Abietane diterpenoids from Phlegmariurus carinatus and their cytotoxic activities

Two new abietane diterpenoids (1 and 2) and two known analogs (3 and 4) were isolated from the whole plants of Phlegmariurus carinatus. Their structures were determined by comprehensive spectroscopic methods (UV, IR, NMR, and HRESIMS). Moreover, all compounds were evaluated for their cytotoxic activities against U251 glioblastoma cells. Notably, compounds 1-4 exhibited potential cytotoxic activities with IC₅₀ values ranging from 19.81 to 81.49 μM. In addition, their stabilities were checked by HPLC in the preservation conditions and in the cell lines medium. The result showed that they were relatively stable in the preservation conditions, except for 3, but that they were decomposed in the incubation process. Finally, the most possible structures of impurities i1, i3 and i4 were deduced by spectroscopic methods (UV, HRESIMS and MS/MS). This work provides potential insights for the development of abietane diterpenoids as candidate drugs for the treatment of glioma.