Homoisoflavonoids from the medicinal plant Portulaca oleracea

Four homoisoflavonoids named portulacanones A-D, identified as 2'-hydroxy- 5,7-dimethoxy-3-benzyl-chroman-4-one, 2'-hydroxy-5,6,7-trimethoxy-3-benzyl-chroman-4-one, 5,2'-dihydroxy-6,7-dimethoxy-3-benzyl-chroman-4-one, and 5,2'-dihydroxy-7-methoxy-3-benzylidene-chroman-4-one, were isolated from aerial parts of the plant Portulaca oleracea along with nine other known metabolites. Their structures were established on the basis of extensive spectroscopic analyses. Portulacanones A-D is the first group of homoisoflavonoids so far reported from the family Portulacaceae. They represent a rare subclass of homoisoflavonoids in nature with a structural feature of a single hydroxyl group substituted at C-2' rather than at C-4' in ring B of the skeleton. Three homoisoflavonoids and the known compound 2,2'-dihydroxy-4',6'-dimethoxychalcone selectively showed in vitro cytotoxic activities towards four human cancer cell lines. Especially 2,2'-dihydroxy-4',6'-dimethoxychalcone showed cytotoxic activity against cell line SGC-7901 with an IC₅₀ value of 1.6 μg/ml, which was more potent than the reference compound mitomycin C (IC₅₀ 13.0 μg/ml).