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Updated: Oct 21, 2026

Enhancing Efficiency and Radiolabeling Yields of Carbon-11 Radioligands for Clinical Research Using the Loop Method
Published on: December 20, 2024
High molar activity [11C]phosgene from [11C]CO2
Edla Kerminen1, Thomas Keller2, Simo Salo2
1Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland. ekkerm@utu.fi.
Background:
[11C]Phosgene is a known but underutilised labelling synthon in PET-tracer development. The production of [11C]phosgene faces many problems such as difficulties in achieving high molar activity, regular key component replacement and complexity of the synthesis, thereby hindering its wider use. In this paper, a robust and semi-automated synthesis route for production of [11C]phosgene from [11C]CO2 was developed to solve issues restricting the use of [11C]phosgene. The high molar activity [11C]phosgene was then used for the labelling of biologically important molecules as a proof of concept.
Results:
[11C]Phosgene was synthesized from [11C]CO by UV-mediated photochemical chlorination with chlorine gas. [11C]CO was produced by the fluoride-activated disilane reduction of cyclotron-produced [11C]CO2. [11C]Phosgene was produced with satisfactory radiochemical yield (13 ± 1 GBq at EOS, 30 ± 4% dc. to SOS) based on [11C]CO2 and molar activity of 249 ± 40 GBq/µmol at EOS (n = 3). The radiosynthesis time was approximately 20 min.
Conclusion:
A robust synthesis route for production of high molar activity [11C]phosgene from [11C]CO2 was developed. The simplicity and mild reaction conditions of the [11C]CO production method used eliminate the previous issues with Zn-based reduction of [11C]CO2. Intermediate purification of [11C]CO guaranteed efficient [11C]phosgene production, and removal of unreacted Cl2 minimised unwanted side reactions. This method utilises a fixed-line device with simple set up and mild conditions. With this method, it is possible to perform syntheses reliably with good radiochemical yields and high molar activities in a short synthesis time.
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