Process design, enantiopure drugs

In order to illustrate an example of process design for the manufacture of enantiopure drug substances on an industrial SMB system, consider manufacturing 10 ton/ year of an enantiopure drug. The racemic drug by definition is a 50 50 mixture of each enantiomer (products A and B). The goal is to process enantiopure drug substances in order to obtain 99 % purity for both the extract and the raffinate. 

Although very efficient, the broad application of the direct preparation is restricted due to the limited number of pure starting enantiomers. The design of a multistep process that includes asymmetric synthesis is cumbersome and the development costs may be quite high. This approach is likely best suited for the multi-ton scale production of commodity enantiomers such as the drugs ibuprofen, naproxen, atenolol, and albuterol. However, even the best asymmetric syntheses do not lead to products in an enantiomerically pure state (100 % enantiomeric excess). Typically, the product is enriched to a certain degree with one enantiomer. Therefore, an additional purification step may be needed to achieve the required enantiopurity. 

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