Liquid chromatography–electrospray ionization mass spectrometry study of the flavonoids of the roots of Astragalus mongholicus and A. membranaceus

High-performance liquid chromatography–electrospray ionization mass spectrometry has been applied to analyze the flavonoids of Huangqi, the roots of Astagalus mongholicus and A. membranaceus. Eight flavonoids were identified as calycosin-7-O-β-d-glucoside, calycosin-7-O-β-d-glucoside-6″-O-malonate (2), ononin, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan-3-O-β-d-glucoside, calycosin, (3R)-7,2′-dihydroxy-3′,4′-dimethoxyisoflavan-7-O-β-d-glucoside, formononetin-7-O-β-d-glucoside-6″-O-malonate and formononetin by direct comparison with the isolated standards from Huangqi. The existence of (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan, (3R)-7,2′-dihydroxy-3′,4′-dimethoxyisoflavan, astrapterocarpanglucoside-6′-O-malonate and astraisoflavanglucoside-6′-O-malonate was detected. This is the first report of flavonoid glycoside malonates in these two Astragalus species, and malonate 2 is a structurally completely identified new compound.