Novel C-17 spirost protostane-type triterpenoids from Alisma plantago-aquatica with anti-inflammatory activity in Caco-2 cells

Twenty-one protostane-type triterpenoids with diverse structures, including nine new compounds (1–9), were isolated from the of Alisma plantago-aquatica Linn. Structurally, alisolides A‒F (1–6), composed of an oxole group coupled to a five-membered ring, represent unusual C-17 spirost protostane-type triterpenoids. Alisolide H (8) is a novel triterpenoid with an unreported endoperoxide bridge. Alisolide I (9) represents the first example of 23,24-acetal triterpenoid. Their structures were elucidated based on spectroscopic analysis, wherein the absolute configurations of 4‒6, 8 were further confirmed by the Mo2(OAc)4-induced ECD method. Furthermore, all isolates were evaluated for their inhibitory effects on LPS-induced NO production in Caco-2 cells, and all the compounds showed remarkable inhibitory activities, with IC50 values in the range of 0.76–38.20 μmol/L.