a bioassay-guided fractionation scheme for characterization of new anti- bacterial compounds from prosopis cineraria aerial parts

background and objectives: due to the importance of finding of new antibacterial agents, the antibacterial properties of prosopis cineraria aerial parts were investigated using a bioassay guided fractionation scheme. materials and methods: the organic extract was prepared via maceration in methanol, followed by the fractionation using n-hexane and ethyl acetate. the mics of fractions were determined against some human pathogenic bacteria using broth micro-dilution assay. the primary characterization and identification of bioactive substance(s) was based on a bio-autograph- ical method using hptlc and flash chromatography in parallel with agar overlay assays. finally the exact mass of effective compound(s) was determined by lc-ms. results: the best antibacterial activities were related to the ethyl acetate fraction. the effective antibacterial compound of the plant were 2 substances with molecular weight of 348 and 184 dalton that inhibited the growth of assessed gram positive bacteria with mic values lower than 125 to 62.5 µg/ml synergistically. conclusion:   further analysis using nuclear magnetic resonance could reveal the exact structure of these two antibacterial substances. these 2 effective antibacterial compounds could be applied as lead compound for synthesis of new antibacterial agents.