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Статті в журналах з теми "Late stage fluorination"

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Автор: Grafiati

Опубліковано: 10 грудня 2022

Оновлено: 28 січня 2023

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1

Tang, Pingping, Takeru Furuya, and Tobias Ritter. "Silver-Catalyzed Late-Stage Fluorination." Journal of the American Chemical Society 132, no. 34 (September 2010): 12150–54. http://dx.doi.org/10.1021/ja105834t.

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2

Campbell, Michael G., and Tobias Ritter. "Late-Stage Fluorination: From Fundamentals to Application." Organic Process Research & Development 18, no. 4 (March 11, 2014): 474–80. http://dx.doi.org/10.1021/op400349g.

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3

Abele, Stefan, and Hans-Jürgen Federsel. "Invited Academic Review on Late-Stage Fluorination." Organic Process Research & Development 18, no. 4 (March 11, 2014): 473. http://dx.doi.org/10.1021/op5000539.

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4

Brooks, Allen F., Joseph J. Topczewski, Naoko Ichiishi, Melanie S. Sanford, and Peter J. H. Scott. "Late-stage [18F]fluorination: new solutions to old problems." Chem. Sci. 5, no. 12 (2014): 4545–53. http://dx.doi.org/10.1039/c4sc02099e.

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5

Wu, Qiuzi, Yang-Jie Mao, Kun Zhou, Shuang Wang, Lei Chen, Zhen-Yuan Xu, Shao-Jie Lou, and Dan-Qian Xu. "Pd-Catalysed direct C(sp2)–H fluorination of aromatic ketones: concise access to anacetrapib." Chemical Communications 57, no. 37 (2021): 4544–47. http://dx.doi.org/10.1039/d1cc01047f.

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6

Neumann, Constanze N., and Tobias Ritter. "Late-Stage Fluorination: Fancy Novelty or Useful Tool?" Angewandte Chemie International Edition 54, no. 11 (February 4, 2015): 3216–21. http://dx.doi.org/10.1002/anie.201410288.

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7

Campbell, Michael G., and Tobias Ritter. "ChemInform Abstract: Late-Stage Fluorination: From Fundamentals to Application." ChemInform 45, no. 25 (June 5, 2014): no. http://dx.doi.org/10.1002/chin.201425239.

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8

Yerien, Damian E., Sergio Bonesi, and Al Postigo. "Fluorination methods in drug discovery." Organic & Biomolecular Chemistry 14, no. 36 (2016): 8398–427. http://dx.doi.org/10.1039/c6ob00764c.

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Анотація:

Late stage fluorination methods applied to biologically-active drugs have provided the pharmaceutical industry with new leads that show improved properties such as modulation of lipophilicity, electronegativity, basicity, bioavailability, and deceleration of metabolic degradation.

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9

Neumann, Constanze N., and Tobias Ritter. "ChemInform Abstract: Late-Stage Fluorination: Fancy Novelty or Useful Tool?" ChemInform 46, no. 19 (April 23, 2015): no. http://dx.doi.org/10.1002/chin.201519317.

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10

S. Clemente, Gonçalo, Tryfon Zarganes-Tzitzikas, Alexander Dömling, and Philip H. Elsinga. "Late-Stage Copper-Catalyzed Radiofluorination of an Arylboronic Ester Derivative of Atorvastatin." Molecules 24, no. 23 (November 20, 2019): 4210. http://dx.doi.org/10.3390/molecules24234210.

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Анотація:

There is an unmet need for late-stage 18F-fluorination strategies to label molecules with a wide range of relevant functionalities to medicinal chemistry, in particular (hetero)arenes, aiming to obtain unique in vivo information on the pharmacokinetics/pharmacodynamics (PK/PD) using positron emission tomography (PET). In the last few years, Cu-mediated oxidative radiofluorination of arylboronic esters/acids arose and has been successful in small molecules containing relatively simple (hetero)aromatic groups. However, this technique is sparsely used in the radiosynthesis of clinically significant molecules containing more complex backbones with several aromatic motifs. In this work, we add a new entry to this very limited database by presenting our recent results on the 18F-fluorination of an arylboronic ester derivative of atorvastatin. The moderate average conversion of [18F]F− (12%), in line with what has been reported for similarly complex molecules, stressed an overview through the literature to understand the radiolabeling variables and limitations preventing consistently higher yields. Nevertheless, the current disparity of procedures reported still hampers a consensual and conclusive output.

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11

Balandeh, Mehrdad, and Saman Sadeghi. "(Invited) Fluorination and No-Carrier-Added Radio-Fluorination of Organic Molecules Using Cation Pool Technique." ECS Meeting Abstracts MA2022-02, no. 30 (October 9, 2022): 1111. http://dx.doi.org/10.1149/ma2022-02301111mtgabs.

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Positron emission tomography (PET) is a molecular imaging method is being employed in preclinical and clinical studies such as oncology or diagnosis of certain diffuse brain diseases. The growth of PET as a powerful method in biomedical research, needs development of more efficient methods for developing the positron-emitting radiotracers. The fluorine radioactive isotope (18F) has a short half-life of 110 min, making it as an ideal PET radiotracer. 18F labeling of electron rich moieties such as aromatic molecules is highly desirable due to their high biostability. In 1990 Yoshida and co-workers developed the cation pool method which stabilized carbamate cationic intermediates generated during a two electron oxidation followed by deprotonation that takes place in the anodic compartment of a two compartment cell under low temperatures.1 The method allows for rapid reactions with nucleophiles that may be unstable during electrolysis and can be added to the reaction mixture at the end of electrolysis to form the final product. Here, we report on the extension of the cation pool method for the application of electrochemical fluorination and radio-fluorination of methyl (phenylthio)acetate. Electrochemical fluorination and no-carrier-added radio-fluorination were successfully achieved using the cation pool method. The cation pool method has tremendous potential for radiofluorination experiments. The excess concentration of cations may provide an efficient reaction mechanism for late-stage fluorination under low fluoride concentrations encountered in radiochemistry. Furthermore, radiochemical yield, which is reduced by decay of the radioisotope, can benefit from a rapid late-stage fluorination reaction. The cation pool can be prepared prior to cyclotron production of 18F isotope, thereby, providing a rapid late-stage fluorination reaction, maximizing radiochemical yield by minimizing decay through a rapid reaction of the previously prepared cations with 18F-fluoride. Synthesis parameters such as temperature, supporting electrolyte concentration and type, and precursor concentration were studied and optimized. Optimum reaction yield was obtained at -20 °C. The products were characterized using gas chromatography–mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), radio-thin-layer chromatography (radio-TLC) and high-performance liquid chromatography (HPLC). References Yoshida, J. et al. Direct Oxidative Carbon−Carbon Bond Formation Using the “Cation Pool” Method. 1. Generation of Iminium Cation Pools and Their Reaction with Carbon Nucleophiles. J. Am. Chem. Soc. 121, 9546–9549 (1999).

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12

Britton, Robert, and Michael Meanwell. "Synthesis of Heterobenzylic Fluorides." Synthesis 50, no. 06 (January 23, 2018): 1228–36. http://dx.doi.org/10.1055/s-0036-1589159.

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Fluorination at heterobenzylic positions can have a significant impact on basicity, lipophilicity, and metabolism of drug leads. As a consequence, the development of new methods to access heterobenzylic fluorides has particular relevance to medicinal chemistry. This short review provides a survey of common methods used to synthesize heterobenzylic fluorides and includes fluoride displacement reactions of previously functionalized molecules (e.g., deoxyfluorination and halide exchange) and electrophilic fluorination of resonance-stabilized heterobenzylic anions. In addition, recent advances in the direct fluorination of heterobenzylic C(sp3)–H bonds and monofluoromethylation of heterocyclic C(sp2)–H bonds are presented.1 Introduction2 Heterobenzylic Fluorides2.1 Deoxyfluorination2.2 Halide Exchange2.3 Electrophilic Fluorination of Heterobenzylic Anions2.4 Late Stage C–H Bond Fluorination2.5 Monofluoromethylation of C(sp2)–H Bonds3 Conclusions

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13

Lee, E., A. S. Kamlet, D. C. Powers, C. N. Neumann, G. B. Boursalian, T. Furuya, D. C. Choi, J. M. Hooker, and T. Ritter. "A Fluoride-Derived Electrophilic Late-Stage Fluorination Reagent for PET Imaging." Science 334, no. 6056 (November 3, 2011): 639–42. http://dx.doi.org/10.1126/science.1212625.

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14

Brooks, Allen F., Joseph J. Topczewski, Naoko Ichiishi, Melanie S. Sanford, and Peter J. H. Scott. "ChemInform Abstract: Late-Stage [18F]Fluorination: New Solutions to Old Problems." ChemInform 45, no. 52 (December 11, 2014): no. http://dx.doi.org/10.1002/chin.201452263.

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15

Stewart, Megan N., Brian G. Hockley, and Peter J. H. Scott. "Green approaches to late-stage fluorination: radiosyntheses of 18F-labelled radiopharmaceuticals in ethanol and water." Chemical Communications 51, no. 79 (2015): 14805–8. http://dx.doi.org/10.1039/c5cc05919d.

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Green strategies for late-stage fluorination with ¹⁸F, in which ethanol and water are the only solvents used throughout the entire radiolabeling process, have been developed and applied to the radiosyntheses of a range of radiopharmaceuticals commonly employed in clinical PET imaging.

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16

Jakobsson, Jimmy Erik, and Patrick Johannes Riss. "Transition metal free, late-stage, regiospecific, aromatic fluorination on a preparative scale using a KF/crypt-222 complex." RSC Advances 8, no. 38 (2018): 21288–91. http://dx.doi.org/10.1039/c8ra03757d.

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17

Cole, Erin, Megan Stewart, Ryan Littich, Raphael Hoareau, and Peter Scott. "Radiosyntheses using Fluorine-18: The Art and Science of Late Stage Fluorination." Current Topics in Medicinal Chemistry 14, no. 7 (March 31, 2014): 875–900. http://dx.doi.org/10.2174/1568026614666140202205035.

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18

Huang, Xiongyi, Wei Liu, Hong Ren, Ramesh Neelamegam, Jacob M. Hooker, and John T. Groves. "Late Stage Benzylic C–H Fluorination with [18F]Fluoride for PET Imaging." Journal of the American Chemical Society 136, no. 19 (May 6, 2014): 6842–45. http://dx.doi.org/10.1021/ja5039819.

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19

Li, Jiakun, Junting Chen, Ruocheng Sang, Won-Seok Ham, Matthew B. Plutschack, Florian Berger, Sonia Chabbra, Alexander Schnegg, Christophe Genicot, and Tobias Ritter. "Photoredox catalysis with aryl sulfonium salts enables site-selective late-stage fluorination." Nature Chemistry 12, no. 1 (November 25, 2019): 56–62. http://dx.doi.org/10.1038/s41557-019-0353-3.

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20

Xu, Peng, Da Zhao, Florian Berger, Aboubakr Hamad, Jens Rickmeier, Roland Petzold, Mykhailo Kondratiuk, Kostiantyn Bohdan, and Tobias Ritter. "Site‐Selective Late‐Stage Aromatic [ 18 F]Fluorination via Aryl Sulfonium Salts." Angewandte Chemie 132, no. 5 (December 12, 2019): 1972–76. http://dx.doi.org/10.1002/ange.201912567.

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21

Bermejo Góme, Antonio, Miguel A. Cortés González, Marvin Lübcke, Magnus J. Johansson, Magnus Schou, and Kálmán J. Szabó. "Synthesis of trifluoromethyl moieties by late-stage copper (I) mediated nucleophilic fluorination." Journal of Fluorine Chemistry 194 (February 2017): 51–57. http://dx.doi.org/10.1016/j.jfluchem.2016.12.017.

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22

Xu, Peng, Da Zhao, Florian Berger, Aboubakr Hamad, Jens Rickmeier, Roland Petzold, Mykhailo Kondratiuk, Kostiantyn Bohdan, and Tobias Ritter. "Site‐Selective Late‐Stage Aromatic [ 18 F]Fluorination via Aryl Sulfonium Salts." Angewandte Chemie International Edition 59, no. 5 (January 27, 2020): 1956–60. http://dx.doi.org/10.1002/anie.201912567.

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23

Fanelli, Roberto, Florine Cavelier та Jean Martinez. "Expedient Synthesis of Fmoc-(S)-γ-Fluoroleucine and Late-Stage Fluorination of Peptides". Synlett 27, № 09 (16 лютого 2016): 1403–7. http://dx.doi.org/10.1055/s-0035-1561568.

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24

Meanwell, Michael, Matthew B. Nodwell, Rainer E. Martin, and Robert Britton. "A Convenient Late-Stage Fluorination of Pyridylic C−H Bonds with N -Fluorobenzenesulfonimide." Angewandte Chemie International Edition 55, no. 42 (October 6, 2016): 13244–48. http://dx.doi.org/10.1002/anie.201606323.

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25

Meanwell, Michael, Matthew B. Nodwell, Rainer E. Martin, and Robert Britton. "A Convenient Late-Stage Fluorination of Pyridylic C−H Bonds with N -Fluorobenzenesulfonimide." Angewandte Chemie 128, no. 42 (October 6, 2016): 13438–42. http://dx.doi.org/10.1002/ange.201606323.

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26

Lou, Shao-Jie, Qi Chen, Yi-Feng Wang, Dan-Qian Xu, Xiao-Hua Du, Jiang-Qi He, Yang-Jie Mao, and Zhen-Yuan Xu. "Selective C–H Bond Fluorination of Phenols with a Removable Directing Group: Late-Stage Fluorination of 2-Phenoxyl Nicotinate Derivatives." ACS Catalysis 5, no. 5 (April 2015): 2846–49. http://dx.doi.org/10.1021/acscatal.5b00306.

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27

Cole, Erin L., Megan N. Stewart, Ryan Littich, Raphael Hoareau, and Peter J. H. Scott. "ChemInform Abstract: Radiosyntheses Using Fluorine-18: The Art and Science of Late Stage Fluorination." ChemInform 45, no. 41 (September 25, 2014): no. http://dx.doi.org/10.1002/chin.201441273.

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28

Fier, Patrick S., and John F. Hartwig. "Synthesis and Late-Stage Functionalization of Complex Molecules through C–H Fluorination and Nucleophilic Aromatic Substitution." Journal of the American Chemical Society 136, no. 28 (July 2014): 10139–47. http://dx.doi.org/10.1021/ja5049303.

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29

Cavaliere, Alessandra, Katrin C. Probst, Stephen J. Paisey, Christopher Marshall, Abdul K. H. Dheere, Franklin Aigbirhio, Christopher McGuigan, and Andrew D. Westwell. "Radiosynthesis of [18F]-Labelled Pro-Nucleotides (ProTides)." Molecules 25, no. 3 (February 6, 2020): 704. http://dx.doi.org/10.3390/molecules25030704.

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Phosphoramidate pro-nucleotides (ProTides) have revolutionized the field of anti-viral and anti-cancer nucleoside therapy, overcoming the major limitations of nucleoside therapies and achieving clinical and commercial success. Despite the translation of ProTide technology into the clinic, there remain unresolved in vivo pharmacokinetic and pharmacodynamic questions. Positron Emission Tomography (PET) imaging using [18F]-labelled model ProTides could directly address key mechanistic questions and predict response to ProTide therapy. Here we report the first radiochemical synthesis of [18F]ProTides as novel probes for PET imaging. As a proof of concept, two chemically distinct radiolabelled ProTides have been synthesized as models of 3′- and 2′-fluorinated ProTides following different radiosynthetic approaches. The 3′-[18F]FLT ProTide was obtained via a late stage [18F]fluorination in radiochemical yields (RCY) of 15–30% (n = 5, decay-corrected from end of bombardment (EoB)), with high radiochemical purities (97%) and molar activities of 56 GBq/μmol (total synthesis time of 130 min.). The 2′-[18F]FIAU ProTide was obtained via an early stage [18F]fluorination approach with an RCY of 1–5% (n = 7, decay-corrected from EoB), with high radiochemical purities (98%) and molar activities of 53 GBq/μmol (total synthesis time of 240 min).

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30

Craig, Austin, Niklas Kolks, Elizaveta A. Urusova, Johannes Zischler, Melanie Brugger, Heike Endepols, Bernd Neumaier, and Boris D. Zlatopolskiy. "Preparation of labeled aromatic amino acids via late-stage 18F-fluorination of chiral nickel and copper complexes." Chemical Communications 56, no. 66 (2020): 9505–8. http://dx.doi.org/10.1039/d0cc02223c.

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31

Yuan, Zheliang, Matthew B. Nodwell, Hua Yang, Noeen Malik, Helen Merkens, François Bénard, Rainer E. Martin, Paul Schaffer, and Robert Britton. "Site-Selective, Late-Stage C−H 18 F-Fluorination on Unprotected Peptides for Positron Emission Tomography Imaging." Angewandte Chemie 130, no. 39 (September 5, 2018): 12915–18. http://dx.doi.org/10.1002/ange.201806966.

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32

Yuan, Zheliang, Matthew B. Nodwell, Hua Yang, Noeen Malik, Helen Merkens, François Bénard, Rainer E. Martin, Paul Schaffer, and Robert Britton. "Site-Selective, Late-Stage C−H 18 F-Fluorination on Unprotected Peptides for Positron Emission Tomography Imaging." Angewandte Chemie International Edition 57, no. 39 (September 5, 2018): 12733–36. http://dx.doi.org/10.1002/anie.201806966.

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33

Fier, Patrick S., and John F. Hartwig. "ChemInform Abstract: Synthesis and Late-Stage Functionalization of Complex Molecules Through C-H Fluorination and Nucleophilic Aromatic Substitution." ChemInform 46, no. 7 (January 29, 2015): no. http://dx.doi.org/10.1002/chin.201507242.

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34

Abularrage, Nile S., Brian J. Levandowski, and Ronald T. Raines. "Synthesis and Diels–Alder Reactivity of 4-Fluoro-4-Methyl-4H-Pyrazoles." International Journal of Molecular Sciences 21, no. 11 (May 31, 2020): 3964. http://dx.doi.org/10.3390/ijms21113964.

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4H-Pyrazoles are emerging scaffolds for “click” chemistry. Late-stage fluorination with Selectfluor® is found to provide a reliable route to 4-fluoro-4-methyl-4H-pyrazoles. 4-Fluoro-4-methyl-3,5-diphenyl-4H-pyrazole (MFP) manifested 7-fold lower Diels–Alder reactivity than did 4,4-difluoro-3,5-diphenyl-4H-pyrazole (DFP), but higher stability in the presence of biological nucleophiles. Calculations indicate that a large decrease in the hyperconjugative antiaromaticity in MFP relative to DFP does not lead to a large loss in Diels–Alder reactivity because the ground-state structure of MFP avoids hyperconjugative antiaromaticity by distorting into an envelope-like conformation like that in the Diels–Alder transition state. This predistortion enhances the reactivity of MFP and offsets the decrease in reactivity from the diminished hyperconjugative antiaromaticity.

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35

Promontorio, Rossella, Jean-Alexandre Richard, and Charles M. Marson. "Late-stage fluorination of bridged scaffolds: Chemoselective generation of a CHF group at three positions of the bicyclo[3.3.1]nonane system." Tetrahedron Letters 59, no. 13 (March 2018): 1226–29. http://dx.doi.org/10.1016/j.tetlet.2018.02.038.

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36

Scroggie, Kymberley R., Lisa J. Alcock, Maria J. Matos, Gonçalo J. L. Bernardes, Michael V. Perkins, and Justin M. Chalker. "A silicon-labelled amino acid suitable for late-stage fluorination and unexpected oxidative cleavage reactions in the preparation of a key intermediate in the Strecker synthesis." Peptide Science 110, no. 3 (April 20, 2018): e24069. http://dx.doi.org/10.1002/pep2.24069.

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37

"Copper-Mediated Late-Stage Fluorination of Arenes Using Photoredox Catalysis." Synfacts 16, no. 02 (January 21, 2020): 0163. http://dx.doi.org/10.1055/s-0039-1691473.

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38

Ajenjo, Javier, Gianluca Destro, Bart Cornelissen, and Véronique Gouverneur. "Closing the gap between 19F and 18F chemistry." EJNMMI Radiopharmacy and Chemistry 6, no. 1 (September 25, 2021). http://dx.doi.org/10.1186/s41181-021-00143-y.

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AbstractPositron emission tomography (PET) has become an invaluable tool for drug discovery and diagnosis. The positron-emitting radionuclide fluorine-18 is frequently used in PET radiopharmaceuticals due to its advantageous characteristics; hence, methods streamlining access to 18F-labelled radiotracers can make a direct impact in medicine. For many years, access to 18F-labelled radiotracers was limited by the paucity of methodologies available, and the poor diversity of precursors amenable to 18F-incorporation. During the last two decades, 18F-radiochemistry has progressed at a fast pace with the appearance of numerous methodologies for late-stage 18F-incorporation onto complex molecules from a range of readily available precursors including those that do not require pre-functionalisation. Key to these advances is the inclusion of new activation modes to facilitate 18F-incorporation. Specifically, new advances in late-stage 19F-fluorination under transition metal catalysis, photoredox catalysis, and organocatalysis combined with the availability of novel 18F-labelled fluorination reagents have enabled the invention of novel processes for 18F-incorporation onto complex (bio)molecules. This review describes these major breakthroughs with a focus on methodologies for C–18F bond formation. This reinvigorated interest in 18F-radiochemistry that we have witnessed in recent years has made a direct impact on 19F-chemistry with many laboratories refocusing their efforts on the development of methods using nucleophilic fluoride instead of fluorination reagents derived from molecular fluorine gas.

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39

Chang, Zhe, Jialin Huang, Si Wang, Geshuyi Chen, Heng Zhao, Rui Wang, and Depeng Zhao. "Copper catalyzed late-stage C(sp3)-H functionalization of nitrogen heterocycles." Nature Communications 12, no. 1 (July 15, 2021). http://dx.doi.org/10.1038/s41467-021-24671-y.

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AbstractNitrogen heterocycle represents a ubiquitous skeleton in natural products and drugs. Late-stage C(sp3)-H bond functionalization of N-heterocycles with broad substrate scope remains a challenge and of particular significance to modern chemical synthesis and pharmaceutical chemistry. Here, we demonstrate copper-catalysed late-stage C(sp3)-H functionalizaion of N-heterocycles using commercially available catalysts under mild reaction conditions. We have investigated 8 types of N-heterocycles which are usually found as medicinally important skeletons. The scope and utility of this approach are demonstrated by late-stage C(sp3)-H modification of these heterocycles including a number of pharmaceuticals with a broad range of nucleophiles, e.g. methylation, arylation, azidination, mono-deuteration and glycoconjugation etc. Preliminary mechanistic studies reveal that the reaction undergoes a C-H fluorination process which is followed by a nucleophilic substitution.

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40

Kim, Jeongmin, Changkun Park, Keewook Yi, Shinae Lee, Sook Ju Kim, Min-Ji Jung, and Albert Chang-sik Cheong. "COM-1 and Hongcheon: New monazite reference materials for the microspot analysis of oxygen isotopic composition." Journal of Analytical Science and Technology 13, no. 1 (October 4, 2022). http://dx.doi.org/10.1186/s40543-022-00342-5.

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Abstract Background Monazite, a moderately common light rare earth element (LREE) and thorium phosphate mineral, has chemical, age, and isotopic characteristics that are useful in the investigation of the origin and evolution of crustal melts and fluid-rock interactions. Multiple stages of growth and partial recrystallization commonly observed in monazite inevitably require microspot chemical and isotopic analyses, for which well-characterized reference materials are essential to correct instrumental biases. In this study, we introduce new monazite reference materials COM-1 and Hongcheon for the use in the microspot analysis of oxygen isotopic composition. Findings COM-1 and Hongcheon were derived from a late Mesoproterozoic (~ 1080 Ma) pegmatite dyke in Colorado, USA, and a Late Triassic (~ 230 Ma) carbonatite-hosted REE ore in central Korea, respectively. The COM-1 monazite has much higher levels of Th (8.77 ± 0.56 wt.%), Si (0.82 ± 0.07 wt.%) and lower REE contents (total REE = 49.5 ± 1.2 wt.%) than does the Hongcheon monazite (Th, 0.23 ± 0.11 wt.%; Si, < 0.1 wt.%; total REE, 59.9 ± 0.7 wt.%). Their oxygen isotopic compositions (δ18OVSMOW) were determined by gas-source mass spectrometry with laser fluorination (COM-1, 6.67 ± 0.08‰; Hongcheon-1, 6.60 ± 0.02‰; Hongcheon-2, 6.08 ± 0.07‰). Oxygen isotope measurements performed by a Cameca IMS1300-HR3 ion probe showed a strong linear dependence (R2 = 0.99) of the instrumental mass fractionation on the total REE contents. Conclusions We characterized chemical and oxygen isotopic compositions of COM-1 and Hongcheon monazites. Their internal homogeneity in oxygen isotopic composition and chemical difference provide an efficient tool for calibrating instrumental mass fractionation occurring during secondary ion mass spectrometry analyses.

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