Two‐step radiosynthesis of [18F]N‐succinimidyl‐4‐fluorobenzoate ([18F]SFB)

The acylation reagent [¹⁸F]N‐succinimidyl‐4‐fluorobenzoate (¹⁸F‐SFB) has been prepared using a new two‐step approach. The starting material p‐[¹⁸F]fluorobenzaldehyde (¹⁸F‐FBA) was obtained by an improved radiosynthesis with a decay‐corrected radiochemical yield of 66±6 % (n=3). Reaction of ¹⁸F‐FBA with (diacetoxyiodine)benzene and N‐hydroxysuccinimide and preparative HPLC purification furnished ¹⁸F‐SFB in an r.c.y. of 49±6 % (n=3), based on the starting radioactivity of ¹⁸F‐FBA. The radiochemical purity of ¹⁸F‐SFB was >99%. Alternatively, purification by solid phase extraction gave ¹⁸F‐SFB with an r.c.y. of 77±9% (n=4) and a radiochemical purity of 89±5% (n=4). This radiochemical synthesis only used non‐aqueous solvents, which simplifies the method and facilitates subsequent applications of ¹⁸F‐SFB. Copyright © 2009 John Wiley & Sons, Ltd.     

A facile automated synthesis of N‐succinimidyl 4‐[18F]fluorobenzoate ([18F]SFB) for 18F‐labeled cell‐penetrating peptide as PET tracer

A fully automated synthesis of N‐succinimidyl 4‐[¹⁸F]fluorobenzoate ([¹⁸F]SFB) was carried out by a convenient three‐step, one‐pot procedure on the modified TRACERlab FX_FN synthesizer, including [¹⁸F]fluorination of ethyl 4‐(trimethylammonium triflate)benzoate as the precursor, saponification of the ethyl 4‐[¹⁸F]fluorobenzoate with aqueous tetrapropylammonium hydroxide instead of sodium hydroxide, and conversion of 4‐[¹⁸F]fluorobenzoate salt ([¹⁸F]FBA) to [¹⁸F]SFB treated with N,N,N′,N′‐tetramethyl‐O‐(N‐succinimidyl)uranium tetrafluoroborate (TSTU). The purified [¹⁸F]SFB was used for the labeling of Tat membrane‐penetrating peptide (containing the Arg‐Lys‐Lys‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Pro‐Leu‐Gly‐Leu‐Ala‐Gly‐Glu‐Glu‐Glu‐Glu‐Glu‐Glu‐Glu sequence, [¹⁸F]CPP) through radiofluorination of lysine amino groups. The uncorrected radiochemical yields of [¹⁸F]SFB were as high as 25–35% (based on [¹⁸F]fluoride) (n=10) with a synthesis time of～40 min. [¹⁸F]CPP was produced in an uncorrected radiochemical yields of 10–20% (n=5) within 30 min (based on [¹⁸F]SFB). The radiochemical purities of [¹⁸F]SFB and [¹⁸F]CPP were greater than 95%. Copyright © 2010 John Wiley & Sons, Ltd.     

Facile synthesis of N‐succinimidyl 4‐[18F]fluorobenzoate ([18F]SFB) for protein labeling

An efficient preparation of N‐succinimidyl 4‐[¹⁸F]fluorobenzoate ([¹⁸F]SFB) based on a convenient three‐step, one‐pot procedure is described. [¹⁸F]Fluorination of the precursor ethyl 4‐(trimethylammonium triflate)benzoate gave ethyl 4‐[¹⁸F]fluorobenzoate. Saponification of the ethyl 4‐[¹⁸F]fluorobenzoate with aqueous tetrapropylammonium hydroxide yielded the corresponding 4‐[¹⁸F]fluorobenzoate salt ([¹⁸F]FBA), which was then treated with N,N,N,N′‐tetramethyl‐O‐(N‐succinimidyl)uronium hexafluorophosphate. The purified [¹⁸F]SFB was used for the labeling of Avastin^? (Bevacizumab) through [¹⁸F]fluorobenzoylation of the Avastin's α‐amino groups. The decay‐corrected radiochemical yields of [¹⁸F]SFB were as high as 44% (based on [¹⁸F]fluoride (n=10) with a synthesis time of less than 60 min. [¹⁸F]Avastin was produced in decay‐corrected radiochemical yields of up to 42% (n=5) within 30 min (based on [¹⁸F]SFB). The radiochemical purities of [¹⁸F]SFB and [¹⁸F]Avastin were greater than 95%. Copyright © 2008 John Wiley & Sons, Ltd.     

Automated synthesis and purification of [18F]fluoro‐[di‐deutero]methyl tosylate

Automated synthetic procedures of [¹⁸F]fluoro‐[di‐deutero]methyl tosylate on a GE TRACERlab FX F‐N module and a non‐commercial synthesis module have been developed. The syntheses included azeotropic drying of the [¹⁸F]fluoride, nucleophilic ¹⁸F‐fluorination of bis(tosyloxy)‐[di‐deutero]methane, HPLC purification and subsequent formulation of the synthesized [¹⁸F]fluoro‐[di‐deutero]methyl tosylate (d₂‐[¹⁸F]FMT) in organic solvents. Automation shortened the total synthesis time to 50 min, resulting in an average radiochemical yield of about 50% and high radiochemical purity (>98%). The possible application of this procedure to commercially available synthesis modules might be of significance for the production of deuterated ¹⁸F‐fluoromethylated imaging probes in the future. Copyright © 2013 John Wiley & Sons, Ltd.     

N3‐Substituted thymidine analogues III: radiosynthesis of N3‐[(4‐[18F]fluoromethyl‐phenyl)butyl]thymidine ([18F]‐FMPBT) and N3‐[(4‐[18F]fluoromethyl‐phenyl)pentyl] thymidine ([18F]‐FMPPT) for PET

Radiosyntheses of two N³‐substituted thymidine analogues, N³‐[(4[¹⁸F]fluoromethyl‐phenyl)butyl]thymidine ([¹⁸F]‐FMPBT) and N³‐[(4[¹⁸F]fluoromethyl‐phenyl)pentyl]thymidine ([¹⁸F]‐FMPPT), are reported. The precursor compounds 9 and 10 were synthesized in six steps and the standard compounds 13 and 14 were synthesized from these precursors. For radiosynthesis, compounds 9 and 10 were fluorinated with n‐Bu₄N[¹⁸F] to produce [¹⁸F]‐ 11 and [¹⁸F]‐ 12 , which by acid hydrolysis yielded [¹⁸F]‐ 13 and [¹⁸F]‐ 14 , respectively. The crude products were purified by high‐performance liquid chromatography to obtain [¹⁸F]‐FMPBT and [¹⁸F]‐FMPPT. The average decay‐corrected radiochemical yield for [¹⁸F]‐ 13 was 15% in five runs, and that for [¹⁸F]‐ 14 was 10% in four runs. The radiochemical purity was >99% and the specific activity was >74 GBq/µmol at the end of synthesis. The synthesis time was 80–90 min from the end of bombardment. Copyright © 2007 John Wiley & Sons, Ltd.     

Batch‐mode microfluidic radiosynthesis of N‐succinimidyl‐4‐[18F]fluorobenzoate for protein labelling

The batch microfluidic technology is a promising system for sequential chemical steps combining the advantages of micro‐scale reactions, while addressing some shortcomings of flow‐through systems. We report herein the convenient three‐step, one‐pot synthesis and purification of [¹⁸F]SFB. [¹⁸F]SFB is a radiolabelling agent that can be used to label sensitive biomolecules, which are not accessible by direct nucleophilic ¹⁸F‐fluorination. Five sequential steps were performed with a batch microfluidic device to obtain the short‐lived positron‐emitter‐labelled molecule. Aqueous [¹⁸F]fluoride was concentrated and further eluted to a microreactor for evaporation. Nucleophilic ¹⁸F‐fluorination of the precursor was carried out at high temperature, prior to hydrolysis and subsequent activation of the 4‐[¹⁸F]fluorobenzoyl group. Purification on miniaturized solid‐phase finally afforded [¹⁸F]SFB in 25 min and 55±6% yield (not decay‐corrected) and >98% radiochemical purity. In this study, microfluidic prepared [¹⁸F]SFB could be further successfully used for labelling the epidermal growth factor protein. These results illustrate how microfluidic batch devices are advantageous for producing radiotracers for molecular imaging, e.g. Positron emission tomography. The technology offers many benefits such as the possibility to use much smaller quantities of starting material, reduced reaction time combined with improved efficiency, and easier purification. Copyright © 2010 John Wiley & Sons, Ltd.     

A fully automated synthesis of [18F]‐FEAU and [18F]‐FMAU using a novel dual reactor radiosynthesis module

2′‐Deoxy‐2′‐[¹⁸F]fluoro‐5‐substituted‐1‐β‐D ‐arabinofuranosyluracils, including 2′‐deoxy‐2′‐[¹⁸F]fluoro‐5‐methyl‐1‐β‐D ‐arabinofuranosyluracil [¹⁸F]FMAU and [¹⁸F]FEAU are established radiolabeled probes to monitor cellular proliferation and herpes simplex virus type 1 thymidine kinase (HSV1‐tk) reporter gene expression with positron emission tomography. For clinical applications, a fully automated CGMP‐compliant radiosynthesis is necessary for production of these probes. However, due to multiple steps in the synthesis, no such automated synthetic protocols have been developed. We report here a fully automated synthesis of [¹⁸F]‐FEAU and [¹⁸F]‐FMAU on a prototype dual reactor module TRACERlab FX FN. The synthesis was performed by using a computer‐programmed standard operating procedure, and the product was purified on a semipreparative high‐performance liquid chromatography (HPLC) integrated with the synthesis module using 12% EtOH in 50 mM Na₂HPO₄. Finally, the percentage of alcohol was adjusted to 7% by adding Na₂HPO₄ and filtered through a Millipore filter to make dose for human. The radiochemical yield on the fluorination was 40±10% (n=10), and the overall yields were 4±1% (d. c.), from the end of the bombardment; [¹⁸F]FEAU (n=7) and [¹⁸F]FMAU (n=3). The radiochemical purity was >99%, specific activity was 1200–1300 mCi/µmol. The synthesis time was 2.5 h. This automated synthesis should be suitable for production of [¹⁸F]FIAU, [¹⁸F]FFAU, [¹⁸F]FCAU, [¹⁸F]FBAU and other 5‐substitued thymidine analogues. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of 3′‐deoxy‐3′‐[18F]fluorothymidine ([18F]FLT) in ionic liquid, [bmim][OTf]

Although 3′‐deoxy‐3′‐[¹⁸F]fluorothymidine ([¹⁸F]FLT) is a prospective radiopharmaceutical for the imaging of proliferating tumor cell, it is difficult to prepare large amount of [¹⁸F]FLT. We herein describe the preparation of [¹⁸F]FLT in an ionic liquid, [bmim][OTf] (1‐butyl‐3‐methyl‐imidazolium trifluoromethanesulfonate). At optimized condition, [¹⁸F]fluorinationin ionic liquid with 5 µl of 1 M KHCO₃ and 5 mg of the precursor yielded 61.5 ± 4.3% (n=10). Total elapsed time was about 70 min including HPLC purification. The rapid synthesis of [¹⁸F]FLT can be achieved by removing all evaporation steps. Overall radiochemical yield and radiochemical purity were 30 ± 5% and >95%, respectively. This method can use a small amount of a nitrobenzenesulfonate precursor and can be adapted for automated production. Copyright © 2006 John Wiley & Sons, Ltd.     

A simplified radiosynthesis of [18F]MK‐6240 for tau PET imaging

[¹⁸F]MK‐6240 (6‐(fluoro)‐3‐(1H‐pyrrolo[2,3‐c]pyridin‐1‐yl)isoquinolin‐5‐amine) is a highly selective PET radiotracer for the in vivo imaging of neurofibrillary tangles (NFTs). [¹⁸F]MK‐6240 was synthesized in one step from its bis‐Boc protected precursor N‐[(tert‐butoxy)carbonyl]‐N‐(6‐nitro‐3‐[1H‐pyrrolo[2,3‐c]pyridin‐1‐yl]isoquinolin‐5‐yl) carbamate in DMSO using [¹⁸F] fluoride with TEA HCO₃ with step‐wise heating up to 150°C, resulting in an isolated radiochemical yield of 9.8% ± 1.8% (n = 3) calculated from the end of bombardment (5.2% ± 1.0% calculated from the end of synthesis). This new synthetic approach eliminates the acidic deprotection of the bis‐Boc ¹⁸F‐labeled intermediate, which reduces the number of operations necessary for the synthesis as well as losses, which occur during deprotection and neutralization of the crude product mixture prior to the HPLC purification. The synthesis was performed automatically with a single‐use cassette on an IBA Synthera+ synthesis module. This synthesis method affords the radioligand with a reliable radiochemical yield, high radiochemical purity, and a high molar activity. [¹⁸F]MK‐6240 synthesized with this method has been regularly (n > 60) used in our ongoing human and animal PET imaging studies.     

Synthesis of an 18F‐labeled cyclin‐dependent kinase‐2 inhibitor

The radiosynthesis of N‐(5‐(((5‐(tert‐butyl)oxazol‐2‐yl)methyl)thio)thiazol‐2‐yl)‐4‐[¹⁸F]fluoro‐benzamide [¹⁸F]2 as a potential radiotracer for molecular imaging of cyclin‐dependent kinase‐2 (CDK‐2) expression in vivo by positron emission tomography is described. Two different synthesis routes were envisaged. The first approach followed direct radiofluorination of respective nitro‐ and trimethylammonium substituted benzamides as labeling precursors with no‐carrier‐added (n.c.a.) [¹⁸F]fluoride. A second synthesis route was based on the acylation reaction of 2‐aminothiazole derivative with labeling agent [¹⁸F]SFB. Direct radiofluorination afforded ¹⁸ F‐labeled CDK‐2 inhibitor in very low yields of 1%–3%, whereas acylation reaction with [¹⁸F]SFB gave ¹⁸ F‐labeled CDK‐2 inhibitor [¹⁸ F]2 in high yields of up to 85% based upon [¹⁸ F]SFB during the optimization experiments. Large scale preparation afforded radiotracer [¹⁸ F]2 in isolated radiochemical yields of 37%–44% (n = 3, decay‐corrected) after HPLC purification within 75 min based upon [¹⁸ F]SFB. This corresponds to a decay‐corrected radiochemical yield of 13%–16% based upon [¹⁸F]fluoride. The radiochemical purity exceeded 95% and the specific activity was determined to be 20 GBq/µmol. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of [18F]‐labeled N‐3(substituted) thymidine analogues: N‐3([18F]fluorobutyl) thymidine ([18F]‐FBT) and N‐3([18F]fluoropentyl) thymidine ([18F]‐FPT) for PET

Syntheses of N‐3(substituted) analogues of thymidine, N‐3([¹⁸F]fluorobutyl)thymidine ([¹⁸F]‐FBT) and N‐3([¹⁸F]fluoropentyl)thymidine ([¹⁸F]‐FPT) are reported. 1,4‐Butane diol and 1,5 pentane diol were converted to their tosyl derivatives 2 and 3 followed by conversion to benzoate esters 4 and 5, respectively. Protected thymidine 1 was coupled separately with 4 and 5 to produce 6 and 7 , which were hydrolyzed to 8 and 9 , then converted to their mesylates 10 and 11 , respectively. Compounds 10 and 11 were fluorinated with n‐Bu₄N[¹⁸F] to produce 12 and 13 , which by acid hydrolysis yielded 14 and 15 , respectively. The crude products were purified by HPLC to obtain [¹⁸F]‐FBT and [¹⁸F]‐FPT. The radiochemical yields were 58–65% decay corrected (d.c.) for 14 and 46–57% (d.c.) for 15 with an average of 56% in three runs per compound. Radiochemical purity was >99% and specific activity was >74 GBq/µmol at the end of synthesis (EOS). The synthesis time was 65–75 min from the end of bombardment (EOB). Copyright © 2006 John Wiley & Sons, Ltd.     

One‐step radiosynthesis of 4‐[18F]flouro‐3‐nitro‐N‐2‐propyn‐1‐yl‐benzamide ([18F]FNPB): a new stable aromatic porosthetic group for efficient labeling of peptides with fluorine‐18

4‐[¹⁸F]flouro‐3‐nitro‐N‐2‐propyn‐1‐yl‐benzamide ([¹⁸F]FNPB) was developed as a new stable aromatic prosthetic group for more efficient click labeling of peptides. A new aromatic precursor 3,4‐dinitro‐N‐2‐propyn‐1‐yl‐benzamide was radiofluorinated using [¹⁸F]KF/K2.2.2 followed by HPLC purification to obtain the desired product [¹⁸F]FNPB. [¹⁸F]FNPB was synthesized with a 58% radiochemical yield, a specific activity > 350 GBq/µmol, and radiochemical purity was exceeded 98% in 40 min. The in vitro stability studies showed no detectable radiodefluorination over 2 h in mouse plasma. The click labeling yield of three different peptides with [¹⁸F]FNPB were all above 87%. The in vitro study suggests that [¹⁸F]FNPB may be stable in vivo and could have general application in labeling peptides with high radiochemical yield for positron emission tomography applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Radiosynthesis of 4‐[18F]fluoromethyl‐L‐phenylalanine and [18F]FET via a same strategy and automated synthesis module

Currently there is still a need for more potent amino acid analogues as tumour imaging agents for peripheral tumour imaging with PET as it was recently reported that the success of O‐(2′‐[¹⁸F]fluoroethyl)‐L ‐tyrosine ([¹⁸F]FET) is limited to brain, head and neck tumours. As the earlier described 2‐Amino‐3‐(2‐[¹⁸F]fluoromethyl‐phenyl)‐propionic acid (2‐[¹⁸F]FMP) suffered from intramolecular‐catalysed defluorination, we synthesized 2‐Amino‐3‐(4‐[¹⁸F]fluoromethyl‐phenyl)‐propionic acid (4‐[¹⁸F]FMP) as an alternative for tumour imaging with PET. Radiosynthesis of 4‐[¹⁸F]FMP, based on Br for [¹⁸F] aliphatic nucleophilic exchange, was performed with a customized modular Scintomics automatic synthesis hotbox^three system in a high overall yield of 30% and with a radiochemical purity of \gt 99%. 4‐[¹⁸F]FMP was found to be stable in its radiopharmaceutical formulation, even at high radioactivity concentrations. Additionally, for a comparative study, [¹⁸F]FET was synthesized using the same setup in 40% overall yield, with a radiochemical purity \gt 99%. The described automated radiosynthesis allows the production of two different amino acid analogues with minor alternations to the parameter settings of the automated system, rendering this unit versatile for both research and clinical practice. Copyright © 2009 John Wiley & Sons, Ltd.     

One‐step radiosynthesis of 4‐nitrophenyl 2‐[18F]fluoropropionate ([18F]NFP); improved preparation of radiolabeled peptides for PET imaging

The versatile ¹⁸F‐labeled prosthetic group, 4‐nitrophenyl 2‐[¹⁸F]fluoropropionate ([¹⁸F]NFP), was synthesized in a single step in 45 min from 4‐nitrophenyl 2‐bromopropionate, with a decay corrected radiochemical yield of 26.2% ± 2.2%. Employing this improved synthesis of [¹⁸F]NFP, [¹⁸F]GalactoRGD — the current ‘gold standard’ tracer for imaging the expression of α_Vβ₃ integrin — was prepared with high specific activity in 90 min and 20% decay corrected radiochemical yield from [¹⁸F]fluoride.     

Preparation and stability of ethanol‐free solution of [18F]florbetapir ([18F]AV‐45) for positron emission tomography amyloid imaging

We have developed an ethanol‐free formulation method of [¹⁸F]florbetapir ([¹⁸F]AV‐45) using a commercially available automated JFE multi‐purpose synthesizer. We have also evaluated the radiochemical stability in an ethanol‐free solution of [¹⁸F]AV‐45 under visible light irradiation and dark conditions by comparison with a conventional 10% ethanol solution of [¹⁸F]AV‐45. [¹⁸F]AV‐45 was obtained with a radiochemical yield of 55.1 ± 2.2% (decay‐corrected to end of bombardment), specific activity of 591.6 ± 90.3 GBq/µmol and radiochemical purity of >99% within a total synthesis time of about 73 min. The radiochemical purity of [¹⁸F]AV‐45 formulated by dissolving the ethanol‐free solution was found to decrease as a function of the period of exposure to visible light. In contrast, the visible light photolysis could be suppressed by adding 10% ethanol to the formulation or by avoiding exposure to visible light. In the radiosynthesis of [¹⁸F]AV‐45 formulated by dissolving the ethanol‐free solution, [¹⁸F]AV‐45 could be obtained with high radiochemical purity and high stability by avoiding exposure to visible light. Copyright © 2013 John Wiley & Sons, Ltd.     

Radiosynthesis of 3‐[18F]fluoropropyl and 4‐[18F]fluorobenzyl triarylphosphonium ions

3‐[¹⁸F]Fluoropropyl‐, 4‐[¹⁸F]fluorobenzyl‐triphenylphosphonium and 4‐[¹⁸F]fluorobenzyltris‐4‐dimethylaminophenylphosphonium cations were synthesized in multi‐step reactions from no carrier added (nca) [¹⁸F]fluoride. The time for synthesis, purification, and formulation was 56, 82, and 79 min with an average radiochemical yield of 12, 6 and 15%, respectively (not corrected for decay). The average specific radioactivity for the three radiolabeled compounds was 14.9 GB q/µmole (403 mCi/µmole) at end of synthesis (EOS). Copyright © 2004 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.     

Radiosynthesis of 6‐([18F]fluoroacetamido)‐1‐hexanoicanilide ([18F]FAHA) for PET imaging of histone deacetylase (HDAC)

Radiosynthesis of a novel substrate for histone deacetylase (HDAC), 6‐([¹⁸F]fluoroacetamido)‐1‐hexanoicanilide ([¹⁸F]FAHA, [¹⁸F]‐ 3 ) is reported. For precursor synthesis, compound 1 (6‐amino‐1‐hexanoicanilide) was prepared by the reaction of 6‐amino hexanoic acid with thionyl chloride in dichloroethane followed by addition of aniline. Compound 1 was reacted with bromoacetic anhydride in tetrahydrofuran (THF) in the presence of triethylamine to produce the precursor compound 6‐(bromoacetamido)‐1‐hexanoicanilide 2 . Fluorination reactions were performed using tetrabutylammonium fluoride in various solvents at 80°C to prepare the unlabeled reference compound 3 . Radiofluorinations were performed using either n‐Bu₄N¹⁸F or K¹⁸F/kryptofix, and the crude product was purified by high performance liquid chromatography (HPLC). The radiochemical yields were 9–13% decay corrected (d.c.) with an average of 11% using K¹⁸F/kryptofix, and specific activity >2 GBq/µmol at the end of synthesis. The synthesis time was 67–75 min from the end of bombardment (EOB). Copyright © 2006 John Wiley & Sons, Ltd.     

Simple and high radiochemical yield synthesis of 2′‐Deoxy‐2′‐[18F]fluorouridine via a new nosylate precursor

We synthesized 2'‐deoxy‐2'‐[¹⁸F]fluorouridine ( 7 ) as a radiotracer for positron emission tomography from a new nosylate precursor ( 6 ). This new precursor was synthesized from uridine in four steps. The overall synthetic yield was 9.4% and we have high stability of >98% purity up to 6 months at 4°C. The optimal manual [¹⁸F]fluorination conditions were 30 mg of the precursor 6 in 500 µl of acetonitrile at 145°C for 15 min with 370 MBq of [¹⁸F]fluoride. The [¹⁸F]fluorination yield was 76.5±2.7% (n = 3). After hydrolysis of protecting groups with 1 N HCl and purification by HPLC, the overall radiochemical yield and purity were 26.5±1.4% and 98.2±2.5%, respectively. The preparation time was 70.0±10.5 min (n = 3 for each result). We also developed an automated method with a radiochemical yield and purity of 24.0±2.8 and 98.0±1.5% (n = 10) using a GE TracerLab MX chemistry module. This new nosylate precursor for 2'‐deoxy‐2'‐[¹⁸F]fluorouridine synthesis showed higher radiochemical yields and reproducibility than previous methods. Copyright © 2006 John Wiley & Sons, Ltd.     

Automated radiosynthesis of [18F]SPA‐RQ for imaging human brain NK1 receptors with PET

[¹⁸F]SPA‐RQ is an effective radioligand for imaging brain neurokinin type‐1 (NK₁) receptors in clinical research and drug discovery with positron emission tomography. For the automated regular production of [¹⁸F]SPA‐RQ for clinical use in the USA under an IND we chose to use a modified commercial synthesis module (TRACERlab FX_F‐N; GE Medical Systems) with an auxiliary custom‐made robotic cooling–heating reactor, after evaluating several alternative radiosynthesis conditions. The automated radiosynthesis and its quality control are described here. [¹⁸F]SPA‐RQ was regularly obtained within 150 min from the start of radiosynthesis in high radiochemical purity (>99%) and chemical purity and with an overall decay‐corrected radiochemical yield of 15±2% (mean±S.D.; n=10) from cyclotron‐produced [¹⁸F]fluoride ion. The specific radioactivity of [¹⁸F]SPA‐RQ at the end of synthesis ranged from 644 to 2140 mCi/µmol (23.8–79.2 GBq/µmol). Copyright © 2005 John Wiley & Sons, Ltd.