Antibacterial and antioxidant activities of Hammada scoparia extracts and its major purified alkaloids

•Tunisian H. scoparia methanolic extract showed strong antibacterial and antioxidant activities.•Fractionation of H. scoparia extract afforded two alkaloids, the Carnegine, and N-methylisosalsoline.•Carnegine showed strong antibacterial activity compared to N-methylisosalsoline.•Time-kill curve of Carnegine showed a potent bactericidal effect.•N-methylisosalsoline exhibited strong antioxidant activity.

This study describes the antimicrobial and antioxidant activities of the extracts of Hammada scoparia (H. scoparia) and its major alkaloids. Total phenolic content showed that the hydroethanolic extract has the highest phenolic concentration (75.32 mg GAE/g) followed by methanolic extract (59.75 mg GAE/g) and the dichloromethane one with a concentration of 35.23 mg GAE/g. The antioxidant activities exhibited by the hydroethanolic extract and the organic ones were assessed by three methods 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene–linoleic acid system, and reducing activity. The hydroethanolic extract showed the highest scavenging activity (EC50 = 24 μg/mL) and a strong β-carotene–linoleate inhibition, better than the activities of the organic extracts. All the extracts, except of the hexane one, showed antibacterial activity against both Gram-positive and Gram-negative microorganisms with diameter inhibition zones ranged from 8 to 30 mm. The fractionation of the crude extract of H. scoparia afforded two major compounds, carnegine (1) and N-methylisosalsoline (2). The study of their antimicrobial activity showed that the carnegine was more active with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) ranging from 0.125 to 0.5 mg/mL and 0.25–2 mg/mL, respectively. The time-kill curves of carnegine showed a potent and rapid bactericidal activity. The investigation of the antioxidant activity of these two alkaloids showed that, contrarily to the carnegine, the N-methylisosalsoline exhibited an antioxidant activity. The structure–activity relationship of these alkaloids was discussed.