Chemical constituents of Millettia barteri and their antimicrobial and antioxidant activities

Context: Millettia barteri (Benth.) Dunn (Fabaceae) is an African medicinal plant used in folk medicine to treat many diseases. This species, as well as other Mellettia species, has been of interest to researchers because of their wide range of traditional uses. Objective: Phytochemical, antimicrobial and 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH)-radical scavenging investigations of the hexane and EtOAc extracts of the stem bark of M. barteri were carried out here for the first time. Materials and methods: The isolation of compounds was done through silica gel column chromatography and their structures were established using spectroscopic analysis, especially, 1D NMR in conjunction with 2D experiments (COSY, HMQC and HMBC), and physical data compared with literature values. The broth micro dilution method was used for antimicrobial test while DPPH radical scavenging assay was used for antioxidant test. Results: Seven compounds, including two guanidine alkaloids: millaurine (2) and milletonine (7); one flavonoid: afzelin (6); four sterols: β-sitosterol (1), β-sitosterol glucoside (3), mixture of stigmasterol (4) and β-sitosterol (5) palmitates have been isolated from stem bark of hexane and ethyl acetate extracts of M. barteri. These extracts showed antimicrobial activity on the set of germs tested with minimum inhibitory concentration values varying from 64 to 512 g/mL, as well as antioxidant activity (IC50 62.74 and 77.23 g/mL). Compounds 2 and 7, tested for the first time, demonstrated antimicrobial and antioxidant activities. Discussion and conclusions: The present study clearly demonstrated that M. barteri and some of its isolates possess antimicrobial and antioxidant properties and may act as potential antioxidant for biological systems susceptible to free radical-mediated reactions. © 2012 Informa Healthcare USA, Inc.