In an attempt to develop potent and selective antitumor agents, a series of novel 1, 4- disubstituted phthalazine derivatives was designed and synthesized. All the prepared compounds were screened for their cytotoxic activities against A549, HT-29 and MDA-MB- 231 cell lines in vitro. Among them, seven compounds (7a–7e, 7j and 7i) displayed excellent selectivity for MDA-MB-231 cells with IC50 values in the nM range, a desirable range for ...