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

Abstract

This study describes the activity-guided isolation of antimicrobial and antioxidant agents from Trilepisium madagascariense stem bark. The 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. The 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). The 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.