Synthesis,biological evaluation,and structure–activity relationship study of novel cytotoxic aza-caffeic acid derivatives

Three series of aza-caffeic acid derivatives with different linkers were designed and synthesized. Each of the synthesized derivatives was then used in cytotoxicity screening on either 8 or 12 human cancer cell lines. The structure–activity relationships on three structural regions A, B, and C are analyzed in detail, indicating that a nine bond linker B, containing a piperazine unit, is the most favorable linker leading to the generation of molecules with potent cytotoxicities. Compound (E)-1-(4-(3,4-dichlorobenzyl)piperazin-1-yl)-3-(4-(4-ethoxybenzyloxy)-3,5-dimethoxyphenyl)prop-2-en-1-one (80) exhibited the most significant and selective cytotoxicity to KB, BEL7404, K562, and Eca109 cell lines, with IC₅₀ values of 0.2, 2.0, 1.7, and 1.1 μM, respectively, stronger than that seen for caffeic acid phenethyl ester (CAPE) and cisplatin (CDDP). Flow cytometric and western blot analysis indicate that compound 80 plays a role in mitochondria-dependent apoptosis activity by suppressing K562 cell proliferation in a concentration- and time-dependent manner.