Conventional enantioselective preparative chromatographic separation using columns packed with chiral stationary phase is characterized by a 50% yield constraint. Racemization of the undesired enantiomer and recycling the formed mixture is an attractive option to tackle this limit. To implement this concept, potential is seen in particular in applying enzymes immobilized in a second fixed bed. However, the identification of suitable operating conditions and the direct connection of a chromatographic column and an enzymatic reactor is not trivial. The paper presents results of an experimental study applying jointly a batch-wise operated chiral Chirobiotic T column to resolve the two enantiomers of mandelic acid (MA) and a mandelate racemase immobilized on Eupergit CM. The general concept could be successfully demonstrated over several cycles focusing on the provision of (S)-MA. A mathematical model was developed in order to illustrate essential process features and to quantitatively describe the coupled separation and racemization processes. The key ingredients of this model, namely, the adsorption isotherms of the two enantiomers on the chiral column and the rate of racemization in the enzymatic reactor, were determined experimentally. The potential of applying the model for further process optimization and generalization is indicated.

中文翻译：

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对映选择性制备色谱和外消旋相结合：实验论证和基于模型的工艺优化

使用填充有手性固定相的色谱柱进行常规对映选择性制备型色谱分离，其收率限制为50％。将不需要的对映异构体消旋并回收形成的混合物是解决该限制的有吸引力的选择。为了实施该概念，特别是在施加固定在第二固定床中的酶方面看到了潜力。然而，确定合适的操作条件以及色谱柱和酶促反应器的直接连接并非易事。本文提出了一项实验研究的结果，该研究联合应用了分批操作的手性Chirobiotic T色谱柱，以解决扁桃酸（MA）和固定在Eupergit CM上的扁桃酸酯消旋酶的两种对映异构体。S）-MA。开发了一个数学模型，以说明基本的过程特征并定量描述耦合的分离和外消旋过程。实验确定了该模型的关键成分，即两种对映异构体在手性色谱柱上的吸附等温线和酶促反应器中的外消旋速率。指出了将该模型用于进一步的过程优化和通用化的潜力。