58 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



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

 hydrolysis with alkali the free glycyl-glycine carboxylic acid, 



HOOC . NH . CH, . CO . NH . CH, . COOH, 



from which, on esterification, 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 Siegfried 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,H 5 OOC . NH . CH, . CO . NH . CH,. COOC,H 8 , 



undergoes a transformation during hydrolysis and is converted into the 

 acid having the lactim formula and belonging to the ^-series, 



C,H 8 OOC . NH . CH, . C(OH)=N . CH, . COOC,H 8 . 

 It was proved by the study of the phenyl derivatives, 



Carbethoxyl-glycyl-N-phenylglycine ester 



C,H 8 OOC . NH . CH, . CO . N(C 6 H 8 ) . CH, . COOC,H 8 , 

 and carbethoxyl-N-phenylglycyl-glytine ester 



C,H 8 OOC . N(C 6 H 8 ) . CH, . CO . NH . CH, . COOC,H 8 . 



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-phenylglycine ester, no 

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

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



NH, . CH, . CO . N(C 8 H 8 ) . CH, . COOH, 

 and this dipeptide was converted on heating into the diketopiperazine, 



, . v 



C 8 H 8 .N/ )NH, 



\CO.CH,' 



which was also obtained from chloracetyl phenylglycine and ammonia. 

 Carbethoxyl-N-phenyl-glycyl-glycine ester on hydrolysis yields 



the acid, 



HOOC . N(C,H 8 ) . CH, . C(OH) = N . CH, . COOH, 



which does not lose carbon dioxide, and is analogous to Fischer's 

 glycyl-glycine carboxylic acid. Phenyl-glycyl-glycine carboxylic acid 

 easily forms the lactone, 



CH * \ 



\C = N . CH, . COOH, 



/ 



