Atropa belladonna

I just noticed how fun it is to draw structures of alkaloids. Here comes another one.

The substance is extracted from atropa belladonna. The name is ambiguous as the substance is. Atropos is one of the three Fates and Greek mythology, determining the way a person is going to die. Belladonna is Latin for beautiful woman. Just like Botox it is a neurotoxin (formerly) used in cosmetics.

Atropine works by blocking acetylcholine-receptors. Therefore it inhibits nerve activity mainly in the parasympathetic nervous system. This makes it a neurotoxin, hence atropa. Applied to the eyes it makes the pupils dilate. Since that apparently looks good the plant has the name belladonna. Of course this is really bad for your retina. It is only used for eye examinations any more.



Atropine is actually the name for the racemic mixture between (S)- and (R)-hyoscyamine. The deadly nightshade only contains the S form. It racemices quickly after isolation.



This is (S)-hyoscyamine. At the bottom you see tropa-acid (3-Hydroxy-2-phenyl-propanoic acid). The chiral center is at its second carbon atom. At the top is the bicyclic tropine group.

You do notice a similarity to acetylcholine. Especially if you think of the nitrogen of tropine protonated.



The tropine group is a [3,2,1]Bicyclooctane derivative. [3,2,1] means you have three, two, and one atoms in between the bridges. The cyclohexane ring can be arranged in a chair conformation. You also see a 5-membered and a 7-membered ring. The oxygen is in endo position, meaning it points toward the bigger part of the remaining ring.