Iridoids from Canthium subcordatum iso-butanol fraction with potent biological activities

The continuous emergence of multi-drug-resistant bacteria drastically reduces the efficacy of antibiotic armory and, consequently, increases the frequency of therapeutic failure. The discovery of new antibacterial drugs is an urgent need. The present study reports the antibacterial and antioxidant activities of the methanol extract, fractions and iridoids from Canthium subcordatum, a plant traditionally used as antidiabetic, anti-inflammatory, and antimicrobial. Broth microdilution assay was used to determine minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of extracts and iridoids against Staphylococcus aureus, Vibrio cholerae and Shigella flexneri. Antioxidant activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and gallic acid equivalent antioxidant capacity (GAEAC) assays. The samples were also tested for their cytotoxicity against human red blood cells (RBC). The methanol extract, hexane, ethyl acetate and iso- butanol fractions from C. subcordatum fruits displayed different degrees of antioxidant (EC 50 = 62.83–70.17 μg/ml; GAEAC = 45.63–58.23 μg/ml) and antibacterial (MIC = 128–512 μg/ml) activities. Canthiumoside 1( 1 ) and linearin ( 7 ) were the most active antioxidant (EC 50 = 1.12–2.03 μg/ml; GAEAC = 79.82–92.35 μg/ml) and antibacterial (MIC = 8–64 μg/ml) compounds while the most sensitive bacterium was Staphylococcus aureus . The tested samples were non-toxic to normal cells. Our results demonstrated that compounds 1 and 7 were potent antibacterial agents and DPPH/ABTS· + radical scavengers, so they warrant further investigation.