Chiralpedia

D-(Dexter, Right)
Definition: A stereochemical prefix denoting a configuration relative to D-glyceraldehyde, not the direction of optical rotation.
Context: Used in carbohydrate and amino acid nomenclature to define absolute configuration based on Fischer projection.
Example: D-glucose corresponds to the configuration of D-glyceraldehyde.
Related Terms: L-; Fischer Projection; Absolute Configuration.
Reference: Fischer, E. "Einfluss der Configuration auf die Wirkung der Enzyme." Ber. Dtsch. Chem. Ges. 24, 1836-1845 (1891).

Deracemization
Definition: Conversion of a racemic mixture to an enantiopure product without external chiral source.
Context: Strategic for late-stage purification and process intensification.
Example: Viedma ripening, enzymatic deracemization.
Related Terms: Viedma Ripening, Absolute Asymmetric Synthesis.
Reference: Blackmond, Angew. Chem. (2010).

Dextro-(d, +)

Paired Concept: Levo- (l, –)

Definition: Denotes a compound that rotates plane-polarized light to the right (clockwise).
Context: Optical rotation descriptors are experimental and distinct from R/S configuration.
Example: D-(+)-glucose.
Related Terms: Levo-, Optical Activity, Specific Rotation.
Reference: IUPAC Gold Book.

Diastereomer (Diastereoisomer)

Paired Concept: Enantiomer

Definition: Stereoisomers not related as mirror images.
Context: Often differ in physical properties, enabling separation and selective synthesis.
Example: Erythro vs threo diols.
Related Terms: Enantiomer, Relative Configuration.
Reference: Eliel & Wilen (1994).

Diastereomeric Excess (de)
Definition: Absolute difference between diastereomer fractions.
Context: QC metric when diastereomers are formed.
Example: 80% syn, 20% anti → 60% de.
Related Terms: dr, Stereoselectivity.
Reference: IUPAC Gold Book.

Diastereomeric Ratio (dr)
Definition: Ratio of diastereomers formed in a reaction.
Context: Guides optimization of diastereoselective steps.
Example: 95:5 syn:anti aldol product.
Related Terms: Diastereomeric Excess, Stereoselectivity.
Reference: IUPAC Gold Book.

Distomer

Paired Concept: Eutomer

Definition: The enantiomer of a chiral drug that exhibits lower desired pharmacological activity or therapeutic potency than its counterpart (the eutomer) at the target receptor or biological system.
Context: The two enantiomers of a chiral drug often differ in their interactions with biological targets because of stereoselective molecular recognition. The distomer may be less active, inactive, possess different pharmacological activity, or, in some cases, contribute to adverse effects or toxicity. However, a distomer is not necessarily undesirable; it may exhibit beneficial pharmacological actions, influence pharmacokinetics, or undergo chiral inversion to the eutomer. The relative potency of the eutomer and distomer is expressed by the eudismic ratio.
Example: R-Ibuprofen is the distomer because it has much lower cyclooxygenase (COX) inhibitory activity than S-ibuprofen, the eutomer. However, R-ibuprofen is partially converted in vivo to the active S-enantiomer by metabolic chiral inversion.
Related Terms: Eutomer, Eudismic Ratio, Enantiomer, Racemate, Chiral Drug, Chiral Inversion, Chiral Switch.
Reference: Ariens, E. J. (1984). "Stereochemistry, a Basis for Sophisticated Nonsense in Pharmacokinetics and Clinical Pharmacology." European Journal of Clinical Pharmacology, 26, 663-668; Ariens, E. J. (1986). "Stereochemistry: A Source of Problems in Medicinal Chemistry." Medicinal Research Reviews, 6(4), 451-466; Nguyen, L. A., He, H., & Pham-Huy, C. (2006). "Chiral Drugs: An Overview." International Journal of Biomedical Science, 2(2), 85-100; Smith, S. W. (2009). "Chiral Toxicology: It's the Same Thing... Only Different." Toxicological Sciences, 110(1), 4-30.
Key Distinction:
Distomer: The enantiomer with lower desired pharmacological activity or therapeutic potency. Eutomer: The enantiomer with the greater desired pharmacological activity or therapeutic potency. Eudismic Ratio: The ratio of the potency of the eutomer to that of the distomer. Chiral Inversion: Metabolic conversion of one enantiomer into its mirror-image enantiomer (e.g., R-ibuprofen ? S-ibuprofen).

DNA Chirality
Definition: DNA adopts right-handed helices (B-form) with chiral sugar backbone.
Context: Chiral recognition of intercalators and drugs depends on helix sense.
Example: D-sugar backbone in nucleic acids.
Related Terms: Helicity, Stereorecognition.
Reference: Watson & Crick; Voet & Voet (2011).

Double Stereodifferentiation
Definition: Outcome determined by interaction of substrate and reagent chirality (matched/mismatched).
Context: Critical in planning complex multi-stereocenter syntheses.
Example: Aldol with chiral enolate and chiral aldehyde.
Related Terms: Matched/Mismatched, Stereocontrol.
Reference: Seebach (1979).

Dynamic Kinetic Asymmetric Transformation (DYKAT)
Definition: Asymmetric reaction converting a racemic substrate mixture to a single enantiomer product via equilibration.
Context: Converts racemic starting materials fully to one enantiomer product.
Example: Pd-catalyzed allylic substitutions.
Related Terms: DKR, Enantioconvergent Synthesis.
Reference: Kagan, Acc. Chem. Res. (1997).

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).

Dynamic NMR (DNMR)
Definition: NMR methods to study exchange processes and barriers (e.g., enantiomerization).
Context: Quantifies ΔG‡ for atropisomer interconversion relevant to stability.
Example: DNMR of hindered biaryls.
Related Terms: Barrier to Rotation, Enantiomerization.
Reference: Sandström, Dynamic NMR (1982).