38 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 at the same time shown to be 

 phenyl-/3-aminopropionic acid. 



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 5 . CHO + CH/ = C 6 H 5 . CH = C\ + H 2 O 



X COOH X COOH 



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

 lactimide, 



/N-CO . C 6 H 5 

 CeHs.CH^C/ I 



x co 



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-/3-phenyl-propionic 

 acid : 



/NH . CO . C 6 H 5 

 C 6 H 5 . CH = C/ + H 2 = C 6 H 5 . 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 5 . CH 2 . CH/ + H 2 = 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, 



/NHCOC 6 H 5 /OH 



C 6 H 5 . CH = C/ + HOH = C 6 H 5 . CONH 2 + C 6 H 5 . CH = c( 



X COOH | X COOH 



C 6 H 5 . CH 2 . CO . COOH 



which Erlenmeyer proved by preparing the oxime and reducing it to 

 phenylalanine : 



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

 Benzoyl-a-amidocinnamic acid is also converted by the action of 

 ammonia into a compound, which yields phenylalanine on hydrolysis. 



