Evaluation of analgesic activities of tremetone derivatives isolated from the Chilean altiplano medicine Parastrephia lepidophylla.

Parastrephia lepidophylla, family Asteraceae, has ancient use in traditional medicine in the region of Tarapacá, Chile. Bioguided fractionation of extracts of this plant was undertaken in the search for compounds with analgesic and antioxidant activity. Two benzofuran derivatives were isolated as the major components of this plant, identified as tremetone 1 and methoxytremetone 6. Remarkably, neither of these showed antioxidant activity, but tremetone 1 exhibited a morphine-like analgesic property. Reduction of this analgesic effect by naloxone suggests a direct effect on opiate receptors as a possible signaling pathway. However, both the low diffusion across lipid membranes (PAMPA assay) and the lipophilicity (Log P) shown by tremetone 1 make elusive the mechanism explaining its induced analgesia.