Two Triterpenoid Saponins with alpha-glucosidase Inhibitory Activity from Harpullia pendula Seed Extract

Background: Harpullia pendula Planch (family Sapindaceae) is a small to medium rainforest tree native to Australia. Objective: This study aims to isolate triterpenoid saponins from H. pendula and test them as α-glucosidase inhibitors. Materials and Methods: The saponin compounds were obtained using variable chromatographic techniques and characterized by spectral analysis. Results: Two new triterpenoid saponins were obtained as an inseparable mixture from H. pendula methanolic seed extract. Their structures were determined as 3-O-β-D-glucopyranosyl-(1→2)-[α-L-arabinofuranosyl-(1→3)]-βD-glucuronopyranosyl22-OangeloylA1- barrigenol and 3-O-β-D-galactopyranosyl-(1→2)-[α-L-arabinofuranosyl-(1→3)]-β-Dglucuronopyranosyl 22-O-(2-methylbutyroyl)-A1 barrigenol, respectively. The triterpene part 22-O-(2-methyl butyroyl) A1-barrigenol has never been characterized before. The α- glucosidase inhibitory activity of the two saponin mixture was evaluated invitro and proved to exhibit strong activity with IC₅₀ value equals to 13.3 ± 5.0 ppm and IC₉₀ value equals to 21.5 ± 8.0 ppm. Conclusion: Two new saponins were characterized from their mixture and found to exhibit α-glucosidase inhibitory activity.