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Milk thistle

Dear Reader,

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.

Isosilybin A

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.

The formation of the radicals by the one electron oxidations

Now the next step is the radical-radical coupling which forms the first C-O bond.

Radical radical coupling step

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.

The final step of the reaction

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.


One Response

  1. illions of compounds are detoxified within each liver cell, or hepatocyte. Inevitably, this wear and tear compromises liver cells and surrounding connective tissue. Hepatotoxicity is fast becoming a major health issue. In fact, many practitioners believe poor liver function caused by toxin accumulation or by liver-function decline may contribute to other seemingly unrelated illnesses, such as rheumatoid arthritis, eczema, migraine headaches and premenstrual syndrome, and may manifest symptoms of its own. As a result, milk thistle (Silybum marianum) is widely prescribed by herbalists throughout Europe and the Americas for liver protection. ..

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