Two new acetophenone derivatives named knepachycarpanone A (1) and knepachycarpanone B (2) together with a new cardanol derivative named knepachycarpanol C (3) were isolated from the EtOAc extract of Knema pachycarpa stems. Their chemical structures were established on the basis of spectral evidences. Compounds 1 and 2 exhibited moderate cytotoxicity against Hela cancer cell line with IC50 values of 26.92 ± 1.46 and 30.20 ± 1.97 μM, respectively.

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 (IC 50 = 7.25 ± 0.94 μM) and ABTS •+ (IC 50 = 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 × 10 8 M −1 s −1 ) in water at physiological pH, however it only exerts weak activity in lipid medium (k overall = 3.02 × 10 2 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.

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Samwirin A (SW), a natural compound isolated from Sambucus williamsii or Rourea harmandiana, is known to exhibit potent antiosteoporosis activity and promote cell proliferation in rat osteoblast-like UMR 106 cells. Antiosteoporosis activity suggests that the compound must also exhibit antioxidant activity but this has not been studied thus far. In the present study, the antioxidant activity of SW was examined by experimental and computational studies. It was found that SW exhibits good hydroperoxyl scavenging activity, particularly in water at physiological pH (k overall = 1.01 × 107 M–1 s–1). The single-electron transfer mechanism defines the HOO• + SW reaction in water, while the activity in the lipid medium is moderate and it follows the formal hydrogen transfer mechanism. The rate constant of the HOO• scavenging reaction in the aqueous solution is about 78 times higher than the reference compound Trolox. The computational results are in line with experimental data underscoring that SW is a promising radical scavenger in aqueous media at physiological pH.