Design and synthesis of natural product derivatives with selective and improved cytotoxicity based on a sesquiterpene scaffold.

Brasilamide E (1) is a bisabolane sesquiterpenoid isolated from the solid-substrate fermentation cultures of a plant endophytic fungus Paraconiothyrium brasiliense. The compound specifically inhibited proliferation of the MCF-7 cells, but did not show cytotoxicity towards the negative controls HaCaT and NIH3T3 cells (IC50>50 μM). To improve its potency while maintain selectivity, a total of 27 derivatives of 1 were designed, synthesized, and evaluated for in vitro cytotoxicity against six tumor cell lines and the negative control NIH3T3 cells. Among these compounds, compound 12b showed significantly improved potency against the MCF-7, HeLa, and HO8910 cells with IC50 values of 0.13-0.25 μM compared to 1 (IC50 8.47-18.00 μM), and remained nontoxic to the NIH3T3 cells.