Synthesis, conformation, and binding properties of cyclodextrin homo- and heterodimers connected through their secondary sides

Abstract

The synthesis of homo- and heterocyclodextrin (CD) dimers, containing two CD moieties that are linked through their secondary sides by alipathic or 2,2'-bipyridyl spacers is described. In these dimers, the glucose units to which the spacers are linked have been transformed into altrose units. The dimers with an octamyethylene spacer show self-complexation of the spacer in one of the CD moieties in aqueous solution, as revealed by 1H and 13C NMR spectroscopy. Using high-resolution (600 and 800 MHz) NMR spectroscopy and a variety of 2D NMR techniques, an assignment of nearly all of the 1H NMR signals of two of the CD dimers was made, affording detailed information about the structure of these compounds in water. The self-inclusion of the spacers leads to lower binding affinities for ditopic guest molecules like p- toluidino-6-naphthalene sulfonate (TNS) derivatives and porphyrins. When a rigid 2,2'-bipyridyl group is used to connect the two CD moieties, self- inclusion of the spacer is not possible. This results in the formation of different complexes with ditopic guest molecules, for example, a 2:2 complex with a porphyrin. The CD heterodimers described in this paper contain an α- CD and a β-CD moiety. These dimers display site-specific binding of guest molecules.