New Structure–Activity Relationships of A- and D-Ring Modified Steroidal Aromatase Inhibitors: Design, Synthesis, and Biochemical Evaluation

A- and D-ring androstenedione derivatives were synthesized and tested for their abilities to inhibit aromatase. In one series, C-3 hydroxyl derivatives were studied leading to a very active compound, when the C-3 hydroxyl group assumes 3β stereochemistry (1, IC(50) = 0.18 μM). In a second series, the influence of double bonds or epoxide functions in different positions along the A-ring was studied. Among epoxides, the 3,4-epoxide 15 showed the best activity (IC(50) = 0.145 μM) revealing the possibility of the 3,4-oxiran oxygen resembling the C-3 carbonyl group of androstenedione. Among olefins, the 4,5-olefin 12 (IC(50) = 0.135 μM) revealed the best activity, pointing out the importance of planarity in the A,B-ring junction near C-5. C-4 acetoxy and acetylsalicyloxy derivatives were also studied showing that bulky substituents in C-4 diminish the activity. In addition, IFD simulations helped to explain the recognition of the C-3 hydroxyl derivatives (1 and 2) as well as 15 within the enzyme.