NMR determination of the structure of Julibroside J1

Julibroside J1 is a new triterpenoid saponin which contains one triterpene, two monoterpenes and nine sugar residues. The structure has been determined almost exclusively by high-resolution NMR methods. The 1H and 13C NMR spectra of Julibroside J1 C5D5N have been assigned by homonuclear and heteronuclear correlation experiments, such as COSY, CH-COSY, TOCSY, HMBC, HMQC-COSY, HMQC-TOCSY and NOESY. Anomeric configurations were obtained by combined use of 1JCH and 3JH1,H2 and NOESY data. The particular sugar residues were identified by utilizing 3JHH values obtained from TOCSY cross-peaks, NOE difference spectra, and several 1D-TOCSY spectra, and three-bond intra-ring cross-peaks from a HMBC spectrum. Linkage assignments were made using the HMBC spectrum, and supplemented by NOE data from the NOESY spectrum. The structure of Julibroside J1 was characterized as 3-O-[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl-(1 → 6)-β-d-glucopyranosyl]-21-O-{(6S)-2-trans-2-hydroxymethyl-6- methyl-6-O-[4-O-((6S)-2-trans-2,6-dimethyl-6-O-(6-deoxy-β-d- glucopyranosy)-2,7-octadienoyl)-6-deoxy-β-d- glycopyranosyl]-2,7-octadienoyl}-acacic acid28-O-{β-d-glucopyranosyl-(1 → 3)-[α-l-arabinofuranosyl-(1 → 4)]-α-l-rhamnopyranosyl-(1 → 2)}-β-d-glucopyranosyl ester.