Phytochemical and antibacterial studies on selected plant of the genus hypericum.

摘要

This thesis describes phytochemical studies on ten of the genus Hypericum and the evaluation of their antibacterial activity. Eighteen compounds were isolated and their structures were characterised by extensive 1- and 2-dimensional NMR. Antibacterial studied includes Mycobacterium bo-vis BCG (M. bovis BCG), Mycobacterium tuberculosis H37RV (M. tuberculosis) and panel of Staphylococcus aureus strains. Minimum inhibitory concentration (MIC) assay was used to evaluate antibacterial activity of the plant extracts and isolated compounds. Enzymatic inhibition of ATP-dependent MurE ligase from M. tuberculosis was assayed using a colorimetric phosphate detection method, mammalian macrophage cell toxicity was also evaluated of interested isolated compounds. The investigation of H. acmosepalum led isolation of eight compounds including beta-sitosterol, hypercalin B and lupeol from hexane extract. Its chloroform extract gave hyperenone A, 1,7-di-hydroxyxanthone and 2-hydroxyxanthone. Catechin and epicatechin were isolated from methanol extract. Hyperenone A and hypercalin B exhibited antibacterial activity against multidrug- resistant strains of Staphylococcus aureus, with MIC values ranging from 2-128 mug/mL to 0.5-128 mug/mL, respectively. Hyperenone A showed growth inhibition against M. tuberculosis H37RV and M. bovis BCG at 75 mug/mL and 100 mug/mL. Neither hyperenone A nor hypercalin B inhibited the growth of Escherichia coli and were not toxic to cultured mammalian macrophage cells. Both compounds were tested for their ability to inhibit the ATP-dependent MurE ligase of M. tuberculosis, a crucial enzyme in the cytoplasmic steps of peptidoglycan biosynthesis. Hyperenone A inhibited MurE having an IC50 value of 320 muM whereas hypercalin B did not have any effect on enzyme activity. Stigmasterol and tritrpenes were isolated from hexane extract of H. patulum. Fractionation of methanol extract of this species afforded a series of flavanoid derivates including quercetin, rutin and flavanoid glycosides. All these isolated compounds were inactive against S. aureus at 256 mug/mL. Fractionation of methanol extract of H. frondosum yielded a mixture of catechin and epicatechin. The hexane extract of the root of H. olympicum led the isolation of two new tri-prenylated xan-thone derivatives. These metabolites were active against S. aureus and MIC values ranged from 16-32 mug/mL to 32-64 mug/mL respectively. Chloroform extract led isolation of 3,4-dihydroxy-4-methylpentanoic acid.