Abstract: A new triterpenoid saponin was isolated from Ardisia pusilla A. DC.which has improved immunological and antitumor and its structure established as 3-O-[β-D-xylopyranosyl (1→2) -β -D-glucopyranosyl(1→4)] [β -D-glucopyranosyl(1→2) -β-D-glucopyranosyl(1→2)]-α -L-arabinopyranosyl cyclamiretin A.The results showed that the chemical structure of oligosaccharide chains 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: Ardisia pusilla A.DC, Structural detemination of saponin, NOE difference spectroscopy in rotating frame, 1D-SEMDY