Fluorine-18
is a positron emitting radioisotope. It has a half-life of 109.8 min, a simple decay
profile and low positron energy as a result of which properties fluorine-18 is
an excellent candidate for use in the production of tracers for positron
emission tomography (PET). Radiochemistry with fluorine-18 starts from the
production of the radioactive isotope, which is then used for the labelling of
bioactive molecules. The labelling can be done by nucleophilic or electrophilic
methods. Nucleophilic 18F-fluorination,
using [18F]F-,
is the most popular approach due to the effective production method. Production
of [18F]F2 is
more challenging and is one of the limiting factors for the use of
electrophilic 18F-fluorination.
Production of [18F]F2
requires the addition of carrier F2,
which reduces the molar activity of the product. The electrophilic labelling
method that gives the highest molar activity utilizes a high voltage discharge
in the production of [18F]F2.

In
this study, the first of the methods developed for the production of [18F]F2
replaces the high voltage discharge with a milder, more reliable
excitation source i.e., high energy photons. In a second method, the toxic,
very reactive F2 gas used as a
carrier is replaced by the very inert SF6 gas.
In addition, new applications of [18F]F2
based labelling syntheses were developed. [18F]F2
and its derivatives were used for stereoselective 18F-fluorination,
for the production of [18F]-4-fluorosydnone,
a new reagent for click chemistry as well as, for the production of 6-[18F]fluoro-marsanidine,
a PET tracer candidate for brain α2A-adrenoceptors
imaging.

 Both
methods developed for the production of [18F]F2
resulted in the production of the desire product in low yield
and with moderated molar activity (Am).
Stereoselective 18Ffluorination resulted
in high yield and products in high enantiomeric excess. [18F]-4-
fluorosydnone, was successfully used for a click reaction, resulting in rapid
complete cycloaddition. 6-[18F]fluoro-marsanidine
was synthetized with a quality sufficient for preclinical evaluation. However,
rapid in vivo metabolism
limits its usefulness for brain α2Aadrenoceptor
imaging in rodents.