Antiplasmodial activity of extract and compounds from Vachellia xanthophloea (Benth.) P.J.H. Hurter (African fever tree)

Vachellia xanthophloea, also known as the fever tree, is used in Zulu folk medicine for malaria treatment and prophylaxis. The leaf and stem bark extracts of the plant were previously reported to have moderate activity against D10 P. falciparum. This study aimed to identify the phytochemicals responsible for the antiplasmodial activity of V. xanthophloea leaf extract. The bioactive compounds in the leaf extract were isolated using chromatographic techniques and their structures were established with spectroscopic and spectrometric techniques. The antiplasmodial activity of the extract and isolated compounds against chloroquine-sensitive 3D7 P. falciparum was evaluated using the parasite lactate dehydrogenase assay and the cytotoxicity against HeLa cells was determined using the resazurin assay. The ethyl acetate fraction of V. xanthophloea leaf extract displayed good antiplasmodial activity with IC₅₀ = 10.6 µg/mL and was not cytotoxic (98% cell viability at 33 µg/mL). Chromatographic purification of this fraction afforded two new flavonoids and fourteen other known compounds, including eight flavonoids, a phenolic ester, and a furofuranlignan. Also, a 1:1 mixture of phytol and lupeol was isolated from the hexanes fraction. All the compounds are reported from V. xanthophloea for the first time. Methyl gallate isolated from the ethyl acetate fraction displayed the best activity against 3D7 P. falciparum (IC₅₀ = 1.2 µg/mL), with 68% viability of HeLa cells at 10 µg/mL. The folkloric use of V. xanthophloea as an antimalarial remedy could be associated with the presence of the compound.