Different Classes of Chiral Selectors

The quest for chiral selectors can be arbitrarily separated in two paths the synthetic route and the natural route. The synthetic route studies the chiral molecule evaluating possible interactions (Table 1) and designs a selector that will interact differently with an enantiomeric form than with its mirror image. The natural route follows Pasteur and uses the fact that the living world is made of countless chiral selectors and produces pure enantiomers. Once a natural chiral selector has been selected, it is tested with its natural chiral target(s) and with many other enantiomers. The observation of the results allows estimating a posteriori possible chiral mechanisms. 

Actually, neither of these two classes of selectors is 100% pure the semi-synthetic class would almost be the actual class since many synthetic selectors are based on a natural molecule and many natural selectors are chemically modified to enhance their initial properties. Table 3 lists most of the selectors used for the separation of enantiomers sorted according to their main origin synthetic or natural. 

Ligand exchange Diastereoisomeric selector/metal ion/analyte complex Coulomb or ion-dipole (lone electron pair coordination) 

Molecular imprinted polymers Key and lock association Selective shape interaction with the imprint 

Chiral crown ethers Inclusion complexation Ion (primary amino group)-dipole 

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