What is the main active ingredient of echinacea purpurea extract?

Maybe none: There are a huge number of chemicals in this pretty flower, as in anything else from Mother Nature, but despite decades of work, nobody's convinced the scientific community that it works for any of the things it's supposed to help -- from the common cold to cancer. This is in contrast to a host of other botanicals that do real stuff. Probably this is why nobody publishes the active ingredient.