PROTEINS 91 



ally vary considerably in solubility, and on concentration one or 

 the other will crystallize out first. A second method consists 

 in allowing various microorganisms to act on the mixture of 

 the two optical isomers. Usually one form will be destroyed 

 by the microorganism, the other to a much smaller degree, or 

 not at all. 



The optically active acids then may be built up into peptids 

 at will. Three methods are in use to effect this synthesis. 



1. Ester method. 



Glycocoll ester is converted into a ring compound 



C 2 H 5 C CH 2 NH 2 



+ -> 2 C 2 H 5 OH + 



H 2 N CH 2 COOC 2 H 5 



CH 2 NH 



CO CO 



NH - - CH 2 



Under the action of alkali this ring compound is split open, 

 forming a dipeptid 



NH 2 CH 2 CO NH CH 2 COOH 



Of course the amino acids used may be varied, and thus differ- 

 ent dipeptids obtained. The method serves only to build up 

 dipeptids, however, and if two different amino acids are used 

 it has certain other disadvantages. 



2. Synthesis by means of acid chlorides. 



If glycocoll is treated with chloracetyl-chloride the following 

 reaction takes place: 



C1CH 2 CO Cl + NH 2 CH 2 COOH -> HC1 + 

 Cl CH 2 CO NH. CH 2 COOH 



By the action of ammonia, the chlorine atom may be replaced 

 by NH 2 , and a dipeptid results. 



NH 2 CH 2 CO 'NH. CH 2 COOH. 



