Racemization, optical resolution and crystallization-induced asymmetric transformation of amino acids and pharmaceutical intermediates.

Tanabe Seiyaku has been investigating an efficient optical resolution method for the productionof optically active amino acids since the 1950s. As one of the practical applications of the resolutionmethods, we focused on crystallization-induced asymmetric transformation, with which it is possibleto obtain more than 50% of one enantiomer of a racemate. In order to achieve the asymmetrictransformation, an elegant method for racemization of optically active amino acids and their saltswas developed. This successful racemization procedure led to efficient and economical preparationpaths for various optically active amino acids by the two crystallization-induced asymmetric transformations,one of which is a combination of enantiomeric resolution and simultaneous racemization and theother is a combination of diastereomeric resolution and simultaneous epimerization. Here, manyexamples of our studies and recent reports of pharmaceutical intermediates are presented.