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).
