Two new flavonols, including one flavan dimer, from the roots of Indigofera stachyodes

•New flavonols (1–2) were isolated from Indigofera stachyodes.•Compound 2 was the flavonol characteristic of a 3-nitropropanoyl moiety.•2 and 3 exhibited good protective effect on CCl4-induced hepatotoxicity to HL-7702.