Prenylated flavonoids with antioxidative activity from Epimedium koreanum Nakai

Epimedium koreanum Nakai (Berberidaceae) has long been used to stimulate hormone secretion, to treat asthmatic attacks and menstrual irregularity in Korean folk medicine. Evaluation of antioxidant components using a DPPH free radical scavenging assay in Epimedium koreanum has led to the isolation of prenylated flavonoids through repeated column chromatographic fractionation. Chemical structures of isolated components were identified on the basis of spectroscopic methods, particularly high resolution (HR) FABMS and 1D and 2D NMR, as des-O-methylhydroicaritin 7-O-[β-D-glucopyranosyl(1→2)-β-D-glucopyranoside](1), 2“-O-Rhamnosylicariside(2), hyperoside(3), epimedin A(4), epimedin B(5), epimedin C(6), icariin(7), hexandraside E(8) and epimedoside A(9). The HR-FABMS of compound 1 indicated a molecular ion of m/z 701.2058. The presence of two two-proton doublets at δ 6.93 ppm(J=9.0Hz), δ 8.03 ppm(J=9.0Hz) and a one-proton singlet at δ 6.58 ppm, suggested that the aglycone should be based on kaempferol with a substituent carbon linked at C-8. The characteristic signals of an isopentenyl group were observed at δ 1.59 ppm and δ 1.73 ppm, each as a three-proton singlet, and at δ 3.14 ppm as a two proton multiplet. The anomeric protons of glucose residue at δ 5.18 ppm(J=8.0Hz) and δ 4.56 ppm(J=7.5Hz) were observed. Chemical shift of inner glucose at δ 81.2 ppm was connected at C-2“ of terminal glucose, since its chemical shift was downfielded. HMBC long range correlations were observed between anomeric proton at δ 5.18 ppm of inner glucose and a carbon at δ 156.9 ppm assigned to C-7, and terminal anomeric proton at δ 4.56 ppm caused a cross peak with a carbon of C-2“ at δ 81.2 ppm. The occurrence of compound 1 had not been reported previously.