Synthesis and biological evaluation of phenolic 4,5-dihydroisoxazoles and 3-hydroxy ketones as estrogen receptor α and β agonists

In this work, 52 diphenyl-4,5-dihydroisoxazoles and -3-hydroxy ketones were prepared and their estrogen receptor α (ERα) and estrogen receptor β (ERβ) activities were explored in order to systematize and maximize their biological activity. The biological activity was firstly screened by using ERE reporter assay to find out how aromatic hydroxylation and methylation of the chiral centers of the compounds affect the ability of ER to mediate biological responses. For selected 19 compounds, the relative binding affinities (RBA, relative to 3,17β-estradiol) and ability to induce transcription of primary E2 target gene pS2 in human MCF-7 breast cancer cells were determined. In the reporter assay, many compounds showed even stronger activity than E2 and some of them showed RBA larger than 1%. The highest RBAs were determined for the enantiomers of 1-hydroxy-6-(4-hydroxy-phenyl)-1-phenyl-hexan-3-one (50a and 50b). Isomer 50a showed high binding affinity both to ERα (with RBA ∼200%) and ERβ (with RBA ∼60%), while the RBAs of 50b were ca. 40% of those. Some of the other compounds (with RBA ∼1–16%) showed also notable ERα binding selectivity. When four most promising ligands (50a, 50b, 45a, and 45b) were studied with respect to their ability to induce the transcription of primary E2 target gene pS2, the compounds acted as agonists or partial agonists. Computer modeling was used to predict receptor binding conformations and to rationalize the RBA differences of the compounds.

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