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 trans-4-(3-hydroxy-4-methoxyphenyl)-3-phenoxy-1-(3,4,5-trimethoxyphenyl)­azetidin-2-one
(78b) and trans-4-(3-amino-4-methoxyphenyl)-3-phenoxy-1-(3,4,5-trimethoxyphenyl)­azetidin-2-one
(90b). 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 trans 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 90b 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 78b and 90b were synthesized, of which the alanine
amide 102b retained potency and is a promising candidate
for further clinical development.