Triterpenoids and Flavonoids from the Leaves of Astragalus membranaceus and Their Inhibitory Effects on Nitric Oxide Production

Abstract

Four new cycloartane triterpenes, named huangqiyegenins V and VI and huangqiyenins K and L (1-4, resp.), together with nine known triterpenoids, 5-13, and eight flavonoids, 14-21, were isolated from a 70%-EtOH extract of Astragalus membranaceus leaves. The structures of the new compounds were elucidated by detailed spectroscopic analyses, and the compounds were identified as (9β,11α,16β,20R,24S)-11,16,25-trihydroxy-20,24-epoxy-9,19-cyclolanostane-3,6-dione (1), (9β,16β,24S)-16,24,25-trihydroxy-9,19-cyclolanostane-3,6-dione (2), (3β,6α,9β,16β,20R,24R)-16,25-dihydroxy-3-(β-D-xylopyranosyloxy)-20,24-epoxy-9,19-cyclolanostan-6-yl acetate (3), and (3β,6α,9β,16β,24E)-26-(β-D-glucopyranosyloxy)-16-hydroxy-3-(β-D-xylopyranosyloxy)-9,19-cyclolanost-24-en-6-yl acetate (4). All isolated compounds were evaluated for their inhibitory activities against LPS-induced NO production in RAW264.7 macrophage cells. Compounds 1-3, 14, 15, and 18 exhibited strong inhibition on LPS-induced NO release by macrophages with IC50 values of 14.4-27.1 μM.

Keywords: Astragalus membranaceus; Flavonoids; Nitric oxide; Triterpenoids.