A highly potent and selective inhibitor of the type 5 17-β-hydroxysteroid dehydrogenase AKR1C3. In repeat assays it showed an IC₅₀ of 0.013 ± 0.003 μM for AKR1C3, compared with 20.3 ± 3.8 μM against AKR1C1 and >30 μM against AKR1C2 and AKR1C4. This inhibitor also showed displays potency in a cellular assay, blocking the ability of AKR1C3 to metabolize a proven substrate. Does not display any COX (cyclooxygenase) inhibition at 10 µM in whole blood assay.