Monoaryl-substituted salicylaldoximes as ligands for estrogen receptor β

Salicylaldoximes possess a hydrogen-bonded pseudocyclic A′ ring in place of the typical phenolic A ring that is characteristic of most estrogen receptor (ER) ligands. Monoaryl-substituted salicylaldoximes were obtained by replacing the phenol moiety (ring A) of the ERβ pharmacophore with the pseudocycle A′ ring, which has previously been shown to behave as a bioequivalent of phenols in nonselective ER ligands. In this series, small substituents (CH₃, CN, Cl) were introduced into the central phenyl scaffold. An efficient sequential halogen-selective double cross-coupling reaction was developed for the synthesis of the methyl-substituted ER ligand. The measured ERβ affinity proved to be very sensitive to the effect of central core substituents. The binding affinities of the compounds herein reported were in good agreement with the results of computational docking analysis. The chloro-substituted derivative showed the highest β affinity and selectivity, and it also proved to be an ERβ partial agonist with an EC₅₀ of 11 nM.