RACEMIZATION OF OPTICALLY ACTIVE AMINO ACID SALTS AND AN APPROACH TO ASYMMETRIC TRANSFORMATION OF DL-AMINO ACIDS.

Article abstract of DOI:10.1246/bcsj.56.3744

In connnection with optical resolution of DL-amino acids, the racemization process of optically active amino acid salts was studied. A wide variety of salts of optically active amino acids with sulfonic acids or mineral acids could be racemized by heating in a medium of acetic acid at 80-100 degree C for 1 h in the presence of 0. 1 molar equivalents of an aldehyde and free DL-amino acid. From the reaction mixture, the racemized DL-amino acid salts were recovered in high yield (86-92%) and in high purity. An asymmetric transformation between two enantiomers of amino acid salt was attempted by the combination of preferential crystallization of the desired enantiomer and racemization of the antipode in the liquid phase. DL-Alanine p-chlorobenzenesulfonate was partially converted to L-isomer (yield 16%, optical purity 97%). Another approach was carried out by transformation between two diastereoisomeric salts.