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Title: Phytochemical and antibacterial studies on selected plant of the genus Hypericum
Author: Khadijo, Osman
ISNI:       0000 0004 2715 4720
Awarding Body: School of Pharmacy (University of London)
Current Institution: University College London (University of London)
Date of Award: 2012
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This thesis describes phytochemical studies on ten of the genes Hypericum and the evaluation of their antibacterial activity. Bio-assay guided fractionation using various chromatography techniques was used in this study. Eighteen compounds were isolated and their structures were characterised by extensive 1- and 2- dimensional NMR. Antibacterial includes Mycobacterium. bovis 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 extract and isolated compounds. Enzymatic inhibition of ATP-dependent MurE ligase from M tuberculosis was assayed using a colorimetric phosphate detection method, mammalian microphage cell toxicity was also evaluated of interested isolated compounds. The investigation of H acmosepalum let isolation of eight compounds including β-sitosterol, hypercalin B and lupeol from hexane extract. Its chloroform extract gave hyperenone A, 1,7- dihydroxyxanthone 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 minimum inhibition concentration values ranging from 2-128 μg/ml, to 0.5-128 μg/ml., respectively. Hyperenone A showed growth inhibition against M tuberculosis H37Rv and M bovis BCG at 75 ug/ml. and 100 ug/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 A TP-dependent MurE ligase of M tuberculosis, a crucial enzyme in the cytoplasmic steps of peptidoglycan biosynthesis. Hyperenone A inhibited MurE selectively 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 μg/ml., Fractionation of methanol extract of H frondosum yielded mixture of catechin and epicatechin The hexane extract of the root of H olympicum led the isolation of two new tri-prylenated xanthones derivatives. These metabolites were active against S. aureus and MIC values ranged from 16-32 μg/ml. to 32-64 μg/ml. respectively. Chloroform extract led isolation of pentenoic acid.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available