Chiral resolution

Chiral resolution separates the two enantiomers in a racemic mixture by exploiting their different interactions with a chiral agent or environment.

Diastereomeric salt resolution: A resolution method that converts enantiomers into separable diastereomeric salts using a chiral acid or base. A classic route: the resolving agent makes salts with different solubilities, allowing crystallization to separate them.
Ibuprofen: A nonsteroidal anti-inflammatory drug whose S-enantiomer is primarily responsible for cyclooxygenase inhibition. Its enantiomers illustrate how resolution can provide a pharmacologically preferred form.
Kinetic resolution: A process that consumes one enantiomer faster than the other through a selective reaction or transformation. Unlike physical separation, it distinguishes enantiomers by their different reaction rates.
Enantiomers: Stereoisomers that are non-superimposable mirror images of each other. These are the paired molecules that chiral resolution distinguishes.
Chiral chromatography: Chromatography that separates enantiomers through their different interactions with a chiral stationary phase. A chiral column can separate enantiomers without first converting them into isolable diastereomeric salts.
Thalidomide: A drug with interconverting enantiomers whose historical use caused severe birth defects. Its racemization shows why separating enantiomers alone may not preserve a drug's stereochemical composition.
Dynamic kinetic resolution: A process combining racemization of a substrate with selective conversion of one enantiomer to improve yield. It can overcome the yield limit of ordinary resolution by replenishing the enantiomer that reacts selectively.
Chirality: The property of an object or molecule that makes it distinguishable from its mirror image by superposition. Resolution depends on molecular handedness and on interactions that recognize it.
Preferential crystallization: A crystallization technique that selectively grows one enantiomer from a supersaturated solution of a conglomerate. This method separates crystals directly when the racemate crystallizes as distinct enantiomeric crystals.
Chiral switch: The development or marketing of a single-enantiomer drug based on a medicine previously used as a racemate. Resolution can supply the single-enantiomer form pursued in a chiral switch.

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