AMINOLYSIS OF ALPHA-HYDROXY ACID-ESTERS WITH ALPHA-AMINO-ACID SALTS -FIRST STEP IN THE SYNTHESIS OF OPTICALLY-ACTIVE 2,5-MORPHOLINEDIONES

A process for preparing optically active 2,5-morpholinediones 1 is des cribed starting from optically active alpha-amino acids and optically active alpha-hydroxy esters. The process involves three steps: In the first step the sodium salt of an alpha-amino acid is condensed with an alpha-hydroxy ester to yield an optically active N-(alpha-hydroxy acy l)-alpha-amino acid 4. In the second step the hydroxy acid obtained is subjected to esterification with ethanol. In the third step the N-(al pha-hydroxy acyl)-alpha-amino acid ethyl ester 5 is subjected to cycli zation with an acidic catalyst. For some examples the cyclization was also performed directly from the hydroxy acid 4. Morpholinediones 1 ar e useful as precursors for the preparation of poly(depsipeptides) 2 an d copolymers containing depsipeptide repeating units.