THE CHEMICAL CONSTITUTION OF ITS UNITS 37 



Phenylalanine. 



In a note published in 1879 Schulze mentioned a substance which 

 he had obtained from the seedlings ofLufltnus luteus ; two years later he 

 and Barbieri showed that this substance had the composition C 9 H n NO 2 , 

 and they described it as phenylamidopropionic acid, because, on oxidation, 

 it gave benzoic acid, and, when heated, it lost carbon dioxide and gave 

 a base, C 8 H n N. In its properties it closely resembled Tiemann's phenyl- 

 aminoacetic acid, and they regarded it therefore as a homologue of this 

 acid, though it differed from the substance described by Posen as phenyl- 

 a-aminopropionic acid. 



About the same time Schutzenberger obtained a substance, which 

 he called tyroleucine, by the action of baryta on proteins ; when heated 

 it gave a sublimate of aminovalerianic acid and a base C 8 H n N, which 

 probably had as mother-substance the same body which was isolated by 

 Schulze and Barbieri. 



Schulze, Barbieri and Bosshard next showed that their substance 

 arose during the germination of the seed, and that it was also obtained 

 from vegetable proteins by hydrolysis, by hydrochloric acid and zinc 

 chloride, or by baryta. It was therefore contained in the protein 

 molecule. 



It had been known for a long time that benzaldehyde and benzoic 

 acid were formed by the oxidation of animal proteins, and that phenyl- 

 propionic and phenylacetic acids were products of putrefaction (Sal- 

 kowski) ; phenylalanine was therefore regarded, as suggested by Tie- 

 mann, as the constituent from which these substances arose, but the 

 actual presence of phenylalanine in the proteins was only proved when 

 E. Fischer commenced his investigations upon the proteins. He then 

 found that in some proteins it exceeded in amount that of tyrosine, 

 and that it was in fact the principal aromatic constituent. Those 

 proteins, such as gelatin, in which its presence was demonstrated by 

 Spiro, and which contains no tyrosine, was found to contain phenyl- 

 alanine as its aromatic constituent. 



The constitution of phenylalanine was determined in 1882 by Erlen- 

 meyer and Lipp, who synthesised it by Strecker's method from phenyl- 

 acetaldehyde, hydrogen cyanide and ammonia : 



C 6 H 5 C 6 H 5 C 6 H 5 



| HCN | H ( ,0 | 

 CH 9 ~> CH > CH 2 



CH. 

 CN COOH 



I + I 



CHO NH 3 CH.NH 2 CH . NH 2 



