Abstract
The mechanisms for chiral recognition by cyclodextrins (CDxs) are discussed. Examples of host–guest systems where the lock-and-key and the three-point rule are applicable are cited and discussed. Most results reported so far suggest that the ability of native CDxs and chemically modified CDxs to discriminate between enantiomers of guests having a central chirality is low in aqueous solutions. Small ΔΔG values for enantioselective complexation of CDxs with amino acids seem to be due to unpredictably small changes in the structures of the complexes of the guest enantiomers. Therefore, it is very difficult to prove the participation of hydrogen bonding in chiral recognition through the three-point rule in these systems. The use of the Coulomb interaction and the coordinate bonds as point interactions is discussed. CDxs might be good hosts to recognize axial chirality or helicity of guests. Hydrogen bonding in water is assumed in the recognition of the helicity of bilirubin. Very large ΔΔG values have been reported for the chiral recognition of the binaphthyl derivatives. Such a system seems to be a suitable model system to study the mechanism of chiral recognition by CDxs. © 1997 John Wiley & Sons, Ltd.
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