Discovery of new dammarane saponins from Actinostemma lobatum: C-3 monoglucosylation governs α-glucosidase inhibition

Abstract

Four new dammarane saponins, named actinostemmosides L-O (1–4), together with five known analogues (5–9), were isolated from the whole plant of Actinostemma lobatum. Their structures were established by HR-ESI-MS, exhaustive 1D/2D-NMR, and chemical methods. All nine saponins exhibited α-glucosidase inhibitory activity (IC₅₀ 40.3–150.9 μM), with actinostemmoside L (1) exhibiting an IC₅₀ of 40.3 μM—twice the potency of acarbose (84.6 μM)—while 5 and 6 were equipotent with the drug. These results expand the chemical space of dammarane saponins and establish A. lobatum as a renewable source of α-glucosidase inhibitors.