Bio-guided isolation of potential antimicrobial and antioxidant agents from the stem bark of Trilepisium madagascariense

AimThis study describes the activity-guided isolation of antimicrobial and antioxidant agents from Trilepisium madagascariense stem bark.MethodsThe methanol crude extract of T. madagascariense was partitioned sequentially into n-hexane, ethyl acetate, n-butanol and the residual aqueous fractions. The ethyl acetate fraction was subjected to column chromatography and the structures of isolated compounds were elucidated using GC–MS and/or NMR data by comparing with those reported in the literature. Antimicrobial activity was assayed by agar well diffusion and broth microdilution techniques on 8 bacteria and 10 yeasts. The antioxidant activity was determined by DPPH radical scavenging method.ResultsThe bioassay-guided fractionation of the crude methanol extract of T. madagascariense afforded two known compounds [vanillic acid (1) and isoliquiritigenin (2)] and two mixtures of fatty acids (n-hexane fraction and first column fraction of ethyl acetate fraction, F1). The fractionation of the crude methanol extract enhanced the antimicrobial activity. Compound 2 was generally more active than compound 1. For all the tested samples, the most sensitive microbes were Enterococcus faecalis ATCC 10541 (MIC range of 60–780 μg/ml) for bacteria and Candida guillermondi (MIC range of 0.01–190 μg/ml) for yeasts. The DPPH radical scavenging activity (RSa) of compound 2 (RSa50 = 28.73 μg/ml) was comparable to that of the crude methanol extract (RSa50 = 29.92 μg/ml).ConclusionThe antimicrobial activities and the antioxidant properties of the methanol crude extract, fractions and compounds 1 and 2 from the stem bark of T. madagascariense are being reported for the first time. These results may justify the traditional use of this plant for the treatment of gastrointestinal disorders.

Research Highlights► This research work entitled “Bio-guided isolation of potential antimicrobial and antioxidant agents from the stem bark of Trilepisium madagascariense” deals with the preparation of methanol crude extract of the powdered stem bark, fractionating sequentially this crude extract (with n-hexane, ethyl acetate and n-butanol). ► The evaluation of the extract and resultant fractions for antibacterial, antifungal and antioxidant activities. ► The most active fraction (ethyl acetate fraction) was further subjected to a series of column chromatography guided by the antimicrobial activities of the collected column subfractions. ► The fractionation steps led to the isolation of two compounds: vanillic acid and isoliquiritigenin, both having antimicrobial and antioxidant activities.