Synthesis of Novel Pyrazole Derivatives and Their Tumor Cell Growth Inhibitory Activity

To find novel antitumor agents, a series of 1H-benzofuro[3,2-c]pyrazole derivatives 4a-e were designed and synthesized. The treatment of 6-methoxybenzofuran-3(2H)-one 3 with LiHMDS in anhydrous tetrahydrofuran (THF) followed by reaction with 3-substitued phenyl isothiocyanate gave the thioamide intermediates, which underwent condensation with hydrazine monohydrate in dioxane/EtOH (1:1) to provide the benzofuropyrazole derivatives 4a–e as well as the unexpected pyrazole derivatives 5a–e. In tumor cell growth inhibitory assay, all the benzofuropyrazole derivatives were not active against the breast tumor MCF-7 cell, only 4a was highly active and more potent than ABT-751 against the leukemia K562 (GI(50) = 0.26 μM) and lung tumor A549 cells (GI(50) = 0.19 μM), while other benzofuropyrazoles showed very weak inhibitory activity. In contrast, the pyrazoles 5a-e were in general more potent than the benzofuropyrazoles 4a–e. Compound 5a exhibited a similar tendency to that of 4a with high potency against K562 and A549 cells but weak effects on MCF-7 cell. Both pyrazoles 5b and 5e exhibited high inhibitory activities against K562, MCF-7 and A549 cells. The most active compound 5b was much more potent than ABT-751 against K562 and A549 cells with GI(50) values of 0.021 and 0.69 μM, respectively. Moreover, 5b was identified as a novel tubulin polymerization inhibitor with an IC(50) of 7.30 μM.