Antimicrobial and Antioxidant Properties of kaempferol-3-O-glucoside and 1-(4-Hydroxyphenyl)-3-phenylpropan-1-one Isolated from the Leaves of Annona muricata (Linn.)

Aim: To evaluate the antimicrobial and antioxidant activities of bioactive compounds isolated from Annona muricata (Linn.) leaf extract.

Study Design: In vitro antimicrobial assay of bioactive compounds isolated from solvent fractions of plant leaf extract against selected clinical bacterial and fungal isolates. Antioxidant assay of plant leaf extract.

Place and Duration of Study: All the work was carried out in the Departments of Chemistry and Microbiology, Obafemi Awolowo University, Ile-Ife, Nigeria between March, 2015 and January, 2016.

Methodology: Isolation of bioactive compounds was by column and thin layer chromatographic techniques. Isolated compounds were characterized by nuclear magnetic resonance spectroscopic analysis. Antimicrobial activities were evaluated by disc diffusion and broth microdilution methods while antioxidant activity was investigated using the 2,2-dipheny-1-picrylhydrazyl (DPPH) radical-scavenging assay.

Results: Two compounds kaempferol-3-O-glucoside (1) and 1-(4-Hydroxyphenyl)-3-Phenylpropan-1-one (2) were isolated from the ethyl acetate fraction of leaf extract of A. muricata. The two compounds showed broad spectrum antimicrobial activities with zones of inhibition ranging from 26.00 ± 1.73 to 31 ± 1.00 mm and 17.33 ± 1.15 to 31.33 ± 1.15 mm respectively, for compounds 1 and 2 for the test bacteria species and 15.33 ± 1.15 to 31.33 ± 1.15 mm and 17.67 ± 0.58 to 29.67 ±1.53 mm respectively, for compounds 1 and 2 for the test fungi. Minimum inhibitory concentrations ranged between 0.625-5.00 µg/mL and 1.25-5.00 µg/ml respectively, for compounds 1 and 2. Minimum bactericidal concentrations ranged between 2.5-10.00 µg/mL for both compounds which compared favourably with the reference drugs used. DPPH radical-scavenging activities were IC50 = 13.41 ± 0.64 µg/mL and 7.42 ± 0.90 µg/mL for compounds 1 and 2 respectively, compared with IC50 = 51.99 ± 1.44 µg/ml obtained for the standard ascorbic acid. The results show that both isolated compounds from A. muricata leaf possess in vitro antimicrobial and antioxidant properties and they may be useful as active ingredients in antimicrobial drug formulations and as agents for the control of free radical-related pathological disorders.