Chiralpedia

Chiral Resolution by Enzymes
Definition: Use of biocatalysts to selectively transform one enantiomer.
Context: Scalable, green alternative to chemical resolution.
Example: Lipase-catalyzed ester hydrolysis.
Related Terms: Biocatalysis, Kinetic Resolution.
Reference: Bornscheuer, Nature (2012).

Dynamic Kinetic Resolution (DKR)

Paired Concept: Kinetic Resolution

Definition: Resolution combined with in situ racemization to yield >50% of the desired enantiomer.
Context: Boosts efficiency in API synthesis.
Example: Lipase DKR of secondary alcohols.
Related Terms: Kinetic Resolution, DYKAT.
Reference: Pellissier, Tetrahedron (2003).

Kinetic Resolution (KR)

Paired Concept: Dynamic Kinetic Resolution

Definition: A process in which the two enantiomers of a racemic mixture react at different rates with a chiral reagent, catalyst, enzyme, or biological system, leading to preferential conversion of one enantiomer while the other remains relatively unreacted.
Context: Kinetic resolution is one of the most widely used methods for obtaining enantiomerically enriched or enantiopure compounds. The separation arises from differences in reaction rates rather than differences in physical properties. Enzymatic resolutions (e.g., lipase-catalyzed esterifications), asymmetric catalytic transformations, and biotransformations are common examples. A classical kinetic resolution has a theoretical maximum yield of 50% for the desired enantiomer because only one enantiomer is selectively transformed while the other is recovered.
Example: The lipase-catalyzed esterification of racemic secondary alcohols often converts one enantiomer faster than the other, yielding an enantiomerically enriched ester and an enantiomerically enriched unreacted alcohol. Industrially, enzymatic kinetic resolution has been used in the preparation of chiral pharmaceutical intermediates.
Related Terms: Dynamic Kinetic Resolution (DKR), Chiral Resolution, Enantiomeric Excess (ee), Enantioselectivity, Racemate, Asymmetric Catalysis, Biocatalysis.
Reference: Kagan, H. B., & Fiaud, J. C. (1988). "Kinetic Resolution." Topics in Stereochemistry, 18, 249-330; Faber, K. (2018). Biotransformations in Organic Chemistry (7th ed.). Springer. ISBN: 978-3319615227; Jacobsen, E. N., Pfaltz, A., & Yamamoto, H. (Eds.). (1999). Comprehensive Asymmetric Catalysis. Springer; International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book) - Definitions related to kinetic resolution and stereoselective reactions.
Key Distinction: Kinetic Resolution (KR): Separates enantiomers based on different reaction rates; maximum theoretical yield = 50% of the desired enantiomer. Dynamic Kinetic Resolution (DKR): Combines kinetic resolution with in situ racemization of the slower-reacting enantiomer; theoretical yield can approach 100%. Chiral Resolution: A broader term encompassing all methods used to separate enantiomers, including kinetic resolution. Enantioselectivity: The preference for formation or consumption of one enantiomer over the other during a reaction.

Resolution (Chiral Resolution)

Paired Concept: Racemization

Alternative Strategy: Chiral Synthesis

Broader Concept: Chiral Separation

Definition: Resolution, also referred to as chiral resolution, is the process of separating the individual enantiomers of a racemic mixture to obtain one or both enantiomers in enantioenriched or enantiopure form.
Synonyms: Chiral Resolution; Optical Resolution (historical term); Enantiomeric Resolution.
Context: Resolution is one of the principal strategies for obtaining optically active compounds from racemic mixtures. Unlike asymmetric synthesis, which creates chirality during chemical synthesis, resolution begins with a racemate and separates its constituent enantiomers. Resolution may be achieved by classical methods (e.g., diastereomeric salt formation and fractional crystallization), chromatographic techniques using chiral stationary phases, enzymatic or kinetic resolution, dynamic kinetic resolution, or preferential crystallization. Resolution remains an indispensable technique in pharmaceutical development, agrochemical production, natural product isolation, and analytical chemistry.
Example: The enantiomers of ibuprofen can be resolved by chiral high-performance liquid chromatography (HPLC) using a chiral stationary phase. Alternatively, racemic amines may be resolved by forming diastereomeric salts with a chiral resolving agent, followed by fractional crystallization.
Related Terms: Classical Resolution, Kinetic Resolution, Dynamic Kinetic Resolution, Optical Resolution, Chiral Separation, Racemate, Enantiopure, Enantioenriched, Chiral Chromatography, Asymmetric Synthesis.
Reference: Jacques, J., Collet, A., & Wilen, S. H. (1994). Enantiomers, Racemates, and Resolutions. Krieger Publishing Company, Malabar, Florida. ISBN: 978-0894648282; Ahuja, S. (2000). Chiral Separation Methods for Pharmaceutical and Biotechnological Products. John Wiley & Sons. ISBN: 978-0471370308; Faber, K. (2018). Biotransformations in Organic Chemistry (7th ed.). Springer. ISBN: 978-3319615227; International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book) - Entries on resolution and enantiomer separation.
Key Distinction
Resolution (Chiral Resolution): Separation of the enantiomers of a racemic mixture into individual enantiomers.
Chiral Separation: A broader term encompassing all methods used to separate enantiomers, whether from a racemate or an enantioenriched mixture.
Asymmetric Synthesis: Direct preparation of one enantiomer from achiral or prochiral starting materials using a chiral source.
Racemization: Conversion of an enantiomerically enriched or enantiopure compound into a racemic mixture, thereby reducing or eliminating enantiomeric excess.
Key Insight
Resolution is the classical and preferred stereochemical term for the separation of a racemic mixture into its constituent enantiomers. Since the process inherently involves chiral molecules, the adjective "chiral" is optional; therefore, Resolution and Chiral Resolution are generally regarded as synonymous in stereochemistry. The term Optical Resolution is an older synonym that originated from the historical use of optical rotation to distinguish and isolate enantiomers.