Development of two synthetic routes to CE-178,253, a CB1 antagonist for the treatment of obesity

CE-178,253 benzenesulfonate (1) is a CB1 antagonist discovered by Pfizer medicinal chemists. Two syntheses of this compound are described. The first, based on the discovery synthesis, involves assembly of an aryl-substituted pyrazolotriazine core onto which the second aryl moiety is installed by a Suzuki coupling; this route has been scaled to provide up to 6 kg of API. A second, more convergent route is also described, which installs the pyrazolotriazine containing both aryl substituents by condensation of a bromoketone with a substituted thiosemicarbazide. This route has been demonstrated on laboratory scale and is viewed as the preferred bond-forming sequence.