A Potent Antioxidant Sesquiterpene, Abelsaginol, from Abelmoschus sagittifolius: Experimental and Theoretical Insights.

The sesquiterpenoid compound abelsaginol (AS) was successfully isolated from Abelmoschus sagittifolius for the first time. The compound was identified using NMR and MS data. The antioxidant activity of AS was also evaluated both theoretically and experimentally. AS was found to be a weak HOO• radical scavenger in organic solvents such as pentyl ethanoate and dimethyl sulfoxide (k overall = ∼ 102 M-1 s-1), in a good agreement with the results of the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assay. However, AS exhibited good HOO• antiradical activity in water at pH 7.40 (k overall = 9.00 × 106 M-1 s-1) through the single-electron transfer mechanism of the anion state. Further calculations also demonstrated that AS could exert good to moderate activity against CH3O•, CH3OO•, CCl3OO•, NO2, and SO4 •- radicals, with k f values from 4.00 × 103 to 1.52 × 107 M-1 s-1. However, AS exerted much lower activity against HO•, CCl3O•, NO, O2 •-, and N3 • radicals under the studied conditions. In general, the activity of AS in water at pH 7.40 is higher than that of Trolox or butylated hydroxytoluene, which are common reference antioxidants. Thus, in an aqueous physiological milieu, AS is a promising natural antioxidant.

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 (koverall = 8.14 × 108 M-1 s-1) in water at physiological pH, however it only exerts weak activity in lipid medium (koverall = 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.