Malaria is a major parasitic infection in many tropical and subtropical regions with the most severe forms of the disease being caused by Plasmodium falciparum. Dramatic increases in the resistance of this mosquito-transmitted parasite to classical treatments have been observed in recent years, and much research effort is now aimed at the discovery of novel natural products with antiplasmodial activities. On the basis of its use in popular medicine, Aspidosperma pyrifolium Mart. (Apocynaceae), a tree popularly known as "pereiro-do-sertão," was selected for detailed study. A phytochemical investigation of the aqueous extract of its stem bark revealed the presence of two known monoterpenoid indole alkaloids, 15-demethoxypyrifoline and aspidofractinine, together with the novel compound N-formylaspidofractinine. The structures of these compounds were established from UV, IR, MS and NMR data, and their 1H- and 13C-NMR spectra have been unambiguously assigned for the first time. © 2007 Springer Science+Business Media B.V.