Electrogenerated chiral cationic glycine equivalents — Part 2: Chiral 3-methoxy-2,5-morpholinediones from (S)-α-hydroxy acids and dimethyl aminomalonate
                                
                                    
                                        作者:Georgios Kardassis、Peter Brungs、Christoph Nothhelfer、Eberhard Steckhan                                    
                                    
                                        DOI:10.1016/s0040-4020(98)00082-9
                                    
                                    
                                        日期:1998.4
                                    
                                    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.