Abstract: Amethystonal was an effectively antineoplastic, antiphlogistic and antibacterial component first isolated from the leaves of Rbdosia amethystoides(Beath) C.Y.WUet Hsuen., a Chinese herbal medicine collected in Henan province of China.The ¹³Cand ¹H NMRspectra were comepletely assigned by decoupled ¹³Cspectrum, DEPT, hetero- and homo-nuclear correlation spectra.The proton coupling constants were measured by resolution-enhanced ID-1Hspectrum and 2D-J-resolved spectrum.The interproton distances between proton i and j were calculated according to 1/r_ij⁶∝, where A_ij was the integration value of the cross peak in phase sensitive NOESYspectrum.The initial spatial structure of amethystonal in solution was computed by WUPHmethod with the structural parameters measured by NMRexperiments as input data, and the minimized three dimensional structure was obtained through the molecular mechanics calculation on the basis of WUPHcalculation.The interproton distances of each proton pairs obtained from the cross peaks in phase sensitive NOESYspectrum were calculated from the atomic coordinates, and the coupling constants of protons were predicted from the dihedral angles given by MM2 method with Karplus equation.The maximum deviation between interproton distances calculated with energy minimizing calculation and that obtained from NOESYexperimental data of amethystonal was 0.045 nm, and the root-mean-square deviation was 0.023 nm.The analysis of interproton distances together with the analysis of coupling constants indicated that the com-binization of WUPHmethod based upon the NMRexperimental data with the molecular mechanics (MM2) calculation could provide the three-dimensional structure of amethystonal in solution.

Key words: 2D-NMR, NOESY, Three-dimensional structrue in solution, Amethystonal