Rapid 'on-column' preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde

Construction of Fused Oxacyclic Compounds via Dual α- and β-C-H Functionalization and Ring Decomposition of Cyclic Ethers

A new synthetic method for the synthesis of bicyclic scaffolds featuring a dihydropyran and tetrahydrofuran (THF) hybrid in the fashion of a fused structure with excellent syn-selectivity is realized via the reactions of enaminones and THF. In addition to displaying a dual role as both a cyclic fragment and a one-carbon synthon, the current method also shows a rarely known mode of two vicinal C-H bonds' functionalization in THF or analogous oxa-heterocycles.

Efficient Reductive N-11C-Methylation Using Arylamines or Alkylamines and In Situ-Generated [11C]Formaldehyde From [11C]Methyl Iodide

Reductive N-11C-methylation using [11C]formaldehyde and amines has been used to prepare N-11C-methylated compounds. However, the yields of the N-11C-methylated compounds are often insufficient. In this study, we developed an efficient method for base-free reductive N-11C-methylation that is applicable to a wide variety of substrates, including arylamines bearing electron-withdrawing and electron-donating substituents. A 2-picoline borane complex, which is a stable and mild reductant, was used. Dimethyl sulfoxide was used as the primary reaction solvent, and glacial acetic acid or aqueous acetic acid was used as a cosolvent. While reductive N-11C-methylation efficiently proceeded under anhydrous conditions in most cases, the addition of water to the reductive N-11C-methylation generally increased the yield of the N-11C-methylated compounds. Substrates with hydroxy, carboxyl, nitrile, nitro, ester, amide, and phenone moieties and amine salts were applicable to the reaction. This proposed method for reductive N-11C-methylation should be applicable to a wide variety of substrates, including thermo-labile and base-sensitive compounds because the reaction was performed under relatively mild conditions (70°C) without the need for a base.

Gas Phase Transformations in Carbon-11 Chemistry

The short-lived positron-emitter carbon-11 (t1/2 = 20.4 min; β+, 99.8%) is prominent for labeling tracers for use in biomedical research with positron emission tomography (PET). Carbon-11 is produced for this purpose with a cyclotron, nowadays almost exclusively by the 14N(p,α)11C nuclear reaction, either on nitrogen containing a low concentration of oxygen (0.1-0.5%) or hydrogen (~5%) to produce [11C]carbon dioxide or [11C]methane, respectively. These primary radioactive products can be produced in high yields and with high molar activities. However, only [11C]carbon dioxide has some utility for directly labeling PET tracers. Primary products are required to be converted rapidly and efficiently into secondary labeling synthons to provide versatile radiochemistry for labeling diverse tracer chemotypes at molecular positions of choice. This review surveys known gas phase transformations of carbon-11 and summarizes the important roles that many of these transformations now play for producing a broad range of labeling synthons in carbon-11 chemistry.

Recent Developments in Carbon-11 Chemistry and Applications for First-In-Human PET Studies

Positron emission tomography (PET) is a molecular imaging technique that makes use of radiolabelled molecules for in vivo evaluation. Carbon-11 is a frequently used radionuclide for the labelling of small molecule PET tracers and can be incorporated into organic molecules without changing their physicochemical properties. While the short half-life of carbon-11 (11C; t½ = 20.4 min) offers other advantages for imaging including multiple PET scans in the same subject on the same day, its use is limited to facilities that have an on-site cyclotron, and the radiochemical transformations are consequently more restrictive. Many researchers have embraced this challenge by discovering novel carbon-11 radiolabelling methodologies to broaden the synthetic versatility of this radionuclide. This review presents new carbon-11 building blocks and radiochemical transformations as well as PET tracers that have advanced to first-in-human studies over the past five years.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

MAIN BODY

This commentary of highlights has resulted in 21 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals.

CONCLUSION

Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field in various topics including new PET-labelling methods, FAPI-tracers and imaging, and radionuclide therapy being the scope of EJNMMI Radiopharmacy and Chemistry.

11C-Labeled Radiotracer for Noninvasive and Quantitative Assessment of the Thiocyanate Efflux System in the Brain

Thiocyanate (SCN^-) alters the potency of certain agonists for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, and dysfunctions in AMPA receptor signaling are considered to underlie a number of neurological diseases. While humans may be exposed to SCN^- from the environment, including food sources, a carrier-mediated system transports SCN^- from the brain into the blood and is an important regulator of SCN^- distribution in the central nervous system. The assessment of this SCN^- efflux system in the brain would thus be useful for understanding the mechanisms underlying the neurotoxicity of SCN^- and for elucidating the relationship between the efflux system and brain diseases. However, the currently available technique for studying SCN^- efflux is severely limited by its invasiveness. Here, we describe the development of a SCN^- protracer, 9-pentyl-6-[¹¹C]thiocyanatopurine ([¹¹C]1), to overcome this limitation. [¹¹C]1 was synthesized by the reaction of the iodo-precursor and [¹¹C]SCN^- or the reaction of the disulfide precursor with [¹¹C]NH₄CN. The protracer [¹¹C]1 entered the brain after intravenous injection into mice and was rapidly metabolized to [¹¹C]SCN^-, which was then eliminated from the brain. The efflux of [¹¹C]SCN^- was dose-dependently inhibited by perchlorate, a monovalent anion, and the highest dose caused an 82% reduction in the efflux rate. Our findings demonstrate that [¹¹C]1 can be used for the noninvasive and quantitative assessment of the SCN^- efflux system in the brain.