Development of a Gram-Scale Synthesis of PBRM, an Irreversible Inhibitor of 17beta-Hydroxysteroid Dehydrogenase Type 1

René Maltais and Donald Poirier
Organic Process Research & Development 2019
DOI: 10.1021/acs.oprd.8b00402

Efforts toward the development of a reliable gram scale synthesis of PBRM, a potent and selective steroidal covalent inhibitor of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), are described. Among the three synthetic routes (C-E) developed herein, route E is the most efficient one with only 6 chemical steps from commercially available estrone, and an overall yield of 13% leading to PBRM with a high HPLC grade purity (99.7%) after recrystallization. Important improvements have been achieved in this sequence from previous reported routes (A and B). Notably, we used a palladium catalyzed Suzuki-Miyaura cross-coupling reaction to rapidly install the requested C3 chain on estrone. Also, catalytic hydrogenation of the C16-enone was shortened by half using Pearlman’s catalyst. Finally, we used a selective bromination through deoxygenation of alcohol at the last step of the sequence to provide PBRM without dehydration of its carboxamide functionality, a persistent problem observed in other routes. Crystals of PBRM were also obtained from recrystallization in acetonitrile and submitted to x-ray analysis, which confirmed the PBRM structure. This work now makes it possible to start a proof-of-principle in a non-human primate model for the treatment of endometriosis, while supporting its future pharmacological development.