Novel synthesis of 5-iodo-1,2,3-triazoles using an aqueous iodination system under air

Halo-1,2,3-triazoles: Valuable Compounds to Access Biologically Relevant Molecules

1,2,3-triazole is an important building block in organic chemistry. It is now well known as a bioisostere for various functions, such as the amide or the ester bond, positioning it as a key pharmacophore in medicinal chemistry and it has found applications in various fields including life sciences. Attention was first focused on the synthesis of 1,4-disubstituted 1,2,3-triazole molecules however 1,4,5-trisubstituted 1,2,3-triazoles have now emerged as valuable molecules due to the possibility to expand the structural modularity. In the last decade, methods mainly derived from the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction have been developed to access halo-triazole compounds and have been applied to nucleosides, carbohydrates, peptides and proteins. In addition, late-stage modification of halo-triazole derivatives by metal-mediated cross-coupling or halo-exchange reactions offer the possibility to access highly functionalized molecules that can be used as tools for chemical biology. This review summarizes the synthesis, the functionalization, and the applications of 1,4,5-trisubstituted halo-1,2,3-triazoles in biologically relevant molecules.

Ligand Control of Copper-Mediated Cycloadditions of Acetylene to Azides: Chemo- and Regio-Selective Formation of Deutero- and Iodo-Substituted 1,2,3-Triazoles

The participation of σ-monocopper and σ-bis-copper acetylide in mechanistic pathways for copper-catalyzed cycloaddition (CuAAC) reactions of acetylene with azides was probed by analysis of deuterium distributions in the 1,2,3-triazole product formed by deuterolysis of initially formed mono- and bis-copper triazoles. The results show that, when Cu(Phen)(PPh3)2NO3 is used as the catalyst for reactions of acetylene with azides in DMF/D2O, 1-substituted-5-deutero-1,2,3-triazoles are generated selectively. This finding demonstrates that the Cu(Phen)(PPh3)2NO3-catalyzed cycloadditions utilize monocopper acetylide as the substrate and produce 5-copper-1,2,3-triazoles initially. Conversely, when DBU or Et3N is the copper ligand, the process takes place through initial formation and cycloaddition of bis-copper acetylide to produce 4,5-bis-copper-triazole, which reacts with D2O to form the corresponding 4,5-bis-deutero-triazole. Moreover, when C2D2 is used as the substrate, Cu(Phen)(PPh3)2NO3 as the Cu ligand, and H2O/DMF as the solvent, mono-C4-deutreo 1,2,3-triazoles are generated in high yields and excellent levels of regioselectivity. Lastly, CuAAC reactions of acetylene with azides, promoted by CuCl2·2H2O and NaI, yield 4,5-diiodo-1,2,3-triazoles with moderate to high efficiencies.

Click Chemistry and Radiochemistry: An Update

The term "click chemistry" describes a class of organic transformations that were developed to make chemical synthesis simpler and easier, in essence allowing chemists to combine molecular subunits as if they were puzzle pieces. Over the last 25 years, the click chemistry toolbox has swelled from the canonical copper-catalyzed azide-alkyne cycloaddition to encompass an array of ligations, including bioorthogonal variants, such as the strain-promoted azide-alkyne cycloaddition and the inverse electron-demand Diels-Alder reaction. Without question, the rise of click chemistry has impacted all areas of chemical and biological science. Yet the unique traits of radiopharmaceutical chemistry have made it particularly fertile ground for this technology. In this update, we seek to provide a comprehensive guide to recent developments at the intersection of click chemistry and radiopharmaceutical chemistry and to illuminate several exciting trends in the field, including the use of emergent click transformations in radiosynthesis, the clinical translation of novel probes synthesized using click chemistry, and the advent of click-based in vivo pretargeting.

Radiosynthesis of 5-[18F]Fluoro-1,2,3-triazoles through Aqueous Iodine-[18F]Fluorine Exchange Reaction

In this report, a simple and efficient process to achieve fluorine-18-labeled 1,2,3-triazole is reported. The heteroaromatic radiofluorination was successfully achieved through an iodine–fluorine-18 exchange in an aqueous medium requiring only trace amounts of base and no azeotropic drying of fluorine-18. This methodology was optimized on a model reaction and further validated on multiple 1,2,3-triazole substrates with 18–60% radiochemical conversions. Using this strategy—the radiosynthesis of a triazole-based thiamin analogue—a potential positron emission tomography (PET) probe for imaging thiamin-dependent enzymes was synthesized with 10–16% isolated radiochemical yield (RCY) in 40 min (uncorrected, n > 5).