Antinociceptive Potential of Zinnia grandiflora.

An aqueous extract prepared from the aerial parts of Zinnia grandiflora was found not to induce acute toxicity (LD₅₀> 5g/kg, p.o.) in mice when tested by the Lorke method. This extract showed notable antinociceptive and anti-inflammatory actions when evaluated by the formalin- (ED₅₀ = 224.62 ± 38.17 mg/kg, p.o.) and the carrageenan-induced paw edema models in mice, respectively. The organic-soluble fractions obtained by partitioning the infusion with CH₂Cl₂ and EtOAc were also active in the formalin test. The most important antinociceptive effect was observed with the CH₂Cl₂ fraction; extensive fractionation of the latter yielded three new elemanolides, namely, zinagranolides D-F (1-3), which were characterized structurally by spectroscopic means. The structure of compound 2 was established unequivocally by an X-ray crystallographic analysis. This compound exerted a significant antinociceptive effect in the formalin assay, better than that of diclofenac used as a positive control.