Mechanistic and Kinetic Studies of the Radical Scavenging Activity of 5‑O‑Methylnorbergenin: Theoretical and Experimental Insights

5-O-Methylnorbergenin (5-OMB), a natural compound isolated from Rourea harmandiana, is a compound with potential antioxidant activity based on its chemical structure; however, this activity has not been investigated thus far. In this study, the antioxidant activity of 5-OMB was evaluated by experimental and computational methods. 5-OMB exhibited high activity in DPPH (IC₅₀ = 7.25 ± 0.94 μM) and ABTS^•+ (IC₅₀ = 4.23 ± 0.12 μM) assays, higher than the reference compound Trolox. The computational results consistently show that 5-OMB is an excellent HOO^• radical scavenger (k_overall = 8.14 × 10⁸ M^–1 s^–1) in water at physiological pH, however it only exerts weak activity in lipid medium (k_overall = 3.02 × 10² M^–1 s^–1). The reaction follows the formal hydrogen transfer mechanism in nonpolar solvents, whereas both the sequential proton loss electron transfer and the formal hydrogen transfer pathways contribute to the activity in aqueous solution. There is a good agreement between experimental and computational data, suggesting that 5-OMB is a promising natural radical scavenger in aqueous physiological environment.