Cyclodextrin inclusion complexes of the central analgesic drug nefopam.

Inclusion complexes of nefopam base (NEF) with various beta-cyclodextrins (betaCDs) were investigated. All tested betaCDs increased the apparent solubility of NEF according to a Higuchi AL type plot (except betaCD: AN type plot), which indicates the formation of 1:1 stoichiometry inclusion complexes. 1H-NMR and 13C-NMR experiments showed that complexation by CDs allowed an easy separation of the R and S enantiomers. Based on spectral data obtained from the two-dimensional rotating frame nuclear Overhauser effect spectroscopy (2D-ROESY), a reasonable geometry for the complexes could be proposed implicating the insertion of the benzoxazocine ring into the wide end of the torus cavity.