PROCESS FOR THE DIASTEREOMERICALLY PURE PREPARATION OF DL/LD-METHIONYLMETHIONINE

The invention relates in particular to a process for the preparation of DL/LD-methionine diketopiperazine (I) characterized in that a DD/LL-methionylmethionine-containing aqueous solution or suspension, which has a pH of 3 to 7, measured using a pH electrode at 20° C., is reacted at a temperature of 150 to 220° C., preferably at 170 to 210° C., until an aqueous solution or suspension has formed containing at least a proportion of 30 mol %, preferably 50 mol %, especially 60 mol % of DL/LD-methionine diketopiperazine, based on the total content of DL/LD- and DD/LL-methionine diketopiperazine in the reaction mixture. This process forms part of an overall process for the preparation of DL/LD-methionylmethionine, which is obtained by hydrolysis from the DL/LD-methionine diketopiperazine (I) produced initially.