Design, synthesis, biological activity evaluation and structure-activity relationships of new steroidal aromatase inhibitors. The case of C-ring and 7β substituted steroids

In this work, new steroidal aromatase inhibitors (AIs) were designed, synthesized, and tested. In one approach, C-ring substituted steroids namely those functionalized at C-11 position with an α or β hydroxyl group or with a carbonyl group as well as C-9/C-11 steroidal olefins and epoxides were studied. It was found that the carbonyl group at C-11 is more beneficial for aromatase inhibition than the hydroxyl group, and that the C-ring epoxides were more potent than the C-ring olefins, leading to the discovery of a very strong AI, compound 7, with an IC50 of 0.011 μM, better than Exemestane, the steroidal AI in clinical use, which presents an IC50 of 0.050 μM. In another approach, we explored the biological activity of A-ring C-1/C-2 steroidal olefins and epoxides in relation to aromatase inhibition and compared it with the biological activity of C-ring C-9/C-11 steroidal olefins and epoxides. On the contrary to what was observed for the C-ring olefins and epoxides, the A-ring epoxides were less potent than A-ring olefins. Finally, the effect of 7β-methyl substitution on aromatase inhibition was compared with 7α-methyl substitution, showing that 7β-methyl is better than 7α-methyl substitution. Molecular modelling studies showed that the 7β-methyl on C-7 seems to protrude into the opening to the access channel of aromatase in comparison to the 7α-methyl. This comparison led to find the best steroidal AI (12a) of this work with IC50 of 0.0058 μM. Compound 12a showed higher aromatase inhibition capacity than two of the three AIs currently in clinical use.