Solvent effect in 1H NMR spectra of 3′-hydroxy-4′-methoxy isoflavonoids from Astragalus membranaceus var. mongholicus

Four 3′-hydroxy-4′-methoxy-isoflavonoids: calycosin-7-O-β-D-glucopyranoside (1), calycosin (2), pratensein-7-O-β-D-glucopyranoside (3), and pratensein (4) were isolated from Astragalus membranaceusvar.mongholicus, among which compound 4 was obtained from this plant for the first time. The solvent effect obscuring 1H signal patterns of B ring of compounds 1–4 was reported to avoid mis-assignments. Previously reported NMR data of compounds 1 and 2 were corrected based on 1D and 2D NMR experiments. Copyright © 2006 John Wiley & Sons, Ltd.