Alisol C 23-acetate from the rhizome of Alisma orientale.

THE TITLE COMPOUND [SYSTEMATIC NAME: 11β-hydr-oxy-24,25-ep-oxy-3,16-oxo-protost-13 (17)-en-23-yl acetate], C(32)H(48)O(6), a protostane-type triterpenoid, was isolated from the Chinese herbal medicine alismatis rhizoma (the rhizome of Alisma orientalis Juzep). The mol-ecule contains four trans-fused rings, viz. three six-membered and one five-membered ring. Two of the six-membered rings have slightly distorted half-chair conformations, while the third exhibits a chair conformation. The five-membered ring is almost planar. An inter-molecular O-H⋯O hydrogen bond between the hydr-oxy and ep-oxy groups and intra- and intermolecular C-H⋯O hydrogen bonds are observed.