RESUMEN
The Rubus species has been used in folk medicine to treat several ailments, including infectious and dolorous diseases. In this work we evaluate the phytochemical and analgesic activity of hydroalcoholic extract (HE), some fractions (hexane, dichloromethane, ethyl acetate and butanolic), as well as a pure compound denoted as 28-methoxytormentic acid (1) obtained from aerial parts of R. rosaefolius. The compounds were isolated and identified by chromatographic and spectroscopic analysis. The antinociceptive action was evaluated by two well know models of pain in mice: writhing and formalin induced-pain. The results showed that the HE, fractions and compound (1), exhibits potent and dose-related analgesic activity when evaluated in both models of pain. Compound (1), which seems to be the main active principle, showed promising analgesic effects, being several times more potent than aspirin and paracetamol, two well-known analgesic and antiinflammatory drugs used as reference. In the writhing test, it showed an ID(50) of 5.10 (3.64-7.14) mg kg(-1) and maximum inhibition (MI) of 64.22%. When analyzed by formalin induced-pain test, this compound showed ID(50) values of 9.98 (8.08-12.31) and 6.31 (5.07-7.98) mg kg(-1) and MI of 59.37 and 90.37% for the first and second phases, respectively. The results justify, at least partially the popular use of this plant for the treatment of dolorous processes, suggesting that 1 is one of the active principles of this plant.