Wednesday 20 December 2006

Glowing gin tonic (quinine)

I know quinine mostly because of the fact that it makes gin tonic glow. But it has some other nice properties, too. Most important is its use to treat malaria. It also works with other medical conditions. I am just going to talk about its structure, though.

This is its structure as seen on Wikipedia. You notice the Methoxy-quinoline, the bicyclic system called quinuclidine, and methanol in between. There are a bunch of asymmetry centers. The most important one is at the methanol. If you change its configuration, you get quinidine.

Before you scroll down, you can exercise your 3-dimensional thinking. What does the bicyclic system look like? I have to admit that I did not get it. But I don't think it is so difficult.

This is the structure as PyMOL's Ray function makes it. The structure was first drawn in ChemSketch and the geometry optimised in ArgusLab.

We needed the 3-dimensional structure mostly for the quinuclidine. Now it can be seen that it is nothing but 3 cyclohexane rings in boat conformation.

The next question would be if the rings are really this ecliptical. I don't know. It does not seem like you can make a chair in there but you could twist the rings. They were twisted after molecular modelling. But with quantum mechanics they became ecliptical. I would think that QM is more accurate than MM. But I have to admit that I could not really do a good calculation on my laptop since the molecule is fairly big.


Anonymous said...

Die 2-D Formel von Chinin (Wikipedia) ist richtig, deine 3-D Struktur ist aber falsch; das stereogene Zentrum am Chinuclidin, wo die Chinolin-hydroxymehtyl-Seitenkette angebracht ist, entspricht dem Chinidin (quasi equatorial). Somit hast Du "Epichinidin" gerechnet.

Die Konsequenz: Epi-chinidin hat eine intramolekulare H-Brücke von OH zu N, was bei den natürlichen Alkaloiden nicht der Fall ist.

Das X-ray von 9-epi-10,11-dihydrocinchonin ist mit der von dir gerechneten Struktur vergleichbar (CSD: XEXQEW; Enantiomer , 4, 389, 1999). Tatsächlich findet man die H-Brücke, und das Chinuclidin ist verdrillt, nicht ekliptisch.

Gruss Lukas

Felix said...

danke für die korrektur. ich habe die graphik aus wikipedia herausgenommen. wahrscheinlich sieht der artikel mit nur der klassischen formel auch am professionellsten aus.

Grüße felix