Thalidomide is the classical example of why using an enantiomerically pure drug instead of a racemic mixture is a good idea. There are now several drugs which were once sold as racemates that are available as single enantiomers. Nexxium™ (esomeprazole) is the S isomer of Prilosec™ (omeprazole). I think there’s enantiomerically pure Prozac also. Some drugs, like Paxil, have always been sold as a single isomer.
Organic synthesis has reached a point where preparing single enantiomers is practical and efficient for most drugs. Though research into new “asymmetric” reactions is ongoing and is a major area of organic chemistry, it’s no longer appreciably more difficult to produce a single enantiomer of a drug than to produce the racemate. Thus, these “new” drugs that are really just one enantiomer of an old racemic drug are primarily a marketing ploy.
So, while nature is still better at asymmetric synthesis than organic chemists are (mostly because enzymes are inherently asymmetric catalysts for a specific reaction), we’re getting pretty good at it.
On stereochemical nomenclature:
The labels d, l, dl- for dextrorotatory, levorotatory and racemic compounds are obsolete; the preferred system is (+),(-),(±)-. This avoids confusion with the labels D, L, DL-, which refer to the orientation of a certain group on the right or left side of a molecule when drawn as a Fischer projection (an old, annoying way of drawing molecules, mostly carbohydrates; DL- means a mixture of D- and L- compounds). Since D, L, DL- is closer akin to R, S- than to d,l-, it’s a good idea to use the new labels.
R,S nomenclature depends on the ‘priority’ of groups attached to a carbon atom according to a system called the Cahn-Ingold-Prelog rules. This is the preferred method of describing stereochemistry. Cis,trans- isomerism has already been described, but this really only applies to double bonds with two different substituents. If more than two non-hydrogen groups are attached to the double bond, E,Z- nomenclature is used. This uses the same Cahn-Ingold-Prelog rules as R,S-. If the two groups having the highest priority are on the same side of the double bond (i.e., a cis-like configuration), then it’s Z, from the German zusammen meaning “together”. If they’re on opposite sides (trans-like), then it’s E, for entgegen “opposite”.
The profoundly confusing world of stereochemical nomenclature isn’t limited to these (but those are most of the types of isomerism found in organic molecules). There’s also re, si-, mer, fac-, delta, lambda-, syn,anti-…
If you want to learn very slightly more about chirality while having an altogether insignificant amount of fun, you should play the Chirality Game at the Nobel website.
I love the part where a snail explains the meaning of “chiral” to another snail:
Look at this molecule. It is non-superposable on its mirror image.
That’s the definition of “enantiomer”; really helpful, isn’t it?