Enzyme supported preferential crystallization of enantiopure amino acids

The production of enantiopure substances has drawn a lot of interest during the last decades. Especially intermediates for the pharmaceutical industry, fine chemicals and feed additives like L-amino acids are of great scientific and economic relevance [1, 2]. Despite an increasing number of stereoselective synthesis there are still a lot of reactions that lead to racemic mixtures of the desired homochiral products. Numerous separation techniques have been developed [3-5], but a major drawback of them is the principal yield limitation to a maximum of 50 %. We present a new approach for the production of enantiopure amino acids (AA) with a theoretical yield of 100 % that integrates preferential crystallization (PC) of a conglomerate and enzymatic in situ racemization (Fig. 1). Starting from a racemic oversaturated AA solution one enantiomer can be crystallized by seeding with homochiral crystals, which leads to an increasing enantiomeric excess (ee) of the counter enantiomer in the crystallization medium. PC is only possible as long as the medium composition remains in the metastable zone of the ternary phase system, thus crystallization of the counter enantiomer will start at a certain point. In order to prevent this, enzymatic in situ racemization can be applied which keeps the ee in the medium at a minimum. By continuous feeding of racemic AA into the system a stationary process can be obtained