THE CHEMICAL CONSTITUTION OF THE UNITS 93 

 Phenylalanine. 



In a note published in 1879 Schulze mentioned a substance which 

 he had obtained from the seedlings ofLufimus 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 oxida- 

 tion, 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 Schiitzenberger 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 U 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 them. He found that 

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

 was in fact the principal aromatic constituent. The protein gelatin, 

 which contains no tyrosine, and in which the presence of phenylalanine 

 was demonstrated by Spiro, was found to contain this amino acid 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 6 C 6 H 5 C B H. 



HCN | 6 H 3 | 6 



H, __ CH, __ CH. 



CHO NH, CH.NH 2 CH . NH 2 



CN COOH 



