Question

Why are enantiomers important to the pharmaceutical industry?

Answer 1

See Below

Explanation:

The simple answer is that usually only one of the enantiomers is active..while the other can represent an unknown.

Enzymes (or proteins that bind molecules but don't react...like G-protein-coupled receptors) bind the molecules the do because of specific geometries and intermolecular forces.

For this reason, Enzymes (and ligand-binding proteins) are one of the only things that can distinguish between two enantiomers. This is why you can digest a potato (with glycogen) but not an oak tree (with cellulose). The difference between the 2 polysaccharides is the difference between a single chiral center - and the enzymes that digest glycogen can't recognize cellulose.

So if you make a drug that targets a specific enzyme, then it needs an exact specific geometry to fit into the active site and bind with sufficient `K_D`. IF that drug has an enantiomer (that has differences in the regions that bind the protein), then the groups that bind groups that bind the protein (hydrogen bonds, polarity, etc) on one enantiomer will be ok, but on the other one they will point in the wrong direction.

This means that if you synthesize this drug, only half of the compounds will work (assuming 50/50....active/inactive). That is ok, but the problem becomes the inactive one. Your target was designed for the active one.....but that means you really don't know where the inactive one will bind. It might not bind anywhere, but if it binds strongly in a different spot, you can have side-effects. SOmetimes these side effects can be very dangerous (lots of drugs have side effects...and its not always because of enantiomers...sometimes it is because the drug has sufficient "`K_D` to bind other targets).

Hope that helps.