THE SYNTHESIS OF THE PROTEINS 17 



explain certain of the phenomena concerning the presence of carbonic 

 acid in blood and in working muscle ; a protein carbonic acid compound 

 may be formed which can give rise to carbonic acid without taking up 

 oxygen. 



Siegfried's results with glycine and glycyl-glycine have been con- 

 firmed by Leuchs, who, in addition, has investigated the combinations 

 of amino acids and of polypeptides with carbonic acid which were pre- 

 pared by Fischer and his pupils by combination with chlorocarbonic 

 ester (see later). 



Carbethoxylglycine which was obtained by combining together 

 chlorocarbonic ester with glycine, 



Cl . COOC 2 H 5 + H 2 N . CH 2 . COOH = HC1 + C 2 H B . O . OC . NH . CH 2 COOH, 



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

 decomposition always occurring with the formation of glycine and 

 carbonic acid; Leuchs, however, in 1907, obtained the free acid in- 

 directly in the following manner: Carbethoxylglycine was converted 

 into its acid chloride, 



C 2 H 5 . . OC . NH . CH 2 . COC1, 



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

 ethyl chloride and was changed into the anhydride, 



OC.NH.CH 2 .CO 



o 1 



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.CH 2 .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 possibly the 

 same substance which Balbiano and Trasciatti (p. 7) obtained by heat- 

 ing glycine with glycerol, or as that obtained by Curtius from the biuret 

 base (p. 7). 



Leuchs and Geiger, in 1908, obtained the anhydrides of C-phenyl- 

 aminoacetic acid, of phenylalanine and of leucine in the same way by 

 heating the acid chlorides of the carbomethoxyl derivatives, which were 



PT. II. 2 



