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Binding to receptors, new drugs and where should drugs come from ?

Well a brother blogger (An alternative medicine doctor) and me have raised some interesting points between us.

In the 1980s and early 1990s the drug companies seemed to think that computational chemistry would be a magic bullet which would give us the next generation of drugs. Sadly it did not work out so well as the drug companies hoped, the thing about computational chemistry is that it is all too easy to favour an answer by your choice of starting instructions (initial coordinates of the atoms). Also the mere binding strength of a drug to a receptor does not give the whole story.

Sadly I have never seen any databases in the public domain for binding strengths of drugs to receptors, but in some papers the binding strengths are listed. I suspect that some drug companies have their own private database of binding constants for some key receptors. One problem I see is that some drugs bind to receptors without turning them on, for example naloxone binds very tightly to the opiate receptors in the human brain but this drug does not turn on these receptors.

I suspect that Christopher will share my view that medicine and the production of medicine should not exist in a vacuum isolated from the rest of society. We need for example to consider the environmental impact of the production of drugs, a good example an early synthesis of ibuprofen produced lots of chemical waste. It used a Friedel-Crafts acylation using aluminium chloride, acetic anhydride and 2-methylpropylbenzene in the first step which will generate lots of aluminium containing waste. The later steps using other reagents also increase the amount of waste produced per kilo of the final drug product. Here is a chemical synthesis scheme for an early ibuprofen synthesis from some of my teaching materials.

An early synthesis of ibuprofen which generates lots of waste, all waste chemicals marked in red.

A later synthesis of the same drug was devised which produces much less waste per kilo of the drug product. This synthesis starts with the same starting materials but instead of using aluminium chloride it uses hydrogen fluoride. While I admit that the HF is a nasty so and so of a chemical (flesh eating horror acid) it is better in industry than the aluminium chloride as the product does not deactivate the catalyst. The key to the synthesis are the two catalytic steps (hydrogenation) and carbonylation using carbon monoxide where no atoms of waste are formed by the reagents when they do their work. This synthesis for the drug is likely to have a smaller impact on the environment.

New synthesis which makes less waste, all waste chemicals marked in blue.

I would like to point out that sometimes a man made pure drug is sometimes better than an poorly defined product from a plant and sometimes the less pure product from the plant is better. Now I will tell you a story about lung cancer and male smoking medical doctors. Some years ago when I was in Aberdeen I went to a lecture given by a man from the Rowett Institute of Nutrition and Health (Now part of Aberdeen University) where he told us some of the latest about vitamins and health. This lecture made me give up vitamin pills and but take up eating more fruit and veg.

We were told about a study where vitamin pills had increased the risk of lung cancer in smokers, ex-smokers and asbestos workers one example of this is G.S. Omenn et. al., New England Journal of Medicine, 1996, 334, 1150-1155 where the experiment was stopped early. This was the CARET study. In this study men were given either 30 mg of beta carotene per day and 25,000 IU of retinol (vitamin A) in the form of retinyl palmitate per day or a placebo pill. The men on the vitamin pills were suffering more cases of lung cancer than the people taking the dummy pills.

Now I know that you all think that vitamins are good for your health, but this study suggested the total reverse. The man from the Rowette suggested that the reason might be that humans need a series of different isomers of the beta carotene and that by flooding the body with large amounts of one isomer will cause a shortage of the other isomers by overloading the transport process for the beta carotenes with one single compound.

In the end it has been shown that high doses of beta carotene do make smoking more dangerous by a different mechanism but it was an interesting hypothesis (I am not sure if it has been fully tested yet) which made me stop trying to fix a bad diet with vitamin pills. I then tried to eat a better diet with more fresh fruit and veg.

OK the score is now pills 0, plants 1. But after I have irked some of the pill pushers I am about to do likewise with the plant pushers in my next post.


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