Stable Isotopically Labeled Compounds

Stable isotopically labeled compounds are non-radioactive chemical substances where one or more element within a compound has been substituted for its stable isotope. Common stable isotopes used in research include ²H (Deuterium or D), ¹³C, ¹⁵N and ¹⁸O.

Stable labeled compounds are often used for drug metabolism and pharmacokinetics (DMPK) studies of the corresponding unlabeled drug, and can increase the accuracy of drug absorption measurements such as C_max/AUC. In contrast to radiolabeling, stable isotope labeling (e.g. deuteration) provides a safe and non-invasive method to study metabolic pathways in living systems.

Deuterated Compounds

A deuterium, or 'heavy hydrogen', ion differs from a hydrogen ion in that its nucleus contains one proton and one neutron, whereas a hydrogen ion has no neutron in its nucleus. Deuterium substitution (deuteration) is regarded as the smallest structural change that is possible in a molecule and as a result, deuterated analogs possess near identical chemical and physical properties to the unlabeled compound.

In general, deuterated compounds match the pharmacological profiles of the unlabeled equivalent. A key difference, however, is that the chemical bond between deuterium and carbon is around 6 to 9 times more stable than the carbon-hydrogen bond. Since carbon-hydrogen bonds are typically broken during drug metabolism, this property can be exploited during drug development in order to alter the metabolism of a given drug and potentially decrease the occurrence of unwanted, toxic metabolites.

Stable Labeled Compounds as Internal Standards

Stable isotopically labeled compounds are also used as internal standards in analytical chemistry to provide a control for extraction, ionization variability and HPLC injection. Internal standards are essential components of robust mass spectrometry-based bioanalysis.

In order to act as an effective internal standard, the labeled compound must show a similar chromatographic retention time, extraction recovery and ionization response to that of the analyte, but the two responses must be sufficiently resolved to enable distinction of the internal standard from the analyte.

Due to the abundance of hydrogen in organic chemistry, deuterium-labeled or 'deuterated' compounds are commonly used as internal standards. ¹³C-labeled compounds can be used as an alternative when hydrogen/deuterium (H/D) exchange is observed.

Custom Synthesis at Tocris

In addition to our range of over 3,000 high performance life science reagents, Tocris offers a wide range of high quality custom chemistry services to researchers worldwide. These include competitively priced stable isotope labeling of molecules (D, ¹³C, ¹⁵N and ¹⁸O) including those available in the Tocris catalog, in addition to their predicted metabolites.

For a competitive quote please complete a quote request form, or contact us directly. Our friendly and professional staff will gladly assist you.