Synthesis and cytotoxic evaluation of usnic acid benzylidene derivatives as potential anticancer agents

A series of usnic acid benzylidene derivatives (groups I-V) were designed, synthesized and evaluated for their anticancer activity in the search for potentially new anticancer agents. Compounds 1a, 5b, 2b, 2e and 2f exhibited the most potent cytotoxcity against K562 cell line with IC₅₀ values of 10.0 ± 3.6, 5.6 ± 0.4, 8.8 ± 1.0, 4.5 ± 0.1 and 8.4 ± 0.4 μM, respectively. It is noteworthy that compound 2e displayed potent cytotoxicity against K562 cells without any cytotoxic effect on HEK293 normal cell line.