In recent years, pharmacutical companies have re-released several of their blockbuster drugs with a new twist. By carefully controlling the spatial arrangement of each atom in the active ingredient, chemists can increase the effectiveness of medications and sometimes prevent unwanted or horrible side effects.
Modafinil (provigil) is a treatment for narcolepsy. It also allows healthy people to stay awake for extended periods of time. Armodafinil (neuvigil) is a newer product that contains only one isomer of the drug.
Methylphenidate (ritalin) is a treatment for attention deficit hyperactivity disorder. More recently, Novartis has introduced dexmethylphenidate (focalin) which contains only a single isomer of the active molecule.
This is a bit heavy: Stereoisomers are molecules that have the same chemical formula and bonds, but a different arrangement of atoms. Enantiomers are a type of stereoisomer that are mirror images of each other — just like a right hand is the mirror image of a left hand. R-stereoisomers can be thought of as “right handed” and L-stereoisomers can be thought of as “left handed”.
In both cases, the generic names of the new drugs say something about their stereochemistry. Armodafinil sounds like R-modafinil, and in fact, it is the R-stereoisomer of the powerful stimulant. The prefix dex- in dexmethylphenidate indicates that when polarized light is shined through a solution of the substance, the polarization will rotate a bit in a clockwise direction.
Eszopiclone (Lunesta), Escitalopram (Lexapro), and Dexedrine are also pure enantiomers. Clearly, our brains are very picky about the shape of their drugs.
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