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

The mechanisms of chiral recognition of methyl a - bromopropionate by modif ied cyclodextrins (CDs), permethylated beta - CD (PMBCD) and heptakis(2,6 - di - O - butyl - 3 - O - butyryl) - beta - CD (DBBBCD) were investigated u sing molecular dynamics (MD) methods. It is found that the preferred bindin g sites for the investigated enantiomers are the interior of the modified C Ds, and chiral recognition of the investigated enantiomers by PMBCD and DBB BCD is involved in the induced - fit interactions during the formation of t he association complexes within the cavity of CDs. The associated enantiome rs can move and rotate within the interior of the cavity, which is differen t from the concept "inclusion complexation". In the final conformations fro m 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 o f chiral carbon C(2) and C(3) of CDs. In addition, the MD simulations can r eproduce the experimental results from enantioselective gas chromatography.