Antioxidant and anti-inflammatory activities of six flavonoids separated from licorice

Licorice, the roots and rhizomes of several Glycyrrhiza species (Leguminosae), is an important natural sweetening agent and a widely used herbal medicine. In this work, six flavonoids, 5-(1,1-dimethylallyl)-3,4,4′-trihydroxy-2-methoxychalcone (1), licochalcone B (2), licochalcone A (3), echinatin (4), glycycoumarin (5) and glyurallin B (6), were isolated from the extracts of licorice (Glycyrrhiza inflata and Glycyrrhiza uralensis). Their structures were elucidated using various spectroscopic methods. To our knowledge, compound 1 was isolated from natural plants for the first time. All the isolates were tested by antioxidant and anti-inflammatory assays. Compounds 2, 4 and 5 showed strong scavenging activity toward the ABTS+ radical, and compounds 1, 2, 3, 5 and 6 exhibited potent inhibition of lipid peroxidation in rat liver microsomes compared with the reference controls. Compounds 1–4 dose-dependently inhibited LPS induced reactive oxygen species (ROS) production in RAW 264.7 cells. Furthermore, compounds 1–5 were demonstrated to inhibit the production of nitric oxide (NO), interleukin-6 (IL-6) and prostaglandin E2 (PGE2) in LPS-induced macrophage cells. Moreover, the contents of the six compounds, in different Glycyrrhiza species, were quantified by HPLC–MS.