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Toward an Asymmetric Total Synthesis of Tuberostemoninol

The stemona species have long been recognized as having anti-tussive, insecticidal, or anthelmintic activities in traditional Chinese and Japanese medicine. To date, more than 50 congeners have been isolated and a lot of efforts have been put into the total synthesis ot stemona alkaloids. Tuberostemoninol was first isolated in 1994 by Wen-Han Lin and coworkers from the root of S. tuberosa Lour in China. In 2002, neotuberstemoninol, having the same key tricyclic core as tuberostemoninol, was isolated from the same species. Unlike the other stenine-type alkaloids (for example, tuberostemonine), the unique tricyclic core with two contiguous quaternary carbon centers of tuberostemoninol render it an attractive synthetic target to us.

Our synthesis features a diastereoselective intramolecular Pauson-Khand (IMPK) reaction to install the (A, B) ring system and the quaternary carbon center. A Wittig olefination followed by removal of the Williams lactone template and a Mitsunobu reaction are envisaged to form the seven-membered C ring. Current efforts, thus far, are focused on the construction of the properly functionalized tricylic core (A, B, C rings) and the completion of an asymmetric total synthesis of Tuberostemoninol.

Synthetic Studies toward Tuberostemoninol