A high yield robotic synthesis of 9-(4-[18F]-fluoro-3-hydroxymethylbutyl)guanine ([18F]FHBG) and 9-[3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine([18F] FHPG) for gene expression imaging.

The aim of this study was to develop an automated synthesis of 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine ([(18)F]FHBG) and 9-[(3-[(18)F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([(18)F]FHPG) using a Scanditronix Anatech RB III robotic system. [(18)F]HF was produced via (18)O(p, n)(18)F using a Scanditronix MC17F cyclotron. On average, a typical run produced [(18)F]FHBG and [(18)F]FHPG with an uncorrected radiochemical yield of 19% and 16%, respectively, at end of synthesis (EOS) from irradiation of 95% enriched [(18)O]water. The total synthesis time was 80 min. The retention time of [(18)F]FHBG and [(18)F]FHPG (the radio-peak) was 3.9 and 4.0 min, respectively, which was consistent with the [(19)F]FHBG and [(19)F]FHPG ultraviolet peak. The radiochemical purity was greater than 97%. A robotic, automated method for [(18)F]FHBG and [(18)F]FHPG radiosynthesis is therefore feasible. The radiation burden for the operator can be reduced as much as possible. Sufficient radioactivities of [(18)F]FHBG and [(18)F]FHPG could be obtained for non-invasive monitoring the expression of transfected gene in vivo with positron emission tomography (PET).     

C-(4-[18F]fluorophenyl)-N-phenyl nitrone: A novel 18F-labeled building block for metal free [3+2]cycloaddition

Radiofluorination via [3+2]-nitrone-alkene cycloaddition was studied using the model reaction between (18)F-labeled C-(4-fluorophenyl)-N-phenyl nitrone ([(18)F]1) and substituted maleimides 2a-c. [(18)F]1 was prepared in RCY of 73.6±5.8% and radiochemical purity of >95%. Cycloaddition of [(18)F]1 to 2a in toluene at 80°C and in EtOH at 110°C gave the respective isoxazolidine [(18)F]5a in >80% RCY at 10min reaction time. Reaction between [(18)F]1 and 2b, c also went smoothly to afford the respective cycloaddition products in high radiochemical yields.     

Fully automated one-pot synthesis of [18F]fluoromisonidazole

A (18)F-labeled fluoromisonidazole (1H-1-(3-[(18)F]fluoro-2-hydroxypropyl)-2-nitroimidazole, [(18)F]FMISO) was prepared via a one-pot, two-step synthesis procedure using a modified commercial Tracerlab FX(F-N) synthesis module. Nucleophilic fluorination of the precursor molecule 1-(2'-nitro-1'-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulphonylpropanediol using no-carrier-added [(18)F]fluoride, followed by hydrolysis of the protecting group with 1 mol/L HCl and purification with Sep-Paks instead of HPLC, gave [(18)F]FMISO. The overall radiochemical yield with no decay correction was greater than 40%, the whole synthesis time was less than 40 min and the radiochemical purity was greater than 95%. The new automated synthesis procedure can be applied to the fully automated synthesis of [(18)F]FMISO using a commercial FDG synthesis module.     

18F]fluoromethyl triflate, a novel and reactive [18F]fluoromethylating agent: preparation and application to the on-column preparation of [18F]fluorocholine.

The production and use of [18F]fluoromethyl triflate ([18F]CH2FOTf), a more reactive [18F]fluoromethylating agent than [18F]fluoromethyl bromide ([18F]CH2BrF), is described. [18F]CH2FOTf was prepared from [18F]CH2BrF. The latter was synthesized by nucleophilic substitution of CH2Br2 with no-carrier-added [18F]fluoride and purified by four Sep-Pak Plus silica cartridges connected in series. It was then quantitatively converted on-line to [18F]CH2FOTf by passing through a heated AgOTf column. Decay-corrected radiochemical yields of [18F]CH2FOTf based on [18F]fluoride were 47 +/- 8% (n = 20). Both [18F]CH2BrF and [18F]CH2FOTf were applied to solid-supported [18F]fluoromethylation of N,N-dimethylaminoethanol on a Sep-Pak Plus C18 cartridge to produce the 18F-labeled choline analogue, (beta-hydroxyethyl)dimethyl-[18F]fluoromethylammonium ([18F]fluorocholine). Depending on flow rate and amount of precursor used, decay corrected radiochemical yields of [18F]fluorocholine from [18F]CH2BrF ranged from 6% to 63%, while [18F]CH2FOTf afforded yields of more than 80%. Thus, by using the latter reagent and a subsequent purification on a Sep-Pak Accell CM cartridge, [18F]fluorocholine was produced from [18F]fluoride in overall radiochemical yields of 40% (decay corrected) in less than 30 min.     

Synthesis of 2'-deoxy-2'-[18F]fluoro-beta-D-arabinofuranosyl nucleosides, [18F]FAU, [18F]FMAU, [18F]FBAU and [18F]FIAU,as potential PET agents for imaging cellular proliferation. Synthesis of [18F]labelled FAU,FMAU, FBAU,FIAU

An efficient and reliable synthesis of 2'-deoxy-2'-[(18)F]fluoro-beta-D-arabinofuranosyl nucleosides is presented. Overall decay-corrected radiochemical yields of 35-45% of 4 analogs, FAU, FMAU, FBAU and FIAU are routinely obtained in >98% radiochemical purity and with specific activities of greater than 3 Ci/micromol (110 MBq/micromol) in a synthesis time of approximately 3 hours. When approximately 220 mCi (8.15 GBq) of starting [(18)F]fluoride is used, 25 -30 mCi (0.93 -1.11 GBq) of product (enough to image two patients sequentially) is typically obtained.     

Module-assisted synthesis of the bifunctional labelling agent N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB).

The three-step radiosynthesis of N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB) was adapted to a remotely controlled synthesis module. After optimization of the reaction conditions, the final [(18)F]SFB was obtained in decay-corrected radiochemical yields of 34-38% (related to [(18)F]fluoride; n=12) within a synthesis time of 68 min. The radiochemical purity was in the range of 93-96%.     

Fully automated synthesis module for preparation of S-(2-[(18)F]fluoroethyl)-L-methionine by direct nucleophilic exchange on a quaternary 4-aminopyridinium resin

A fully automated preparation of S-(2-[(18)F]fluoroethyl)-L-methionine (FEMET), an amino acid tracer for tumor imaging with positron emission tomography, is described. [(18)F]F(-) was produced via nuclear reaction (18)O(p,n) [(18)F] at PETtrace Cyclotron. Direction nucleophilic fluorination reaction of [(18)F]fluoride with 1,2-di(4-methylphenylsulfonyloxy)ethane on a quaternary 4-(4-methylpiperidinyl)pyridinium functionalized polystyrene anion exchange resin gave 2-[(18)F]-1-(4-methylphenyl-sulfonyloxy)ethane, and then [(18)F]fluoroalkylation of L-homocysteine thiolactone with 2-[(18)F]-1-(4-methylphenylsulfonyloxy)ethane yielded FEMET. The overall radiochemical yield with no decay correction was about 10%, the whole synthesis time was about 52 min, and the radiochemical purity was above 95%.     

Evaluation of F-18-labeled amino acid derivatives and [18F]FDG as PET probes in a brain tumor-bearing animal model

2-Deoxy-2-[(18)F]fluoro-d-glucose ([(18)F]FDG) has been extensively used as positron emission tomography (PET) tracer in clinical tumor imaging. This study compared the pharmacokinetics of two (18)F-labeled amino acid derivatives, O-2-[(18)F]fluoroethyl-l-tyrosine (l-[(18)F]FET) and 4-borono-2-[(18)F]fluoro-l-phenylalanine-fructose (l-[(18)F]FBPA-Fr), to that of [(18)F]FDG in an animal brain tumor model. METHODS: A self-modified automated PET tracer synthesizer was used to produce no-carrier-added (nca) l-[(18)F]FET. The cellular uptake, biodistribution, autoradiography and microPET imaging of l-[(18)F]FET, l-[(18)F]FBPA-Fr and [(18)F]FDG were performed with F98 glioma cell culture and F98 glioma-bearing Fischer344 rats. RESULTS: The radiochemical purity of l-[(18)F]FET was >98% and the radiochemical yield was 50% in average of 16 runs. The uptake of l-[(18)F]FET and l-[(18)F]FBPA-Fr in the F98 glioma cells increased rapidly for the first 5 min and reached a steady-state level after 10 min of incubation, whereas the cellular uptake of [(18)F]FDG kept increasing during the study period. The biodistribution of l-[(18)F]FET, l-[(18)F]FBPA-Fr and [(18)F]FDG in the brain tumors was 1.26+/-0.22, 0.86+/-0.08 and 2.77+/-0.44 %ID/g at 60 min postinjection, respectively, while the tumor-to-normal brain ratios of l-[(18)F]FET (3.15) and l-[(18)F]FBPA-Fr (3.44) were higher than that of [(18)F]FDG (1.44). Both microPET images and autoradiograms of l-[(18)F]FET and l-[(18)F]FBPA-Fr exhibited remarkable uptake with high contrast in the brain tumor, whereas [(18)F]FDG showed high uptake in the normal brain and gave blurred brain tumor images. CONCLUSION: Both l-[(18)F]FET and l-[(18)F]FBPA-Fr are superior to [(18)F]FDG for the brain tumor imaging as shown in this study with microPET.     

Automated preparation of hypoxic cell marker [18F]FRP-170 by on-column hydrolysis.

An automated synthesis for the preparation of the novel hypoxic cell marker, [(18)F]FRP-170 3, [(18)F]1-[2-fluoro-1-(hydroxymethyl)ethoxy]methyl-2- nitroimidazole, was developed using an on-column basic-hydrolysis step. The (18)F-labeled protected intermediate 2 was retained on a Sep-Pak Plus C18 cartridge and, in the same cartridge at room temperature, hydrolyzed by NaOH for deacetylation to give [(18)F]FRP-170. The elution method from the cartridge was optimized for direct injection of the crude product into an HPLC column. Thus, [(18)F]FRP-170 was prepared in 20-30% decay-corrected radiochemical yield within 60 min.     

Novel one-pot one-step synthesis of 2'-[(18)F]fluoroflumazenil (FFMZ) for benzodiazepine receptor imaging

We describe the synthesis of 2'-[(18)F]fluoroflumazenil (FFMZ), which differs from the typically used [(18)F]fluoroethylflumazenil (FEFMZ) for benzodiazepine receptor imaging. For one-pot one-step labeling, the precursors, 2'-tosyloxyflumazenil (TFMZ) and 2'-mesyloxyflumazenil (MFMZ), were synthesized in three steps. The precursors were successfully labeled with no-carrier-added (18)F-fluoride which was activated by repeated azeotropic distillation with Kryptofix 2.2.2./potassium carbonate in MeCN. An automated system for labeling and purification of [(18)F]FFMZ was developed. Labeling efficiency and radiochemical purity of [(18)F]FFMZ after synthesis by the automated system were 68% and 98%, respectively. Specific binding of [(18)F]FFMZ to central benzodiazepine receptor of rats was demonstrated by phosphoimaging.     

Synthesis and evaluation of (S)-2-(2-[18F]fluoroethoxy)-4-([3-methyl-1-(2-piperidin-1-yl-phenyl)-butyl-carbamoyl]-methyl)-benzoic acid ([18F]repaglinide): a promising radioligand for quantification of pancreatic beta-cell mass with positron emission tomography (PET)

18F-labeled non-sulfonylurea hypoglycemic agent (S)-2-(2-[(18)F]fluoroethoxy)-4-((3-methyl-1-(2-piperidin-1-yl-phenyl)-butylcarbamoyl)-methyl)-benzoic acid ([(18)F]repaglinide), a derivative of the sulfonylurea-receptor (SUR) ligand repaglinide, was synthesized as a potential tracer for the non-invasive investigation of the sulfonylurea 1 receptor status of pancreatic beta-cells by positron emission tomography (PET) in the context of type 1 and type 2 diabetes. [(18)F]Repaglinide could be obtained in an overall radiochemical yield (RCY) of 20% after 135 min with a radiochemical purity higher than 98% applying the secondary labeling precursor 2-[(18)F]fluoroethyltosylate. Specific activity was in the range of 50-60 GBq/micromol. Labeling was conducted by exchanging the ethoxy-moiety into a 2-[(18)F]fluoroethoxy group. To characterize the properties of fluorinated repaglinide, the affinity of the analogous non-radioactive (19)F-compound for binding to the human SUR1 isoform was assessed. [(19)F]Repaglinide induced a complete monophasic inhibition curve with a Hill coefficient close to 1 (1.03) yielding a dissociation constant (K(D)) of 134 nM. Biological activity was proven via insulin secretion experiments on isolated rat islets and was comparable to that of repaglinide. Finally, biodistribution of [(18)F]repaglinide was investigated in rats by measuring the concentration of the compound in different organs after i.v. injection. Pancreatic tissue displayed a stable accumulation of approximately 0.12% of the injected dose from 10 min to 30 min p.i. 50% of the radioactive tracer could be displaced by additional injection of unlabeled repaglinide, indicating that [(18)F]repaglinide might be suitable for in vivo investigation with PET.     

Automatic synthesis of 16 alpha-[(18)F]fluoro-17beta-estradiol using a cassette-type [(18)F]fluorodeoxyglucose synthesizer

16 alpha-[(18)F]fluoro-17beta-estradiol ([(18)F]FES) is a radiotracer for imaging estrogen receptors by positron emission tomography. We developed a clinically applicable automatic preparation system for [(18)F]FES by modifying a cassette-type [(18)F]fluorodeoxyglucose synthesizer. Two milligrams of 3-O-methoxymethyl-16,17-O-sulfuryl-16-epiestriol in acetonitrile was heated at 105 degrees C for 10 min with dried [(18)F]fluoride. The resultant solution was evaporated and hydrolyzed with 0.2 N HCl in 90% acetonitrile/water at 95 degrees C for 10 min under pressurized condition. The neutralization was carried out with 2.8% NaHCO(3), and then the high-performance liquid chromatography (HPLC) purification was performed. The desired radioactive fraction was collected and the solvent was replaced by 10 ml of saline, and then passed through a 0.22-microm filter into a pyrogen-free vial as the final product. The HPLC purification data demonstrated that [(18)F]FES was synthesized with a yield of 76.4+/-1.9% (n=5). The yield as the final product for clinical use was 42.4+/-3.2% (n=5, decay corrected). The total preparation time was 88.2+/-6.4 min, including the HPLC purification and the solvent replacement process. The radiochemical purity of the final product was >99%, and the specific activity was more than 111 GBq/micromol. The final product was stable for more than 6 h in saline containing sodium ascorbate. This new preparation system enables us to produce [(18)F]FES safe for clinical use with high and reproducible yield.     

New approach to fully automated synthesis of sodium [18F]fluoroacetate -- a simple and fast method using a commercial synthesizer

A simple, rapid and fully automated preparation of sodium [(18)F]fluoroacetate has been developed by taking advantage of the similarities between the reaction pathways of [(18)F]fluoroacetate and [(18)F]-2-fluoro-deoxyglucose (FDG). The automated synthesis of sodium [(18)F]fluoroacetate was achieved with a commercial [(18)F]FDG synthesizer, the TRACERlab MX(FDG). The method produced the desired compound in a short synthesis time (32 min) and with a high and reproducible radiochemical yield (50.2 +/- 4.8%, decay corrected). The radiochemical purity of sodium [(18)F]fluoroacetate was greater than 99%.     

Automated synthesis of 11beta-methoxy-4,16alpha-[16alpha-(18)F]difluoroestradiol (4F-M[(18)F]FES) for estrogen receptor imaging by positron emission tomography

Addition of both a 4-fluoro and 11beta-methoxy group onto 16alpha-[(18)F]fluoroestradiol ([(18)F]FES) yields 11beta-methoxy-4,16alpha-[16alpha-(18)F]difluoroestradiol (4F-M[(18)F]FES) with potential improved properties for positron emission tomography (PET) imaging of estrogen receptor densities in breast cancer patients. In order to provide 4F-M[(18)F]FES as a radiopharmaceutical for clinical trials, we developed an automated synthesis procedure using 3-O-methoxymethyl-11beta-methoxy-4-fluoro-16,17-O-sulfuryl-16-epiestriol as precursor. The radio synthesis involves stereoselective opening of the protected cyclic sulfone precursor via nucleophilic fluorination with [(18)F]fluoride in acetonitrile. After removal of the protecting ether and 17beta-sulphate groups by rapid hydrolysis in acidic ethanol and subsequent reversed-phase HPLC purification, the pure 4F-M[(18)F]FES was obtained as a sterile physiological saline solution in 45-50% radiochemical yield (decay corrected). The radiochemical purity of the final product was >98% and the effective specific activity (ESA) of 4F-M[(18)F]FES prepared under optimized conditions was >15,000 Ci/mmol. The total preparation time was 110+/-5 min and the product was shown to be stable for at least 6 h.     

An automated one-step one-pot [(18)F]FCWAY synthesis: development and minimization of chemical impurities

[(18)F]FCWAY (N-{2-[4-(2-methoxyphenyl)piperazino]}-N-(2-pyridinyl)trans-4-fluorocyclohexanecarboxamide) has been prepared routinely as a serotonin 5-HT(1A) receptor ligand for clinical human studies. We have developed an automated one-step radiosynthesis using a modified Nuclear Interface C-11 Methylation System. The chemical synthesis of an appropriate methanesulfonate precursor for single-step nucleophilic substitution with [(18)F]fluoride ion and the adaptation of radiochemical synthesis to an automated production module were accomplished. Following purification of a substrate using countercurrent chromatography, radiochemical yield increased from 18.9+/-0.3% to 21.9+/-2.2%. In addition, reduction of chemical impurities from about 40% to about 20% of total mass was observed. Further improvements in chemical purity were achieved by minimization of side reactions by modification of reaction conditions and optimization of the high-performance liquid chromatography method for the purification of the final radiopharmaceutical. Optimized automated synthesis produced [(18)F]FCWAY in a radiochemical yield of 28+/-6% at a chemical purity of 99.3% based on the absorbance of FCWAY at 254 nm and with a specific activity of 3433+/-1015 mCi/micromol at the end of bombardment, all calculated from the same 50 runs.     

The automated radiosynthesis of [18F]FP-TZTP

[(18)F]FP-TZTP (3-(3-(3-[(18)F]fluoropropylthio)-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine) is a muscarinic ligand that displays in vivo selectivity for the M2 subtype. We have developed a one-step radiosynthesis of [(18)F]FP-TZTP that can be conducted with an automated synthesis unit. A number of hardware and software modifications to a Nuclear Interface C-11 Methylation System provided the equipment for the automated radiosynthesis. The manual synthesis produced [(18)F]FP-TZTP in a radiochemical yield of 23.4% +/- 4.3% (EOS, n = 69) with a specific activity of 4377 +/- 2011 mCi/micromol (EOB, n = 100). The automated synthesis unit provided the product in a radiochemical yield of 18.8% +/- 2.4% (EOS, n = 25) with a specific activity of 4112 +/- 2572 mCi/micromol (EOB, n = 25).     

A robotic synthesis of [18F]fluoromisonidazole ([18F]FMISO).

This study aimed to develop an automated synthesis of [18F]fluoromisonidazole ([18F]FMISO) using a Scanditronix Anatech RB III robotic system. [18F]HF was produced via the 18O(p,n)18F reaction using a Scanditronix MC17F cyclotron. On average, a typical run produced [18F]FMISO with an uncorrected radiochemical yield of 30+/-5% at end of synthesis (EOS) from the irradiation of 95% enriched [18O]water. The total synthesis time was 65 min. The retention time of [18F]FMISO (the radio-peak) was 4.9 min, which was consistent with the authentic FMISO (the ultraviolet peak). The radiochemical purity was greater than 97%. Preparation of [18F]FMISO using the automated robotic system is highly reliable and reproducible, and the radiation burden for the operator can be largely reduced. Sufficient radioactivities of [18F]FMISO could be obtained for non-invasive tumor hypoxia imaging in vivo with positron emission tomography (PET).     

An automated synthesis of N,N-dimethyl-2-(2-amino-4-[18F]fluorophenylthio)benzylamine (4-[18F]-ADAM) for imaging serotonin transporters.

N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM, 3) is a potent serotonin transporter (SERT) imaging agent. In order to fulfill the demand of pre-clinical studies, we have developed an automated synthesis unit to synthesize this radioligand. The 4-[(18)F]-ADAM was synthesized using TracerLab FN and FE modules and a modified module control program (TracerLab-Fx). The synthesis sequences were similar to that of the manual synthesis, i.e. nucleophilic fluorination of N,N-dimethyl-2-(2,4-dinitrophenylthio)benzylamine (1) with K[(18)F]/K(2.2.2) followed by reduction with NaBH(4)/Cu(OAc)(2) and purifications with high-performance liquid chromatography (HPLC) and solid phase extraction. The radiochemical yield of 3 was 1.5+/-0.3% (n=13, EOS). The synthesis time was 120 min and the specific activity was 1.75+/-0.77 Ci/micromol (n=13, EOS). The 4-[(18)F]-ADAM synthesized by this module was stable over 4h at room temperature and is suitable for imaging SERT in humans.     

18F]FBAU 3',5'-dibenzoate, a lipophilic prodrug, enhances brain uptake of the cell proliferation tracer [18F]FBAU

INTRODUCTION: 1-(2-deoxy-2-[(18)F]fluoro-beta-D-arabinofuranosyl)-5-bromouracil ([(18)F]FBAU) is a cell proliferation tracer. However, it does not pass readily through the blood-brain barrier. We synthesized a lipophilic prodrug of [(18)F]FBAU that was intended to enhance brain uptake of [(18)F]FBAU to improve the imaging of brain cell proliferation. METHODS: [(18)F]FBAU was synthesized according to the methods described by Alauddin [J Med Chem 39 (1996) 2835-2843]. The prodrug, 1-(2-deoxy-3,5-O-dibenzoyl-2-[(18)F]fluoro-beta-D-arabinofuranosyl)-5-bromouracil ([(18)F]FBAU 3',5'-dibenzoate), was purified from an intermediate of [(18)F]FBAU. Their lipophilicity was determined by performing octanol/water partition coefficient (log P) measurements. In vitro metabolic fates of the prodrug were examined in rat and mouse plasma and brain homogenates. Brain uptake was determined following iv injection of the radiotracers by killing animals at various time points and dissecting and counting the radioactivity accumulation in the various tissues. RESULTS: Values of log P for [(18)F]FBAU 3',5'-dibenzoate and [(18)F]FBAU were 3.95 and -0.35, respectively. In rat plasma, the prodrug was gradually hydrolyzed to [(18)F]FBAU. Thirty minutes after mixing [(18)F]FBAU 3',5'-dibenzoate in the plasma, 25% of the prodrug had been hydrolyzed. The hydrolysis went more slowly in brain homogenates. At 15 min post injection, relative to animals injected with [(18)F]FBAU, brain uptake of radioactivity in animals injected with [(18)F]FBAU 3',5'-dibenzoate was increased by 150% (P=.005) and 78% (P=.037) in rats and mice, respectively. At 60 min post injection, the radioactive contents extracted from the brain were mostly [(18)F]FBAU. CONCLUSION: The synthesized novel prodrug [(18)F]FBAU 3',5'-dibenzoate has enhanced brain uptake in rodents, suggesting it may be useful as an imaging agent for tracing brain cell proliferation.     

Fully automated synthesis of PET TSPO radioligands [11C]DAA1106 and [18F]FEDAA1106

[(11)C]DAA1106 was prepared by O-[(11)C]methylation of DAA1123 with [(11)C]CH(3)OTf and NaH in CH(3)CN at 80°C and isolated by HPLC combined with SPE purification in 60-70% decay corrected radiochemical yield. [(18)F]FEDAA1106 was synthesized by the nucleophilic substitution of tosyloxy-FEDAA1106 in DMSO with K[(18)F]F/Kryptofix 2.2.2 at 140°C and isolated by HPLC combined with SPE purification in 30-60% decay corrected radiochemical yield. The specific activity for [(11)C]DAA1106 and [(18)F]FEDAA1106 was 370-740GBq/μmol and 37-222GBq/μmol at EOB, respectively.