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Estrogen chemistry

Dear Reader,

I was going to write about the case of Julian Assange but I think that rather than reading about how the UK courts are trying to choose what to do with an alleged sex criminal you would rather read about some organic chemistry. For those of you who have spotted this blog because the word “sex” appears in it I am sorry to disappoint you but this is not going to be a lurid blog post all about sex.

Instead of a crude post we have an frank, blunt, explicit and no holds barred bit of organic chemistry. Do not worry it is safe for work !

Recently my lovely female westie (Rosie) has been not quite right, in the interests of canine medical privacy I am not going to discuss what is right and wrong with her body on my blog. But today she had to go off to see the vet, after being examined by the vet she has been put on a course of estrogen pills.

This made me think about estrogen, the estrogens are a series of steroidal compounds which has an important role in female mammals. It is part of the system of hormones which regulate a series of bodily functions. By the way if you are still reading, you will have a good laugh at those who went to the red hot action site expecting to see something rude, it was a page devoted to blacksmithing. Well blacksmiths tend to beat red hot steel into shape which is a bit macho.

One example of the estrogens is estradiol. Estradiol is an aromatic compound, it is like the other steroids a tetracyclic compound. It has an aromatic ring at the opposite end to the five membered ring. It is important to understand that the two hydroxyl groups in the molecule will be very different. Different because of the electronic effects of the aromatic system.

Now before we get onto estrogen, you should cast your mind back to that blog post on overgrown snakes, like that German one which had grabbed his tail (Ouroboros). Always bear in mind that a aromatic system has to have a pi cloud which is a ring which goes on and on for ever. The story is that one chemist (Kekulé) was sitting beside a fire and he had a dream about snakes which grabbed hold of their tails and pulsated about (resonance) which is very close to what we know from modern science about benzene rings.

Before we go any further it is important to bear in mind how estrogen is made in the lab, one way is to use a combination of cobalt carbonyl chemistry and a Diels-Alder reaction. Do not worry about the cobalt step, that is some very advanced chemistry (organometallic chemistry), the important parts are the next two steps.


The core of a lab synthesis for estrogen type steroids using the Peter C. Vollhardt method.

The core of a lab synthesis of a steroid using Peter Vollhardt’s method.

Those of you who have been on my course may recall that anything with a unsaturated ring which has four electrons in it has the clear potential to be antiaromatic. The easy way to understand what
antiaromaticity does to a molecule’s stability is to imagine aromaticity as an almighty virtue. Think of the nicest person you can think of, think of all their good points as being like the super stable calmness of an aromatic molecule like benzene.

Now think of the worst person you can imagine, think of a person who is the total opposite of the best person you can imagine.

OK I will tell you about someone I admire, Verka the nun. She is kind, well read, keen to pass on the good things she knows to others, generous and a joy to know. Now imagine anti-Verka she would be cruel, ignorant (and proud of it), keen to never pass on anything useful to another soul, mean minded and a total nightmare to know. If aromatic is all the good things you can think of then antiaromatic is all the worst things about human nature you can think of.

In the case of the ring opening which converts the benzocyclobutane into the thing which does the [4+2] the ring opening reaction occurs via a transition state which has a cyclic pi system with four electrons. To avoid having an antiaromatic transition state the pi system gives its self a twist to end up being like a Möbius strip. If you do advanced organic chemistry then you may get to learn about this sort of thing.

The [4+2] reaction (Diels-Alder) goes via an aromatic transition state which has 4n+2 pi electrons (n=1) so it should not come to be too much of a shock to know that the transition state has a
conventional aromatic nature. It only exists for a small moment and then it is gone !

In the biosynthesis of steroids it starts with a simple monoterpene which is related to 2-methylbutadiene, this is converted via a series of intermediates to form squalene (hexaterpene) which is cyclised to form lanosterol


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