β-Cyclodextrin dimers linked through their secondary faces with rigid spacer arms as hosts for bile salts.

A convenient synthesis of β-cyclodextrin dimers in which the two cyclodextrin units are linked by rigid tethers of relatively short length through their secondary sides is reported. Compounds hexa-2,4-diynediyl- and 1,4-phenylenediethyne-briged β-cyclodextrin dimers are obtained in good yields from mono-2-O-propargyl-β-cyclodextrin through Pd-mediated oxidative homo- and heterocoupling reactions. Isothermal titration calorimetry and NMR spectroscopy (PGSE and 2D-ROESY) are used to determine the thermodynamic parameters (K, ΔH, and TΔS°) for the complexation of such β-cyclodextrin dimers with sodium cholate, deoxycholate, and chenodeoxycholate as well as to estimate the size of the supramolecular structures. The binding of bile salts is enhanced relative to that of native β-cyclodextrin. Although chenodeoxycholate salt binds in a 1:1 fashion, cholate and deoxycholate salts bind in a 1:2 sequential mode.