Towards the evaluation in an animal disease model: Fluorinated 17β-HSD1 inhibitors showing strong activity towards both the human and the rat enzyme

17β-Estradiol (E2), the most potent human estrogen, is known to be involved in the etiology of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) catalyses the last step of E2 biosynthesis and is thus a promising target for the treatment of EDD. The previously described bicyclic substituted hydroxyphenylmethanones (BSHs) display high inhibitory potency towards human 17β-HSD1, but marginal activity towards rodent 17β-HSD1, precluding a proof of principle study in an animal endometriosis model. The aim of this work was to perform structural optimizations in the BSHs class to enhance inhibitory activity against rodent (mouse and rat) 17β-HSD1 while maintaining activity against the human enzyme. The introduction of fluorine atoms on the benzoyl moiety resulted in compounds with the desired properties. Molecular docking and homology modeling were applied to elucidate the binding mode and interspecies differences in activity. Compound 33 is the most potent inhibitor of both human and rat 17β-HSD1 up to date (IC₅₀ = 2 nM and 97 nM, respectively).