18 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



prepared by the action of thionyl chloride, whereby methyl chloride 

 was eliminated, 



/NH CO /NH CO /NH CO 



C 6 H 5 .CH/ | C 6 H 5 .CH 2 .CH/ | (CH 3 ) 2 . CH . CH 2 . CH^ | 



\CO-O \CO-0 \CO-O 



and then warming in the presence of traces of water, when carbon 

 dioxide was evolved with the formation of the anhydrides, 



/ /NH X f /NH X , /NH 



C 6 H 5 .CH/ | \ C 6 H 5 .CH 2 .CH/ | (CH 3 ) 2 . CH . CH 2 . CH/ | 



Carbethoxyl-glycyl-glycine ester was found by Fischer to yield on 

 hydrolysis the free glycyl-glycine carboxylic acid, from which, on esteri- 

 fication, an ester was obtained, which was isomeric with the original 

 carbethoxyl-glycyl-glycine ester. This acid was extremely stable in 

 comparison with the glycyl-glycine- N -carboxylic acid obtained by Sieg- 

 fried in 1906 and also by Leuchs. 



The difference between these compounds was shown by Leuchs and 

 Manasse, in 1907, to be due to the fact that the original ester, which has 

 the lactam formula and belongs to the a-series, 



C 2 H 5 . . OC . NH . CH 2 . CO . NH . CH 2 . COOC 2 H 5 , 



undergoes a transformation during hydrolysis and is converted into the 

 acid having the lactim formula and belonging to the /3-series, 



C 2 H 5 . O . OC . NH . CH 2 . C(OH)=N . CH 2 . COOC 2 H 5 . 



This was proved by the study of the phenyl derivatives, 



Carbethoxyl-glycyl-N-phenyl-glycine ester C 2 H 5 . O . OC . NH . CH 2 . CO . N(C 6 H 5 ) . CH 2 . 

 COOC 2 H 5 , and carbethoxyl-N-phenylglycyl-glycine ester C 2 H 5 . O . OC . N(C 6 H 5 ) . 

 CH 2 . CO . NH . CH 2 . COOC 2 H 5 . 



The former was prepared from carbethoxyl-glycyl chloride and 

 phenylglycine ester, the latter from carbethoxyl-N-phenylglycyl chloride 

 and glycine ester. 



Owing to the substitution of the hydrogen atom by phenyl in the 

 position represented in carbethoxyl-glycyl-N-phenyl-glycine ester, no 

 transformation into the lactim form can take place. On hydrolysis it 

 yielded the dipeptide glycyl-phenylglycine, with loss of carbonic acid, 



NH 2 . CH 2 . CO . N(C 6 H 5 ) . CH, . COOH, 



and this dipeptide was converted on heating into the diketopiperazine, 



CH 2 . CO 



N.Ph< )NH, 



\CO.CH 2 / 



which was also obtained from chloracetylphenylglycine and ammonia. 



