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A new method for the synthesis of the highly selective delta opioid receptor (DOR) antagonist radiotracer N1 '-([11 C]methyl)naltrindole ([11 C]MeNTI) is described. The original synthesis required hydrogenation of a benzyl protecting group after 11 C-labeling, which is challenging in modern radiochemistry laboratories that tend to be heavily automated and operate according to current good manufacturing practice. To address this challenge, we describe development of a novel MeNTI precursor bearing a methoxymethyl acetal (MOM) protecting group, which is easily removed with HCl, and employ it in an updated synthesis of [11 C]MeNTI. The new synthesis is fully automated and validated for clinical use. The total synthesis time is 45 min and provides [11 C]MeNTI in good activity yield (49 ± 8 mCi), molar activity (3,926 ± 326 Ci/mmol) and radiochemical purity (97% ± 2%).

When utilizing [18F]tetrabutylammonium fluoride ([18F]TBAF) in the synthesis of 18F-labeled radiotracers for clinical positron emission tomography (PET) imaging, it is necessary to confirm that residual TBA levels in formulated doses do not exceed established specifications (≤2.6 mg per patient dose). Historically this has been accomplished using HPLC, but this is time consuming for short-lived PET radiotracers and limited by the need for expensive equipment. This motivated us to introduce a TLC spot test for determining residual TBA, and we have developed a new method which employs the Dragendorff reagent. Herein we report details of the TLC method and use it to quantify residual TBA in different formulations of 6-[18F]fluoro-DOPA.

A new method for the synthesis of the highly selective delta opioid receptor (DOR) antagonist radiotracer N

When utilizing [

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