Journal of labelled compounds and radiopharmaceuticals p. 345 - 356 (2006)
Update date:2022-08-04
Topics:
Abrahim, Aiman
Angelberger, Peter
Kletter, Kurt
Mueller, Markus
Joukhadar, Christian
Erker, Thomas
Langer, Oliver
A one-pot radiosynthesis method to prepare the new fluorine-18-labelled fluoropyridine derivatives 5-[18F]fluoro-2-pyridinamine and 6-[ 18F]fluoro-2-pyridinamine in two to three reaction steps was developed. The first step consisted of no-carrier-added nucleophilic aromatic substitution of commercially available halogen-substituted 2-pyridinecarboxamide or 2-pyridinecarbonitrile derivatives with K[18F]F-K222 in DMSO at 150-180°C. The [18F]fluoride incorporation yields ranged from 67 to 98% for all studied precursor molecules. It is remarkable that 5-bromo-2-pyridinecarbonitrile gave almost quantitative [18F] fluoride incorporation at the meta-position (5-position) of the pyridine ring after only 5 min of heating at 150°C. After base-catalysed hydrolysis of the [18F]fluorinated pyridinecarbonitriles into their corresponding carboxamides, the latter were transformed in a Hofmann-type rearrangement reaction into the respective amines by treatment of crude reaction mixtures with bromine and aqueous base (20-30% conversion yield). Reaction mixtures were purified by reversed-phase semipreparative HPLC followed by strong cation exchange solid-phase extraction to afford 5-[18F]fluoro-2- pyridinamine and 6-[18F]fluoro-2-pyridinamine in non-decay-corrected radiochemical yields of 6-10% in a total synthesis time of 83-112 min. The preparation of 5-[18F]fluoro-2-pyridinamine is one of very few examples demonstrating the feasibility of nucleophilic meta-[ 18F]fluorination of a pyridine derivative. Both 5-[ 18F]fluoro-2-pyridinamine and 6-[18F]fluoro-2-pyridinamine are new potentially useful radiolabelled synthons for radiopharmaceutical chemistry. Copyright
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(2006)