Complex Formation of Cyclomaltononaose d-Cyclodextrin (d-CD) with Macrocyclic Compounds

posed of a-1,4-linked glucose units, and a-, band g-CD, which are composed of 6, 7 and 8 glucose units, have been well studied and used in various fields because of their inclusion complex formation ability. However, their cavities are too small to form inclusion complexes with large guest molecules with molecular weights higher than several hundred. Large-ring CDs (LR-CDs) composed of more than nine glucose units do exist in nature and have large cavities. Purification of LR-CDs and portions of their X-ray crystal structure have been reported. The macrocyclic rings of a-, band g-CD are round in shape, but d-CD has a considerably warped macrocyclic ring. Recently, we studied the properties and complex formation abilities of these LR-CDs with some small compounds, but the relationship between complex forming ability and the guest molecule structure has not yet been elucidated in detail. The object of this study was to identify the structural relationship between LR-CDs and guest molecules. We selected a cyclomaltononaose (dCD) composed of nine glucose units as a LR-CD, as well as 7 kinds of macrocyclic compounds (MCCs) with 8—15 carbon atoms in the ring, as models of large guest molecules (Fig. 1). The complex forming ability of d-CD was studied in aqueous solution and compared with the complexation properties of a-, band g-CD. Preliminary structural analysis of cycloundecanone (11 carbon atoms in the ring)/d-CD complex was also performed using X-ray crystallography.