Flavonoids from the flowers and leaves of Rhodotypos scandens (Thunb.) Makino (Rosaceae) and their antioxidant activity

Eighteen and 31 flavonoids including flavones, flavonols, and C-glycosylflavones were isolated from the flowers and leaves of Rhodotypos scandens (Thunb.) Makino, respectively, and identified by UV, HR-MS, LC-MS, acid hydrolysis, NMR, and TLC and HPLC comparisons with authentic samples. Among them, two flavonoids were new compounds and identified as kaempferol 7,4'-dimethyl ether 3-O-[rhamnopyranosyl-(1→6)-glucopyranoside]-5-O-glucopyranoside (1) and luteolin 7-O-rhamnopyranosyl-(1→2)-glucuronopyranoside (20). Moreover, selected 23 flavonoids were measured the antioxidant activity by H-ORAC method. Kaempferol 3-O-robinobioside (8) showed the highest antioxidant activity (10097 mmol TE/mol). Conversely, two kaempferol 7,4'-dimethyl ether glycosides (1 and 2) showed the lower value (1669 mmol TE/mol). Thus, it was presumed that many flavonoids of the species act as antioxidant compounds.