in ON THE SYNTHESIS OF ALBUMINS 129 



HO . OC[NHCH 2 CO] 3 NHCH 2 CO . OH = 



triglycylglycin-dicarboxylic acid ; 



C 2 H 5 O . OC [NHCH 2 CO] 3 NHCH 2 CO. NH 2 - 



carbethoxy-triglycyl-glycin-amide. 



Analogously by uniting HCN with glycyl-glycin-ester there is formed 

 a urea-compound, namely, carbamino-glycyl-glycin -ester : 



NH 2 CO . NHCH 2 CO . NHCH 2 CO . OC 2 H 5 , 



and similarly it is possible to form /2-naphthalinsulpho-derivatives of 

 dipeptids, and thereby readily to separate dipeptids from mixtures. 



This method of converting amino-acids into their carboxethyls and 

 subsequently into chlorides, enables one to couple mono- with di- and 

 with oxy-ammo acids, but it has the disadvantage that th6 carbethoxyl- 

 group, CO . OC 9 H 5 , or in the free acids, the carboxyl-radical, CO . OH 

 cannot be got rid of. 1 



To overcome this difficulty Fischer devised an entirely new 

 method. Instead of linking amino-acids together by their carboxyl- 

 COOH-end, he joined them by their other or NH 2 -end. We saw 

 above that after converting an amino-acid into its carbethoxyl-deriva- 

 tive it was possible to introduce into the carboxyl-radical a chlorine 

 atome, which during synthesis became replaced by the NH-radical of 

 an ami no-acid-ester. Now, Fischer introduced a halogen-containing 

 acid-chloride into the NH 2 -radical of an amino-acid, and then substi- 

 tuted in the synthetised product a molecule of ammonia for the 

 chlorine-atom. 



Such acid radicals, as just referred to, are, for example, chloracetyl- 

 chloride, CH Q C1 COC1, and the chlorides of brompropionyl, a-brom- 

 iso-capronyl, a-8-dibromvaleryl, and phenyl-a-brompropionyl. By 

 means of these five compounds it was possible to introduce glycyl, 

 alanyl, leucyl, prolyl, and phenyl-alanyl, on the following lines : 



By the action of chloracetyl chloride C1CH COC1, on alanin- 

 ester, there is formed C1CH 2 CO NH . CH(CH 3 )CO . OC 2 H 5 , or 

 chloracetyl-alanin-ester, which, on being treated with alcoholic NH 3 , 

 has its chlorine replaced by NH 2 ; alcohol is split off simultaneously 

 and ring-formation occurs, there being formed methyl-diacipiperazin, 



1 By the use of an excess of alkalies, glycyl-glycin-ester is converted into glycyl- 

 glycin-carboxylic acid, HO . OC . NHCH 2 CO . NHCH 2 . CO . OH, which can again be 

 converted into a neutral ester by means of alcoholic HC1, but the newly formed ester 

 differs in its properties from the original one. This remarkable fact seems to hold good 

 also for other amino-acids, Fischer calls the original ester, the a-ester, and the 

 secondarily-formed ester, /3-ester. 



K 



