was 

 effected by a special enzyme which was readily decomposed by 

 acid. 



Diglycinimide, NH, . CH 8 . CO NH OC. CH, . NH 8 , was pre- 



