Chemical Structure and NMR of a New Saponin from Dipsacus japonicus (Dipsacaceae)

A new triterpenoid saponin containing five sugars was isolated from the ethanolic root extract of Dipsacus japonicus Miq., and its structure was established as 3-O-［β-D-glucopyranosyl(1→4)］［α-L-rhamnopyranosyl(1→3)］-β-D-glucopyranosyl(1→3)-α-L-rhamnopyranosyl(1→2)-α-L-arabinopyranosyl-oleanoic acid. The sites of glycosylation and the sequence of sugars in the glycoside can be determined unambiguously and total assignment of severely overlapping proton resonance of sugar residues were achieved by a combined use of the 1D-SEMDY and NOE difference spectroscopy in rotating frame techniques, without having recourse to chemical degration or modification. The results showed that these new NMR techniques are very effective and convenient for the structure determination and spectral assignment of this class of compounds.