In vitro isolation and characterization of biolarvicidal compounds from micropropagated plants of Spilanthes acmella.

Spilanthes acmella (Family: Asteraceae) commonly known as "toothache plant" is known to possess strong insecticidal and larvicidal properties. Experiments have been conducted to isolate and characterise the biolarvicidal compounds from the flower head extract of micropropagated S. acmella plants employing various tools like FT-IR, TLC, CC, NMR. FT-IR spectroscopy of the crude hexane extract sample revealed the presence of amide (secondary metabolite) as functional group in S. acmella flower heads. The crude extract was separated into 85 fractions (100 ml each) through silica gel column chromatography using hexane-ethyl acetate mobile phase. All fractions were tested for their larvicidal activity against late III/early IV instar Anopheles stephensi larvae and fraction showing maximum bioefficacy against aforesaid larvae was further resolved into three separate bands on Preparative TLC plate, the respective R (f) values being (a) 0.18, (b) 0.23 and (c) 0.27. Based on Proton NMR spectrum of the eluted compounds and their comparison with published results, three different compounds were identified: N-isobutyl-2,6,8-decatrienamide (compound 1), undeca-2E,7Z,9E-trienoic acid isobutylamide (compound 2) from band a and (2E)-N-(2-methylbutyl)-2-undecene-8,10-diynamide (compound 3) from band b. The amount of the compounds obtained were 338 mg (compounds 1 and 2) and 188.4 mg (compound 3), respectively. This is the first report of biolarvicidal compounds isolation and characterisation from micropropagated S. acmella plants.