Effects of pH and temperature on the stability of sesquiterpene lactones

As part of a series of our research on sesquiterpene lactones, we report here on the stability of different sesquiterpene lactones, isolated from the species Anthemis melanolepis [1] and Centaurea spinosa [2], under various pH and temperature conditions. The stability of five sesquiterpene lactones bearing or not a side chain was calculated at pH 5.5, 7.4 (buffer solutions) and RPMI 5% and at temperatures 25 0C and 37 0C for 96 hours. Sesquiterpene lactones bearing a side chain lost this side chain at pH 7.4 and 37 0C, while they were stable at pH 5.5. Sesquiterpene lactones not bearing a side chain seemed to be stable at all conditions. The structure of the products was elucidated by spectroscopic methods, particularly high-field NMR spectroscopy (1H-NMR).