Free radical scavenging activities of verbascoside and isoverbascoside from the leaves of Odontonema strictum (Acanthaceae).

The aqueous extract of the leaves of Odontonema strictum, a plant from tropical regions, is used by traditional physicians in Burkina Faso for its antihypertensive properties. Verbascoside and isoverbascoside, known phenylpropanoid glycosides with high solubility in water, have been isolated from the leaves. We evaluated their antioxidant properties in vitro by radical scavenging using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide (HO). Verbascoside and isoverbascoside demonstrated high levels of DPPH radical scavenging activity, with IC values of 0.09 ± 0.03 μg/mL and 0.16 ± 0.07 μg/mL, respectively, compared to 0.05 ± 0.0 μg/mL for ascorbic acid as a control. These two phenylpropanoid glycosides were also more potent (2.6 ± 0.36 μg/mL and 3.0 ± 0.01 μg/mL) in scavenging HO than the ascorbic acid control (4.1 ± 0.97 µg/mL). This is the first time that the antioxidant properties of verbascoside and isoverbascoside from O. strictum have been evaluated. These results can explain the use of this plant for hypertension in folk medicine.