Abstract

Lyophilized Acmella oleracea capitula, leaves and stems were extracted with methanol at 100 °C and 10 MPa (100 atm) pressure in a sealed container and analyzed by LC-HRMS and NMR. This solubilized 28.3% of the leaves, 24.7% of the stems and 31.1% of the capitula. The NMR spectra were dominated by signals due to the CHO and CH2O of carbohydrates. Spilanthol and other Nalkamides were present in the methanolic extracts at concentrations that were too low to enable their detection by NMR. In contrast, LC-HRMS was able to quantify spilanthol (deca-2E,6Z,8E-trienoic acid isobutylamide, syn. affinin, C₁₄H₂₃NO) and detect at least ten other N-alkamides as [M+H]+ ions with the following molecular formulas and m/z values: C₁₃H₁₇NO (1), C₁₇H₁₇NO (2), C₁₅H₁₉NO (3), C₁₅H₂₁NO (4), C₁₆H₂₃NO (5), C₁₇H₂₃NO (6), C₁₄H₂₅NO (7), C₁₅H₂₅NO (8), C₁₄H₂₁NO (9) and C₁₆H₂₅NO (10). The concentrations of spilanthol in the capitula, leaves and stems were 16.5, 0.344 and 0.241 mg/g dry weight. To confirm its presence by NMR, partial purification was required. So, a portion of the residues remaining after evaporating off the methanol were partitioned between chloroform and deionized water. The percentage of amphiphilic compounds in the capitula, leaves and stems were 7.69, 8.42 and 3.09% dry weight, respectively. NMR signals due to spilanthol were seen in their spectra.

Keywords: Acmella oleracea, LC-HRMS, NMR, spilanthol, N-alkamides.

Graphical Abstract