Anti-leishmanial activity of some surface compounds of Tarchonanthus camphoratus – Investigational Medicinal Chemistry and Pharmacology

Abstract

Background:The world health organization recognizes leishmaniasis as a major tropical disease with no effective vaccine against it. Chemotherapy, the only effective way to treat all forms of the disease, is toxic and expensive. Hence, there is need for scientists to scale up the search for new anti-leishmanial agents. The present study investigated the in vitro anti-leishmanial activity of five surface compounds of Tarchonanthus camphoratus.

Methods: The surface exudates were obtained by rinsing the aerial parts of the plant with 100% ethyl acetate and acetone. Five compounds were isolated from the exudates and purified by column (CC) and Thin Layer Chromatographic (TLC) techniques respectively. The structures of the compounds were elucidated by use of Nuclear Magnetic Resonance spectroscopy (NMR) and Electrospray Ionization High-Resolution Mass Spectroscopy (EIHRMS). The identified compounds were then screened for anti-leishmanial activity using Leishmania donovani as the standard strain.

Results: The five compounds were a sesquiterpene, (-)-parthenolide (1), and four known methoxylated flavonoids; 5,7,3´,4´-tetrahydroxy-3-methoxyflavone (2), 5,7,4´-trihydroxy-6-methoxyflavone (3), 5,7,3´,4´-tetrahydroxy-6-methoxyflavone (4) and 5-hydroxy-7,8-dimethoxyflavanone (5). Compound 2 exhibited moderate anti-leishmanial activities against Leishmania donovani with IC₅₀ value of 12.84 ± 0.62 µg/mL. (vs 0.85 ± 0.04 for pentamidine and 0.12 ± 0.02 µg/mL for amphotericin B). Compound 4 and 5 also showed anti-leishmanial activities with IC₅₀ values of 26.24 ± 0.14 and 23.15 ± 0.84 µg/mL respectively. Compound 1 and 3 were inactive at the tested concentration as they inhibited <70% of growth of L. donovani standard drug.

Conclusion: Compounds 2, 4 and 5 were active against standard strain and can be targets for synthetic modification for activity optimization.

Keywords: sesquiterpene; parthenolide; flavonoids; Leishmania donovani.

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