116 CHEMISTRY OF THE PROTEIDS CHAP. 



The y-acid of 1881 had its constitution, however, only explained in 

 1904 by Curtius and Benrath, 1 after Curtius and Wiistenf eld 2 had 

 found, that in building up glycyl- chains by means of acid-azides all 

 the higher chains beginning with the triglycyl compound gave the 

 biuret-reaction. 



The so-called 'biuret-base' of Curtius was first obtained in 1883 3 

 by the spontaneous decomposition of glycocollester, which can readily 

 be obtained by suspending glycocoll in ethylalcohol ; passing dry 

 HC1 into the alcohol ; suspending the glycocollethylester chloride in 

 ether and shaking it with dry silveroxide, then removing the silver- 

 chloride by filtration, drying the ether with barium oxide and distilling. 

 Glycocollethylester is a clear, basic fluid, boiling at 148 to 149 . 4 



The glycocoll-ester obtained in this way gave rise, in addition to 

 the biuret-base, to glycin-anhydride (NHCH 2 CO) 2 . 5 



The nature of the ' biuret-base ' could not be explained by Curtius 

 till E. Fisher 7 succeeded in converting the cyclic glycin-anhydride 

 into the open-chain glycylglycin, which is the mother substance of 

 the hippuryl-amino-acetic acid prepared by Curtius in 1881 (see above). 



HN CH 2 C = H 2 N CH 2 C = 



I I -> I 



= C CH 2 NH HO . OC CH 2 NH 



Glycocoll anhydride. Glycylglycin. 



Schwarzschild 8 is of the opinion that the biuret-base of Curtius is 

 built up of 7 glycocoll-molecules in an open chain, which would make 

 the base into 



NH 2 . CH 2 . CO (NHCH 2 CO) 5 NHCH 2 . CO . OC 2 H 5 



Aminoacetyl-pentaglycyl-amino-acetic acid-ethyl -ester. 



Curtius, Gumlich, and Levy 9 state, however, that the biuret-base 

 which results from the spontaneous transformation of glycocollester is 

 a tetraglycyl-compound : 



NH 2 . CH 2 . CO (NHCH 2 C0) 2 NHCH 2 CO. OC 2 H 5 



Aminoacetyl-bisglycyl-amino-acetic-acid-ethyl-ester. 



1 Th. Curtius and Benrath, Ber. d. deutsch. chem. Gesell. 37. 1279 (1904). 



2 Th. Curtius, ibid. 35. 3226 (1902) ; R. Wiistenfeld, fiber ,d. Bildung von Glycyl- 

 ketten mittels Saureaziden, Dissertation, Heidelberg, 1903. 



3 Th. Curtius, Ber. d. deutsch. chem. Gesell. 16. 755 (1883). 



4 Curtius and Goebel, Journ.f. prakt. Chem. [2] 37. 170 (1888). 



5 Th. Curtius, ibid. 23. 3041 (1891). 



6 Th. Curtius and Goebel, ibid. [2] 37. 170 (1888). 



7 Fischer and E. Fourneau, Ber. d. deutsch. chem. Ges. 34. 2868 (1901). 



8 Schwarzschild, Hofmeister's Beit. 4. 162 (1904). 



9 Th. Curtius, Ber. d. deutsch. chem. Gesell. 37. 1284 (1904). 





