Study On The Preparation Of Two Acidic D-amino Acids

D-amino acids as the significant compounds, have been widely applied in pharmacy,food additive and fine chemicals. The studies on the preparation of D-amino acids have been an attractive area.D-glutamic acid and D-aspartic acid are two important D-amino acids, they are of great value in the areas such as pharmacy, new material synthesis and food additive production. Therefore, it is valuable to search a new method to prepare the two D-amino acids.D-glutamic acid and D-aspartic acid are prepared from their L-isomers by the esterfication, racemization, chemical resolution and hydrolyzation, and the reaction conditions are studiedL-glutamic acidγ-ethyl ester was synthesized by reaction of L-glutamic acid and ethanol in the presence of sulfuric acid at 60℃for 4 hours, the yield 94.3%. Influence of the ratio of reactants, time, temperature on the esterfication were studied. Racemization of L-glutamic acidγ-ethyl ester in acetic acid, in the presence of salicylaldehyde at 80℃for 2 hours gives DL-glutamic acidγ-ethyl ester with the yield of 85.6% and recamization percent of 100%. Influence of the reaction conditions on the racemization was studieded. In similar way, L-aspartic acidβ-methyl ester and DL-aspartic acidβ-methyl ester were prepared with yield of above 90% and 80% respectively, and racemization percent of DL-aspartic acidβ- methyl ester is 100%. L-2,3-dibenzoyl tartaric acid (L-DBTA )can be used to resolve DL-glutamic acidγ-ethyl ester and DL-aspartic acidβ-methyl ester in water to prepare D-glutamic acid and D-aspartic acid. The yield of D-glutamic acid and D-aspartic acid is 59.6% and above 60% respectively, optical purity of them are all above 99%. L-DBTA can be recovered and reused with recover yield of above 80%. The result showed that L-DBTA has good selectivity, it could formed salt with D-glutamic acidγ-ethyl ester and D-aspartic acidβ-methyl ester. The salts precipitated easily from water because of its low solubility. The influences of resolution reagent, temperature, time and some other factors on the resolution were studied, and the best condition was confirmed. Products and intermediates were characterized by melting point, optical rotation, IR, 1HNMR and HPLC.