Isolation and characterization of antimicrobial compounds from berries of Harrisonia abyssinica (Simaroubaceae).

Abstract

Plants are a potential source of antimicrobial compounds. In this study, a plant from the family Simaroubaceae, Harrisonia abyssinica, traditionally used to treat a number of diseases was used. Research has been carried out on its stem bark, root bark and leaves and a number of chemical constituents have been isolated but no research has been carried out on its berries. Therefore the berries of this plant were chosen in order to investigate for antimicrobial compounds. The berries of the plants were collected, defatted using hexane and extracted using a mixture of methanol and dichloromethane solvents in a ratio of 1:1. The extract was screened for antimicrobial activity (agar diffusion assay) and it was found to have significant activity against tested microorganisms. Fractionation by column chromatography yielded 35 fractions that were pooled to three main fractions by the aid of TLC analysis. The three were further purified by repeated column chromatography and gel filtration method. The pure compounds were coded HRF1, HRF2 and HRF3 and they were subjected to antimicrobial (agar diffusion assay) to confirm their antimicrobial activity. Compound HRF1 showed substantial activity and therefore was chosen and screened for its antimicrobial activity using serial dilution assay. The compound was found to have a minimum inhibitory concentration (MIC) of 5 μg/ml against Candida albicans, 6 μg/ml against Bacillus cereus and >20 μg/ml against other test microorganisms. The compounds were subjected to spectroscopic techniques; 1D NMR (1H NMR, 13C NMR), 2D NMR (COSY, DEPT, HSQC, HMBC and NOESY). HRF2 and HRF3 were found to obtain similar spectral features a part from the noise signals in HRF2 hence was found to be the same compound. The structures were confirmed using HRESIMS spectrometry. Compound HRF1 was named harronin I and HRF3 as harronin II, these compounds belong to a class of acetophenones and they are being isolated for the first time.