POLYPEPTIDES 57 



Carbethoxylglycine, which was obtained by combining together 

 chlorocarbonic ester with glycine, 



Cl . COOC,H 8 + H,N . CH, . COOH - HCI + C,H B OOC . NH . CH, . COOH, 



even by careful hydrolysis could not be converted into the free add, 

 decomposition always occurring with the formation of glycine and 

 carbonic acid; Leuchs, in 1907, obtained the free acid indirectly in 

 the following manner : Carbethoxylglycine was converted into its acid 

 chloride, 



CjHgOOC . NH . CH, . COC1, 



by the action of thionylchloride, and this compound, when heated, lost 

 ethyl chloride and was changed into the anhydride, 



OC . NH . CH, . CO 



A _ I 



which, when warmed with water to 1 5 C., decomposed into glycine and 

 carbonic acid, but, when treated with the calculated quantity of baryta, 

 yielded the barium salt of glycine carboxylic acid, 



OC.NH.CHj.CO 

 O- Ba O 



This was identical with the barium salt obtained by Siegfried from 

 glycine, carbonic acid and barium hydrate. 



It is of interest to observe that Leuchs found that the anhydride, 

 when treated with a small quantity of water, gave an anhydride of 

 glycine which was not identical with diketopiperazine, but was possibly 

 the same substance which Balbiano and Trasciatti (p. 1 8) obtained by 

 heating glycine with glycerol, or as that obtained by Curtius from 

 the biuret base (p. 18). 



In the same way Leuchs and Geiger, in 1908, obtained the anhy- 

 drides of C-phenyl-aminoacetic acid, of phenylalanine and of leucine 



/NH CO /NH CO /NH CO 



C,H,.CH/ | C 9 H B .CH,.CH/ | (CH^.CH.CHj.CH/ 



\CO-O \CO-O \CO-O 



by heating the acid chlorides of their carbomethoxyl derivatives, 

 prepared by the action of thionyl chloride, methyl chloride being 

 eliminated in the reaction. On warming these anhydrides in the 

 presence of traces of water, carbon dioxide was evolved with the 

 formation of the following anhydrides, 



xNH N , /NHv , /NH, 



/ I / 



CO 



x N , /v , 



(C,H B .CH/ I ) (C,H B .CH,.CH<| ) f(CHJ,. CH.CH,. CH 

 V \CO/ V \CO/ > 



