Antiplasmodial and antioxidant constituents from the stem bark of Haematostaphis barteri Hook.f. (Anacardiaceae): isolation and bioactivity evaluation.

ETHNOPHARMACOLOGICAL RELEVANCE: Haematostaphis barteri Hook.f. (Anacardiaceae) is widely used in African traditional medicine for the management of malaria and other ailments. However, its active antiplasmodial constituents remain insufficiently characterized.

AIM OF THE STUDY: To evaluate the antiplasmodial and antioxidant activities of the stem bark extract of H. barteri, identify its major bioactive constituents, and explore their potential interactions with falcipain-2 through exploratory docking studies in order to better understand compounds that may contribute to its traditional medicinal use.

MATERIALS AND METHODS: A hydroethanolic stem bark extract was evaluated for in vitro antiplasmodial activity against Plasmodium falciparum Dd2 (multidrug-resistant) and 3D7 (chloroquine-sensitive) strains. The extract was fractionated by column chromatography into four fractions (A-D), which were similarly tested. Further chromatographic purification of fractions A, B, and C yielded six known compounds: 3-O-methylellagic acid-4'-O-α-rhamnopyranoside (1), stigmast-4-en-3,6-dione (2), stigmast-3,6-dione (3), β-sitosterol (4), 6-hydroxystigmast-4-en-3-one (5), and β-sitosterol-3-O-β-D-glucoside (6). Structures were elucidated using NMR and MS techniques. Exploratory molecular docking was conducted to investigate potential binding modes toward falcipain-2. Antioxidant activity was assessed using DPPH and FRAP assays, and isolated compounds were screened for antiplasmodial activity against both parasite strains.

RESULTS: The crude extract exhibited good antiplasmodial activity with IC50 values of 13.0 ± 2.0 μg/mL (PfDd2) and 8.6 ± 2.3 μg/mL (Pf3D7). Among the fractions, fraction C showed the highest activity (12.7 ± 0.2 μg/mL; 8.0 ± 1.5 μg/mL), followed by fraction B, A, and D. Six known compounds were isolated, with compounds 1, 3, and 5 reported for the first time in the Anacardiaceae family. Docking analysis yielded modest predicted binding energies (-5.4 to -6.8 kcal/mol) and did not show a clear correlation with experimental antiplasmodial activity, suggesting that strong falcipain-2 inhibition is unlikely to represent the primary mechanism of action. All samples demonstrated antioxidant activity, and compound 1 exhibited the strongest effect (DPPH IC50 = 59.6 ± 10.4 μg/mL; FRAP IC50 = 69.1 ± 0.2 μg/mL). In antiplasmodial assay, the isolated compounds exhibited weak to moderate activity, with compound 1 showing the lowest IC50 values among them (31.6 ± 2.9 μM for PfDd2 and 22.1 ± 0.1 μM for Pf3D7).

CONCLUSION: The findings provide preliminary pharmacological support for the traditional antimalarial use of H. barteri. In vitro assays indicate that several constituents may contribute to the observed inhibition of Plasmodium growth, with compound 1 showing moderate activity. Compounds 1, 3, and 5 were identified in the Anacardiaceae family for the first time, highlighting their potential as phytochemical markers.