They also isolated a series of terpenoids from T. nucifera as anti‐SARS‐CoV Mpro agents (Figure 33). 187  Among them, ferruginol (139; IC50 49.6 µM) was the most active compound. Additionally, they isolated quinone‐methide triterpenoids celastrol (140), pritimererin (141), and tingenone (142) from methanol extracts of Tripterygium regelii which exhibited fair inhibition activity (IC50 2.6, 9.9, 5.5 µM, respectively). SAR studies indicated that for effective inhibition, the quinone‐methide group in ring A and the more lipophilic ring E were critical. All compounds were characterized as competitive inhibitors using kinetic analyses.