Synthesis and evaluation of 4-substituted-4-androstene-3,17-dione derivatives as aromatase inhibitors

The synthesis and biological evaluation of 4-amino-, 4-alkoxy-, 4-aryloxy-, 4-alkyl- and 4-aryl-4-androstenedione derivatives as inhibitors of estrogen synthetase (aromatase) are described. Inhibitory activity of synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1β-³H]androstenedione as substrate. Synthesized compounds exhibiting aromatase inhibitory activity were evaluated further under initial velocity conditions to determine apparent K_i values. Several compounds were effective competitive inhibitors and have apparent K_i values ranging from 38 to 1290 nM, with the apparent K_m for androstenedione being 47 nM. Alkylation or arylation of 4-N, S, or O-substituted steroids results in compounds that are effective competitive inhibitors that are devoid of time-dependent inactivation and that the free pair of electrons on N, S, or O is not an essential requirement for 4-substituted androstenedione derivatives to be effective aromatase inhibitors. The results obtained from this investigation are consistent with our previous studies which show that aromatase has a hydrophobic pocket in the active site around the C-4α region of androstenedione.