Pharmacognostic study of 5 medicinal plant species from Western Cape Province (South Africa) for anti-tubercular activity

Doctoral Thesis


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University of Cape Town

In our search for new anti-tuberculosis lead molecules, five medicinal plant species, Olea capensis (L.l, Tulbaghia alliacea (L.), Inula graveolens (L.), Leyssera gnaphaloides (L.), and Buddleja saligna (L.) were collected in Cape Town and surrounding area and investigated for antimycobacterial activity following report of their therapeutic use in traditional medicine to treat infectious diseases such as tuberculosis. A bioassay guided fractionation of the acetone/water (4:1) crude extracts of O. capensis (leaves) and T. alliacea (rhizomes) showed no activity against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 252923, and Mycobacterium aurum A+. In contrast, the orgamc fractions (hexane, dichloromethane) of the acetone/water (4: 1) crude extracts of 1. graveolens, L. gnaphaloides, and B. saligna exhibited significant activity against M. tuberculosis H37Rv, M. avium 25291, M. microti ATCC 19422, and M. scrofulaceum ATCC 19987. The isolation and structure determination of the bioactive led to the identification of pentacyclic triterpenoids, ursolic acid (UA) and oleanolic acid as major antitubercular constituents of B. saligna, L. gnaphaloides, and 1. graveolens. The in vitro cytotoxicity assays of the isolated bioactive constituents showed no cytotoxicity against Chinese Hamster Ovarian (CHO) cells line. Subsequently, given the pharmaceutical value of the above finding, a survey on structure activity of pentacyclic triterpenoids was conducted. It was was found, for instance that selective substitutions at C-3 and/or C-28 and the double bond at UA, OA and betulinic and (1) BA) were made in order to improve anti-tumour and anti-HIV activity. However, thought a great number of modified bioactive pentacyclic triterpenoids is reported, none was tested against Mtb. Therefore, this study also explored a new synthetic route (scheme 1) toward a generation of (5), which may allow improving antitubercular, anti-HIV or anti-tumour activity, and/or specificity.

Includes bibliographical references (leaves 126-140).