HYDROGEN-BONDING IN STEROIDOGENESIS - STUDIES ON NEW HETEROCYCLIC-ANALOGS OF ESTRONE THAT INHIBIT HUMAN ESTRADIOL 17-BETA-DEHYDROGENASE

New heterocyclic analogs of estrone are reported that inhibit estradiol 17β-dehydrogenase (E2-17βDH) from human placenta. The inhibitors are efficiently synthesized in two steps from estrone (or its 3-0-methyl ether), giving fully characterized analogs with pyrazole or isoxazole fused to the 16,17-position on the D ring. Dixon plots of enzyme kinetic data show the heterocyclic steroids are competitive inhibitors of E2-17βDH. Correlating molecular structures of the inhibitors with their Ki-values yields a pattern suggesting intermolecular hydrogen bonding stabilizes the [(pyrazole)inhibitor-E2-17βDH] complexes. A free energy difference of 2.74 Kcal/mol calculated from Ki-value differences between hydrogen bonded (4.08 μM) and non-bonded (425 μM) [inhibitor-E2-17βDH] complexes is in the range for intermolecular hydrogen bonding. We conclude that specific intermolecular hydrogen bonds stabilize [hydroxysteroid-enzyme] complexes, thereby making important contributions to the affinity between hydroxysteroids and steroid-specific enzymes of steroidogenesis. © 1991 Academic Press, Inc.