A new triterpenoid saponin was isolated from the ethanolic extract of the root of Dipsacus asperoids C.Y.Cheng et T.M. A. The structure was elucidated as 3-O-α-L-rhamnopyranosyl (1--3)-β-D-ghycopyranosyl (1--3)-α-L-rhamnopyranosyl (1--2)-β-L- arabinopyranosyl-hederagenin. In the present study, 1D-SEMDY in combination with triple irradiation NOE difference spectroscopy has been successfully used for determining the glycosidation position in an aglycome moiety and the sequence of sugar moiety in the compound 1.The results obtained showed that The efficiency of magnetization transfer among the sugar residue of glycoside is much better for 1D-SEMDY than that for conventional 1D-HOHAHA and 1D-multiple relay COSY experiments. For example, for sugar residues such as arabinose which have coupling of 1-1.5 Hz between 4-H and 5-H proton, complete ^1H NMR subspectra can be obtained. This technique provides the. possibility to acquire pure- phase subspectra without the use of the Z-filter, thus allowing for identification of individual sugar components and spectra assignments in complex overlapping proton spectra. Triple irradiation NOE Difference Spectroscopy is based on the simultaneous irradiation of both lines in a doublet of the sugar] anomeric proton with a low decoupling power during the preirradiation time, by which SPT and Bloch-Siegert shift effects can be removed from difference spectra.

Key words: PROTON MAGNETIC RESONANCE SPECTROMETRY, TRITERPENE, SAPONINS, PYRANOSE, RHAMNOSE