Phenolics from Mikania micrantha and Their Antioxidant Activity.

A phytochemical study on the aerial parts of led to the isolation of two new phenolic compounds, benzyl 5--β-d-glucopyranosyl-2,5-dihydroxybenzoate () and (7,8)--dihydroxydehydrodiconiferyl alcohol 9-acetate (), together with twelve known compounds, benzyl 2--β-d-glucopyranosyl-2,6-dihydroxybenzoate (), 4-allyl-2,6-dimethoxyphenol glucoside (), (+)-isolariciresinol (), icariol A₂ (), 9,10-dihydroxythymol (), 8,9,10-trihydroxythymol (), caffeic acid (), -coumaric acid (), ethyl protocatechuate (), procatechuic aldehyde (), 4-hydroxybenzoic acid (), and hydroquinone (). Their structures were elucidated on the basis of extensive spectroscopic analysis. Except and , all the other compounds were isolated from this plant species for the first time. The antioxidant activity of those isolated compounds were evaluated using three different assays. Compounds , , , , , , and demonstrated significant 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) free radical cation scavenging activity ranging from SC 0.31 to 4.86 µM, which were more potent than l-ascorbic acid (SC = 10.48 µM). Compounds , , , and exhibited more potent 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (SC = 16.24-21.67 µM) than l-ascorbic acid (39.48 µM). Moreover, the ferric reducing antioxidant power (FRAP) of compounds , , , and were discovered to be also comparable to or even more potent than l-ascorbic acid.