Search for antimalarial compounds from Pycnanthus angolensis

Malaria is presently one of the most concerning infectious diseases, especially in African countries due to resistance of Plasmodium falciparum to the clinical available drugs. In these countries, traditional medicine plays a crucial role, as population has few means of accessing medical treatment. Important antimalarial compounds have been isolated from plants, such as quinine and artemisinin. Resistance to the main antimalarials underscores the need to search for new active compounds from plants used in traditional medicine. Pycnanthus angolensis Welw. Ward (Myristicaceae) is a plant used in traditional medicine against several diseases. Its bark has been used to treat fever and malaria in São Tomé and Príncipe islands. The dichloromethane extract of the bark revealed antimalarial activity against 3D7 P. falciparum strain (IC₅₀=1.6µg/mL) and was submitted to chromatographic bio-guided fractionation yielding the lignans 4,4'-dihydroxy-3-methoxylignan, heliobuphthalmin, (-)-dihydroguaiaretic acid, talaumidin, hinokinin, the labdane diterpene ozic acid and the steroids stigmast-4-en-6β-ol-3-one, stigmasterol and β-sitosterol. Furthermore, other compounds were obtained by derivatization. Structural identification was achieved by physical and spectroscopic methods (IR, EIMS, ¹H NMR, ¹³C NMR and 2D NMR experiments). The in vitro antimalarial activity of the compounds was evaluated against 3D7 and Dd2 P. falciparum strains.

In contrast with the crude extract and fractions, the compounds have not shown significant antimalarial activity in both strains. Unless the active compounds were lost during fractionation, these results might be explained by synergistic effects between the different components of the complex extracts and could suggest that a standardization of the bark extract might be the best solution to a rational use of this traditional antimalarial plant.