Analogues of aminoglutethimide based on 1-phenyl-3-azabicyclo[3.1.0]hexane-2,4-dione: selective inhibition of aromatase activity.

In exploring the structural features responsible for the inhibitory activity of aminoglutethimide [3-(4-aminophenyl)-3-ethylpiperidine-2,6-dione] (1) toward the cholesterol side chain cleavage (CSCC) enzyme from bovine adrenals and the human placental aromatase enzyme, analogues have been synthesized in which the piperidine-2,6-dione ring is replaced by substituted or unsubstituted azabicyclo[3.1.0]hexane-2,4-dione rings. The unsubstituted analogue 1-(4-aminophenyl)-3-azabicyclo[3.1.0]hexane-2,4-dione (9a) is a slightly more potent inhibitor of aromatase than 1 (Ki = 1.2 microM, cf. 1.8 microM for 1) but is noninhibitory toward the CSCC enzyme. The substituted analogues 1-(4-aminophenyl)-3-butyl-3-azabicyclo[3.1.0]hexane-2,4-dione (9e) and 1-(4-aminophenyl)-3-pentyl-3-azabicyclo[3.1.0]hexane-2,4-dione (9f) are approximately 100 times more potent than 1 (Ki values of 1, 9e, and 9f are 1.8, 0.015, and 0.02 microM, respectively) in inhibiting aromatase, with no significant activity toward the CSCC enzyme. Type II difference spectra were exhibited by 1, 9a, and 9f in their interaction with the aromatase enzyme (respective Ks values of 1, 9a, and 9f are 0.13, 0.08, and 0.01 microM). Modification of the para amino function by alkylation, its relocation, replacement by H, or replacement by a methyl, aldehyde, or secondary alcohol group produced analogues that were inactive toward both enzyme systems.

Synthesis and biochemical evaluation of analogues of aminoglutethimide based on phenylpyrrolidine-2,5-dione.

A series of (aminophenyl)pyrrolidine-2,5-diones has been prepared that bear structural similarities to aminoglutethimide (1, 3-(4-aminophenyl)-3-ethylpiperidine-2,6-dione). The inhibitory activity of these compounds was evaluated toward human placental aromatase and bovine adrenal cholesterol side chain cleavage (CSCC) enzyme assay systems. Selective, competitive inhibition of the aromatase enzyme system was demonstrated by 5 (3-(4-aminophenyl)-1-methyl-pyrrolidine-2,5-dione, Ki = 1.75 microM), 6 (3-(4-aminophenyl)-1,3-dimethylpyrrolidine-2,5-dione, Ki = 1.75 microM), 7 (3-(4-aminophenyl)-3-methylpyrrolidine-2,5-dione, Ki = 0.8 microM), and 8 (3-(4-aminophenyl)-3-ethylpyrrolidine-2,5-dione, Ki = 1.0 microM). Compound 15 (3-(4-aminophenyl)pyrrolidine-2,5-dione) proved unexpectedly difficult to prepare following standard methods and was only moderately inhibitory toward aromatase (IC50 = 20 microM). Compound 16 (3-(4-aminophenyl)-3-ethyl-1-methylpyrrolidine-2,5-dione) was weakly inhibitory toward testosterone aromatization and totally inactive toward androstenedione aromatization. These compounds were either weak or ineffective inhibitors of the CSCC enzyme systems, while 1 gave Ki values toward aromatase and CSCC enzymes of 0.68 and 14 microM, respectively. The unsubstituted phenylpyrrolidinediones were inactive in either system, and the 4-nitrophenyl derivatives exhibited weak, nonselective inhibition, indicating the importance of the primary amine moiety for potent inhibition of aromatase activity.