3-Hydroxybutyrate-containing triterpenoid saponins from Brachyscome angustifolia and their immunogenic activity.

Three unique hydroxybutyrate-containing triterpenoid saponins, angustiside A-C (1-3), were isolated from the shoots of Brachyscome angustifolia (Asteraceae). The extensive spectroscopic study showed that their aglycone is a previously undescribed one, 16-hydroxy olean-18-en-28-oic acid, named as angustic acid (1a), and 2 and 3 contain hydroxybutyrate moiety in their side chains. The absolute configuration of 1a was determined to be (3R,5R,9R,13S,16S) by X-ray crystallography. The immunity assay revealed that 2 and 3 containing both acyl chains and branched saccharides significantly enhanced the proliferation of OT-I CD8 T cells and secretion of interferon gamma (IFN-γ), presenting their immunogenic activity.