Chirality essentially means ‘mirror-image, non-superimposable molecules’, and to say that a molecule is chiral is to say that its mirror image (it must have one) is not the same as it self. At molecular level, chirality is a property of individual molecules, properly characterized as a molecule having two forms which is a molecule of identical composition but arranged in a non-super imposable mirror image configuration.
Thalidomide was prescribed widely to pregnant women between 1957 and 1962 for its benefits in reducing morning sickness.
After the drug began to be marketed, children born to women taking it displayed horrific birth defects–often extremely shortened arms and hands that were not functional. Less obvious abnormalities were defects in children’s eyes and hearts, deformed alimentary canals and urinary tracts. The drug was pulled from the market after these problems, along with death rates approaching 50%, were reported. This disaster helped lead to the creation of the modern drug testing and approval regime in the United States and Europe.
Further research revealed that thalidomide exist in two varients owing to chirality as mentioned above. Out of this, only the form on the right (the “R” form) was therapeutically active; the one on the left (the “S” form) was not only ineffective, it was the source of the birth defects. This is one instance where in chirality lead to different effect on human beings and lead to further researches where in chiral compounds are further tested to ensure the safety of the drugs.