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

Abstract 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 IC 50 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.