Moving Metal-Mediated (18)F-Fluorination from Concept to Clinic

Light-Driven Radiochemistry with Fluorine-18, Carbon-11 and Zirconium-89

This review discusses recent advances in light-driven radiochemistry for three key isotopes: fluorine-18, carbon-11, and zirconium-89, and their applications in positron emission tomography (PET). In the case of fluorine-18, the predominant approach involves the use of cyclotron-produced [18F]fluoride or reagents derived thereof. Light serves to activate either the substrate or the fluorine-18 labeled reagent. Advancements in carbon-11 photo-mediated radiochemistry have been leveraged for the radiolabeling of small molecules, achieving various transformations, including 11C-methylation, 11C-carboxylation, 11C-carbonylation, and 11C-cyanation. Contrastingly, zirconium-89 photo-mediated radiochemistry differs from fluorine-18 and carbon-11 approaches. In these cases, light facilitates a postlabeling click reaction, which has proven valuable for the labeling of large biomolecules such as monoclonal antibodies (mAbs). New technological developments, such as the incorporation of photoreactors in commercial radiosynthesizers, illustrate the commitment the field is making in embracing photochemistry. Taken together, these advances in photo-mediated radiochemistry enable radiochemists to apply new retrosynthetic strategies in accessing novel PET radiotracers.

Tandem Iridium-Catalyzed C-H Borylation/Copper-Mediated Radiofluorination of Aromatic C-H Bonds with [18F]TBAF

Direct C-H functionalization of (hetero)aromatic C-H bonds with iridium-catalyzed borylation followed by copper-mediated radiofluorination of the in situ generated organoboronates affords fluorine-18 labeled aromatics in high radiochemical conversions and meta-selectivities. This protocol describes the benchtop reaction assembly of the C-H borylation and radiofluorination steps, which can be utilized for the fluorine-18 labeling of densely functionalized bioactive scaffolds.

Radiochemistry: A Hot Field with Opportunities for Cool Chemistry

Recent Food and Drug Administration (FDA) approval of diagnostic and therapeutic radiopharmaceuticals and concurrent miniaturization of particle accelerators leading to improved access has fueled interest in the development of chemical transformations suitable for short-lived radioactive isotopes on the tracer scale. This recent renaissance of radiochemistry is paired with new opportunities to study fundamental chemical behavior and reactivity of elements to improve their production, separation, and incorporation into bioactive molecules to generate new radiopharmaceuticals. This outlook outlines pertinent challenges in the field of radiochemistry and indicates areas of opportunity for chemical discovery and development, including those of clinically established (C-11, F-18) and experimental radionuclides in preclinical development across the periodic table.

PET radiotracers and fluorescent probes for imaging human carbonic anhydrase IX and XII in hypoxic tumors

Positron emission tomography (PET) and fluorescent imaging play a pivotal role in medical diagnosis, biomedical oncologic research, and drug development process, which include identification of target location, target engagement, but also prove on mechanism of action or pharmacokinetics of new drug candidates. PET estimates physiological changes at the molecular level using specific radiotracers containing a short-lived positron emitting radionuclide such as fluorine-18 or carbon-11, whereas fluorescent imaging techniques use fluorescent probes labeled with suitable drug candidates for detection at the molecular level. The human carbonic anhydrase (hCA) isoforms IX and XII are overexpressed in hypoxic cancer cells, promoting tumor growth by regulating extra/intracellular pH, ferroptosis, and metabolism, being recognized as promising targets for anticancer theranostic agents. In this review, we have focused on PET radiotracers as well as fluorescent probes for diagnosis and treatment of tumors expressing hCA IX and hCA XII.

An Organometallic Gold(III) Reagent for 18F Labeling of Unprotected Peptides and Sugars in Aqueous Media

The ¹⁸F labeling of unprotected peptides and sugars with a Au(III)-[¹⁸F]fluoroaryl complex is reported. The chemoselective method generates ¹⁸F-labeled S-aryl bioconjugates in an aqueous environment in 15 min with high radiochemical yields and displays excellent functional group tolerance. This approach utilizes an air and moisture stable, robust organometallic Au(III) complex and highlights the versatility of designer organometallic reagents as efficient agents for rapid radiolabeling.

Direct Cu-mediated aromatic 18F-labeling of highly reactive tetrazines for pretargeted bioorthogonal PET imaging

Pretargeted imaging can be used to visualize and quantify slow-accumulating targeting vectors with short-lived radionuclides such as fluorine-18 - the most popular clinically applied Positron Emission Tomography (PET) radionuclide. Pretargeting results in higher target-to-background ratios compared to conventional imaging approaches using long-lived radionuclides. Currently, the tetrazine ligation is the most popular bioorthogonal reaction for pretargeted imaging, but a direct 18F-labeling strategy for highly reactive tetrazines, which would be highly beneficial if not essential for clinical translation, has thus far not been reported. In this work, a simple, scalable and reliable direct 18F-labeling procedure has been developed. We initially studied the applicability of different leaving groups and labeling methods to develop this procedure. The copper-mediated 18F-labeling exploiting stannane precursors showed the most promising results. This approach was then successfully applied to a set of tetrazines, including highly reactive H-tetrazines, suitable for pretargeted PET imaging. The labeling succeeded in radiochemical yields (RCYs) of up to approx. 25%. The new procedure was then applied to develop a pretargeting tetrazine-based imaging agent. The tracer was synthesized in a satisfactory RCY of ca. 10%, with a molar activity of 134 ± 22 GBq μmol-1 and a radiochemical purity of >99%. Further evaluation showed that the tracer displayed favorable characteristics (target-to-background ratios and clearance) that may qualify it for future clinical translation.

Sequential Ir/Cu-Mediated Method for the Meta-Selective C-H Radiofluorination of (Hetero)Arenes

This article describes a sequential Ir/Cu-mediated process for the meta-selective C-H radiofluorination of (hetero)arene substrates. In the first step, Ir-catalyzed C(sp²)-H borylation affords (hetero)aryl pinacolboronate (BPin) esters. The intermediate organoboronates are then directly subjected to copper-mediated radiofluorination with [¹⁸F]tetrabutylammonium fluoride to afford fluorine-18 labeled (hetero)arenes in high radiochemical yield and radiochemical purity. This entire process is performed on a benchtop without Schlenk or glovebox techniques and circumvents the need to isolate (hetero)aryl boronate esters. The reaction was automated on a TracerLab FX_FN module with 1,3-dimethoxybenzene and a meta-tyrosine derivative. The products, [¹⁸F]1-fluoro-3,5-dimethoxybenzene and an ¹⁸F-labeled meta-tyrosine derivative, were obtained in 37 ± 5% isolated radiochemical yield and >99% radiochemical purity and 25% isolated radiochemical yield and 99% radiochemical purity, and 0.52 Ci/μmol (19.24 GBq/μmol) molar activity (A_m), respectively.

Synthesis and [*C]CO-labelling of (C,N) gem-dimethylbenzylamine-palladium complexes for potential applications in positron emission tomography

Various aryl-palladium complexes were synthesised from gem-dimethylbenzylamine derivatives by C-H activation under extremely mild conditions. Interestingly, these highly stable structures reacted with [13C]carbon monoxide to produce the desired labelled lactams in 29% to 51% yields over the C-H activation/carbonylation steps. As representative examples, a non-natural amino acid and an estradiol-based conjugate were prepared and labelled in model experiments with [13C]CO in homogeneous or heterogeneous conditions. Especially, the latter was radiolabelled with [11C]CO using a convenient procedure from the resin-supported palladium complex precursor. Thus, these results strongly suggest that cyclometallated palladium complexes obtained from gem-dimethylbenzylamine moieties are promising precursors for the practical synthesis of new [11C]tracers for Positron Emission Tomography.

Direct incorporation of [18F] into Aliphatic Systems: A promising Mn-catalysed Labelling Technique for PET Imaging

BACKGROUND

One of the challenges in positron emission tomography (PET) is labelling complex aliphatic molecules.

OBJECTIVE

This study aimed to develop a method of metal-catalysed radiofluorination that is site-selective and works in moderate to good yields under facile conditions.

METHODS

Herein, we report on the optimisation of an aliphatic C-H to C-18F bond transformation catalysed by a Mn(porphyrin) complex.

RESULTS

The successful oxidation of 11 aliphatic molecules, including progesterone, is reported. Radiochemical Incorporations (RCIs) up to 69% were achieved within 60 min without the need for pre-activation or special equipment.

CONCLUSION

The method features mild conditions (60 °C) and promises to constitute a valuable approach to labelling of biomolecules and drug substances.

Copper-Mediated Late-stage Radiofluorination: Five Years of Impact on Pre-clinical and Clinical PET Imaging

Purpose

Copper-mediated radiofluorination (CMRF) is emerging as the method of choice for the formation of aromatic C-¹⁸F bonds. This minireview examines proof-of-concept, pre-clinical, and in-human imaging studies of new and established imaging agents containing aromatic C-¹⁸F bonds synthesized with CMRF. An exhaustive discussion of CMRF methods is not provided, although key developments that have enabled or improved upon the syntheses of fluorine-18 imaging agents are discussed.

Methods

A comprehensive literature search from April 2014 onwards of the Web of Science and PubMed library databases was performed to find reports that utilize CMRF for the synthesis of fluorine-18 radiopharmaceuticals, and these represent the primary body of research discussed in this minireview. Select conference proceedings, previous reports describing alternative methods for the synthesis of imaging agents, and preceding fluorine-19 methodologies have also been included for discussion.

Conclusions

CMRF has significantly expanded the chemical space that is accessible to fluorine-18 radiolabeling with production methods that can meet the regulatory requirements for use in Nuclear Medicine. Furthermore, it has enabled novel and improved syntheses of radiopharmaceuticals and facilitated subsequent PET imaging studies. The rapid adoption of CMRF will undoubtedly continue to simplify the production of imaging agents and inspire the development of new radiofluorination methodologies.

Synthesis of [18F]-γ-fluoro-α,β,-unsaturated esters and ketones via vinylogous 18F-fluorination of α-diazoacetates with [18F]AgF

This communication reports a method for the vinylogous radiofluorination of α-diazoacetates to generate γ-[¹⁸F]fluoro-α,β-unsaturated esters and ketones in moderate to good radiochemical yields. The method uses no-carrier-added [¹⁸F]AgF and is compatible with aromatic and non-aromatic substrates and a number of different functional groups. The labeling method is showcased in the synthesis of a fluorinated 5-cholesten-3-one derivative as well as a difluorinated product pertinent to drug discovery.

Synthesis and in vivo evaluation of [18F]UCB-J for PET imaging of synaptic vesicle glycoprotein 2A (SV2A)

PURPOSE

Synaptic abnormalities have been implicated in a variety of neuropsychiatric disorders, including epilepsy, Alzheimer's disease, and schizophrenia. Hence, PET imaging of the synaptic vesicle glycoprotein 2A (SV2A) may be a valuable in vivo biomarker for neurologic and psychiatric diseases. We previously developed [¹¹C]UCB-J, a PET radiotracer with high affinity and selectivity toward SV2A; however, the short radioactive half-life (20 min for ¹¹C) places some limitations on its broader application. Herein, we report the first synthesis of the longer-lived ¹⁸F-labeled counterpart (half-life: 110 min), [¹⁸F]UCB-J, and its evaluation in nonhuman primates.

METHODS

[¹⁸F]UCB-J was synthesized from the iodonium precursors. PET imaging experiments with [¹⁸F]UCB-J were conducted in rhesus monkeys to assess the pharmacokinetic and in vivo binding properties. Arterial samples were taken for analysis of radioactive metabolites and generation of input functions. Regional time-activity curves were analyzed using the one-tissue compartment model to derive regional distribution volumes and binding potentials for comparison with [¹¹C]UCB-J.

RESULTS

[¹⁸F]UCB-J was prepared in high radiochemical and enantiomeric purity, but low radiochemical yield. Evaluation in nonhuman primates indicated that the radiotracer displayed pharmacokinetic and imaging characteristics similar to those of [¹¹C]UCB-J, with moderate metabolism rate, high brain uptake, fast and reversible binding kinetics, and high specific binding signals.

CONCLUSION

We have accomplished the first synthesis of the novel SV2A radiotracer [¹⁸F]UCB-J. [¹⁸F]UCB-J is demonstrated to be an excellent imaging agent and may prove to be useful for imaging and quantification of SV2A expression, and synaptic density, in humans.

Radiosynthesis of the norepinephrine transporter tracer [18 F]NS12137 via copper-mediated 18 F-labelling

[¹⁸F]NS12137 (exo‐3‐[(6‐[¹⁸F]fluoro‐2‐pyridyl)oxy]8‐azabicyclo[3.2.1]octane) is a highly selective norepinephrine transporter (NET) tracer. NETs are responsible for the reuptake of norepinephrine and dopamine and are linked to several neurodegenerative and neuropsychiatric disorders. The aim of this study was to develop a copper‐mediated ¹⁸F‐fluorination method for the production of [¹⁸F]NS12137 with straightforward synthesis conditions and high radiochemical yield and molar activity. [¹⁸F]NS12137 was produced in two steps. Radiofluorination of [¹⁸F]NS12137 was performed via a copper‐mediated pathway starting with a stannane precursor and using [¹⁸F]F⁻ as the source of the fluorine‐18 isotope. Deprotection was performed via acid hydrolysis. The radiofluorination reaction was nearly quantitative as was the deprotection based on HPLC analysis. The radiochemical yield of the synthesis was 15.1 ± 0.5%. Molar activity of [¹⁸F]NS12137 was up to 300 GBq/μmol. The synthesis procedure is straightforward and can easily be automated and adapted for clinical production.

Synthesis and in Vivo Evaluation of a Novel PET Radiotracer for Imaging of Synaptic Vesicle Glycoprotein 2A (SV2A) in Nonhuman Primates

Structural disruption and alterations of synapses are associated with many brain disorders including Alzheimer's disease, epilepsy, depression, and schizophrenia. We have previously developed the PET radiotracer ¹¹C-UCB-J for imaging and quantification of synaptic vesicle glycoprotein 2A (SV2A) and synaptic density in nonhuman primates and humans. Here we report the synthesis of a novel radiotracer ¹⁸F-SDM-8 and its in vivo evaluation in rhesus monkeys. The in vitro binding assay of SDM-8 showed high SV2A binding affinity ( K_i = 0.58 nM). ¹⁸F-SDM-8 was prepared in high molar activity (241.7 MBq/nmol) and radiochemical purity (>98%). In the brain, ¹⁸F-SDM-8 displayed very high uptake with peak standardized uptake value (SVU) greater than 8 and fast and reversible kinetics. A displacement study with levetiracetam and blocking studies with UCB-J and levetiracetam demonstrated its binding reversibility and specificity toward SV2A. Regional binding potential values were calculated and ranged from 0.8 in the brainstem to 4.5 in the cingulate cortex. By comparing to ¹¹C-UCB-J, ¹⁸F-SDM-8 displayed the same attractive imaging properties: very high brain uptake, appropriate tissue kinetics, and high levels of specific binding. Given the longer half-life of F-18 and the feasibility for central production and multisite distribution, ¹⁸F-SDM-8 holds promise as an excellent radiotracer for SV2A and as a biomarker for synaptic density measurement in neurodegenerative diseases and psychiatric disorders.

Copper-Mediated Aminoquinoline-Directed Radiofluorination of Aromatic C-H Bonds with K18 F

A Cu-mediated ortho-C-H radiofluorination of aromatic carboxylic acids that are protected as 8-aminoquinoline benzamides is described. The method uses K¹⁸ F and is compatible with a wide range of functional groups. The reaction is showcased in the high specific activity automated synthesis of the RARβ2 agonist [¹⁸ F]AC261066.

An Automated Multidose Synthesis of the Potentiometric PET Probe 4-[18F]Fluorobenzyl-Triphenylphosphonium ([18F]FBnTP)

PURPOSE

The aim of this study was the automated synthesis of the mitochondrial membrane potential sensor 4-[¹⁸F]fluorobenzyl-triphenylphosphonium ([¹⁸F]FBnTP) on a commercially available synthesizer in activity yields (AY) that allow for imaging of multiple patients.

PROCEDURES

A three-pot, four-step synthesis was implemented on the ELIXYS FLEX/CHEM radiosynthesizer (Sofie Biosciences) and optimized for radiochemical yield (RCY), radiochemical purity (RCP) as well as chemical purity during several production runs (n = 24). The compound was purified by solid-phase extraction (SPE) with a Sep-Pak Plus Accell CM cartridge, thereby avoiding HPLC purification.

RESULTS

Under optimized conditions, AY of 1.4-2.2 GBq of [¹⁸F]FBnTP were obtained from 9.4 to 12.0 GBq [¹⁸F]fluoride in 90-92 min (RCY = 28.6 ± 5.1 % with n = 3). Molar activities ranged from 80 to 99 GBq/μmol at the end of synthesis. RCP of final formulations was > 99 % at the end of synthesis and > 95 % after 8 h. With starting activities of 23.2-33.0 GBq, RCY decreased to 16.1 ± 0.4 % (n = 3). The main cause of the decline in RCY when high amounts of [¹⁸F]fluoride are used is radiolytic decomposition of [¹⁸F]FBnTP during SPE purification.

CONCLUSIONS

In initial attempts, the probe was synthesized with RCY < 0.6 % when starting activities up to 44.6 GBq were used. Rapid radiolysis of the intermediate 4-[¹⁸F]fluorobenzaldehyde and the final product [¹⁸F]FBnTP during purification was identified as the main cause for low yields in high-activity runs. Radiolytic decomposition was hindered by the addition of radical scavengers during synthesis, purification, and formulation, thereby improving AY and RCP. The formulated probe in injectable form was synthesized without the use of HPLC and passed all applicable quality control tests.

Rhodium-mediated 18F-oxyfluorination of diazoketones using a fluorine-18-containing hypervalent iodine reagent

α-[¹⁸F]Fluoro ethers were obtained from diazocarbonyl compounds using a hypervalent iodine based fluorine-18 reagent.

Bioconjugated arylpalladium complexes on solid supports for a convenient last-step synthesis of 11C-labelled tracers for positron emission tomography

Bioconjugated arylpalladium complexes anchored onto polystyrene beads provided [¹¹C]CO-labelled compounds with excellent radiochemical purities after a simple filtration.

N-Arylation of DABCO with Diaryliodonium Salts: General Synthesis of N-Aryl-DABCO Salts as Precursors for 1,4-Disubstituted Piperazines

Employing DABCO as a substrate, aryl(mesityl)iodonium triflates are introduced as arylating agents for a tertiary sp³-nitrogen. Mild conditions and exceptional selectivity of the aryl group transfer allow unprecedented N-aryl-DABCO salts to be obtained, bearing substituents of different electronic natures. This metal-free methodology has no analogy among known transition-metal-based reactions. The utility of isolated N-aryl-DABCO salts is demonstrated for the preparation of flibanserin.

Automated synthesis of PET radiotracers by copper-mediated 18 F-fluorination of organoborons: Importance of the order of addition and competing protodeborylation

In this paper, we describe the use of Cu-mediated [18 F]fluorodeboronation for the automated production of positron emission tomography radiotracers suitable for clinical use. Two recurrent issues with the method, low radiochemical conversion on automation and protoarene byproduct purification issues, have been successfully addressed. The new method was utilized to produce sterile injectable doses of [18 F]-(±)-IPMICF17, a positron emission tomography radiotracer for tropomyosin receptor kinase B/C, using an automated synthesis module. The product was isolated in 1.9 ± 0.1% isolated radiochemical yield, excellent radiochemical purity (>99%), and high specific activity (5294 ± 1227 Ci/mmol). Quality control testing confirmed that doses were suitable for clinical use.

[18F]fluoro-benziodoxole: a no-carrier-added electrophilic fluorinating reagent. Rapid, simple radiosynthesis, purification and application for fluorine-18 labelling

An electrophilic ¹⁸F transfer reagent was synthetized by rapid, operationally simple ligand exchange from a hypervalent iodine and [¹⁸F]TBAF.

Boron reagents for divergent radiochemistry

This review discusses boron reagents as precursors for divergent radiolabelling with a focus on carbon-11, fluorine-18 and iodine-123, -125, -131.

Site-selective 18F fluorination of unactivated C-H bonds mediated by a manganese porphyrin

A direct aliphatic C–H ¹⁸F labeling method using [¹⁸F]fluoride ion at inaccessible and unreactive sites is reported.

The first direct C–H ¹⁸F fluorination reaction of unactivated aliphatic sites using no-carrier-added [¹⁸F]fluoride is reported. Under the influence of a manganese porphyrin/iodosylbenzene system, a variety of unactivated aliphatic C–H bonds can be selectively converted to C–¹⁸F bonds. The mild conditions, broad substrate scope and generally inaccessible regiochemistry make this radio-fluorination a powerful alternate to established nucleophilic substitution for the preparation of ¹⁸F labeled radio tracers.

Cu-Mediated C-H 18F-Fluorination of Electron-Rich (Hetero)arenes

This communication describes a method for the nucleophilic radiofluorination of electron-rich arenes. The reaction involves the initial C(sp2)-H functionalization of an electron-rich arene with MesI(OH)OTs to form a (mesityl)(aryl)iodonium salt. This salt is then used in situ in a Cu-mediated radiofluorination with [18F]KF. This approach leverages the stability and availability of electron-rich arene starting materials to enable mild late-stage radiofluorination of toluene, anisole, aniline, pyrrole, and thiophene derivatives. The radiofluorination has been automated to access a 41 mCi dose of an 18F-labeled nimesulide derivative in high (2800 ± 700 Ci/mmol) specific activity.

Development of Customized [18F]Fluoride Elution Techniques for the Enhancement of Copper-Mediated Late-Stage Radiofluorination

In a relatively short period of time, transition metal-mediated radiofluorination reactions have changed the PET radiochemistry landscape. These reactions have enabled the radiofluorination of a wide range of substrates, facilitating access to radiopharmaceuticals that were challenging to synthesize using traditional fluorine-18 radiochemistry. However, the process of adapting these new reactions for automated radiopharmaceutical production has revealed limitations in fitting them into the confines of traditional radiochemistry systems. In particular, the presence of bases (e.g. K₂CO₃) and/or phase transfer catalysts (PTC) (e.g. kryptofix 2.2.2) associated with fluorine-18 preparation has been found to be detrimental to reaction yields. We hypothesized that these limitations could be addressed through the development of alternate techniques for preparing [¹⁸F]fluoride. This approach also opens the possibility that an eluent can be individually tailored to meet the specific needs of a metal-catalyzed reaction of interest. In this communication, we demonstrate that various solutions of copper salts, bases, and ancillary ligands can be utilized to elute [¹⁸F]fluoride from ion exchange cartridges. The new procedures are effective for fluorine-18 radiochemistry and, as proof of concept, have been used to optimize an otherwise base-sensitive copper-mediated radiofluorination reaction.

Development of Customized [18F]Fluoride Elution Techniques for the Enhancement of Copper-Mediated Late-Stage Radiofluorination

In a relatively short period of time, transition metal-mediated radiofluorination reactions have changed the PET radiochemistry landscape. These reactions have enabled the radiofluorination of a wide range of substrates, facilitating access to radiopharmaceuticals that were challenging to synthesize using traditional fluorine-18 radiochemistry. However, the process of adapting these new reactions for automated radiopharmaceutical production has revealed limitations in fitting them into the confines of traditional radiochemistry systems. In particular, the presence of bases (e.g. K2CO3) and/or phase transfer catalysts (PTC) (e.g. kryptofix 2.2.2) associated with fluorine-18 preparation has been found to be detrimental to reaction yields. We hypothesized that these limitations could be addressed through the development of alternate techniques for preparing [18F]fluoride. This approach also opens the possibility that an eluent can be individually tailored to meet the specific needs of a metal-catalyzed reaction of interest. In this communication, we demonstrate that various solutions of copper salts, bases, and ancillary ligands can be utilized to elute [18F]fluoride from ion exchange cartridges. The new procedures are effective for fluorine-18 radiochemistry and, as proof of concept, have been used to optimize an otherwise base-sensitive copper-mediated radiofluorination reaction.

Fluorinative ring-opening of cyclopropanes by hypervalent iodine reagents. An efficient method for 1,3-oxyfluorination and 1,3-difluorination

A new method is presented for 1,3-difluorination and 1,3-oxyfluorination reactions. The process is based on iodonium mediated opening of 1,1-disubstituted cyclopropanes. The reaction proceeds with high chemo- and regioselectivity under mild reaction conditions typically at room temperature in a couple of hours. The reaction probably occurs via electrophilic ring-opening of cyclopropanes.

Copper-Mediated Radiofluorination of Arylstannanes with [18F]KF

A copper-mediated nucleophilic radiofluorination of aryl- and vinylstannanes with [¹⁸F]KF is described. This method is fast, uses commercially available reagents, and is compatible with both electron-rich and electron-deficient arene substrates. This method has been applied to the manual synthesis of a variety of clinically relevant radiotracers including protected [¹⁸F]F-phenylalanine and [¹⁸F]F-DOPA. In addition, an automated synthesis of [¹⁸F]MPPF is demonstrated that delivers a clinically validated dose of 200 ± 20 mCi with a high specific activity of 2400 ± 900 Ci/mmol.

Fluorine-18 patents (2009-2015). Part 2: new radiochemistry

Fluorine-18 ((18)F) is one of the most common positron-emitting radionuclides used in the synthesis of positron emission tomography radiotracers due to its ready availability, convenient half-life and outstanding imaging properties. In Part 1 of this review, we presented the first analysis of patents issued for novel radiotracers labeled with fluorine-18. In Part 2, we follow-up with a focus on patents issued for new radiochemistry methodology using fluorine-18 issued between January 2009 and December 2015.