Chiral recognition of dipeptide methyl esters by an anionic beta-cyclodextrin

Area of Science:

• Supramolecular Chemistry
• Analytical Chemistry
• Organic Chemistry

Background:

• Chiral recognition is crucial for separating enantiomers.
• Cyclodextrins are versatile hosts for molecular complexation.
• Anionic cyclodextrins offer unique binding properties due to charge interactions.

Purpose of the Study:

• To investigate the chiral recognition capabilities of anionic heptakis[6-carboxymethylthio-6-deoxy]-beta-cyclodextrin (per-CO(2)(-)-beta-CD) towards various dipeptide methyl esters.
• To elucidate the binding interactions and enantioselectivity governing the complexation process.

Main Methods:

• (1)H NMR spectroscopy was employed to study the host-guest interactions.
• NMR titration was used to determine binding constants (K).
• Deuterium oxide (D(2)O) at pD 7.0 was used as the solvent.

Main Results:

• Binding constants increased with hydrophobicity of the dipeptide methyl esters (Ala-Ala-OMe < Ala-Leu-OMe < Ala-Trp-OMe).
• Van der Waals and Coulomb interactions were identified as key attractive forces.
• Per-CO(2)(-)-beta-CD showed stronger binding with (R,R)-enantiomers than (S,S)-enantiomers.
• Enantioselectivity was primarily influenced by the C-terminal amino acid residue.

Conclusions:

• Anionic beta-cyclodextrin derivatives effectively perform chiral recognition of dipeptide methyl esters.
• The observed enantioselectivity is governed by a combination of factors including guest hydrophobicity, host-guest interactions, and the nature of the C-terminal residue.
• The unique cavity shape of the cyclodextrin derivative is essential for chiral discrimination.