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[18F]Difluorocarbene for positron emission tomography

Abstract

The advent of total-body positron emission tomography (PET) has vastly broadened the range of research and clinical applications of this powerful molecular imaging technology1. Such possibilities have accelerated progress in fluorine-18 (18F) radiochemistry with numerous methods available to 18F-label (hetero)arenes and alkanes2. However, access to 18F-difluoromethylated molecules in high molar activity is mostly an unsolved problem, despite the indispensability of the difluoromethyl group for pharmaceutical drug discovery3. Here we report a general solution by introducing carbene chemistry to the field of nuclear imaging with a [18F]difluorocarbene reagent capable of a myriad of 18F-difluoromethylation processes. In contrast to the tens of known difluorocarbene reagents, this 18F-reagent is carefully designed for facile accessibility, high molar activity and versatility. The issue of molar activity is solved using an assay examining the likelihood of isotopic dilution on variation of the electronics of the difluorocarbene precursor. Versatility is demonstrated with multiple [18F]difluorocarbene-based reactions including O–H, S–H and N–H insertions, and cross-couplings that harness the reactivity of ubiquitous functional groups such as (thio)phenols, N-heteroarenes and aryl boronic acids that are easy to install. The impact is illustrated with the labelling of highly complex and functionalized biologically relevant molecules and radiotracers.

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Fig. 1: Difluorocarbene chemistry, radiosynthesis and divergent reactivity of [18F]1.
Fig. 2: Scope of [18F]OCF2H, [18F]SCF2H and [18F]NCF2H from (thio)phenols and N-heterocycles.
Fig. 3: Scope of [18F]OCF2H and [18F]NCF2H.
Fig. 4: Scope of [18F]ArCF2H.

Data availability

Materials and methods, optimization studies, experimental procedures, mechanistic studies, 1H NMR, 13C NMR and 19F NMR spectra, and high-resolution mass spectrometry, infrared and HPLC data are available in the Supplementary Information.

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Acknowledgements

This research has received funding from the Engineering and Physical Sciences Research Council (EP/V013041/1, J.B.I.S.), Pfizer, Janssen, UCB, the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement number 721902 (C.F.M., S.M.H. and T.A.M.). J.F. is grateful to the Centre for Doctoral Training in Synthesis for Biology and Medicine for a studentship, generously supported by GlaxoSmithKline, MSD, Syngenta and Vertex. J.B.I.S. acknowledges financial support from an EPSRC Doctoral Prize (EP/T517811/1). R.S.P. acknowledges the RMACC Summit supercomputer at the University of Colorado Boulder and Colorado State University, the Extreme Science and Engineering Discovery Environment (XSEDE) through allocation TG-CHE180056, and support from the National Science Foundation (NSF CHE-1955876). We thank B. G. Davis, S. Verhoog and T. C. Wilson for comments, and T. Khotavivattana for preliminary experiments.

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Contributions

J.B.I.S. and C.F.M. labelled the tBu-substituted difluorocarbene reagent and performed all insertions and cycloadditions with this reagent. J.B.I.S., C.F.M. and J.F. prepared the substrates and performed all automation experiments. J.B.I.S. and J.F. performed the cross-coupling reactions, one-pot procedures, the synthesis of the radiotracer for the imaging study, the radiosynthesis of all difluorocarbene reagents, and the experiments with the Cl-substituted difluorocarbene reagent, and developed the NMR assay to probe isotopic dilution. J.B.I.S. and N.J.W.S. performed preliminary studies for the radiosynthesis of the tBu-substituted difluorocarbene reagent. A.B.D. and R.S.P. performed and analysed the computational studies. T.A.M. and C.F.M. did an initial metabolic stability study. J.B.I.S., J.F., M.J.L. and S.J.P. performed all the in vivo experiments. S.M.H. prepared selected substrates. J.B.I.S., J.F. and V.G. conducted the revisions. J.B.I.S., R.S.P. and V.G. wrote the manuscript. All authors read and commented on the paper. V.G. conceived and supervised the project.

Corresponding author

Correspondence to Véronique Gouverneur.

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Competing interests

C.G. is an employee of UCB Pharma. C.W.a.E. is an employee of Pfizer Inc. A patent application (no. GB2113561.1; Difluorocarbene radiosynthesis) has been filed, from which V.G., J.B.I.S., C.F.M., M.T., N.J.W.S., S.M.H. and A.A.T. may benefit from royalties. The other authors declare no competing interests.

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This file contains: Materials and methods, Supplementary Text, Figs. 1–69, Tables 1–14, NMR spectra and References.

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Sap, J.B.I., Meyer, C.F., Ford, J. et al. [18F]Difluorocarbene for positron emission tomography. Nature 606, 102–108 (2022). https://doi.org/10.1038/s41586-022-04669-2

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