Thesis

Phytochemical and antimicrobial studies on Ludwigia Adscendens, Trewia Nudiflora and Hygrophila Auriculata from Bangladesh

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Awarding institution
  • University of Strathclyde
Date of award
  • 2009
Thesis identifier
  • T12459
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Department, School or Faculty
Abstract
  • This thesis describes the isolation and structure elucidation of secondary metabolites of three selected medicinal plants from Bangladesh. The work also focused on the evaluation of the plant extracts and some of the isolated compounds for activity in vitro against a panel of Gram-positive and Gram-negative bacteria including Mycobacterium aurum. Compounds active against M. aurum were further tested in combination with selected antitubercular drugs. A total of 30 compounds, including a mixture of two steroids were isolated from the three plants investigated. Two compounds were identified as novel natural products, namely (5a)-19-hydroxy sarmetogenin 3-O-a-L-rhamnopyranoside and 5a- sarmentogenin 3-O-[P-D-glucopyranosyl-(l—>4)-a-L-rhamnopyranoside]. Phytochemical investigation of Ludwigia adscendens led to the isolation of four triterpenes (squalene, betulinic acid, betulin, betulonic acid), a mixture of two steroids (6p-hydroxy-stigmast-4-en-3-one and 6p-hydroxy-stigmasta-4,22-dien-3- one), two ellagic acid derivatives (pteleoellagic acid and 3,3',4'-tri-O-methyl ellagic acid), one flavonol (quercetin), one dihydroflavonol (taxifolin), three flavonol glycosides (afzelin, quercitrin, myricitrin) and three simple phenolics (gallic acid, protocatechuic acid and methyl gallate). All compounds, except for quercitrin and myricitrin, are reported for the first time from this species. Phytochemical investigation of the stem bark of Trewia nudiflora led to the isolation of a known cardenolide (alliotoxin) and two novel structures identified as (5a)-19- hydroxy sarmetogenin 3-O-a-L-rhamnopyranoside and 5a-sarmentogenin 3-0-1P-D- glucopyranosyl-(l—>4)-a-L-rhamnopyranoside], The remaining eight compounds were characterised as three ellagic acid derivatives, namely 3,3'-di-(9-methyl ellagic acid, 3,3'-di-O-methyl ellagic acid 4-O-a-L-rhamnopyranoside, 3-O-methyl ellagic acid 4'-O-a-L-rhamnopyranoside, one coumarin (scopoletin), one alkaloid (indole-3- carboxylic acid), two steroids (5a,8a-epidioxyergosta-6,22-dien-3P-ol and daucosterol) and one triterpene (3P-acetyl aleuritolic acid). Scopoletin and indole-3- carboxylic acid are reported for the first time from this species. The ethyl acetate extract of Hygrophila auriculata afforded five simple phenolic compounds identified as 4-hydroxypthalide, 4-hydroxybenzoic acid, protocatechuic acid, gallic acid and caffeic acid. All compounds are reported for the first time from this species. When screened for activity against a panel of Gram-positive and Gram-negative bacteria, squalene displayed activity against Escherichia coli (MIC 1.22 pM). Gallic acid, quercitrin, afzelin and 3,3',4'-tri-O-methyl ellagic acid were active against Streptococcus pyogenes (MIC values of 5.88, 2.23, 1.16, and 0.36 pM, respectively). The mixture of 6p-hydroxy-stigmast-4-en-3-one and 6p-hydroxy-stigmasta-4,22- dien-3-one was also active against 5. pyogenes (MIC 125 pg/mL). The MIC values of myricitrin and protocatechuic acid against Staphylococcus aureus, Enterococcus faecalis, S. pyogenes and Staphylococcus epidermidis were in the range of 1.08-2.15 and 0.81-1.62 pM, respectively. Methyl gallate and protocatechuic acid were weakly active against Pseudomonas aeruginosa (MIC 5.88 and 6.49 pM, respectively). Daucosterol was active against S. aureus, E. faecalis, S. pyogenes and E. coli with MIC values in the range of 0.22 to 0.44 pM. 3-O-methyl ellagic acid 4'-O-a-L- rhamnopyranoside was active only against E. faecalis (MIC 1.08 pM). Among the ellagic acid derivatives tested against Mycobacterium aurum, pteleoellagic acid and 3,3'-di-O-methyl ellagic acid 4-O-a-L-rhamnopyranoside were found to be active with MIC values of 0.02 and 0.53 pM. Pteleoellagic acid potentiated the effect of the antitubercular drug rifampicin (FIC = 0.35) and showed partial synergy with isoniazid (FIC = 0.60) while 3,3'-di-O-methyl ellagic acid 4-O- a-L-rhamnopyranoside showed partial synergy with rifampicin (FIC 0.75) and additive effect with isoniazid (FIC = 1.25). This is first report of the activity of ellagic acid derivatives against M. aurum and their potentiating effect of antitubercular agents.
Advisor / supervisor
  • Seidel, Veronique
  • Gray, Alexander I.
Resource Type
DOI
EThOS ID
  • uk.bl.ethos.510832

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