Phenolic antioxidants from Rosa soulieana flowers.

Rosa soulieana has been widely used in traditional medicine to treat cardiovascular disorders. In this study, antioxidant activity-guided fractionation and purification of the methanol extract from the flowers of R. soulieana has led to the isolation of nine phenolic antioxidants, which were identified as catechin (1), tiliroside (2), astragalin (3), isoquercitrin (4), nicotiflorin (5), eugenol 4-O-β-d-(6'-O-galloyl) glucoside (6), michehedyosides D (7), citrusin C (8) and strictinin (9), respectively. Among them, compounds 5-9 were reported from the genus Rosa for the first time. All the compounds were also assayed by in vitro ABTS [2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt] radical cation scavenging activity. Among these bioactive isolates (1-9), compounds 1, 6, 7 and 9 exhibited strong scavenging activity in ABTS (SC50 = 10.17, 7.38, 8.60, 4.72 μmol/L, respectively) compared with the positive control l-ascorbic acid (SC50 = 15.97 μmol/L).