Importance of the Position of Vinyl Group on β-Cyclodextrin for the Effective Imprinting of Amino Acid Derivatives and Oligopeptides in Water

Two kinds of vinyl monomers of β-cyclodextrin (β-CyD) that tether a vinyl group on either wider rim of the truncated cone or its smaller rim were synthesized and applied to the imprinting toward amino acid derivatives and oligopeptides in water. Mono-3-(N-acrylamido)-3-deoxy-altro-β-cyclodextrin (3-AAm-CyD) showed a remarkable imprinting effect for the enantioselective recognition of protected amino acids such as N-benzyloxycarbonyltyrosine (Z-Tyr). However, the imprinted polymer from mono-6-(N-acrylamido)-6-deoxy-β-cyclodextrin (6-AAm-CyD) hardly showed enantioselectivity. According to NOESY analysis on the preorganized β-CyD/Z-Tyr complex in D₂O, the aromatic moieties of Z-Tyr were included into the cavity of β-CyD from its wider rim. Since the vinyl group of 3-AAm-CyD protruded toward the template and was polymerized there, the detailed shape of the template was precisely copied on the polymer by the imprinting. In the case of 6-AAm-CyD, however, the shape of template could not be well transcribed because its vinyl group was located at opposite side of the cavity, and thus copolymerization occurred far from the template molecule. On the other hand, the imprinted polymers from both β-CyD vinyl monomers were effective for the recognition of sequences of tetrapeptides composed of two glycines and two phenylalanines, although the selectivity itself was not remarkable. In these polymers, even the β-CyD residues of 6-AAm-CyD were immobilized complementarily to the phenyl rings and bound them.