When I was reading a recent copy of a magazine from Aldrich (The Reporter) which in some ways is a series of adverts by Aldrich telling me about the latest analytical gadgets, gizmos, GC columns and other things I saw something interesting. It was on page 6 of the April edition of volume 50.
It was all about C-18 HPLC columns, now in common with many articles in the Reporter the writers show a application. In their case they choose the complex mixture of secondary metabolites from a plant called milk thistle. These include the the silybins and isosilybins. The herb is thought to be good for the liver and has some other medical applications.
When I looked at them I noticed something about the silybins and isosilybins. Here for your information is isosilybin A. I have highlighted in red the part which stood out to me.
I have put in red the part of the molecule which looks like it is very similar to eugenol, I looked in the chemical literature and I found that a biomimetic synthesis of a mixture of isosilybins and the silybins. L. Merlini, A. Zanarotti, A. Pelter, M.P. Rochefort and R. Hänsel, Perkin Transactions I, 1980, pages 775-778.
This is a synthesis which used taxifolin and coniferyl alcohol. The synthesis is an oxidation of a mixture of the two compounds in a mixture of benzene and acetone with silver(I) oxide. The first step is the production of some resonance stablised free radicals, these will be much less reactive and more stable than a typical alkyl free radical. As right now I can not be bothered to draw out the whole of the molecule and to make it more clear for you and to keep with the best traditions of organic chemistry I have represented the taxifolin part of the molecule with a simple 1,2-dihydroxybenzene.
Now the next step is the radical-radical coupling which forms the first C-O bond.
The next step is a nucleophilic attack by the phenol oxygen on the conjugated system in the right hand part of the molecule. This gives us the final product.
I will discuss the synthesis of taxifolin in another post, I saw a paper by Yang, et. al. in Journal of Medicinal Chemistry, 2009 , volume 52, issue 23, pages 7732 to 7752. This is a synthesis of this compound from small molecules. It was done using a combination of aldol and epoxide chemistry. I will write about it soon.