Antioxidant and antibacterial effects of a new macrocyclic bis(bibenzyl) ether from Combretum molle (Combretaceae)

A new compound, combrebisbibenzyl (1) as well as two sterols including stigmasterol (2) and 3-O-β-D-glucopyranoside of β-sitosterol (3) and seven triterpenoids namely mollic acid (4), oleanolic acid (5), ursolic acid (6), arjunglucoside I (7), arjungenin (8), bellericagenin B (9) and combregenin (10) were isolated from the root of Combretum molle. Compounds 1, 7 and 9, AcOEt and MeOH extracts exhibited moderate antioxidant activity with an IC₅₀ value of 179.32, 185.21, 195.11 197.41 and 170.21 μg/mL, respectively, for reactive oxygen species inhibition and, inhibition percent value of 57.23, 64.52, 53.55, 67.42 and 65.04, respectively, for DPPH free-radical scavenging. The E. MeOH presented a moderate antibacterial activity against Staphylococcus aureus with DIZs value of 10.1 ± 0.2 from 800 μg/mL while the others tested strains were not sensitive. However, most of the tested bacteria, (S. aureus, Escherichia coli and Salmonella typhimurium) were moderately sensitive to E. AcOEt from 800 μg/mL with DIZs value of 8.2 ± 0.1. From the E. AcOEt, five of the isolated compounds were tested against four bacteria strains using the disc-dilusion method. The results showed that compound 1 and 2 exhibited very good antibacterial activity against all the tested bacteria at the concentration of 30 μg/mL with respective DIZ value of 22.2 and 25.4 for E. coli, 20.2 and 30.2 for S. typhimurium, 22.3 and 23.1 for S. aureus and, 22.1 and 24.1 for Streptococcus faecalis. This antibacterial activity significantly depends on the concentration.