Molecular dynamics simulations of chiral recognition of methyl α-bromopropionate by modified cyclodextrins

The mechanisms of chiral recognition of methyl a - bromopropionate by modified cyclodextrins (CDs), permethylated beta - CD (PMBCD) and heptakis(2,6 - di - O - butyl - 3 - O - butyryl) - beta - CD (DBBBCD) were investigated using molecular dynamics (MD) methods. It is found that the preferred binding sites for the investigated enantiomers are the interior of the modified CDs, and chiral recognition of the investigated enantiomers by PMBCD and DBBBCD is involved in the induced - fit interactions during the formation of the association complexes within the cavity of CDs. The associated enantiomers can move and rotate within the interior of the cavity, which is different from the concept "inclusion complexation". In the final conformations from MD simulations, the stereocenters of the investigated enantiomers locate near the secondary rim of the modified cyclodextrins. It is first proposed that chiral recognition is closely involved in the chiral region composed of chiral carbon C(2) and C(3) of CDs. In addition, the MD simulations can reproduce the experimental results from enantioselective gas chromatography.