I know that the drug Thalidomide is a chiral compound with one chiral center, therefore it has 2 enantiomers. I also know that one enantiomer is harmless, but the other is very harmful and causes birth defects. How exactly does this happen? Does it have something to do with the rotation of the molecule? Does it have something to do with how steric the compound becomes in its mirror image? I never fully understood this topic, and I can never seem to understand why a mirrored image of essentially the same compound has different properties.
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This should become clear when you realise that the proteins in your body are also three-dimensional. Drugs interact with the body by binding to the proteins – either to the surface or a cavity on the protein. For the protein, a mirror image of the drug is not the same shape, and it doesn’t fit the intended binding site. So the mirrored molecule might be without effect or bind to a different site, or different protein, causing different, potentially undesired effects.
(Think about dextrometorphan, an antitussive cough medicine that has a mirrored morphinan scaffold. The mirror image levomethorphan is a potent opioid, but dextromethorphan has only weak affinity to opioid receptors, instead binding elsewhere.)
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