Antioxidant Constituents and a New Triterpenoid Glycoside from Flos Lonicerae

As a component of our continuing investigations into herb-derived antioxidant agents, we have evaluated the antioxidant effects of Flos Lonicerae (Lonicera japonica flowers), via 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical, total reactive oxygen species (ROS), hydroxyl radical (¡¤OH), and peroxynitrite (ONOO¨C) assays. Among the methanolic extract and the dichloromethane, ethyl acetate, n-butanol, and water fractions, the EtOAc fraction of Flos Lonicerae exhibited marked scavenging/inhibitory activities, as follows: IC50 values of 4.37, 27.58 ¡À 0.71, 0.47 ¡À 0.05, and 12.13 ¡À 0.79 ¦Ìg/mL in the DPPH, total ROS, ONOO¨C, and ¡¤OH assays, respectively. Via a bioactivity-guided fractionation approach, a new triterpenoid glycoside, oleanolic acid 28-O-¦Á-L-rhamnopyranosyl-(1¡ú2)-[¦Â-D-xylopyranosyl(1¡ú6)]-¦Â-D-glucopyranosyl ester (12), along with eleven known compounds, including chrysoeriol (1), luteolin (2), 5- hydroxymethyl-2-furfural (3), caffeic acid (4), protocatechuic acid (5), chrysoeriol 7-O-¦Â-D-glucopyranoside (6), isorhamnetin 3-O-¦Â-D-glucopyranoside (7), kaempferol 3-O-¦Â-D-glucopyranoside (8), quercetin 3-O-¦Â-D-glucopyranoside (9), hederagenin 3-O-¦Á-L-arabinopyranoside (10), and luteolin 7-O-¦Â-D-glucopyranoside (11), were isolated from the EtOAc fraction. The structures of isolated compounds 1-12 were elucidated via spectroscopic analyses. Compound 12 was isolated from a natural source for the first time. Compounds 2, 4, 5, 7, 9, and 11 evidenced marked scavenging activities, with IC50 values of 2.08-11.76 ¦ÌM for DPPH radicals, and 1.47-6.98 ¦ÌM for ONOO¨C.

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