Studies on the Constituents of Thladiantha dubia BUNGE. I. : The Structures of Dubiosides A, B and C, the Quillaic Acid Glucuronide Saponins Isolated from the Tuber

Abstract

Three bisdesmosidic glucuronide saponins of quillaic acid, named dubiosides A, B and C, were isolated as their methyl esters from the tuber of Thladiantha dubia BUNGE(Cucurbitaceae). Their structures were elucidated on the basis of chemical and spectral evidence.All the dubiosides have a common prosapogenin structure, quillaic acid-3-O-β-D-galactopyranosyl(1→2)-β-D-glucuronopyranoside, and differ only in the structures of the 28-O-linked sugar moieties. Dubioside A is a 28-O-α-L-rhamnopyranosyl(1→2)-α-L-arabinopyranoside, dubioside B, a 28-O-β-D-xylopyranosyl(1→4)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside and dubioside C, a 28-O-β-D-xylopyranosyl(1→3)-β-D-xylopyranosyl(1→4)-α-L-rham-nopyranosyl(1→2)-α-L-arabinopyranoside.