Selective binding of bile salts by β-cyclodextrin derivatives with appended quinolyl arms

Two β-cyclodextrin derivatives bearing appended quinolyl and isoquinolyl arms,i.e.mono-（6-quinolyl- 6-deoxy）-β-cyclodextrin（1） and mono-（6-isoquinolyl-6-deoxy）-β-cyclodextrin（2） were synthesized in satisfactory yields and fully characterized.Their original conformations and binding behaviors toward four bile salt guests,that is,sodium cholate（CA）,sodium deoxycholate（DCA）,sodium glycocholate （GCA）,and sodium taurocholate（TCA）,were investigated by means of fluorescence,circular dichroism and 2D NMR spectroscopy.The study of solution structures revealed that both quinolyl and isoquinolyl arms were located outside the cyclodextrin cavity.The results obtained from the fluorescence titrations showed that the binding abilities of hosts 1 and 2 with selected bile salts varied in an order of DCA 〉 CA 〉 GCA.The selective binding of hosts toward bile salt guests was discussed from the viewpoints of induced-fit and multiple binding.