Isolation and characterization of antimicrobial constituents of Searsia chirindensis L. (Anacardiaceae) leaf extracts

Abstract

Ethnopharmacological relevance: Searsia chirindensis is used in South African traditional medicine for management of bacterial infections such as diarrhoea. Aim of the study was to examine the phytochemical composition from the leaves of Searsia chirindensis that is responsible for the ethnomedicinal use of this plant.

Materials and methods: The crude extract (80% methanol) was extracted sequentially with dichloromethane (DCM), ethyl acetate (EtOAc) and n-butanol. The extracts and isolated compounds were tested for their antibacterial activity against Gram-negative (Campylobacter jejuni, Escherichia coli and Shigella flexneri) and Gram-positive (Staphylococcus aureus) bacterial strains using the microdilution method. Bioguided fractionation of EtOAc fraction afforded five phenolic compounds. Structural elucidation was carried out using NMR (1D and 2D) spectroscopic analyses.

Results: Of the three fractions obtained from the crude extract, EtOAc was the most active and its fractionation afforded methyl gallate (1), and four flavonol glycosides: myricetin-3-O-arabinopyranoside (2), myricetrin-3-O-rhamnoside (3), kaempferol-3-O-rhamnoside (4) and quercetin-3-O-arabinofuranoside (5). These compounds are reported from Searsia chirindensis for the first time. All the compounds showed good antibacterial activity against all bacterial strains tested. Their minimum inhibitory concentrations ranged from 30 to 250 µg/mL.

Conclusions: Antibacterial activity demonstrated by the extracts and isolated compounds provides credence to the ethnomedicinal use of Searsia chirindensis against diarrhoea.

Keywords: AIDS; ATCC; American type culture collection; Anacardiaceae; Antimicrobial; CFU; DCM; Diarrhoea; EtOAc; Flavonol glycosides; HIV; INT; MH; MHz; MIC; MeOH; Mueller-hinton; NMR; No.1; Searsia chirindensis; TLC; UKZN; University of KwaZulu-Natal; WHO; World Health Organization; acquired immunodeficiency syndrome; colony forming unit; dichloromethane; ethyl acetate; human immunodeficiency virus; iodonitrotetrazolium chloride; megahertz; methanol; minimum inhibition concentration; nuclear magnetic resonance; number 1; part per million; ppm; thin layer chromatography.