Antiplasmodial activity of lignans and extracts from Pycnanthus angolensis

The dichloromethane, methanol and aqueous ethanol extracts of the stem bark of Pycnanthus angolensis were evaluated for their in vitro activity against the 3D7 Plasmodium falciparum strain. The CH₂C1₂ extract was the most active showing an 1C₅₀= 1.6 μg/ mL. From this extract, a new dibenzylbutane lignan, threo-4,4′-dihydroxy-3-methoxylignan (1) named pycnantolol, together with the known lignans (-)-dihydroguaiaretic acid (2), helio-buphthalmin (3), talaumidin (4), hinokinin (5), the labdane-type diterpene ozic acid (6), and the steroids stigmast-4-en-6β-ol-3-one (7), β3-sitosterol (8) and stigmasterol (9) were isolated. Their structures were established on the basis of physical and spectroscopic methods, including 2 D NMR experiments (COSY, HMQC, HMBC and NOESY). The antimalarial activity of compounds 1-7 was evaluated against 3D7 and Dd2 P. falciparum strains. Despite the significant activity displayed by the crude CH₂C1₂ extract, the isolated compounds showed weaker antiplasmodial activity. The lowest IC₅₀ value was obtained for talaumidin (4) (IC₅₀ = 20.7μg/mL against the Dd2-chloroquine resistant P. falciparum strain).