Mechanisms for Chiral Recognition by Cyclodextrins

Abstract

The mechanisms for chiral recognition by cyclodextrins (CDxs) are discussed. Examples of host-guest systems where the 'lock-and-key mechanism' 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 ⌬⌬G 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 'threepoint 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 ⌬⌬G 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.

A Phase Solubility Study on the Chiral Discrimination of Ibuprofen by β-Cyclodextrin Complexes

“…Star notation indicates the position of the asymmetric centre, responsible for two enantiomeric (R)-and (S)-forms. Arbitrary atom numbering is for convenience, adopted for 1 H NMR assignments showed that β-CD complexes were mainly present in the precipitate, whereas Me-β-CD complexes were recovered by liquid phase. Electrospray ionization mass spectrometry (ESI-MS, Esquire™ Bruker-Daltonics ion trap mass spectrometer) measurements allowed confirming the effective complex formation and obtaining information on its stoichiometry, which turned out to be 1:1.…”

“…Experiments were carried out in triplicate; solubility data were averaged and used to calculate the binding constant for the complexes formation by UV-Vis absorption spectroscopy. 1 …”

“…[1][2][3] In fact, the pharmacodynamic effects of the enantiomers of many racemic drugs are still unknown, and the pharmacological activity is very often enhanced for one of the two enantiomers, whereas the other one can even be toxic. 4,5 In this context, many reports concerning the development of enantiomeric separation methods using cyclodextrins (CDs) as resolving chiral agents appeared in recent years.…”

Complexation and Chiral Recognition of Chiral Binaphthyl Derivatives and β-Cyclodextrins in Solution Probed by Triplet Excited State Relaxation

“…The knowledge about the photochemistry of BNP in solution remained limited [30][31][32][33][34][35]. In fact, the singlet excited state of BNP has been characterized to some extent.…”

FeBr3–cyclodextrin complexes as efficient and chemoselective catalysts for sulfoxidation reactions

“…The cyclodextrins form complexes with a great variety of organic [40] and inorganic molecules [41][42][43] and also are known to induce enantioselectivity in several reactions [44,45]. Particularly, the asymmetric oxidation of organic sulfides in presence of CDs was reported in the literature [46].…”