SYNTHETIC APPROACH TO EPIBATIDINE FROM 1-(PHENYLSULFONYL)PYRROLE

by VanNess, Brandon G.

The goal of this research was to synthesize the natural product epibatidine, a non-opiate analgesic and nicotinic acetylcholine agonist isolated from Epipedobates tricolor. A synthetic pathway utilizing a Diels-Alder cycloaddition of a 3-pyridyl substituted pyrrole and tosylacetylene was conceived based upon the original mass spectral fragmentation pathway of epibatidine determined by Daly. Although this pathway had been previously attempted using 1-(triisopropyl)-3-[5-(2-chloropyridyl)]pyrrole in the key Diels-Alder step, the lack of cycloadduct suggested that a pyrrole with a more electron withdrawing protecting group was required for this step. Therefore, synthesis of 1-(phenylsulfonyl)-3-[5-(2-chloropyridyl)]pyrrole via a palladium catalyzed cross-coupling reaction of 1-(phenylsulfonyl)-3-pyrroline and 2-chloro-5-iodopyridine was set as a synthetic goal and accomplished. The Diels-Alder reaction required further investigation to determine the extent to which 1-(phenylsulfonyl)pyrrole would undergo cycloaddition with dimethyl acetylenedicarboxylate and tosylacetylene. Once this was completed, the Diels-Alder reaction of 1-(phenylsulfonyl)-3-[5-(2-chloropyridyl)]pyrrole was attempted with tosylacetylene but the desired cycloadduct could not be found.