Three Acylated Saponins and a Related Compound from Pithecellobium dulce

Four new oleanane-type triterpene glycosides, pithedulosides H−K (1−4), were isolated from the seeds of Pithecellobium dulce. Their structures were established by extensive NMR experiments and chemical methods. Compounds 1−3 comprised acacic acid as the aglycon and either monoterpene carboxylic acid and its xyloside or monoterpene carboxylic acid as the acyl moiety at C-21. The oligosaccharide moieties linked to C-3 and C-28 were determined as α-l-arabinopyranosyl-(l→2)-α-l-arabinopyranosyl-(1→6)-[β-d-glucopyranosyl-(l→2)]-β-d-glucopyranosyl and α-l-arabinofuranosyl-(l→4)-[β-d-glucopyranosyl-(l→3)]-α-l-rhamnopyranosyl-(l→2)-β-d-glucopyranosyl ester, respectively. Compound 4 was established as an echinocystic acid 3-O-glycoside having the same sugar sequences as 1−3. Also obtained in this investigation was the known compound 5, which was identified as echinocystic acid 3-O-β-d-xylopyranosyl-(l→2)-α-l-arabinopyranosyl-(1→6)-[β-d-glucopyranosyl-(l→2)]-β-d-glucopyranoside.