Positron emission tomography is an ultra-sensitive, in vivo molecular imaging technique that allows the determination of the spatiotemporal distribution of a positron emitter labeled radiotracer after administration into living organisms. Among all existing positron emitters, (18) F has been by far the most widely used both in clinical diagnosis and in preclinical investigation, while the use of (11) C significantly increased after the 1980s because of the widespread installation of biomedical cyclotrons. The use of other shorter-lived positron emitters such as (13) N (T1/2  = 9.97 min) has been historically more restricted. Paradoxically, its stable isotope ((14) N) is present in many biological active molecules; consequently, the development of strategies for the efficient incorporation of (13) N into radiotracers would represent an interesting alternative to (11) C- and (18) F-labeling. In the current paper, the developments related to (13) N chemistry are reviewed, including different production routes of primary precursors and their applications to the preparation of more complex (13) N-labeled molecules. The current situation and future perspectives are also briefly discussed.

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Microfluidics has recently emerged as a useful alternative to traditional methods for the preparation of radiotracers labelled with positron emitters. Up to date, microfluidics technology has been applied to the radiosynthesis of 18F‐labelled and 11C‐labelled compounds; however, application to other shorter‐lived positron emitters has not been investigated. The radiosynthesis of S‐[13N]nitrosothiols and N‐[13N]nitrosamines was approached in microfluidic system by reaction of the corresponding thiol or secondary amine, respectively, with [13N]NO2− in the presence of mineral acid. The radiosynthesis of azo compounds was carried out by reaction of the same labelling agent with primary aromatic amines in acidic media to yield the corresponding diazonium salts, which were further reacted with aromatic amines and alcohols to yield the corresponding 13N‐labelled azo compounds. Radiochemical conversion values for S‐[13N]nitrosothiols and 13N‐labelled azo compounds calculated from chromatographic profiles improved our previous results by using conventional methods. The formation of N‐[13N]nitrosamines could not be detected, independently of experimental conditions. In conclusion, the preparation of S‐[13N]nitrosothiols and 13N‐labelled azo compounds was successfully achieved by using microfluidics technology. Higher radiochemical conversions than those previously reported using conventional synthetic strategies have been obtained. Copyright © 2012 John Wiley & Sons, Ltd.

The increased interest in 89Zr-labelled immunoPET imaging probes for use in preclinical and clinical studies has led to a rising demand for the isotope. The highly penetrating 511 and 909 keV photons emitted by 89Zr deliver an undesirably high radiation dose, which makes it difficult to produce large amounts manually. Additionally, there is a growing demand for Good Manufacturing Practices (GMP)-grade radionuclides for clinical applications. In this study, we have adopted the commercially available TRASIS mini AllinOne (miniAiO) automated synthesis unit to achieve efficient and reproducible batches of 89Zr. This automated module is used for the target dissolution and separation of 89Zr from the yttrium target material. The 89Zr is eluted with a very small volume of oxalic acid (1.5 mL) directly over the sterile filter into the final vial. Using this sophisticated automated purification method, we obtained satisfactory amount of 89Zr in high radionuclidic and radiochemical purities in excess of 99.99%. The specific activity of three production batches were calculated and was found to be in the range of 1351–2323 MBq/µmol. ICP-MS analysis of final solutions showed impurity levels always below 1 ppm.