142 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



and Locquin has prepared, by means of the formyl derivative, d-iso- 

 leucine. 



In the case of serine, no separation could be effected by means of 

 these 'derivatives, but, by making the p-nitrobenzoyl compound, 

 Fischer and Jacobs obtained d- and 1-serine. 



Proline was separated in 1909 by Fischer and Zemplen by the 

 fractional crystallisation of the cinchonine salt of its m-nitrobenzoyl 

 compound. This was prepared from m-nitrobenzoyl-S-amino-valerianic 

 acid by the same reaction as was employed in its synthesis (p. 131). 



Isoserine and diaminopropionic acid must also be added to the 

 list of optically active amino acids separated by Fischer and his 

 pupils. 



In all these cases the acidic function of an amino acid has been 

 made use of for purposes of separation. The first case in which the 

 basic function of an amino acid was requisitioned was that of Betti and 

 Mayer in 1908, who separated a-aminophenylacetic acid into its 

 isomers by combining it with d-camphorsulphonic acid. Fischer and 

 Scheibler, in 1911, found that this was the only means of obtaining the 

 isomers of ^3-aminobutyric acid. 



Pyman, in 1911, used the basic function of histidine to obtain the 

 natural isomer ; the racemic compound was easily separated by the 

 fractional crystallisation of its salt with d-tartaric acid. 



The specific rotatory powers of the natural and synthetical amino 

 acids are given in Table B, p. 149. 



