D-chiro-inositol (DCI) is prepared by the immobilized enzyme reaction which uses myo-inositol (MI) as the substrate and the conversion rate is about 13%. The aim of this study was to develop a separation method for high purity DCI crystals from a reaction solution including low purity DCI only by the crystallization process. We succeeded in separating DCI crystals of 96% purity by water cooling crystallization, but it was presumed that scale-up was difficult. Although we tried anti-solvent crystallization similar to water cooling crystallization, high purity DCI crystals were not obtained. Therefore, we proposed the crystallization separation process by controlling metastable zones. The purity of a desired compound is controlled by this process, because solid-liquid separation is achieved before crystallization of compound in metastable zone. By the crystallization using this method, the DCI crystals of 97% purity were obtained. Although the yield per batch is about 50%, the actual yield is improved as the last mother liquor returns into the process of the following batch. When this process was repeated, the purity and the yield of DCI were reproduced and the robustness of this process was proved. It is expected that scale-up of this process will be successful, and this purification method could be applicable to similar systems such as separation of isomers and analogs.
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