Abstract: A new triterpenoid saponin was isolated from the ethanolic extract of the root of Dipsocus japonicus and its structure was established as 3-O-[β-D-glucopyrano-syl(1→4)] [α-L-rhamnopyranosyl(1→3)]-β-D-glucopyranosyl(1→3)-α-L-rhamnopyranosyl(1→2)-α-L-arabinopyranosyl-hederagenin. The results obtained showed that the chemical structure of oligosaccharide chain of the saponin could be elucidated by the combination of 1D-SEMDY and NOE difference spectroscopy in rotating frame techniques, without having recourse to chemical degration or modification. Complete assignments of severely overlapping proton resonance of the sugar residues were obtained.

Key words: Dipsocus japonicus, Structural determination of Oligosaccharide Chain, NOE difference spectroscopy in rotating frame, 1D SEMDY