The structure of spilanthol, the pungent, insecticidal constituent of the flower heads was shown to be N-isobutyldeca-2, 6,8-trienamide and (Jacobson 1957; Yasuda et al. (1980) and to be identical with that of affinin obtained from roots of Heliopsis longipes (Jacobson 1957). Two sesquiterpenes, with structures identical to polygodial and eudesmanolide, were isolated from the flower heads of S. acmella together with spilanthol (Nagashima and Nakatani 1992b). Spilanthol and three pungent alkamides (2E–N-(2-methylbutyl)-2-undecene-8,10-diynamide; 2E,7Z–N-isobutyl-2,7-tridecadiene-10,12-diynamide; and 7Z–N-isobutyl-7-tridecene-10,12-diynamide) (Nakatani and Nagashima 1992) and spilanthol plus six alkylamides were isolated from the flower head (Nagashima and Nakatani 1992a). Three N-isobutyl amides spilanthol, undeca-2E,7Z,9E-trienoic acid isobutylamide and undeca-2E-en-8,10-diynoic acid isobutylamide were isolated from the dried flower buds (Ramsewak et al. 1999). Three alkamide compounds were identified from the flower head: N-isobutyl-2,6,8-decatrienamide (compound 1), undeca-2E,7Z,9E-trienoic acid isobutylamide (compound 2) and (2E)-N-(2-methylbutyl)-2-undecene-8,10-diynamide (compound 3) (Pandey et al. 2011). The amount of the compounds obtained were 338 mg (compounds 1 and 2) and 188.4 mg (compound 3), respectively. A mixture of C22–C35 normal hydrocarbons was isolated from S. acmella flower heads (Baruah and Pathak 1999).

Eight N-isobutylamides, two 2-methylbutylamides and one 2-phenylethylamide were detected, with spilanthol as most abundant N-alkylamide (88.8 %) in S. acmella ethanol flower extract (Boonen et al. 2010a). The N-alkylamides included the following: (2E,6Z,8E)-N-isobutyl-2, 6, 8-decatrienamide (spilanthol); (2E,4E,8Z, 10Z)-N-isobutyl-doceca-2,4,8-10-tetraenamide; (2E, 7Z)-N-isobutyl-2,7-tridecadiene-10,12-diyamide; (2E,4Z)-N-isobutyl-2,4-undecadiene-8,10-diynamide; (2E,6Z,8E)-N-(2-methylbutyl)-2,6,8-decatrienamide; 2(Z)-N-isobutyl-2-nonene-6,8-diynamide; N-phenylethyl-2,3-epoxy-6,8-nonadiynamide; (2E)-N-isobutyl-2-undecene-8-10-diynamide; (2E)-N-(2-methybutyl)-2-undecene-8,10-diyamide; and two unidentified alkylamides. Five N-isobutylamides, one 2-methylbutylamide and one 2-phenylethylamide were identified in the ethanol extracts of Spilanthes acmella flowers (Sharma et al. 2011). These included (2E,6Z,8E)-N-isobutyl-2,6,8-decatrienamide (spilanthol); (2E,4E,8Z,10Z)-N-isobutyl-dodeca-2,4,8,10-tetraenamide; (2E,7Z)-N-isobutyl-2,7-tridecadiene-10,12-diynamide; (2Z)-N-phenethyl-2-nonene-6,8-diynamide; (2E,4Z)-N-isobutyl-2,4-undecadiene-8,10-diynamide; (2E,7Z)-N-isobutyl-2,7-decadienamide; and (2E,6Z,8E)-N-(2-methylbutyl)-2,6,8-decatrienamide. The following alkylamides were identified from the methanol flower extract of S. acmella: spilanthol (0.07 %), (Z)-non-2-en-6,8-diynoic acid isobutylamide (0.01 %), (2E)-N-isobutylundeca-2-ene-8,10-diynamide (0.01 %) and spilanthic acid 2-methylbutylamide (0.04 %) (Mbeunkui et al. 2011). Supercritical fluid extraction using CO₂ showed S. acmella flowers were richer in spilanthol than leaves and stems and presented the highest antioxidant/total phenolic ratio as well as the highest antiinflammatory activity (Dias et al. 2012). Approximately 95 % of the total amount of extracted spilanthol was obtained during the SFE(CO₂) extraction step.

Twenty compounds were identified in the essential oil from S. acmella flower heads; limonene (23.6 %), β-caryophyllene (20.9 %), (Z)-β-ocimene (14.0 %), germacrene D (10.8 %) and myrcene (9.5 %) were found to be the major constituents of the oil (Baruah and Leclercq 1993).

Ethanol leaf extract of Acmella oleracea afforded a larvicidal hexane fraction (LC₅₀ = 145.6 ppm) and a nonlarvicidal dichloromethane one (Simas et al. 2013). From the inactive fraction, three amides were identified, deca-6,9-dihydroxy-(2E,7E)-dienoic acid isobutylamide; deca-8,9-dihydroxy-(2E,6Z)-dienoic acid isobutylamide; and the known nona-2,3-dihydroxy-6,8-diynoic acid 2-phenylethylamide. From the hexane partition mixture of two acetylenic 2-phenylethylamides, nona-(2Z)-en-6,8-diynoic acid 2-phenylethylamide and deca-(2Z)-en-6,8-diynoic acid 2-phenylethlylamide were isolated. Studies by Singh and Chaturvedi (2012) showed that in-vitro tissue cultures of S. acmella could be utilized for spilanthol production, an alkylamide used in cosmetics. Significantly higher amount of spilanthol was found in in-vitro plantlet leaves (3294.36 μg/g DW) compared to those taken from field-grown mother plants (2703.66 μg/g DW).

Fourteen volatile compounds isolated from the essential leaf oil of S. acmella are as follows: germacrene-D 54.38 %, trans-β-caryophyllene 15.58 %, β-elemene 4.53 %, nor-copaanone 2.44 %, bicyclogermacrene 2.15 %, valencene 2.14 %, unidentified 1.66 %, α-humulene 1.53 %, cis–trans-α-bisabolene 1.34 %, 2-tridecanone 1.25 %, caryophyllene oxide 1.23 %, neophytadiene 1.21 %, δ-cadinene 1.09 % and β-oplopenone 1.02 % (Kawaree et al. 2008). Three alkamide compounds were identified from the flower head: N-isobutyl-2,6,8-decatrienamide (compound 1), undeca-2E,7Z,9E-trienoic acid isobutylamide (compound 2) and (2E)-N-(2-methylbutyl)-2-undecene-8,10-diynamide (compound 3) (Pandey et al. 2011). The amount of the compounds obtained were 338 mg (compounds 1 and 2) and 188.4 mg (compound 3), respectively.

β-Sitosterol, stigmasterol, fatty acid esters of α- and β-amyrin, myricyl alcohol, stigmasterol and stigmasteryl glucoside including β-sitosteryl-3-O-β-d-glucoside (Krishnaswamy et al. 1975), and stigmasterol and myricyl alcohol (Tiwari and Kakkar 1990) were isolated from S. acmella. In addition to spilanthol [= affinin, (2E,6Z,8E)-deca-2,6,8-trienoic acid isobutylamide], the corresponding 2-methyl-butylamide and two new acetylenic alkamides, namely, (Z)-non-2-en-6,8-diynoic acid isobutylamide and (Z)-dec-2-en-6,8-diynoic acid isobutylamide, were isolated from Spilanthes oleracea (Greger et al. 1985).

Fractionation of the chloroform extract of S. acmella aerial parts afforded stigmasterol, stigmasteryl-3-O-β-d-glucopyranoside together with a mixture of long-chain hydrocarbon esters (Prachayasittikul et al. 2009). Fractionation of the ethyl acetate extract gave three compounds: 3-acetylaleuritolic acid, vanillic acid and β-sitostenone. The methanol extract fractions provided four compounds: scopoletin, trans-ferulic acid, trans-isoferulic acid and a mixture of stigmasteryl-3-O-β-d-glucopyranoside and β-sitosteryl-3-O-β-d-glucopyranoside.

Besides the long known tingling compounds (2E,6Z,8E)-deca-2,6,8-trienoic acid N-isobutyl amide (spilanthol) and (2E,6Z,8E)-deca-2,6,8-trienoic acid N-(2-methylbutyl) amide, as a minor constituent, a new 2-ketol ester (7Z,9E)-2-oxo-undeca-7,9-dienyl 3-methylbut-2-enoate (acmellonate) was isolated from the plant (Ley et al. 2006). Acmellonate elicited a weak tingling and numbing effect on the tongue and contributed only to a small extend to the overall flavour of the plant. The following three alkamides were isolated from a hexane extract of the aerial parts of A. oleracea: spilanthol; (E)-N-isobutylundeca-2-en-8,10-diynamide; and (R, E)-N-(2-methylbutyl)undeca-2-en-8,10-diynamide. Spilanthol and undeca-2E-ene-8,10-diynoic acid isobutylamide were isolated from the water extract of S. acmella (Spelman et al. 2011). Spilanthol was only detected in S. acmella mother plants, flower heads and in-vitro plantlets but was not found in the callus or cell cultures (Tan et al. 2011). However, N-isobutyl-2E, 4Z, 8Z, 10E-dodecatetraenamide was absent in mother plants but could be detected in the in-vitro plantlets. The antioxidant butylated hydroxytoluene (BHT) and fatty acids, n-hexadecanoic acid (palmitic acid) and tetradecanoic acid, were found in each of the sample extracts, namely, mother plant, flower heads, in-vitro plantlets, callus, air-dried cells, freeze-dried cells and fresh cells.