Über aktivierte Ester V. Verwendung der Cyanmethylester‐Methode zur Herstellung von (N‐Carbobenzoxy‐S‐benzyl‐ L ‐cysteinyl)‐ L ‐tyrosyl‐ L ‐isoleucin auf verschiedenen Wegen

A study on the synthesis of (N‐carbobenzoxy‐S‐benzyl‐ L ‐cysteinyl)‐ L ‐tyrosyl‐ L ‐isoleucine (XII) by the activated ester method has shown that the cyanomethyl esters prove useful for preparing relatively complicated peptides, especially if acetic acid is used as a catalyst. An important feature of the method is the fact that the cyanomethyl ester of (N‐carbobenzoxy‐S‐benzyl‐ L ‐cysteinyl)‐ L ‐tyrosine on hydrolysis or aminolysis produces derivatives of L ‐cysteinyl‐ L ‐tyrosine without any signs of racemisation.