Schistosomicidal and antioxidant flavonoids from Astragalus englerianus.

Astragalus englerianus is a close relative of the traditional Chinese medicine plant Radix Astragali (Huang-qi) and is mainly distributed in Yunnan. It has been traditionally used as a substitute of "Huang-qi" for reducing fatigue and enhancing immunity by local folks. A phytochemical study of the methanol extract of the roots led to the isolation of three new flavonoids including one aurone (1) and two chalcones (2 and 3), as well as two known flavonoids (4 and 5). Their structures were elucidated based on the analyses of extensive spectroscopic data and comparison of their physicochemical properties. This is the first report on the occurrence of β-hydroxydihydrochalcone, 2',5'-dioxygenchalcones, and 2',5'-dioxygenaurone in the genus Astragalus. All the isolated compounds were tested in vitro for their schistosomicidal and antioxidant activities. Compounds 2 and 4 showed schistosomicidal activities with worm mortality rates of 100 % within 12 h in a drug-containing (0.70 and 0.77 mM, respectively) RPMI 1640 medium. Compounds 1 and 2 exhibited antioxidant activities in 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl free radical scavenging assays, with IC50 values of 35.9 ± 1.1 and 12.2 ± 1.1 µM, respectively.