Leonurusoleanolides E-J, Minor Spirocyclic Triterpenoids from Leonurus japonicus Fruits

Six new (leonurusoleanolides E-J, 1-6) and five known (7-11) nortriterpenoids were isolated and characterized from the dried fruits of Leonurus japonicus. They all contain a distinctive 19(18 -> 17)-abeo-28-noroleanane-type spirocylclic skeleton with a trans or a cis acyl substituent at C-3 or C-23. Similar to the previously known leonurusoleanolides A/B (7/8) and C/D (9/10), compounds 1/2 and 3/4 were also found to exist as equilibrium mixtures of trans and cis isomers. The isolated pure compounds and mixtures were evaluated for their cytotoxicity against a small panel of human cancer cell lines (BGC-823 and KE-97 gastric carcinoma, Huh-7 hepatocarcinoma, Jurkat T cell lymphoblasts, and MCF-7 breast adenocarcinoma) using the CellTiter-Glo luminescent cell viability assay method. Among them, (2 alpha,3 beta,17R*,18 beta)-3-O-(trans-caffeoyl)-19(18 -> 17)-abeo-28-norolean-12-ene-2,18,23-triol (leonurusoleanolide J, 6) showed the most potent cytotoxic activity, with IC50 values less than 10 mu M.