Polymeric membranes for chiral separation of pharmaceuticals and chemicals

The optical resolution or chiral separation of one specific enantiomer from others is in demand for the production of pharmaceuticals because many pharmaceuticals exist as stereoisomers, with each enantiomer having different biological activity. There is considerable demand for separation techniques appropriate for the large-scale resolution of chiral molecules. Chiral separation of racemic mixtures of pharmaceuticals through chiral or achiral polymeric membranes with or without a chiral selector represents a promising system for future commercial application. This article reviews several polymeric materials for the chiral separation of pharmaceuticals. Several chiral separation membranes were prepared from chiral polymers where enantioselectivity was generated from chiral carbons in the main chain. However, it is rather difficult to generate excellent chiral separation membranes from chiral polymers alone, because racemic penetrants mainly encounter the flexible side chains of the membrane polymers. Therefore, chiral separation membranes were also prepared using polymers with a chiral branch. Furthermore, several molecules have been used for specific interactions between the molecules and specific pharmaceuticals or drugs in chiral separation membranes. Cyclodextrins, crown ether derivatives, albumin, and DNA are commonly used as stereoselective ligands in chiral separation membranes. Finally, this article discusses future trends in polymeric materials for chiral separation membranes.