New Isoflavonoid Glycosides and Related Constituents from Astragali Radix (Astragalus membranaceus) and Their Inhibitory Activity on Nitric Oxide Production

Twenty-four secondary metabolites, induding 16 isoflavonoids, 7 astragalasides, and 1 benzoquinone, have been isolated from the roots of Astragalus membranaceus (Astragali radix). Among these isolated isoflavonoids, (-)-methylinissolin 3-O-beta-D-(6'-acetyl)-glucoside (1), (-)-methylinissolin 3-O-beta-D-{6'-[(E)-but-2-enoyl]}-glucoside (2), and calycosin 7-O-beta-D-(6-acetyl)-glucoside (3) have been identified as new compounds on the basis of spectroscopic analysis; (-)-methylinissolin 3-O-beta-D-glucoside (4) was isolated from the natural products for the first time. The nitric oxide (NO) production inhibitory activity of the major compounds has been assessed in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. To identify A. membranaceus, a fingerprint method was developed by using a high-performance liquid chromatography-evaporative light scattering detector (HPLC-ELSD) method. Furthermore, characteristic peaks for the 11 major compounds in the chromatogram were unambiguously confirmed.