Authors:
Noeen Malik University of Ulm Clinic for Nuclear Medicine Albert-Einstein-Allee 23 89081 Ulm Germany

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Christoph Solbach University of Ulm Clinic for Nuclear Medicine Albert-Einstein-Allee 23 89081 Ulm Germany

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Wolfgang Voelter Eberhard-Karls-University Interfacultary Institute for Biochemistry Tübingen Germany

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Hans-Jürgen Machulla Eberhard-Karls-University Radiopharmacy Tübingen Germany

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Abstract  

For the radiofluorination of benzenes and benzene derivatives, the electrophilic reaction with [18F]F2 is a very common route. Yet, aromatic nucleophilic substitution (SNAr) by n.c.a [18F]fluoride, which can be produced efficiently in high amounts, has been considered to be very desirable. However, to facilitate 18F-labelling via SNAr at an electron rich aromatic system, an appropriate leaving group must be present together with an auxiliary group in ortho or para position to the leaving group. An interesting alternative for the auxiliary group is the heteroatom of a heteroaromatic system, for which pyridine is a leading example. Dolci et al. (J Label Compd Radiopharm 42:975–985, <cite>1999</cite>) have evaluated the scope of the nucleophilic aromatic fluorination of 2-substituted pyridine rings using the activated K [18F]F-K222 complex. As methyl and methoxy groups are known to enhance the electron density of an aromatic system by the +I and the +M effect, respectively, SNAr is unlikely to occur. Until now, the effect of these substituents has not been studied towards the 18F-radiofluorination of substituted 2-nitropyridines by use of [18F]fluoride. Therefore, we have investigated the effect of methoxy and methyl groups in 2-nitropyridines. The results showed that 3-methoxy-2-nitropyridine and 3-methyl-2-nitropyridine can efficiently be substituted by [18F]fluoride with high RCY’s (70–89%) in short reaction times (1–30 min) at a reaction temperature of 140 °C. Moreover, 3-methoxy-6-methyl-2-[18F]fluoropyridine was obtained from the corresponding nitro-precursor in a high yield of 81 ± 1% after 30 min at 140 °C. In case of 2-nitropyridines data indicates the effect of methyl and methoxy groups on SNAr to be of minor importance.

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Journal of Radionalytical and Nuclear Chemistry
Language English
Size A4
Year of
Foundation
1968
Volumes
per Year
1
Issues
per Year
12
Founder Akadémiai Kiadó
Founder's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Publisher Akadémiai Kiadó
Springer Nature Switzerland AG
Publisher's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
CH-6330 Cham, Switzerland Gewerbestrasse 11.
Responsible
Publisher
Chief Executive Officer, Akadémiai Kiadó
ISSN 0236-5731 (Print)
ISSN 1588-2780 (Online)