[Studies on the composition and stability constant of inclusion complexes of beta-cyclodextrin with fluorouracil and ftorafur by NMR].

The composition and stability constants of the host-guest inclusion complexes of beta-cyclodextrin (beta-CD) with fluorouracil (5-Fu) and ftorafur (FT-207) were studied by 19F NMR. The 19F chemical shift changes (delta) of 5-Fu and FT-207 on complexation with beta-CD were used to determine the stoichiometry of these inclusion complexes by Job plot. It was shown that both 5-Fu and FT-207 formed 1:1 inclusion complexes with beta-CD. The stability constants (Kc) of their complexes. with beta-CD, calculated from the slope of linear relation between delta/CCD0 and delta(CCD0 being the initial concentration of beta-CD) were found to be 17.0 +/- 1.7 mol-1.L and 9.0 +/- 0.1 mol-1.L at 40 degrees C respectively. The 19F chemical shifts of these complexes relative to their free forms were also obtained and discussed in terms of the structures of these beta-CD inclusion complexes in aqueous solution.