Synthesis, structure elucidation, and biochemical evaluation of 7 alpha- and 7 beta-arylaliphatic-substituted androst-4-ene-3,17-diones as inhibitors of aromatase.

The inhibition of aromatase, the cytochrome P450 enzyme complex responsible for the conversion of androgens to estrogens, may be useful for the endocrine treatment of breast cancer. Previously, several 7 alpha-thio-substituted androstenediones have been shown to be potent inhibitors of aromatase. Recent research has focused on producing a more metabolically stable aromatase inhibitor by replacing the carbon-sulfur bond at the 7 alpha-position with a carbon-carbon bond. The new inhibitors, 7 alpha-arylaliphatic-substituted androst-4-ene-3,17-diones (2-4), have alkyl chains of varying length between the steroid and the aryl ring at the 7 alpha-position. The desired targets were synthesized via a 1,6-conjugate addition of the appropriate cuprate to 17 beta-(tert-butyldimethylsiloxy)androsta-4,6-dien-3-one (7). The synthesis also resulted in the formation of the 7 beta-substituted diastereomers (10-11 and 13) as minor products. Initial assignments of the 7 alpha-phenethyl and 7 beta-phenethyl diastereomers were made using highfield 1-D and 2-D NMR studies. The assignment of the diastereomers was confirmed using X-ray crystallography. These compounds were all good inhibitors of aromatase in vitro when assayed using microsomes isolated from human placenta. The 7 alpha-substituted androst-4-ene-3,17-diones (2-4) were effective inhibitors with apparent Kis of 13-19 nM. The corresponding 17 beta-hydroxy analogs (8 and 14) and the 7 beta-substituted androstenediones (13 and 16) were less effective inhibitors with apparent Kis of 36-44 nM. Thus, a new series of 7 alpha-arylaliphatic-substituted androst-4-ene-3,17-diones has been synthesized, and the compounds are potent competitive inhibitors of aromatase.