Two New β-Dihydroagarofuran Sesquiterpenes from Celastrus orbiculatus Thunb and Their Anti-Proliferative Activity

Two new β-dihydroagarofuran-type sesquiterpenes (1-2) were isolated and identified from the fruit of Celastrus orbiculatus Thunb, together with seventeen known compounds (3-19). The structures of the isolated new compounds were elucidated based on extensive spectroscopic analyses. The cytotoxic activities of the 19 sesquiterpenes on three cell lines, human acute promyelocytic leukemia HL-60, human leukemic K562, and human colon cancer HCT-116 cells, were evaluated in vitro. Compound 4 exhibited potent cytotoxic activity against HL-60, K562, and HCT116 cell lines with IC₅₀ values of 3.61 μΜ, 17.13 μΜ and 10.15 μΜ, respectively, and the other compounds displayed moderate activity.