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

Abstract

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 IC₅₀ value of 2.8 ± 0.2 μg/mL, whereas patuletin (2) (IC₅₀ = 4.3 ± 0.25 µg/mL) was comparable to quercetin and rutin but significantly better than patulitrin (3) (IC₅₀ = 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.

Keywords::

• Analgesic
• antioxidant
• patuletin
• patuletin derivatives

Acknowledgment

This paper was first presented as a poster for the Tenth International Symposium on Natural Product Chemistry held in Karachi, Pakistan, 6-9 January 2006.

Declaration of interest

Two of the authors, Samina Bano and Lubna acknowledge the Higher Education Commission Islamabad, Pakistan for financial support for Project No. 20–161 entitled “Medicinal and pesticidal agents based on Tagetes species” through the National Research Program for Universities (NRPU). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.