摘要:
Chiral 3-methoxy-2,5-morpholinediones which are cyclic N,O-acetals have proved to be excellent chiral cationic amino acid equivalents, especially if larger nucleophiles are employed. They are easily obtained from dipeptolides formed between chiral alpha-hydroxy acids and dimethyl amino malonate via regioselective electrochemical methoxylation followed by intramolecular lactonization after decarboxylation. The lactonization can be performed quantitatively from the open-chain peptolide by condenzation under reduced pressure at elevated temperature. The easy separation of the desired amino acid and the alpha-hydroxy acid being the chiral auxiliary by extraction is valuable. (C) 1998 Elsevier Science Ltd. All rights reserved.