Synthesis and Biochemical Evaluation of 3‑Phenoxy-1,4-diarylazetidin-2-ones as Tubulin-Targeting Antitumor Agents

Structure–activity relationships for a series of 3-phenoxy-1,4-diarylazetidin-2-ones were investigated, leading to the discovery of a number of potent antiproliferative compounds, including <i>trans</i>-4-(3-hydroxy-4-methoxyphenyl)-3-phenoxy-1-(3,4,5-trimethoxyphenyl)­azetidin-2-one (<b>78b</b>) and <i>trans</i>-4-(3-amino-4-methoxyphenyl)-3-phenoxy-1-(3,4,5-trimethoxyphenyl)­azetidin-2-one (<b>90b</b>). X-ray crystallography studies indicate the potential importance of the torsional angle between the 1-phenyl “A” ring and 4-phenyl “B” ring for potent antiproliferative activity and that a <i>trans</i> configuration between the 3-phenoxy and 4-phenyl rings is generally optimal. These compounds displayed IC₅₀ values of 38 and 19 nM, respectively, in MCF-7 breast cancer cells, inhibited the polymerization of isolated tubulin in vitro, disrupted the microtubular structure in MCF-7 cells as visualized by confocal microscopy, and caused G₂/M arrest and apoptosis. Compound <b>90b</b> possessed a mean GI₅₀ value of 22 nM in the NCI60 cell line screen, displayed minimal cytotoxicity, and was shown to interact at the colchicine-binding site on β-tubulin. Phosphate and amino acid prodrugs of both <b>78b</b> and <b>90b</b> were synthesized, of which the alanine amide <b>102b</b> retained potency and is a promising candidate for further clinical development