The Synthesis and Characterization of a Pyridine-Linked Cyclodextrin Dimer

A cyclodextrin dimer has been synthesized in an overall 29% yield from β-cyclodextrin. This compound contains a pyridine bridge that links the secondary faces of two cyclodextrin units. A complete ¹H and ¹³C NMR analysis was performed using a combination of one- and two-dimensional NMR pulse sequences. The results are consistent with the notion that each β-cyclodextrin moiety contains seven spectrally unique sugar residues. In addition, an analysis of key coupling constants suggest that the modified sugar moiety in the individual cyclodextrin units has undergone a chair inversion. This analysis represents the first complete NMR characterization of a cyclodextrin dimer. Finally, the binding properties of the cyclodextrin dimer for several guest molecules are reported. To the best of our knowledge, the association constant obtained with ethyl orange (1.6 ± 0.2 × 10⁷) represents the largest formation constant ever reported for a dye molecule with a cyclodextrin-based host.