52 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



converted into aspartic acid. In the same way Dessaignes obtained 

 aspartic acid from acid ammonium fumarate and maleate. At Liebig's 

 suggestion these reactions were confirmed by Wolff. It was shown by 

 Engel, in 1887, tnat aspartic acid could be obtained directly by heating 

 maleic or fumaric acid with alcoholic ammonia to 140-150 without 

 the formation of the intermediate substance which is fumarimide, and 

 to which the following constitutional formulae have been given : 

 COv. CO N CO 



CH N CtT CH 2 



i / i r 



CH 2 / CH 2 CH 



I / I / I 



CO/ CO N CO 



These syntheses give -no indication as to the structure of aspartic 

 acid, the constitutional formula of which is based upon Kolbe's work, 

 that it is amino-succinic acid ; the only synthesis of aspartic acid 

 which confirms this constitution appears to be that by Piutti in 1887. 

 Sodium oxalacetic ester, prepared from oxalic ester and acetic ester in 

 the presence of sodium ethylate : 



COOC 2 H 5 COOC 2 H 5 



COOC 2 H 6 CO 



+ NaOC 2 H 5 = 2C 2 H 5 OH + I 

 CH 3 CHNa 



COOC 2 H 5 COOC 2 H 5 



gives an oxime when treated with hydroxylamine hydrochloride : 

 COOC 2 H 5 COOC 2 H 5 



CO C = NOH 



I + H 2 NOH = I + NaCl + H 2 O 



CHNa CH 2 



COOC 2 H 5 COOC 2 H 5 



and this is reduced by sodium amalgam to sodium aspartate 

 COOC 2 H 5 COONa 



C = NOH CHNH 2 



I + 4 H + aNaOH = | + 2C 2 H 5 OH + H 2 O 



CH 2 CH 2 



COOC 2 H 5 COONa 



From this oxime Piutti has also prepared the two isomeric aspara- 

 gines : 



COOH CONH 2 



CH.NH 2 CH.NH 2 



CH 2 CH 2 



CONH, COOH 



