In vitro DPPH Radical Scavenging Activity of α-Pyrones from Odontonema strictum (Acanthaceae)

An ethyl acetate leaf extract from Odontonema strictum has been reported to have potent antihypertensive activity by inhibiting coronary artery contractions in porcine heart. However, the phytochemistry of the active fraction was unknown. Here we report, for the first time, the isolation and characterization of four known α-pyrones from the active fraction. The antioxidant activity of umuravumbolide (IC₅₀ = 55.7±0.027 µg/mL), deacetylumuravumbolide (IC₅₀ = 0.24±0.0002 µg/mL), dideacetylboronolide (IC₅₀ = 149±0 µg/mL) and deacetylboronolide (IC₅₀ = 24±0 µg/mL) was evaluated in vitro against 2,2-diphenyl-1-picrylhydrazyl radicals. Ascorbic acid was used as a positive control (IC₅₀ = 1.73×10^-3±0.3 µg/mL). The presence of 6-substituted 5,6-dihydro-α-pyrones and phenylpropanoid glucosides in the active fraction was suggested to be responsible for the antihypertensive activity. This is the first time that the antioxidant potential of these phytochemicals has been evaluated, and the results indicate that O. strictum has potential as an herbal medicine. Thus, further chemotaxonomic studies among the genera Odontonema and Tetradenia, a known source of α-pyrones, are recommended.