94 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



This synthetical substance closely resembled Schulze and Barbieri's 

 natural compound, and their identity was established. Posen's prepara- 

 tion, described under this name, was then regarded as phenyl-yQ-amino- 

 propionic acid. It has since been shown to be phenyl-/3-oxypropion- 

 amide. 



In 1893, a new method of synthesising amino acids, starting from 

 hippuric acid, was introduced by Erlenmeyer jun., phenylalanine being 

 the first product to be prepared. 



When benzaldehyde is condensed with hippuric acid in the presence 

 of acetic anhydride a Perkin's reaction takes place and benzoyl-a-amido- 

 cinnamic acid is formed : 



/NH . CO . C 6 H 5 /NH . CO . C 6 H 5 



C 6 H 6 .CHO + CH 2 / =C 6 H 6 .CH = C< + H 2 O 



X COOH X COOH 



Under the influence of the acetic anhydride, this is converted into the 

 azlactone, 



which, by hydrolysis by acids or by alkalies, is reconverted into benzoyl- 

 a-amidocinnamic acid. 



Benzoyl-a-amidocinnamic acid is reduced by sodium amalgam, or 

 by zinc and hydrochloric acid, to benzoyl-a-amino-y3-phenyl-propionic 

 acid : - 



/NH . CO . C 6 H 5 /NH . COC 6 H B 



C 6 H B . CH = C/ + H 2 = C 6 H 6 . CH 2 . CH< 



X COOH X COOH 



from which the benzoyl group is easily removed by hydrolysis with the 

 formation of phenylalanine : 



/NH . COC 6 H 5 



C 6 H 6 . CH 2 . CH/ + H 2 O= C 6 H 5 . CH 2 . CH(NH 2 ) . COOH + C 6 H 5 . COOH 



X COOH 



Benzoyl-a-amidocinnamic acid is converted by the action of acids, or 

 alkalies, into phenylpyruvic acid and benzamide, 



yNHCOC 6 H 5 /OH 



C 6 H S . CH = C/ + HOH = C 6 H 5 . CONH a + C 6 H 5 . CH = c( 



X COOH J, X COOH 



C 6 H 5 . CH a . CO . COOH 



which Erlenmeyer proved by preparing the oxime and reducing it to 



phenylalanine 1 : u 



C 6 H 6 .CH 2 . CO. COOH -^C 6 H 5 .CH 2 .C(NOH).COOH->C 6 H 6 .CH 2 .CH.NH 2 . COOH 



1 Knoop and Hoessli find that the oxime of phenylpyruvic acid is most easily reduced to 

 phenylalanine by aluminium amalgam. 



