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J Nucl Med. 2008; 49 (Supplement 1):142P
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Radiopharmaceutical Chemistry: New Chemistry-Neurosciences

Radiotracers - Receptors and Transporters

New nucleophilic three-step synthesis of 6-[18F]fluoro-L-DOPA

Franziska Wagner1, Johannes Ermert1 and Heinz Coenen1

1 Institute of Neuroscience and Biophysics: Nuclear Chemistry, Forschungszentrum Juelich GmbH, Juelich, Germany

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Objectives: 6-[18F]Fluoro-L-DOPA is one of the few established radiopharmaceuticals, which is used for the diagnosis of central motor disorders and also of brain and peripheral endocrine tumors with PET. The presently used method of preparation of the radiotracer by electrophilic labelling is limited to low amounts of activity at relatively high costs. The hitherto developed nucleophilic syntheses result either in insufficient enantiomeric purity or the multi-step syntheses are very complex to be automated and thus limited to a few labs. In this study a novel nucleophilic approach for the preparation of 6-[18F]fluoro-L-DOPA was developed and evaluated, using a direct nucleophilic 18F-fluorination of a protected amino acid precursor.

Methods: The general suitability of a (S)-BOC-BMI-derivative for the synthesis of 18F-labeled aromatic amino acids, which is activated by a formyl group for a nucleophilic 18F-exchange, has been studied. The precursor for the preparation of c.a. 6-[18F]fluoro-L-DOPA, (2S,5S)-tert.-butyl-5-(4-benzyloxy-2-fluoro-formylbenzyl)-2-tert.-butyl-3-methyl-4-oxoimidazolidine-1-carboxylate, was synthesized in 11 steps. After its 18F-labelling and two further radiosynthetic steps, including a Baeyer-Villiger-oxidation with mCPBA and a hydrolysis with HBr, c.a. 6-[18F]fluoro-L-DOPA was isolated by semi-preparative HPLC. Optimation studies are still being performed.

Results: The complete preparation and isolation of c.a. 6-[18F]fluoro-L-DOPA thus far resulted in a radiochemical yield of about 22 % within a synthesis time of 105 minutes. The enantiomeric excess of the desired L-isomer was > 98 %.

Conclusions: A new developed precursor enables the nucleophilic radiosynthesis of 6-[18F]fluoro-L-DOPA in a more efficient way and, furthermore, lends itself to easier automation.





This Article
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Right arrow Articles by Wagner, F.
Right arrow Articles by Coenen, H.
PubMed
Right arrow Articles by Wagner, F.
Right arrow Articles by Coenen, H.