Many therapeutic drugs are racemates;i.e. they are chiral molecules consisting of “left”- and “right-handed” enantiomers (stereoisomers that are mirror images of each other, and are non-superimposable). In some cases, both enantiomers of the drug contribute to some extent (or equally) to the therapeutic effect;in other cases they contribute not at all. The same is true for the adverse effects of racemate drugs: the adverse effects of a racemate drug can be greater-than, less-than, or equal to one or the other enantiomer. An unusual situation arises when a drug consists of “atropisomers”, stereoisomers arising because of hindered rotation about a single chemical bond. We summarize the concept of atropisomerism, and give examples.
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