Design and synthesis of iodocarborane-containing ligands with high affinity and selectivity toward ERß.

The selectivity and the binding affinity of previously reported carborane-containing ligands 2 and 3 toward ERß remains to be optimized. To improve their biological profiles, a series of iodinated carboranyl phenol derivatives (4-6) were designed and synthesized as prospective ERß-selective ligands with high affinity. Several iodinated carboranyl phenols showed high relative binding affinity (RBA) values for both ERs, and especially for ERß, due to suitable hydrophobic interactions of the iodine atoms with the hydrophobic amino acid residues of the ERß ligand-binding domains. Among these derivatives, 9,10-diiodo-m-carborane 5f exhibited a more than 100% increase of the RBA values toward ERß, a 14-fold increased selectivity for ERß over ERα, and ER-agonistic activity in MCF-7 cell proliferation assays.