Novel flavonolignans from the roots of Indigofera stachyodes

Two pairs of new enantiomeric flavonolignans, ±stachyols A and B (±1 and ± 2), along with two novel isoflavanelignans, stachyols C and D (3 and 4) were isolated from the roots of Indigofera stachyodes. Their chemical structures and absolute configurations were determined using nuclear magnetic resonance and comparison of experimental and theoretical electronic circular dichroism (ECD) spectra, as well as quantum chemical calculations. Of those compounds, 1 and 2 represented the first examples of flavonolignans with 5-deoxyflavonoids adduct phenylpropanoids. Moreover, 3 and 4 possess an unprecedented skeleton with isoflavanes adduct phenylpropanoids. The antioxidant activity was evaluated for all compounds in terms of ABTS⁺ and DPPH bioassays. Compounds 3 and 4 exhibited significant radical-scavenging activity in the ABTS⁺ assay, with IC₅₀ values of 15.15 and 5.83 μM, respectively.