New Efficient Asymmetric Synthesis of Taranabant, a CB1R Inverse Agonist for the Treatment of Obesity

Taranabant (1) is a cannabinoid-1 receptor (CB1R) inverse agonist that was recently in late-stage clinical development for the treatment of obesity. The previously employed synthesis exhibited a number of shortcomings for continuing development, and in this paper we report an improved synthesis of the target molecule that is suitable for large-scale implementation. Palladium-catalyzed amidation of an enol tosylate afforded a stereodefined tetrasubstituted enamide, and asymmetric hydrogenation thereof provided the target molecule.