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

Eighteen and 31 flavonoids including flavones, flavonols, and <i>C</i>-glycosylflavones were isolated from the flowers and leaves of <i>Rhodotypos scandens</i> (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-<i>O</i>-[rhamnopyranosyl-(1→6)-glucopyranoside]-5-<i>O</i>-glucopyranoside (<b>1</b>) and luteolin 7-<i>O</i>-rhamnopyranosyl-(1→2)-glucuronopyranoside (<b>20</b>). Moreover, selected 23 flavonoids were measured the antioxidant activity by H-ORAC method. Kaempferol 3-<i>O</i>-robinobioside (<b>8</b>) showed the highest antioxidant activity (10097 mmol TE/mol). Conversely, two kaempferol 7,4'-dimethyl ether glycosides (<b>1</b> and <b>2</b>) showed the lower value (1669 mmol TE/mol). Thus, it was presumed that many flavonoids of the species act as antioxidant compounds.