THE CHEMICAL CONSTITUTION OF THE UNITS 85 



Alanine. 



Of the naturally occurring amino acids alanine alone was prepared 

 synthetically, many years before it was discovered as a constituent of the 

 protein molecule. Its name was given to it by its discoverer, Strecker, 

 who prepared it in 1850 from aldehyde ammonia, which, when treated 

 with hydrogen cyanide gives the aminocyanohydrin, and this, by hy- 

 drolysis, is then converted into the amino acid : 



CH 8 CH S 



I OH 

 CH + HCN = CH - NH 2 + H 2 O 



CN 



CH 3 CH 3 



CH NH 2 + 2 H 2 = CH NH 2 + NH a 



CN COOH 



Owing to the ease with which the aldehyde resinifies in presence of 

 alkali and potassium cyanide the yield of alanine is very poor. If, 

 however, the reaction be carried out in the presence of excess of 

 ammonium chloride and if the potassium cyanide be slowly added to 

 the aldehyde dissolved in ether, a yield of alanine amounting to 60 to 

 70 per cent, can be obtained, as has been recently shown by Zelinsky 

 and Stadnikoff. 



This is the first of the general methods employed in the synthesis 

 of the amino acids. 



Alanine was prepared in 1860 by Kolbe by the second general 

 method, i.e. by the action of ammonia upon a-chloropropionic acid : 

 CH 3 . CHCl . COOH + NH 3 = HC1 + CH 3 . CH(NH 2 ) . COOH, 



and in 1 864 by Kekule" from monobromopropionic acid and alcoholic 

 ammonia. 



A synthesis of acetylalanine, from which alanine can be obtained 

 by hydrolysis, was described in 1900 by de Jong. Pyruvic acid was 

 neutralised with ammonium carbonate ; there was a considerable rise in 

 temperature, carbon dioxide being evolved, and the ammonium salt of 

 acetylalanine crystallised out The explanation of this reaction is based 

 upon Erlenmeyer and Kunlin's synthesis of phenylalanine from phenyl- 

 pyruvic acid and it proceeds as follows : 



Ammonium pyruvate, which is first formed, is tautomeric with a- 

 amino-oxypropionic acid, into which it changes : 



