Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Reductive Deuteration of Nitriles: The Synthesis of α,α-Dideuterio Amines by Sodium-Mediated Electron Transfer Reactions

The first general reductive deuteration of nitriles under single-electron transfer conditions has been developed for the synthesis of α,α-dideuterio amines. This practical and cost-efficient protocol requires only bench stable and commercially available sodium dispersions and EtOD- d₁ and allows for the reductive deuteration of a variety of nitriles in excellent yields and deuterium incorporations.

Synthesis of deuterium-labeled crizotinib, a potent and selective dual inhibitor of mesenchymal-epithelial transition factor (c-MET) kinase and anaplastic lymphoma kinase (ALK)

To more accurately and rapidly achieve quantitative detection of clinical crizotinib samples, stable isotope labeled crizotinib was required as an internal standard. We have developed a method to prepare racemic [D₉ ] crizotinib using a base-catalyzed H/D exchange of both nitroso compound 2 and the acetophenone compound 6 with D₂ O and NaBD₄ reduction of 7 as the key steps to introduce the 9 deuterium atoms. Starting with 4-hydroxypiperidine, 14-step synthesis furnished the desired racemic [D₉ ] crizotinib 18. The deuterium-labeled compound 18 with the chemical purity of 99.62% was applicable for use as internal standards in the drug clinical study.

Selective α-Monomethylation by an Amine-Borane/N,N-Dimethylformamide System as the Methyl Source

A new and practical α-monomethylation strategy using an amine-borane/N,N-dimethylformamide (R₃ N-BH₃ /DMF) system as the methyl source was developed. This protocol has been found to be effective in the α-monomethylation of arylacetonitriles and arylacetamides. Mechanistic studies revealed that the formyl group of DMF delivered the carbon and one hydrogen atoms of the methyl group, and R₃ N-BH₃ donated the remaining two hydrogen atoms. Such a unique reaction pathway enabled controllable assemblies of CDH₂ -, CD₂ H-, and CD₃ - units using Me₂ NH-BH₃ /d₇ -DMF, Me₃ N-BD₃ /DMF and Me₃ N-BD₃ /d₇ -DMF systems, respectively. Further application of this method to the facile synthesis of anti-inflammatory flurbiprofen and its varied deuterium-labeled derivatives was demonstrated.

Late-Stage Isotopic Carbon Labeling of Pharmaceutically Relevant Cyclic Ureas Directly from CO2

A robust, click-chemistry-inspired procedure for radiolabeling of cyclic ureas was developed. This protocol, suitable for all carbon isotopes (11 C, 13 C, 14 C), is based on the direct functionalization of carbon dioxide: the universal building block for carbon radiolabeling. The strategy is operationally simple and reproducible in different radiochemistry centers, exhibits remarkably wide substrate scope with short reaction times, and demonstrates superior reactivity as compared to previously reported systems. With this procedure, a variety of pharmaceuticals and an unprotected peptide were labeled with high radiochemical efficiency.

Highly Selective Directed Iridium-Catalyzed Hydrogen Isotope Exchange Reactions of Aliphatic Amides

For the first time, we describe highly selective homogeneous iridium-catalyzed hydrogen isotope exchange (HIE) of unactivated C(sp3 ) centers in aliphatic amides. When using the commercially available Kerr catalyst, the HIE with a series of common antibody-drug conjugate (ADC) linker side chains proceeds with high yields, high regioselectivity, and with deuterium incorporation up to 99 %. The method is fully translatable to the specific requirements of tritium chemistry and its effectiveness was demonstrated by direct tritium labelling of a maytansinoid. The scope of the method can be extended to simple amino acids, with high HIE activity observed for glycine and alanine. In di- and tripeptides, a very interesting protecting-group-dependent tunable selectivity was observed. DFT calculations gave insight into the energies of the transition states, thereby explaining the observed selectivity and the influence of the amino acid protecting groups.

New trends and applications in cyanation isotope chemistry

In this review, newly developed cyanation methods are evaluated in regards to their usefulness in synthetic isotope chemistry. In combination with already established protocols in ^13/14 C- or ¹¹ C-isotope chemistry, this manuscript should help isotope scientists to choose the best possible method for their scientific cyanation problem, but with the main focus on ¹⁴ C-applications. Perhaps, most promising of the described novel cyanation reaction is the decarboxylation-cyanation-hydrolysis approach which makes a 1-step late-stage functionalization procedure possible.

Ruthenium-catalyzed hydrogen isotope exchange of C(sp3)-H bonds directed by a sulfur atom

We present here the first example of C(sp³)-H activation directed by a sulfur atom. Based on this transformation catalyzed by Ru/C, we have developed a hydrogen isotope exchange reaction for the deuterium and tritium labelling of thioether substructures in complex molecules.