Enantioselektiv

Enantioselectivity refers to the property of a chemical reaction or process to preferentially form one enantiomer over the other when chiral environments are involved. Enantiomers are non-superimposable mirror images and can exhibit notably different biological activities and physical properties. A key measure of enantioselectivity is the enantiomeric excess (ee), defined as ee = |[R] − [S]| / ([R] + [S]) × 100%, where [R] and [S] are the concentrations or amounts of the two enantiomers. Another common measure is the enantiomeric ratio (er), the ratio of the amounts of the two enantiomers in the product.

Enantioselectivity arises from a chiral environment—such as a catalyst, ligand, enzyme, or reagent—that stabilizes one transition state relative to the other, steering the reaction toward one enantiomer. Methods to achieve enantioselectivity include asymmetric synthesis using chiral catalysts (including organocatalysts and metal complexes with chiral ligands), as well as biocatalysis with enzymes. Kinetic resolution and dynamic kinetic resolution are strategies that convert racemic substrates into enantioenriched products.

Applications of enantioselective processes are widespread in pharmaceuticals, agrochemicals, and materials science, where the two enantiomers can have different efficacy or safety profiles. Enantioselective synthesis is central to many natural product syntheses and drug development programs.

Measurement of enantioselectivity typically employs chiral chromatography or spectroscopic methods to determine ee. Limitations in practice include catalyst cost, substrate scope, and achieving high selectivity across diverse reactions. The field continues to advance with advances in biocatalysis, organocatalysis, and new chiral catalyst designs.