Stability studies of cynaropicrin–major sesquiterpene lactone of Cynara cardunculus leaves

BACKGROUND Cynaropicrin, the major sesquiterpene lactone in Cynara cardunculus leaves, exhibits phytotoxic activity and is a promising candidate for sustainable weed management. However, its environmental stability and the biological activity of its transformation products under agronomic and soil conditions remain poorly understood. This study investigated its stability under high temperature (50 °C) and pH (5 and 8), mimicking agronomic extremes, and under soil context. RESULTS Cynaropicrin remained stable at 50 °C and pH 5 for up to 72 h but degraded extensively at pH 8, with an 80% concentration reduction over 7 days. Deacylcynaropicrin emerged as the major degradation product under alkaline conditions. In soil, complete degradation occurred within 7 days, producing dehydrocynaropicrin and a new compound, 4,15‐dihydro‐dehydrocynaropicrin. Bioassays demonstrated that both degradation products exhibited higher phytotoxic activity against P. oleracea than cynaropicrin and deacylcynaropicrin. CONCLUSION This research is the first to highlight cynaropicrin's stability, characterize the structures of its degradation products, and their phytotoxicity, showing the strong impact of environmental factors and microbes. The findings underscore its ecological importance and potential for sustainable weed control.