Patent ID: 7326794

Claim:
A process for the preparation of 1-{2(S)-[1(S)-(ethoxycarbonyl)butylamino]propionyl}-(3aS,7aS)octahydroindol-2(S)-carboxylic acid of Formula I and the t-butylamine salt thereof of Formula I′ free of contaminations derivable from dicyclohexyl carbodiimide selected from the compounds of Formulas VII′ and VIII′: wherein a compound of Formula II is acylated with a carbonic acid derivative selected from an alkyl chloroformate, benzyl chloroformate, and di-alkyl-dicarbonate to yield a compound of Formula III wherein R represents lower alkyl or aryl-lower alkyl; the compound of Formula III thus obtained is activated with thionyl chloride; the activated intermediate thus obtained is reacted with a compound of Formula IV to provide the compound of Formula I, and, if desired, the compound of Formula I thus obtained is reacted with t-butylamine to provide the compound of Formula I′.