New optical resolution method for Racemic DL-Aspartic acid by crystallization in the presence of D- or L-Asparagine as a tailor-made additive

Abstract

A new optical resolution method is proposed in which one enantiomer of a racemic mixture is replaced with a tailor-made additive, and the displaced enantiomer is crystallized. DL-Aspartic acid (Asp) was examined as a model racemic compound. First, L-Asp crystallization was examined in the presence of L-asparagine (Asn) or D-Asn. The effect of Asn was chirality-specific; L-Asn specifically replaced some of the L-Asp in the crystal lattice and solid solutions of L-Asp with L-Asn formed. Secondly, DL-Asp crystallization was examined in the presence of L-Asn, and the obtained crystals were solid solutions of DL-Asp with L-Asn partially replacing L-Asp in the DL-Asp crystal lattice. Finally, crystallization of the L-Asp in the filtrate of the DL-Asp crystallization in the presence of L-Asn was examined. The obtained crystals were a mixture of solid solutions of L-Asp with L-Asn and solid solutions of DL-Asp with L-Asn. Moreover, when D-Asn was added to the DL-Asp crystallization, a mixture of solid solutions of D-Asp with D-Asn and solid solutions of DL-Asp with D-Asn was crystallized from the filtrate. These results show that racemic compounds could be resolved by the proposed method.