The sesquiterpenes with the COVID-19 M pro inhibitory activity from the Carpesium abrotanoides L.

The extract of the whole plant of Carpesium abrotanoides L. yielded four new sesquiterpenes including a novel skeleton (claroguaiane A, 1), two guaianolides (claroguaianes B–C, 2–3), and one eudesmanolide (claroeudesmane A, 4), together with three known sesquiterpenoids (5–7). The structures of the new compounds were elucidated by spectroscopic analysis especially 1D and 2D NMR spectroscopy and HRESIMS data. Additionally, all the isolated compounds were preliminarily evaluated for the inhibitive activity of COVID-19 M^pro. As a result, compound 5 showed moderate activity with an IC₅₀ value of 36.81 μM and compound 6 exhibited a potent inhibitory effect with an IC₅₀ value of 16.58 µM, while other compounds were devoid of noticeable activity (IC₅₀ > 50 μM).