Design, synthesis and biological evaluation of Exemestane derivatives as potent inhibitors of Aromatase

Aromatase is a member of the cytochrome P450 superfamily, responsible for a key step in the biosynthesis of estrogens, allowing the aromatization of androgens into estrogens. For this reason, it is a very valuable therapeutic target for the selective treatment of estrogen-dependent breast cancer. Among aromatase inhibitors (AIs), Exemestane is an irreversible, steroidal aromatase inactivator of type I of clinical use. X-Ray studies revealed the existence of an access channel cavity (ACC) in correspondence of the C-4 and C-6 positions of the androstenedione complexed with aromatase [1]. This led to the design of C-6 alkyl-substituted steroids in order to better anchor in the described ACC, resulting in very efficient inhibition [2]. Starting from this evidence, we have designed, synthesized and biologically tested new series of steroidal androstanes having additional C-6 or C-7 methyl, allyl or hydroxyl groups. Among them, compound 13 (Figure 1) showed a potency and affinity to aromatase similar to Exemestane. Molecular modelling studies guided by the GRID MIFs, were useful to rationalize the best inhibition potency of 13 [3]

C-6α- vs C-7α-Substituted Steroidal Aromatase Inhibitors: Which Is Better? Synthesis, Biochemical Evaluation, Docking Studies, and Structure-Activity Relationships

C-6α and C-7α androstanes were studied to disclose which position among them is more convenient to functionalize to reach superior aromatase inhibition. In the first series, the study of C-6 versus C-7 methyl derivatives led to the very active compound 9 with IC50 of 0.06 μM and Ki = 0.025 μM (competitive inhibition). In the second series, the study of C-6 versus C-7 allyl derivatives led to the best aromatase inhibitor 13 of this work with IC50 of 0.055 μM and Ki = 0.0225 μM (irreversible inhibition). Beyond these findings, it was concluded that position C-6α is better to functionalize than C-7α, except when there is a C-4 substituent simultaneously. In addition, the methyl group was the best substituent, followed by the allyl group and next by the hydroxyl group. To rationalize the structure–activity relationship of the best inhibitor 13, molecular modeling studies were carried out