7.7 Enantiomers and Biochemistry
The way enantiomers interact with plane-polarized light is not the only way enantiomers act differently. As was mentioned earlier with thalidomide, enantiomers can interact with the human body in different ways. The reason enantiomers behave differently is that much of the human body is chiral. Our amino acids are chiral. We only have one enantiomer of amino acids in our body. These enantiomeric amino acids make enantiomeric proteins and enantiomeric enzymes. One enantiomer of a compound can fit into an enzyme, but the mirror image enantiomer cannot.
Enantiomers of compounds can even smell differently to us. (R)-carvone smells like spearmint while (S)-carvone smells like caraway seeds. (R)-limonene smells like oranges while (S)-limonene smells like lemons.
We need to be very careful when making medicines because of this effect in the human body. If a chiral compound helps cure a disease, we need to make sure its enantiomer is removed from the sample given to people, a very expensive proposition, or does not cause harm.