Catnip Fuels Route To Cancer Killer

Starting from the psychoactive ingredient in catnip, researchers have completed the first enantioselective total synthesis of (+)-englerin A (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200905032). Englerin A, a natural product isolated from a plant native to Tanzania, has a complex sesquiterpene architecture and promising activity against kidney cancer cell lines. But its absolute stereochemistry remained unknown until now. A multi-institutional team led by Mathias Christmann of Dortmund University of Technology, in Germany, determined englerin A’s absolute configuration by total synthesis. The team’s starting material was the cis,trans stereoisomer of nepetalactone, the kitty-crazing active ingredient in catnip. A contraction of nepetalactone’s six-membered lactone ring set the stage for a diastereoselective allylation reaction that furnished the carbon framework for englerin A’s multiring core. An olefin metathesis reaction provided a key seven-membered ring in the natural product’s skeleton, and a late-stage epoxide opening gave the final ring. The team plans to use the route to make the naturally occurring enantiomer, (–)-englerin A, along with analogs to explore their bioactivity.