RESUMO
Rauvolfia mannii is a plant from western and eastern areas of African continent and is widely used in folk medicine for the treatment of various diseases including malaria. Herein, one previously undescribed acylated triterpene (1), together with five already published natural products (2-6) were removed from its roots. The chemical structures of these compounds were determined by spectroscopic and spectrometric means (NMR, HRESIMS, IR and UV). In addition to the isolated triterpenoids, components 5 and 6 are also newly reported from the genus Rauvolfia. Moreover, some constituents were further tested against the chloroquine-sensitive strain of P. falciparum (3D7). It has been found that 3 and 4 showed a moderate antiplasmodial activity with IC50 values of 46.25 and 39.79 µM respectively.
RESUMO
In some compounds in lichens, the carboxylic acid is ortho-substituted by an 2-oxoalkyl chain. This particular structure induces the existence of δ-keto-acid ka or hydroxy-lactone hl isomers, clearly identified by their NMR data and chemical properties, such as dehydration, methylation and behaviour in thermal conditions. Internal hydrogen bonding between the carboxylic acid and substituent in the ortho' position is proposed as an isomerization modulator: an H-bond acceptor (OCH3) leads to ka isomers, whereas hl isomers are obtained with an H-bond donor (OH).