A syringic acid derivative and two iridoid glycosides from the roots of <i>Stachys geobombycis</i> and their antioxidant properties

<p>A new derivative of syringic acid, stageobester A (<b>1</b>) and two iridoid glycosides which including a new one, stageoboside A (<b>2</b>), were isolated from the roots of <i>Stachys geobombycis</i>. Their structures were elucidated on the basis of spectroscopic methods, including extensive NMR and MS spectra. In addition, all the isolates were tested for their antioxidant capacity. Compounds <b>1</b> and <b>2</b> showed moderate antioxidant activities against DPPH radical, with IC₅₀ values of 113.33 ± 1.53 and 40.33 ± 2.08 mg/L, respectively.