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

•Six flavonoids were isolated from two Glycyrrhiza species.•Some of the isolates displayed potent antioxidant and/or anti-inflammatory activity.•The antioxidant and/or anti-inflammatory activities of three flavonoids were first reported.•These isolated flavonoids were quantified in four Glycyrrhiza species.

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.