Synthesis of a spin-labeled anti-estrogen as a dynamic motion probe for the estrogen receptor ligand binding domain

The preparation and characterization of a novel nitroxide spin probe based on a steroidal anti-estrogen is described. The probe 5 demonstrated very high binding affinity for both the alpha and beta isoforms of the estrogen receptor–ligand binding domain. EPR spectrometric studies demonstrate conformational constraints for the ligand, consistent with the nitroxyl moiety occupying a position just beyond the receptor-solvent interface.

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