Substituted 6-Phenyl-2-naphthols. Potent and Selective Nonsteroidal Inhibitors of 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1): Design, Synthesis, Biological Evaluation, and Pharmacokinetics

17beta-Estradiol (E2) is implicated in the genesis and the development of estrogen-dependent diseases. Its concentration is mainly regulated by 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), which catalyzes the reduction of the weak estrogen estrone (E1) to the highly potent E2. This enzyme is thus an important target for the treatment of hormone-dependent diseases. Thirty-seven novel substituted 6-phenyl-2-naphthols were synthesized and evaluated for 17beta-HSD1 inhibition, selectivity toward 17beta-HSD2 and the estrogen receptors (ERs) alpha and beta, and pharmacokinetic properties. SAR studies revealed that the compounds most likely bind according to binding mode B to the active site, i.e., the 6-phenyl moiety mimicking the steroidal A-ring. While substitution at the phenyl ring decreased activity, introduction of substituents at the naphthol moiety led to highly active compounds, especially in position 1. The 1-phenyl compound 32 showed a very high inhibitory activity for 17beta-HSD1 (IC50 = 20 nM) and good selectivity (17beta-HSD2 and ERs) and pharmacokinetic properties after peroral application.