New ent-kaurane diterpenes with chiral epoxyangelate moieties from Wedelia prostrata

Four new ent-kaurane diterpenes with chiral epoxyangelate moieties, (2′R,3′R)-3α-(2′,3′-epoxyangeloyloxy)-kaur-16-en-19-oic acid (1), (2′S,3′S)-3α-(2′,3′-epoxyangeloyloxy)-kaur-16-en-19-oic acid (2), (2′S,3′R)-3α-(2′,3′-epoxyangeloyloxy)-kaur-16-en-19-oic acid (3) and (2′R,3′S)-3α-(2′,3′-epoxyangeloyloxy)-kaur-16-en-19-oic acid (4), along with eight known diterpenes (5−12), were isolated from Wedelia prostrata. The absolute configurations of the new structures were determined by X-ray crystallography, ECD calculations and chemical methods. All compounds were evaluated for their cytotoxicity activities on human HepG-2 cells, with IC50 values of 11.72 ± 0.22 μmol/L to 54.75 ± 1.12 μmol/L.