SYNTHESIS AND MOLECULAR RECOGNITION PROPERTIES OF A BETA-CYCLODEXTRIN TETRAMER

The synthesis and binding properties of a cyclodextrin tetramer are described. This species is composed of four individual cyclodextrin subunits covalently appended to a central aromatic core. The tetramer is prepared from beta-cyclodextrin in five steps in an overall 14% yield. We have performed a preliminary survey of the binding properties of this species. The structure of tetramertetraarylporphryin complexes was examined by both NMR and mass spectrometry. The results are consistent with a 1:1 stoichiometry in which the aromatic substituents of the porphyrin moiety are incorporated into the individual cyclodextrin subunits of the tetramer. The cyclodextrin tetramer exhibits a high affinity for both tetraarylporphyrins and metalloporphyrins, with binding constants as large as 10(8) M(-1). Finally, we have compared and contrasted the behavior of the tetrameric species with that of two related cyclodextrin dimers. While all of these hosts bind both porphyrins and metalloporphyrins, the tetramer exhibits a special affinity for those guests that contain a neutral inner porphyrin core.