First phytochemical study of the leaves and stem bark of Grewia brunnea K. Schum. (Malvaceae) and antiplasmodial evaluation of the isolated compounds

The first phytochemical investigation of the leaves and stem bark of Grewia brunnea K. Schum. led to the isolation and structural elucidation of twelve compounds, namely ursolic acid (1), rotundic acid (2), oleanolic acid (3), lupeol (4), 2α-hydroxylupeol (5), betulinic acid (6), lupenone (7), kaempferol (8), β-sitosterol (9), stigmastane-3,6-dione (10), stigmasterol (11), and stigmasterol-3-O-β-d-glucopyranoside (12). Among these, two compounds (2 and 5) are reported for the first time within the Malvaceae family, contributing valuable chemotaxonomic insight. Structural elucidation was accomplished using comprehensive spectroscopic techniques, including 1D and 2D NMR analyses, supported by chemical data and comparisons with literature references. Selected compounds (1, 3–4, and 6–8) were subsequently evaluated for their in vitro antiplasmodial activity against Plasmodium falciparum strains K1 and 3D7. Among the tested compounds, lupenone (7) exhibited strong inhibitory effect on both strains, with IC₅₀ values of 4.7 ± 0.6 μM (K1) and 5.7 ± 0.8 μM (3D7). Betulinic acid (6) and lupeol (4) also demonstrated notable activity against the 3D7 strain, with IC₅₀ values of 2.1 ± 0.3 μM and 4.3 ± 0.7 μM, respectively. In contrast, compounds 1, 3, and 8 showed only weak activity against the tested strains. These findings support the classification of G. brunnea within the Grewia genus and highlight its potential as a promising source of antiplasmodial lead compounds for future drug discovery.