Bioassay-guided isolation of antioxidant agents with analgesic properties from flowers of Tagetes patula.

CONTEXT

Tagetes patula L. is one of the French marigold group of the Asteraceae family. It is recognized in folklore for its medicinal and pesticidal properties.

OBJECTIVE

In search of more effective, but non-toxic compounds with antioxidative potential led to the bioassay guided isolation studies on the extracts of T. patula.

MATERIALS AND METHODS

The bioassay on Tagetes patula flowers were carried out guided by in vitro antioxidant activity using DPPH assay. A minor but proven plant constituent methyl protocatechuate (1) was isolated by column chromatography, while patuletin (2) and patulitrin (3) obtained in bulk by employing solvent partition of methanol extract. Derivatization of patuletin into benzoyl, cinnamoyl and methyl was conducted to establish the structure activity relationship (SAR). Analgesic activity of compound 2 was evaluated using acetic acid-induced writhing test and hot-plate test in mice. The toxicity of methanol extract and compound 2 were also determined.

RESULTS

Polar extracts, fractions and phases demonstrated better antioxidant activity. The synthetic methyl protocatechuate (1) showed IC(50) value of 2.8 ± 0.2 μg/mL, whereas patuletin (2) (IC(50) = 4.3 ± 0.25 µg/mL) was comparable to quercetin and rutin but significantly better than patulitrin (3) (IC(50) = 10.17 ± 1.16 µg/mL). Toxicity test for the methanol extract and compound 2 did not elicit any behavioral changes or cause mortality in mice. Compound 2 also demonstrated mild analgesic property.

DISCUSSION AND CONCLUSION

These findings demonstrate that the plant polar extracts and fractions possess significant antioxidant property with non-toxic effect. Compound 1 is a genuine plant constituent of T. patula.