Process for the preparation of N-carboxy-t-leucine anhydride

Process for the preparation of N-carboxy-t-leucine anhydride in which the corresponding N-carboxy-t-leucine is subjected to a cyclization with the aid of an acyl halogenide. Preferably, acetyl chloride is used as acyl halogenide. The N-carboxy-t-leucine anhydride obtained optionally is subsequently converted into a t-leucine-N-substituted amide with the aid of the corresponding amine. Preferably, methyl amine is chosen as the amine, and the reaction is carried out in a mixture of water and methanol as solvent.