There was an Alzheimer's Phase II study in the UK completed in 2005. I'm still searching for results, but here is info from one of their reports (emphasis is mine)

Now, in the neuro-degenerative disease area, we’ve developed a family of synthetic neuro-regenerative compounds from an Asian plant that are first in class therapeutic agents. They make ageing nerve cells re-grow when they have begun to degenerate due to either toxic damage or damage due to the ageing process. We are currently in Phase II in Alzheimer’s disease with our lead compound coded PYM50028, which was discovered using this approach of ours, of taking medicinal plants and doing trials in man. Following the successful demonstration in a clinical trial of the effects of the plant extract in reversing Alzheimer’s dementia, we initiated a program of pharmacological research that isolated the active compound, confirmed its mechanism of action, and lead to the development of a large library of synthetic compounds that share the same activity profile. PYM50028 is a synthetic chemical similar to the one found in the plant, but we can make it at very low cost.

http://www.twst.com/pdf/YAA607.pdf