Abstract
The powdered roots of the medicinal plant Acacia nilotica were extracted with hexane and ethyl acetate, and the extracts were subjected to column chromatography for the isolation of potentially bioactive compounds and their screening against kinetoplastid pathogens. NMR and HREI mass spectrometric analyses identified two new diterpenes, characterized as 16, 19-dihydroxycassa-12-en-15-one (Sandynone, 1) and (5S, 7R, 8R, 9R, 10S, 13Z, 17S)-7,8:7,17:16,17-triepoxy-7,8-seco-cassa-13-ene (niloticane B, 2). The previously reported (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-diene-7,17-diol (3), (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol-17-al (4), and (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol (5) a, mixture of stigmasterol (6a) and sitosterol (6b), and lupeol (7) were also isolated. Several column fractions displayed significant activity against a panel of Trypanosoma and Leishmania spp., and from the most active fraction, compound 4 was isolated with high purity. The compound displayed high activity, particularly against T. brucei, T. evansi, and L. mexicana (0.88–11.7 µM) but only a modest effect against human embryonic kidney cells and no cross-resistance with the commonly used melaminophenyl arsenical and diamidine classes of trypanocides. The effect of compound 4 against L. mexicana promastigotes was irreversible after a 5-h exposure, leading to the sterilization of the culture between 24 and 48 h.
Highlights
Parasitic kinetoplastid diseases, including trypanosomiasis and leishmaniasis, threaten millions of people in resource-poor countries around the world
While the number of new human African trypanosomiasis (HAT, or sleeping sickness) infections has significantly decreased in recent years, New Diterpenes From Acacia nilotica with only 977 cases recorded in 2018 (WHO, 2019b), African animal trypanosomiasis (AAT) still remains a major constraint to the use of livestock in the region (Geerts et al, 2001)
Thin-layer chromatography (TLC) was performed on precoated aluminum sheets coated with silica gel F250 (Merck, Germany)
Summary
Parasitic kinetoplastid diseases, including trypanosomiasis and leishmaniasis, threaten millions of people in resource-poor countries around the world. Trypanosoma spp. and Leishmania spp., belonging to the family Trypanosomatida and the order Kinetoplastida, are among the most important agents of neglected tropical diseases (Butler, 2007; Vieira de Morais et al, 2015). These diseases occur mostly in the tropics where the humidity and high environmental temperatures favor both vector and parasite growth and attract insufficient resources (Patz et al, 2000). Beyond Africa, surra and dourine, caused by T. evansi and T. equiperdum, respectively, affect millions of high-value animals in Asia, Europe, Australia, and South America (Brun et al, 1998; Desquesnes et al, 2013)
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