Total synthesis of cynaropicrin.

Cynaropicrin is found in artichoke (Cynara scolymus) and is the source of its bitter taste and it is a sesquiterpene lactone with a 5-7-5 tricyclic skeleton, six chiral centers, and four exo-olefins. This natural product has numerous attractive biological activities including the inhibition of NF-κB activation, antihepatitis C activity, and antitrypanosomal activity. In this study, the first total synthesis of cynaropicrin was achieved starting from (S)-α-pinene. The synthesis involved a stereoselective Favorskii rearrangement and an indium-promoted diastereoselective Barbier reaction.