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Abstract
Bioassay-guided fractionation of the methanol extract of the stem bark of Klainedoxa gabonensis Pierre ex Engl. (Irvingiaceae) afforded 12 compounds, namely, ellagic acid (1), ellagic acid 3,3′-dimethylether (2), gallic acid (3), methyl gallate (4), lupeol (5), β-amyrin (7), erythrodiol (8), oleanolic acid (9), betulinic acid (6), hederagenin (10), bayogenin acid (11), and stigmasterol-3-O-β-d-glucopyranoside (12). Compounds 1-3 and 7-12 were isolated for the first time from this genus. The structures were established on the basis of 1D/2D NMR experiments and mass spectrometric data. Crude extract, fractions (A, B, C and D) and pure compounds were tested for their antimicrobial activity using paper disk agar diffusion assay. The test delivered a range of low to high activities for phenolic compounds 1-4, low or missing activities for terpenoid compounds 5-11, and impressive very high antibacterial/antifungal values for two fractions C and D probably due to synergistic effects of compounds. The broth microdilution assay revealed MICs of 15.4-115.1 μg/mL for phenolic compounds, MICs higher than 1 mg/mL for terpenoids and MICs of 4.5-30.3 μg/mL for fractions C and D. The determination of the radical scavenging activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay gave high antioxidant values for the methanol extract and fraction D (IC50 10.45 and 5.50 μg/mL) as well as for the phenolic compounds 1-4 (IC50 45.50-48.25 mM) compared to the standard 3-t-butyl-4-hydroxyanisole (BHA) (IC50 44.20 mM).
Acknowledgements
This paper is dedicated to the memory of our late supervisor Professor Z. Tanee Fomum.
Declaration of interest
We wish to acknowledge the International Foundation for Science (IFS) for providing financial support (F/3978-2), Alexander von Humboldt (AvH) Foundation, Germany, for the post doctoral fellowship to J.D. Wansi and K.P. Devkota, and the European Commission for the Marie Curie IIF fellowship of B.N. Lenta.