Improved synthesis of EM-1745, preparation of its C17-ketone analogue and comparison of their inhibitory potency on 17β-hydroxysteroid dehydrogenase type 1

Endocrine therapies are widely used for the treatment of estrogen-sensitive diseases. 17 beta-hydroxysteroid dehydrogenase type 1 (17 beta-HSD1) is involved in the last step of the biosynthesis of potent estrogen estradiol (E-2). This enzyme catalyzes the reduction of the C17-ketosteroid estrone (E-1) into the C17 beta-hydroxy steroid E2 using the cofactor NAD(P)H. The X-ray analysis of E-2/adenosine bisubstrate inhibitor EM-1745 proven that this compound interacts with both the substrate-and the cofactor-binding sites. However, E-1 is a better substrate of 17 beta-HSD1 than E2. Thus, in order to improve the inhibitory potency of EM-1745, the C17-ketone analogue was prepared. During this work, a new and more efficient method for synthesizing EM-1745 was developed using an esterification and a cross-metathesis as key steps. Contrary to what was expected, the C17-ketone analogue of EM-1745 is a less potent inhibitor (IC50 = 12 nM) than the C17-alcohol (IC50 = 4 nM) in homogenated HEK-293 cells overexpressing 17 beta-HSD1. Our results contribute to the knowledge of an unexpected observation: the C17-ketone steroidal inhibitors of 17 beta-HSD1 are less potent than their corresponding C17-alcohol derivatives.