Design, synthesis, and biological evaluation of Antimycobacterial agents from plant derived Betulinic acid, Oleanolic acid and their derivatives
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Date
2015
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University of Zululand
Abstract
Tuberculosis (TB) is a dangerous disease that has killed several millions of people globally in recent times. The available drugs for the treatment of the disease are not effective for complete cure and in most cases, usually come with side effects, as a result of which new set of potent drugs are needed. In a quest to develop potent hit/drug leads for TB, betulinic acid (BA) and oleanolic acid (OA) were isolated respectively from Curtisia dentata and Syzigum aromaticum. The 3-O- acetyl analogue of BA and OA were synthesized. The cinnamic acid conjugates at C-28 position of the four (4) synthesized compounds were all characterized using IR, MS and 1H and 13C NMR. Co-crystal compound synthesized from the isolated BA and OA with foremost first line antitubercular drug isoniazid (INH) was carried out for the first time. The co-crystal compounds were synthesized using three different conditions: I. Solvent evaporation method, II. Solvent drop method and III. Dry co-grinding method. The synthesized co-crystal compounds were characterized by P-XRD, TGA, and SEM. The isolated triterpenes and their synthesized derivatives were then evaluated for anti-mycobacterial activity (MABA test, against H37RV [ATCC27294] strain), cytotoxicity (MTT test using human embryonic kidney [HEK293] and human hepato-cellular carcinoma [HepG2] cell lines), and DNA polymerase β (pol β) inhibitor activity (with the POLB human ELISA kit). All the test compounds exhibited anti-TB activity, albeit to different levels of efficacy. The MIC values of the two pentacyclic triterpenes (BA and OA) against the mycobacterium ranged from >109.48 uM and 42.04 uM respectively. The acetylation of BA and OA at C-3 position did not observably improve their activity (MIC value of 39.70 uM and 100.26 uM) and neither did the cinnamic acid derivatives of BA and OA at C-28 position enhance the anti-TB activity (MIC value of >85.20 uM and 48.05 uM respectively). The di-substituted, 3-O-acetyl and 28- cinnamic acid ester of BA and OA however exhibited some enhanced anti-TB activity with MIC value of 17.88 uM. The co-crystallization of the triterpenes to INH drastically increased the efficacy of the triterpenes (MIC values in the range of 0.45 uM to 1.06 uM were obtained). The DNA polymerase β inhibitor activity of oleanolic acid and betulinic acid, their acetate derivatives, along with their cinnamic acid hybrid indicated that their inhibition of pol β was concentration dependent. The cytotoxicity of the test compounds to the two human cell lines (HEK293 and HepG2) was in the range of IC50 ≥ 300 μg, indicating low toxicity level. Conclusively, BA and OA may be explored as template for the syntheses of potent anti-TB drug hit/lead when combined with other compounds with known moderate anti-TB activity index.
Description
A dissertation submitted to the Faculty of Science and Agriculture in fulfilment of the requirements for the degree of Doctor of Philosophy (Phd) in the Department of Chemistry at the University Of Zululand, South Africa, 2015
Keywords
curtisia dentata --syzigum aromaticum --BA --OA --molecular hybridization --co-crystal synthesis --solvent evaporation --solvent drop --co-grinding --anti-mycobacterial activity --DNA polymerase β inhibitors --cytotoxicity --HEK293 and HepG2