Yesterday we started Stereochemistry in my Organic Class, and on Monday Azmanam on the Chemistry Blog had a post on Chiral Drugs. Take a look at the structures below:
Both are used to treat gastroesophageal reflux desease (GERD, commonly known as acid reflux). Can you see the difference in the structures? Click the image to see a larger version. Prilosec is sold as a racemic mixture: a 50-50 mix of the R and S enantiomers. Nexium contains just one enantiomer - the S isomer. This is an example of a chiral molecule whose stereogenic center is not a carbon, but rather a sulfur. The fourth group attached to the sulfur - the one with the lowest priority - is a lone pair of electrons. Read Azmanam 's post for a good discussion of the two.
Chemistry Blog - Nexium’s Dirty Little Secret