Two Undescribed Protostane Triterpenoids from the Rhizome of Alisma plantago‐aquatica

Abstract

Two undescribed protostane triterpenoids, 11‐deoxy‐13(17),15‐dehydro‐alisol B 23‐acetate (2) and alisol S (3), together with 21 known ones (1, 4‐23), were isolated from the dried rhizome of Alisma plantago‐aquatica. Of these compounds, 13(17),15‐Dehydro‐alisol B 23‐acetate (1) and 11‐deoxy‐alisol Q 23‐acetate (2) are two protostane trierpenoids containing conjugated double bonds in the five‐membered ring D that are rarely found from nature resource, while alisol S (3) is a protostane triterpenoid with undescribed tetrahydrofuran moiety linked via C20‐O‐C24 at the side chain. Additionally, compound 18 is a new natural product, and cycloartenol triterpenoid 23 is a non protostane triterpenoid firstly isolated from genus Alisma. Their structures were elucidated by extensive spectral analysis of the UV, IR, MS, 1D and 2D NMR, and comparison of the experimental and calculated CD curves.