Simplified and robust one‐step radiosynthesis of [18F]DCFPyL via direct radiofluorination and cartridge‐based purification

[¹⁸F]DCFPyL is a clinical‐stage PET radiotracer used to image prostate cancer. This report details the efficient production of [¹⁸F]DCFPyL using single‐step direct radiofluorination, without the use of carboxylic acid‐protecting groups. Radiolabeling reaction optimization studies revealed an inverse correlation between the amount of precursor used and the radiochemical yield. This simplified approach enabled automated preparation of [¹⁸F]DCFPyL within 28 minutes using HPLC purification (26% ± 6%, at EOS, n = 4), which was then scaled up for large‐batch production to generate 1.46 ± 0.23 Ci of [¹⁸F]DCFPyL at EOS (n = 7) in high molar activity (37 933 ± 4158 mCi/μmol, 1403 ± 153 GBq/μmol, at EOS, n = 7). Further, this work enabled the development of [¹⁸F]DCFPyL production in 21 minutes using an easy cartridge‐based purification (25% ± 9% radiochemical yield, at EOS, n = 3).     

Synthesis and quality control of [18F]T807 for tau PET imaging

The detailed synthesis and quality control of [¹⁸F]T807, radiotracer for tau protein aggregate imaging, are described. The radiotracer synthesis was accomplished in an average of 48 min with an average specific activity at end‐of‐synthesis of over 4.4 TBq/µmole (120 Ci/µmole) and an average radiochemical yield of 32%. Compliance with all standard US Pharmacopeia Chapter <823> acceptance tests was observed.     

cGMP production of the radiopharmaceutical [18F]MK‐6240 for PET imaging of human neurofibrillary tangles

Fluorine‐18–labelled 6‐(fluoro)‐3‐(1H‐pyrrolo[2,3‐c]pyridin‐1‐yl)isoquinolin‐5‐amine ([¹⁸F]MK‐6240) is a novel potent and selective positron emission tomography (PET) radiopharmaceutical for detecting human neurofibrillary tangles, which are made up of aggregated tau protein. Herein, we report the fully automated 2‐step radiosynthesis of [¹⁸F]MK‐6240 using a commercially available radiosynthesis module, GE Healthcare TRACERlab FX_FN. Nucleophilic fluorination of the 5‐diBoc‐6‐nitro precursor with potassium cryptand [¹⁸F]fluoride (K[¹⁸F]/K₂₂₂) was performed by conventional heating, followed by acid deprotection and semipreparative high‐performance liquid chromatography under isocratic conditions. The isolated product was diluted with formulation solution and sterile filtered under Current Good Manufacturing Practices, and quality control procedures were established to validate this radiopharmaceutical for human use. At the end of synthesis, 6.3 to 9.3 GBq (170‐250 mCi) of [¹⁸F]MK‐6240 was formulated and ready for injection, in an uncorrected radiochemical yield of 7.5% ± 1.9% (relative to starting [¹⁸F]fluoride) with a specific activity of 222 ± 67 GBq/μmol (6.0 ± 1.8 Ci/μmol) at the end of synthesis (90 minutes; n = 3). [¹⁸F]MK‐6240 was successfully validated for human PET studies meeting all Food and Drug Administration and United States Pharmacopeia requirements for a PET radiopharmaceutical. The present method can be easily adopted for use with other radiofluorination modules for widespread clinical research use.     

Radiosynthesis and validation of [Carboxy‐11C]4‐Aminobenzoic acid ([11C]PABA), a PET radiotracer for imaging bacterial infections

In this practitioner protocol, the radiochemical synthesis of [¹¹C] PABA is described in detail, and a quality control summary of three validation productions is presented. The results indicate that the radiotracer product can be produced in good radiochemical yield (14% at end‐of‐synthesis (EOS)) at high specific activity (molar activity 11 Ci/μmole EOS; 407 GBq/μmole) and high chemical and radiochemical purity as a sterile, pyrogen‐free solution suitable for injection conforming to current Good Manufacturing Practice (cGMP) requirements.     

A concisely automated synthesis of TSPO radiotracer [18F]FDPA based on spirocyclic iodonium ylide method and validation for human use

Fluorine-18 labeled N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide ([¹⁸F]FDPA) is a potent and selective radiotracer for positron-emission tomography (PET) imaging of the translocator protein 18 kDa (TSPO). Our previous in vitro and in vivo evaluations have proven that this tracer is promising for further human translation. Our study addresses the need to streamline the automatic synthesis of this radiotracer to make it more accessible for widespread clinical evaluation and application. Here, we successfully demonstrate a one-step radiolabeling of [¹⁸F]FDPA based on a novel spirocyclic iodonium ylide (SCIDY) precursor using tetra-n-butyl ammonium methanesulfonate (TBAOMs), which has demonstrated the highest radiochemical yields and molar activity from readily available [¹⁸F]fluoride ion. The nucleophilic radiofluorination was completed on a GE TRACERlab FX2 N synthesis module, and the formulated [¹⁸F]FDPA was obtained in nondecay corrected (n.d.c) radiochemical yields of 15.6 ± 4.2%, with molar activities of 529.2 ± 22.5 GBq/μmol (14.3 ± 0.6 Ci/μmol) at the end of synthesis (60 minutes, n = 3) and validated for human use. This methodology facilitates efficient synthesis of [¹⁸F]FDPA in a commercially available synthesis module, which would be broadly applicable for routine production and widespread clinical PET imaging studies.     

Radiofluorination and reductive amination using a microfluidic device

A commercial microfluidic device (NanoTek, Advion) was used as a synthesis platform for the preparation of fluorine‐18 labelled tertiary amines in two consecutive steps. Firstly, the nucleophilic radiofluorination of an aromatic aldehyde and secondly, the reductive amination to produce the corresponding amine. Fluorine‐18 labelled [¹⁸F]fluorobenzaldehyde ([¹⁸F]2) was obtained in an analytical radiochemical yield (rcy) of 93% and a preparative yield of 60% (decay corrected). The produced [¹⁸F]2 was applied in two model reactions yielding [¹⁸F]5 and [¹⁸F]6 in analytical rcy 70 and 75%, respectively. To further test the utility of this methodology, a delta opioid agonist, [¹⁸F]8, was also radiolabelled using the same setup in an analytical rcy of 29%. In a preparative run, 1050 MBq (28.4 mCi) isolated product ([¹⁸F]6) was obtained in a 37.5% decay corrected overall rcy calculated from [¹⁸F]fluoride. The radiochemical purity of [¹⁸F]6 was greater than 99% and the specific radioactivity 298 GBq/µmol (8052 Ci/mmol) at end of synthesis.     

Automated one‐step radiosynthesis of the CB1 receptor imaging agent [18F]MK‐9470

The fluorine‐18‐labeled positron emission tomography (PET) radiotracer [¹⁸F]MK‐9470 is a selective, high affinity inverse agonist that has been used to image the cannabinoid receptor type 1 in human brain in healthy and disease states. This report describes a simplified, one‐step [¹⁸F]radiofluorination approach using a GE TRACERlab FX_FN module for the routine production of this tracer. The one‐step synthesis, by [¹⁸F]fluoride displacement of a primary tosylate precursor, gives a six‐fold increase in yield over the previous two‐step method employing O‐alkylation of a phenol precursor with 1,2‐[¹⁸F]fluorobromoethane. The average radiochemical yield of [¹⁸F]MK‐9470 using the one‐step method was 30.3 ± 11.7% (n = 12), with specific activity in excess of 6 Ci/µmol and radiochemical purity of 97.2 ± 1.5% (n = 12), in less than 60 min. This simplified, high yielding, automated process was validated for routine GMP production of [¹⁸F]MK‐9470 for clinical studies.     

A report of the automated radiosynthesis of the tau positron emission tomography radiopharmaceutical, [18F]‐THK‐5351

The radiotracer, [¹⁸F]‐THK‐5351, is a highly selective and high‐binding affinity PET imaging agent for aggregates of hyper‐phosphorylated tau protein. Our report is a simplified 1‐pot, 2‐step radiosynthesis of [¹⁸F]‐THK‐5351. This report is broadly applicable for routine clinical production and multi‐center trials on account of favorable half‐life of flourine‐18 and the use of a commercially available radiosynthesis module, the GE TRACERlab™ FX_FN. First, the O‐THP protected tosyl precursor underwent nucleophilic fluorinating reaction with potassium cryptand fluoride ([¹⁸F] fluoride (K[¹⁸F]/K₂₂₂)) in Dimethyl sulfoxide at 110°C for 10 minutes followed by O‐THP removal by using diluted hydrochloric acid (HCl) at same temperature. [¹⁸F]‐THK‐5351 was purified via semi‐preparative high‐performance liquid chromatography and formulated by using 10% EtOH, United States Pharmacopeia (USP) in 0.9% sodium chloride for injection, USP and an uncorrected radiochemical yield of 21 ± 3.5%, with a specific activity of 153.11 ± 25.9 GBq/μmol (4138 ± 700 mCi/μmol) at the end of synthesis (63 minutes; n  = 3).     

Microwave‐assisted radiosynthesis of [18F]ASEM,a radiolabeled α7‐nicotinic acetylcholine receptor antagonist

An improvement of the original radiochemical synthesis of [¹⁸F]ASEM, an α7‐nicotinic acetylcholinergic receptor radioligand, is reported. The new procedure utilizes microwave‐assisted radiofluorination. In addition, a new preparative HPLC method was developed to eliminate a chemical impurity in the final product. Quality control procedures were also enhanced to improve detection of product with enhanced resolution of potential impurities. [¹⁸F]ASEM was produced in 20.1 ± 8.9% non‐decay corrected (NDC) yield with an average synthesis time of 57 min and an average specific radioactivity of 856 ± 332 GBq/µmol (23 ± 9 Ci/µmol).     

Radiosynthesis of the norepinephrine transporter tracer [18F]NS12137 via copper‐mediated 18F‐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.     

A novel probe for imaging amyloid‐β: Synthesis of F‐18 labelled BF‐108, an Acridine Orange analog

The synthesis of 3‐(2‐[¹⁸F]fluoroethyl)ethylamino‐6‐diethylaminoacridine ([¹⁸F]BF‐108), a potential positron‐labelled probe for imaging amyloid‐β is described. The precursor tosylate derivative was fluorinated with [¹⁸F]KF/ Kryptofix 222 in acetonitrile, and the crude product was purified by semi‐preparative HPLC to give the radiolabelled BF‐108. The radiochemical purity was >95% and the maximum specific activity was 33.9 TBq/mmol at the end of the synthesis (EOS). The synthesis time was 130 min from the end of bombardment (EOB). Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of [18F]‐labeled 2′‐deoxy‐2′‐fluoro‐5‐methyl‐1‐β‐D‐arabinofuranosyluracil ([18F]‐FMAU)

Synthesis of 2′‐deoxy‐2′‐[¹⁸F]fluoro‐5‐methyl‐1‐β‐D‐arabinofuranosyluracil ([¹⁸F]‐FMAU) is reported. 2‐Deoxy‐2‐[¹⁸F]fluoro‐1,3,5‐tri‐O‐benzoyl‐α‐D‐arabinofuranose 2 was prepared by the reaction of the respective triflate 1 with tetrabutylammonium[¹⁸F]fluoride. The fluorosugar 2 was converted to its 1‐bromo‐derivative 3 and coupled with protected thymine 4 . The crude product mixture ( 5a and 5b ) was hydrolyzed in base and purified by HPLC to obtain the radiolabeled FMAU 6a . The radiochemical yield of 6a was 20–30% decay corrected (d.c.) in four steps with an average of 25% in four runs. Radiochemical purity was >99% and average specific activity was 2300 mCi/μmol at the end of synthesis (EOS). The synthesis time was 3.5–4.0 h from the end of bombardment (EOB). Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of (4‐[18F]fluorophenyl)triphenylphosphonium as a potential imaging agent for mitochondrial dysfunction

Tetraphenylphosphonium (TPP) cation is able to function as a molecular probe for monitoring mitochondrial disease. The F‐18 labeled TPP, (4‐[¹⁸F]fluorophenyl) triphenylphosphonium (¹⁸FTPP), was therefore developed as a PET radioligand for in vivo molecular imaging of mitochondrial dysfunction. ¹⁸FTPP was synthesized via direct nucleophilic substitution of no‐carrier‐added [¹⁸F]fluoride with the precursor 4‐nitrophenyltriphenylphosphonium. After purification by HPLC, the average radiochemical yield was determined to be 10–15% and the specific activity was >500 Ci/mmol at the end of synthesis. The total synthesis time was within 60 min, and the radiochemical purity of the ¹⁸FTPP was above 95%. Copyright © 2005 John Wiley & Sons, Ltd.     

Automated synthesis of N‐(2‐[18F]Fluoropropionyl)‐l‐glutamic acid as an amino acid tracer for tumor imaging on a modified [18F]FDG synthesis module

N‐(2‐[¹⁸F]Fluoropropionyl)‐l ‐glutamic acid ([¹⁸F]FPGLU) is a potential amino acid tracer for tumor imaging with positron emission tomography. However, due to the complicated multistep synthesis, the routine production of [¹⁸F]FPGLU presents many challenging laboratory requirements. To simplify the synthesis process of this interesting radiopharmaceutical, an efficient automated synthesis of [¹⁸F]FPGLU was performed on a modified commercial fluorodeoxyglucose synthesizer via a 2‐step on‐column hydrolysis procedure, including ¹⁸F‐fluorination and on‐column hydrolysis reaction. [¹⁸F]FPGLU was synthesized in 12 ± 2% (n = 10, uncorrected) radiochemical yield based on [¹⁸F]fluoride using the tosylated precursor 2 . The radiochemical purity was ≥98%, and the overall synthesis time was 35 minutes. To further optimize the radiosynthesis conditions of [¹⁸F]FPGLU, a brominated precursor 3 was also used for the preparation of [¹⁸F]FPGLU, and the improved radiochemical yield was up to 20 ± 3% (n  = 10, uncorrected) in 35 minutes. Moreover, all these results were achieved using the similar on‐column hydrolysis procedure on the modified fluorodeoxyglucose synthesis module.     

Preparation of fluorine‐18‐labelled fluoromisonidazole using two different synthesis methods

¹⁸F‐labelled fluoromisonidazole [1H‐1‐(3‐[¹⁸F]fluoro‐2‐hydroxypropyl)‐2‐nitroimida‐zole; ([¹⁸F]FMISO)] is used as an in vivo marker of hypoxic cells in tumours and ischaemic areas of the heart and the brain. The compound plays an important role in evaluating the oxygenation status in tumours during radiotherapy. In this paper, we report experiments carried out in our laboratory in synthesizing [¹⁸F]FMISO using two different methods. The first method (I) for the [¹⁸F]FMISO synthesis was the fluorination of (2R)‐(?)‐glycidyl tosylate to [¹⁸F]epifluorohydrin. The subsequent nucleophilic ring opening, achieved with 2‐nitroimidazole, leads to labelled FMISO. The second method (II) was the fluorination of the protected precursor 1‐(2′‐nitro‐1′‐imidazolyl)‐2‐O‐tetrahydropyranyl‐3‐O‐toluenesulphonyl‐propanediol, followed by a rapid removal of the protecting group. With the first method, the radiochemical yield was about 10% at the end of the synthesis (EOS), and the radiochemical purity was over 99%. The radiochemical yield in the second method was 21% (EOS) on an average, and the radiochemical purity was over 97%. When an automated commercial synthesis module was used with method II, slightly better and more reproducible yields were achieved. The improvement in the synthesis yield with the automated apparatus will be valuable when working with high activities, and therefore it is under further development. Copyright © 2003 John Wiley & Sons, Ltd.     

Fully automated,high yielding production of N‐succinimidyl 4‐[18F]fluorobenzoate ([18F]SFB), and its use in microwave‐enhanced radiochemical coupling reactions

A General Electric Medical Systems (GEMS) Tracerlab FX_FN fluorine‐18 synthesis module has been reconfigured to allow rapid (45 min), fully automated production of N‐succinimidyl 4‐[¹⁸F]fluorobenzoate ([¹⁸F]SFB) using the established three‐step, one‐pot synthesis procedure. Purification is by sep‐pak only and [¹⁸F]SFB is routinely obtained in 38% non‐decay corrected yield,>1 Ci/µmol specific activity, and >95% radiochemical purity (n=20). Moreover, this report includes our preliminary research efforts into improving peptide coupling reactions with [¹⁸F]SFB using microwave‐enhanced radiochemistry. Reaction times can be reduced by>90%, when compared with traditional thermal reactions, with no significant effect on radiochemical reaction yield. Copyright © 2010 John Wiley & Sons, Ltd.     

Radiosynthesis of the HIV integrase inhibitor [18F]MK‐0518 (Isentress)

The human immunodeficiency virus integrase inhibitor, [¹⁸F]MK‐0518, was prepared via a three‐step, one‐pot radiosynthesis. [¹⁸F]4‐Fluorobenzylamine was produced from the fluorination of 4‐cyano‐N,N,N‐trimethylammonium triflate with [¹⁸F]fluoride and reduction with borane methylsulfide complex in 50–68% radiochemical yield. The final step, the coupling of [¹⁸F]4‐fluorobenzylamine with an ester coupling partner, achieved an overall uncorrected radiochemical yield after HPLC purification of ～2%, based on the starting [¹⁸F]fluoride. In a typical run, the total synthesis time was about 90 min and gave 0.37–1.74 GBq (10–47 mCi) of [¹⁸F]MK‐0518. The radiochemical purity of [¹⁸F]MK‐0518 was>98% and the specific activity was 243–1275 Ci/mmol (EOS, n=4). A convenient three‐step, one‐pot radiosynthesis of [¹⁸F]MK‐0518 via [¹⁸F]4‐fluorobenzylamine has been developed, giving sufficient quantities of [¹⁸F]MK‐0518 for animal positron emission tomography studies. Copyright © 2010 John Wiley & Sons, Ltd.     

“In‐loop” 18F‐fluorination: A proof‐of‐concept study

There is a great demand to develop more cost‐efficient and robust manufacturing processes for fluorine‐18 (¹⁸F) labelled compounds and radiopharmaceuticals. Herein, we present to our knowledge the first radiofluorination “in‐loop,” where [¹⁸F]triflyl fluoride was used as the labelling agent. Initial development of the “in‐loop” [¹⁸F]fluorination method was optimized by reacting [¹⁸F]triflyl fluoride with 1,4‐dinitrobenzene to form [¹⁸F]1‐fluoro‐4‐nitrobenzene. This methodology was then applied for the syntheses of two well‐known radiopharmaceuticals, namely, [¹⁸F]T807 for imaging of tau protein and [¹⁸F]FEPPA for imaging the translocator protein 18 KDa. Both radiotracers were synthesized and formulated using an automated radiosynthesis module with nondecay corrected radiochemical yields of 27% and 29% (relative [¹⁸F]F^?), respectively. The overall syntheses times for [¹⁸F]T807 and [¹⁸F]FEPPA were 65 and 55 minutes, respectively. In these cases, our “in‐loop” radiofluorination methodology enabled us to obtain equal or superior yields compared with conventional reactions in a vial. The radiochemical purities were more than 99%, and the molar activities were more than 350 GBq/μmol at the end‐of‐synthesis for both radiotracers. This novel method is simple, efficient, and allows for a reliable production of radiofluorinated compounds and radiopharmaceuticals.     

Radiosynthesis of [11C]paclitaxel

[¹¹C]paclitaxel, a potential solid tumor imaging agent, was synthesized by reacting [α‐¹¹C]benzoyl chloride with the primary amine precursor of paclitaxel. The time for synthesis, purification, and formulation was 38 min from end of bombardment with an average specific radioactivity of 49.9 GBq/μmol (1349 mCi/μmol) at end of synthesis. The average decay corrected radiochemical yield was 7% with greater than 99% radiochemical purity. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 2‐[18F]fluoroadenosine (2‐[18F]FAD) as potential radiotracer for studying malignancies by PET

2‐[¹⁸F]fluoroadenosine (2‐[¹⁸F]FAD), a potential radioligand for assessment of adenylate metabolism, was synthesized by carrier‐added and no‐carrier‐added procedures via nucleophilic radiofluorination of 2‐fluoroadenosine and 2‐iodoadenosine. The radiochemical yield, specific radioactivity and radiochemical purity of carrier‐added and no‐carrier‐added 2‐[¹⁸F]FAD were 5%, 22–30 mCi/µmol and 99%, and 0.5%, 1200–1700 mCi/µmol and 99%, respectively. Copyright © 2006 John Wiley & Sons, Ltd.