Chem. Pharm. Bull. 52(6) 708—713 (2004)

rides, the best known being cyclodextrin. Other cyclic oligosaccharides have been prepared by means of enzymes and chemical syntheses. Cyclo-[→6]-a -D-glucopyranosyl-(1→3)-a -D-glucopyranosyl-(1→6)-a -D-glucopyranosyl-(1→3)-a -D-glucopyranosyl-(1→), a cyclic tetrasaccharide (CTS), is prepared by enzymic hydrolysis of the polysaccharide alternan. Recently, CTS has also been synthesized by glycosyltransferase. This tetrasaccharide attracts increased interest due to relative resistance to microbial and enzymic degradation. Most of the signals in proton and carbon NMR spectra were assigned. The structure of CTS was determined by X-ray analysis of single crystals and molecular dynamics simulations: CTS has a plate shape. Cyclodextrins can entrap many compounds in their cavities. As a result, cyclodextrin is an interesting host compound from the academic viewpoint and is applied in chemicals, pharmaceuticals and foods industries. Cyclogentiotetraose peracetate, a cyclic tetrasaccharide, can bind alkali cations in organic solvents. The ability of CTS to bind metal cations in aqueous solutions has very recently been investigated. To our knowledge, there is no report on the affinity of CTS (Fig. 1) to organic compounds. In the present work, we aimed to estimate the three-dimensional structure of CTS in aqueous solution by proton NMR and molecular mechanics calculations as well as the inclusion property of CTS. The assignment of H6S and H6R was established by spectral simulations and the vicinal spin–spin coupling constants J5–6S and J5–6R were determined. These data revealed a clear difference in the internal rotation of the C5–C6 bond between the crystal and solution structures. The rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectrum of CTS was compared with the crystal structure and the structures predicted by molecular mechanics in the presence and absence of water. Because the cavity of CTS is very small, large organic compounds will be not accommodated therein. Therefore we chose ethanol, a relatively small organic molecule and investigated complex formation between it and CTS on the basis of chemical shift data.