Synthesis of ¹³N-labelled radiotracers by using microfluidic technology

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.