Thyroid receptor ligands. Part 5: novel bicyclic agonist ligands selective for the thyroid hormone receptor beta.

Based on the examination of the crystal structure of rat TRbeta complexed with 3,5,3'-triiodo-l-thyronine (2) a novel TRbeta-selective indole derivative 6b was prepared and tested in vitro. This compound was found to be 14 times selective for TRbeta over TRalpha in binding and its beta-selectivity could be rationalized through the comparison of the X-ray crystallographic structures of 6b complexed with TRalpha and TRbeta.