Abstract
In a screening of Sudanese medicinal plants for antiprotozoal activity, the chloroform fractions obtained by liquid-liquid partitioning from ethanolic extracts of fruits of Croton gratissimus var. gratissimus and stems of Cuscuta hyalina Roth ex Schult. exhibited in vitro activity against axenically grown Leishmania donovani amastigotes. This antileishmanial activity was localized by HPLC-based activity profiling. Targeted preparative isolation afforded flavonoids 1–6, 3-methoxy-4-hydroxybenzoic acid (7), and benzyltetrahydroisoquinoline alkaloids laudanine (8) and laudanosine (9) from C. gratissimus, and pinoresinol (10), isorhamnetin (11), (-)-pseudosemiglabrin (12), and kaempferol (13) from C. hyalina. The antiprotozoal activity of 1–13 against L. donovani (axenic and intracellular amastigotes), Trypanosoma brucei rhodesiense (bloodstream forms), and Plasmodium falciparum (erythrocytic stages), and the cytotoxicity in L6 murine myoblast cells were determined in vitro. Quercetin-3,7-dimethylether (6) showed the highest activity against axenic L. donovani (IC50, 4.5 µM; selectivity index [SI], 12.3), P. falciparum (IC50, 7.3 µM; SI, 7.6), and T. b. rhodesiense (IC50, 2.4 µM; SI, 23.2). The congener ayanin (2) exhibited moderate antileishmanial (IC50, 8.2 µM; SI, 12.2), antiplasmodial (IC50, 7.8 µM; SI, 12.9), and antitrypanosomal activity (IC50, 11.2 µM; SI, 8.9). None of the compounds showed notable activity against the intramacrophage form of L. donovani.
Highlights
Parasitic protozoa are the causative agents of devastating, yet often neglected diseases
These diseases are human African trypanosomiasis (HAT) caused by Trypanosoma brucei spp., Chagas’ disease caused by Trypanosoma cruzi, and Leishmaniasis caused by Leishmania spp. (Stuart et al, 2008)
The apicomplexan parasite Plasmodium falciparum is the causative agent of malaria tropica which claims more than 400,000 lives every year (Organization, W.H. 2019)
Summary
Parasitic protozoa are the causative agents of devastating, yet often neglected diseases. The kinetoplastids, a group of flagellated protozoa, cause neglected tropical diseases that put more than one billion people around the globe at risk (WHO|World Health Organization, n.d.; Khalid, 2012). The apicomplexan parasite Plasmodium falciparum is the causative agent of malaria tropica which claims more than 400,000 lives every year (Organization, W.H. 2019) These infections are of high public health relevance and socioeconomic impact. The genus Cuscuta comprises over 200 species distributed worldwide They are stem obligate holoparasitic plants possessing neither roots nor fully expanded leaves. In an earlier screening of Sudanese medicinal plants for antiprotozoal activity, the ethanolic extracts of Croton gratissimus fruits and Cuscuta hyalina stems had been found to exhibit in vitro antiprotozoal activity against axenic L. donovani (MHOM/ET/67/L82). We here report on the targeted isolation and structure elucidation of compounds responsible for the activity, and on their in vitro activity against T. b. rhodesiense (STIB 900), axenic and intramacrophage amastigotes of L. donovani (MHOM/ET/67/L82), and P. falciparum (NF54)
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