Enantiomeric selection stationary phase preparation

Advances in preparative enantioseparation by simulated moving bed (SMB) chromatography have occurred in the last 10 years. SMB was invented in the 1960s and was used by the petrochemical and sugar industries. Now with the improvements in stationary phases and hardware it is an option for the large-scale preparation of enantiomerically pure material. The majority of the latest published data are using either amylose- or cellulose-based phases because of their selectivity. There are now examples in the literature of the commercial separation on the multi-ton scale.8... 

For example, using non covalent bonding, Mossbach et al. have prepared a stationary phase for HPLC in order to resolve ( )-timolol [2). MIP s have fiinctional groups arranged in such a manner that they are complementary in shape and electronic features to the template. Therefore, Wulf et al. have selectively prepared L-Threonine with an enantiomeric excess of 36% by using a polymer which was imprinted with L-DOPA [3). 

Liquid chromatographic resolutions based on highly selective host-guest, metal chelate and charge-transfer com-plexations have been described (1,2). Recently, a chiral diamide-bonded stationary phase (I) has been prepared, which relies entirely on hydrogen bond associations for the material to be resolved. Despite the weak and flexible interaction in this system, direct resolution of enantiomeric N-acyl-fl-amino acid esters (II) was accomplished with the advent of a highly efficient column technology (2- ). 

There are a large number of possible derivatives that can be prepared and almost every one will probably possess some unique property that will enhance the separation of certain enantiomeric pairs. The examples given in figure 8.18 are those selected by the chiral stationary phase manufacturer ASTEC as those more broadly useful for chiral separations. Other stationary phase manufacturers may well select other types of derivatives for optimal use. 

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