Flavonoids from Fragaria ananassa calyx and their antioxidant capacities
The calyx of Fragaria ananassa (Rosaceae) has not been investigated for its chemical constituents and biological activity. This study focused on the isolation of active metabolites from the calyx of this plant. Compounds from F. ananassa calyx were extracted in 80 % aqueous MeOH and the concentrated extract was successively partitioned into EtOAc, n-BuOH, and H2O fractions. Repeated silica gel, octadecyl silica gel, and Sephadex LH-20 column chromatographies afforded six purified flavonoids. On the basis of spectroscopic methods, including 1H, 13C nuclear magnetic resonance spectrometry (NMR), DEPT, and 2D NMR (gCOSY, gHSQC, gHMBC), the flavonoids were identified as kaempferol (1), astragalin (2), quercetin (3), isoquercitrin (4), sexangularetin (5), and sinensin (6). All the flavonoids were isolated for the first time from the F. ananassa calyx in this study. The flavonoids were evaluated for radical-scavenging capacity 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid ammonium salt), 2,2-diphenyl-1-picrylhydrazyl, and oxygen radical absorbance capacity methods. In conclusion, quercetin (3) consistently showed the highest ABTS, DPPH, and ORAC radical-scavenging activities compared with the other isolated flavonoids.