30 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Phthalimidoacetic ester is obtained by the action of chloracetic ester 

 upon potassium phthalimide ; this is first hydrolysed by alkali to glyco- 

 coll phthaloylic acid, and then by 20 per cent, hydrochloric acid to 

 glycocoll and phthalic acid : 



/ co \ / co \ 



C 6 H / \NK + Cl . CH 2 . COOC 2 H 5 = KC1 + C 6 H/ \N . CH 2 . COOC 2 H 5 



^ccr ^ccr 



Phthalimidoacetic ester 



C0 /COOH 



/ 



\ 



N . CH 2 . COOC 2 H 6 + 2 H 2 = C 6 H +C 2 H 5 OH 



.NH.CH 2 .COOH 

 Glycocoll phthaloylic acid 



/COOH /COOH 



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



X CO.NH.CH 2 .COOH X COOH 



Alanine. 



Of the naturally occurring amino acids alanine only 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 

 hydrolysis is then converted into the amino acid : 

 CH 3 CH 3 



I /OH 



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



\NH 2 d N 



CH 3 CH 3 



CH NH 2 + 2H 2 O= CH NH 2 + NH 3 

 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 StadnikofT. 



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, by the action of ammonia upon a-chloropropionic acid : 

 CH 3 . CHC1 . COOH + NH 3 = HC1 + CH 3 . CH(NH 2 ) . COOH, 



