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Updated: Jun 22, 2026

18F-Labeling of Radiotracers Functionalized with a Silicon Fluoride Acceptor (SiFA) for Positron Emission Tomography
Published on: January 11, 2020
Nucleophile assisting leaving groups: a strategy for aliphatic 18F-fluorination.
Shuiyu Lu1, Salvatore D Lepore, Song Ye Li
1Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892-1003, USA. shuiyu.lu@mail.nih.gov
New arylsulfonate nucleophile assisting leaving groups (NALGs) enhance halogenation and radiofluorination reactions. These novel leaving groups improve yields, offering a stable alternative to traditional methods.
Area of Science:
- Organic Chemistry
- Medicinal Chemistry
- Radiochemistry
Background:
- Nucleophile assisting leaving groups (NALGs) are crucial for efficient chemical transformations.
- Developing novel leaving groups with enhanced reactivity and stability is an ongoing challenge.
- Arylsulfonates are common leaving groups, but their reactivity can be limited.
Purpose of the Study:
- To synthesize and evaluate novel arylsulfonate nucleophile assisting leaving groups (NALGs) with metal-chelating units.
- To investigate the mechanism of rate enhancement in halogenation reactions facilitated by these NALGs.
- To assess the utility of these NALGs in radiofluorination reactions, particularly for (18)F labeling.
Main Methods:
- Synthesis of arylsulfonate NALGs with ether-linked metal chelating units.
- Halogenation reactions using metal halides to assess NALG performance.
- Kinetic studies to probe the mechanism of rate enhancement.
- (18)F-fluorination reactions using no-carrier-added [18F]fluoride ion under microwave irradiation.
Main Results:
- The newly prepared NALGs demonstrated significant rate enhancements in halogenation reactions.
- Studies indicated that transition state stabilization, not strong precomplexation, drives rate enhancements.
- Substrates with these NALGs showed reactivity comparable to or exceeding triflates under nucleophilic conditions.
- (18)F-fluorination yields were substantially improved (2-3 fold) using select NALGs compared to traditional leaving groups, even without cryptands.
Conclusions:
- Arylsulfonate NALGs with ether-linked chelating units represent a promising class of leaving groups.
- These NALGs offer improved reactivity and stability for halogenation and radiofluorination.
- The findings facilitate efficient (18)F labeling for applications in radiochemistry and drug development.
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