THE LINKING TOGETHER OF AMINO ACIDS 



By the action of benzoyl chloride upon the silver salt of glycine, 

 Curtius, in 1881, obtained in addition to the expected hippuric acid, 



C 8 H 5 COC1 + H,N . CH,. COOH = HC1 + C 8 H 8 CO NH . CH,. COOH, 

 two other acids of higher molecular weight. One of these was hippuryl- 

 glycine or benzoyl-glycyl-glycine, 



C 6 H, . CO HN . CH, . CO NH . CH, . COOH, 



as was proved by the study of its salts, its ethyl ester and amide and 

 by its hydrolysis into hippuric acid and glycine. It was the first 

 definite compound known which contained two amino acid residues 

 combined together. 



The constitution of the other acid, called the y-acid, could not be 

 determined ; it had the formula C 10 H 12 N 3 O 4 , was soluble with difficulty 

 in water and gave the biuret reaction. It was obtained in larger 

 quantities when hippuric ester was fused with glycine, but under these 

 conditions another compound benzoyl-bisglycyl-glycine was formed 

 at the same time, so that in this way a series of compounds resulted, 

 each succeeding member containing a glycyl NH 2 . CH 2 . CO group 

 more than the preceding one. 



Further investigations upon the constitution of these compounds 

 were only carried out in 1904 by Curtius and Benrath, who found that 

 the 7-acid from the analysis of its silver salt, ester, etc., had the formula 

 C 19 H 84 N 6 O 8 , and that it was benzoyl-pentaglycyl-glycine, 



C e H 8 . CO (NH . CH, . CO) B NH . CH, . COOH, 



its ester being identical with the compound synthesised by Curtius and 

 Wiistenfeld (see below). 



Two other compounds hippuryl-glycine and benzoyl-triglycyl- 

 glycine were found to be formed by fusing together hippuric ester and 

 glycine, but not the previously isolated benzoyl-bisglycyl-glycine. 

 Longer chains than the six membered 7-acid are not believed by Curtius 

 and Benrath to be formed in this reaction. 



In 1890 Curtius, by the action of hydrazine upon benzoyl chloride, 

 benzamide or benzoic ester, obtained benzoylhydrazine, 



C,H 8 . COOC.H. + H,N . NH, = C,H, . CO . HN . NH, + HOC.H,, 



19 a* 



