A remotely controlled production system for routine preparation of [methyl-11C]thymidine

A remotely controlled system has been developed for the routine production of [methyl-¹¹C]thymidine starting from [¹¹C]methyl iodide.The system features semi-automated operation from [¹¹C]methyl iodide production over the [¹¹C] methylation reaction, HPLC purification to filtration of the final product and collection in a sterile vial.The preparations are completed within 45 min after irradiation and ca 7.4 GBq (0.2 Ci) chemically and radiochemically pure [methyl-¹¹C]thymidine are produced with a sp. act. of 11 GBq μmol⁻¹ (0.3 Ci μmol⁻¹) at the end of production.Sterile and pyrogen free [methyl-¹¹C]thymidine suitable for animal and human injections is prepared routinely using this synthesis system.The technical set up is also useful for the production of other nucleosides like: 5-ethyl-[¹¹C]-2′-deoxyuridine and 6-methyl-[¹¹C]-2′-deoxyuridine.     

Two routes to [11C-carbonyl]organo-isocyanates utilizing [11C]phosgene ([11C]organo-isocyanates from [11C]phosgene).

Two generic radiosynthetic routes for the preparation of [¹¹C-carbonyl]isocyanates have been developed. Reaction of N-organo-sulfinylamines; RNSO, (R = Me, Et, allyl, cyclohexyl and phenyl) with [¹¹C]phosgene gave the corresponding [¹¹C-carbonyl]isocyanates in good radiochemical yield (53–68%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. Alternatively, the reaction of [¹¹C]phosgene with N,N′-organo-ureas; (RNH)₂CO, (R = Me, Et, Pr and phenyl) also gave the corresponding [¹¹C-carbonyl]isocyanates in moderate radiochemical yield (9–37%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. For identification, the [¹¹C-carbonyl]organo-isocyanates were derivatized with 1-(2-methoxyphenyl)piperazine in situ to [¹¹C-carbonyl]carboxamides and the position of radiolabelling in the carbonyl group confirmed by [^11/13C]co-labeling and subsequent carbon-13 NMR spectroscopy.     

Radiosynthesis of [2-11C-carbonyl]dantrolene using [11C]phosgene for PET

Automated radiosynthesis of [2-¹¹C-carbonyl]dantrolene, the substrate of breast cancer resistance protein (BCRP/ABCG2), was performed for the first time through a multi-step/one-pot labeling sequence that started with ethyl 2-{2-[5-(4-nitrophenyl)furfurylidene]hydrazino}acetate and used [¹¹C]phosgene as a labeling agent. After optimization of the automated synthesis conditions and parameters, [2-¹¹C-carbonyl]dantrolene was obtained at a radiochemical yield of 34.0±8.4% (decay-corrected). The radiochemical purity was greater than 98% and the specific activity was 46.8±15.2 GBq/μmol at the end of the synthesis.     

A semi-automated synthesis system for routine preparation of [11C]YM-09151-2 and [11C]pyrilamine from [11C]methyl iodide

A synthesis system has been developed for routine preparation of the ¹¹C-labeled receptor ligands, [¹¹C]YM-09151-2 and [¹¹C]pyrilamine, from [¹¹C]methyl iodide produced automatically. The system features semi-automated operation, from the reaction of the desmethyl derivative with [¹¹C]methyl iodide to filtration with a specifically developed syringe pump of the final product in saline into a sterile vial. The preparations were completed within 45 min after irradiation and approx. 1 GBq (27 mCi) of [¹¹C]YM-09151-2 or [¹¹C]pyrilamine was obtained with a radiochemical and chemical purity of >99% and an average specific activity of 44 GBq/μmol (1.2 Ci/μmol) at the end of synthesis. Sterile and pyrogen-free ¹¹C-labeled receptor ligands suitable for human injection are routinely prepared using the present synthesis system.     

Synthesis and autoradiographic localization of muscarinic cholinergic antagonist (+)N-[11C]methyl-3-piperidyl benzilate as a potent radioligand for positron emission tomography.

(+)N-[11C]methyl-3-piperidyl benzilate, a relatively low affinity muscarinic cholinergic receptor antagonist was synthesized by N-[11C]methylation of (+)3-piperidyl benzilate using [11C]methyl iodide. The product was isolated by HPLC, and obtained with radiochemical yield of 60-70% from [11C]methyl iodide, and a specific activity of 500-1000 Ci mmol-1 (18.5-37 GBq mumol-1) at EOS and radiochemical purity of > 98%. In vitro autoradiographic studies showed selective binding for this radiotracer in the different regions of the rat brain: high in corpus striatum, hippocampus and cerebral cortex, and low in cerebellum, consistent with muscarinic cholinergic receptor distributions. This radiotracer thus had potential as radioligand for positron emission tomography.     

Use of 11C as a tracer for studying the synthesis of [11C]urea from [11C]cyanide

The use of reversed-phase liquid chromatography and radiochemical detection with carbon-11 (t1/2 = 20.4 min) as a tracer allowed the study of the preparation of [11C]urea from [11C]cyanide at no-carrier-added concentrations. [11C]cyanate was readily prepared by permanganate oxidation of [11C]cyanide at 75 degrees C. The conversion of NH4O11CN (approximately 0.03 mM) to [11C]urea in the presence of excess ammonium ions (0.28 M) was found to best fit pseudo first order reaction kinetics with a rate constant of 0.065 +/- 0.008 min-1 at 75 degrees C. Heating at higher temperatures (180-200 degrees C) revealed that the conversion of NH4O11CN to [11C]urea occurred in high yield in less than 3 min. The hydrolysis of [11C]cyanate to [11C]carbonate, a possible side reaction, was found to proceed at a rate of 0.010 +/- 0.001 min-1 at 113 degrees C.     

Production of [2-11C]thymidine for quantification of cellular proliferation with PET

A three-step synthesis of [2-¹¹C]thymidine, using [¹¹C]urea as precursor, is described. [2-¹¹C]Thymine was obtained by cyclization of [¹¹C]urea and diethyl β-methylmalate in fuming sulfuric acid. After purification of the reaction mixture, [2-¹¹C]thymine and 2′-deoxyribose-1-phosphate were incubated in the presence of thymidine phosphorylase to form [2-¹¹C]thymidine. The whole synthesis procedure, including purification and pharmaceutical package, was achieved within 60 min with a decay corrected yield of 30–35%.     

On-line preparation of [11C]carbon dioxide from [11C]methane

[¹¹C]Methane, produced from the (p, α) nuclear reaction on a nitrogen-5.6% hydrogen target, has been oxidized in an “on-line” synthetic train to yield [¹¹C]carbon dioxide. [¹¹C]methane is quantitatively adsorbed from the target gas on a Porapak Q column cooled to liquid nitrogen temperature. Following absorptive concentration, the [¹¹C]methane is oxidized by passage over cobalt(II–III) oxide powder heated to 500°C in a stream of nitrogen-2.0% oxygen. The isotopic dilution occurring during this conversion was determined to be 60%.     

Radiosynthesis of NCA [carbonyl-11C]6-fluoromelatonin

A method is described for the preparation of [carbonyl]-¹¹C]6-fluoromelatonin for intravenous injection and potential study of the melatonin system in vivo by positron emission tomography. The preparation is based on the acetylation of 6-fluoro-5-methoxytryptamine with NCA [1-¹¹C]acetyl chloride (itself prepared from cyclotron-produced [¹¹C]carbon dioxide) and purification by HPLC. It gives chemically and radiochemically pure [carbonyl-¹¹C]6-fluoromelatonin in 35% radiochemical yield (from [¹¹C]CO₂, decay-corrected) within 35 min from the end of radionuclide production and with high specific activity e.g. 1.6 GBq/μmol (43 mCi/μmol) at the end of synthesis from 1.1 GBq (30 mCi) of [¹¹C]carbon dioxide.     

A simplified and improved synthesis of [11C]phosgene with iron and iron (III) oxide

[11C]Phosgene ([11C]COCl2), a useful precursor for labeling several radiopharmaceuticals, is generally produced by catalytic oxidation of [11C]carbon tetrachloride over Fe granules, although in low yields or with poor reproducibility. In order to develop am improved synthesis of [11C]phosgene, two oxidizing agents, Fe2O3 and CuO, were examined. The yield of [11C]phosgene was significantly increased using Fe2O3 powder mixed with Fe granules, while the use of CuO alone, or CuO powder mixed with Fe granules resulted in an insignificant yield. The yield and specific activity of S- (-) [11C]CGP-12177 synthesized using Fe2O3 powder mixed with Fe granules were markedly higher than those synthesized by the previous methods using Fe granules alone or Fe granules mixed with Fe powder. Thus, in the present study, we developed a simple and practical method for the synthesis of [11C]phosgene, which provided an improved yield of S- (-) [11C]CGP-12177.     

The synthesis of (R)- and (S)-[N-methyl-11C]beta, beta-difluoromethamphetamine for the investigation of the binding mechanism of biogenic amines in vivo.

In an attempt to elucidate the contribution of the extent of nitrogen protonation on the in vivo binding of methamphetamine in the brain, the enantiomers of [N-methyl-11C]beta, beta-difluoroamphetamine (4) were prepared for use in positron emission tomography (PET) studies. Thus, the enantiomers of beta, beta-difluoroamphetamine were prepared from trans-beta-methylstyrene, via bromination, conversion into the azirine, fluorination and resolution as the tartrate salts. (R)- and (S)-beta, beta-difluoroamphetamine (3) were then each labelled with carbon-11 (tt/2 = 20.4 min) by N-methylation of the corresponding homochiral beta, beta-difluoroamphetamine with [11C]methyl iodide. The labelled products were each synthesised, purified and formulated in 35 min, starting from [11C]carbon dioxide in 15-16% decay-corrected radiochemical yield, with a radiochemical purity of > 99% and specific radioactivity of 50-150 GBq mumol-1 at end of synthesis.     

Two routes to [C-carbonyl]organo-isocyanates utilizing [C]phosgene ([C]organo-isocyanates from [C]phosgene)

Two generic radiosynthetic routes for the preparation of [¹¹C-carbonyl]isocyanates have been developed. Reaction of N-organo-sulfinylamines; RNSO, (R = Me, Et, allyl, cyclohexyl and phenyl) with [¹¹C]phosgene gave the corresponding [¹¹C-carbonyl]isocyanates in good radiochemical yield (53–68%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. Alternatively, the reaction of [¹¹C]phosgene with N,N′-organo-ureas; (RNH)₂CO, (R = Me, Et, Pr and phenyl) also gave the corresponding [¹¹C-carbonyl]isocyanates in moderate radiochemical yield (9–37%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. For identification, the [¹¹C-carbonyl]organo-isocyanates were derivatized with 1-(2-methoxyphenyl)piperazine in situ to [¹¹C-carbonyl]carboxamides and the position of radiolabelling in the carbonyl group confirmed by [^11/13C]co-labeling and subsequent carbon-13 NMR spectroscopy.     

Simple and effective method for producing [11C]phosgene using an environmental CCl4 gas detection tube

IntroductionCarbon-11-labeled phosgene is an important labeling precursor for PET molecular probes. Despite the usefulness of [¹¹C]phosgene, some difficulties, especially in the formation of [¹¹C]phosgene process from [¹¹C]CCl₄, hamper its use. The present article shows a simple preparation method for [¹¹C]phosgene.Method[¹¹C]CCl₄ was obtained using the conventional method by passing a mixture of [¹¹C]CH₄ and Cl₂ through a heated quartz tube. The [¹¹C]CCl₄ was transformed to [¹¹C]phosgene simply by passing through a pretreatment tube of a Kitagawa gas detection system for the working-environmental CCl₄ concentration measurement at room temperature with a flow rate of 50 ml/min.ResultThis tube successfully transformed [¹¹C]CCl₄ to [¹¹C]phosgene at room temperature. [¹¹C]Phosgene was obtained at nearly 80% radiochemical yield (EOB) in a short synthesis time with high reproducibility.ConclusionA high yield and reliable [¹¹C]phosgene production method using a gas detector tube system for working-environmental CCl₄ concentration measurement was developed.     

An improved synthesis of dopamine D2/D3 receptor radioligands [11C]fallypride and [18F]fallypride

Improved syntheses of dopamine D₂/D₃ receptor radioligands [¹¹C]Fallypride and [¹⁸F]Fallypride are reported. The phenolic precursor (9) for C-11 labeling and the Fallypride (10) reference standard were synthesized from the starting material 2-hydroxy-3-methoxy-5-(2-propenyl)benzoic acid methyl ester (1) in 7 and 8 steps with 16% and 5% overall chemical yields, respectively. The tosylated precursor (15) for F-18 labeling was synthesized from compound 1 in 5 steps with 32% overall chemical yield. An alternate synthetic approach for Fallypride has been developed using the same starting material 1 in 5 steps with 26% overall chemical yield. [¹¹C]Fallypride ([¹¹C]10) was prepared by O-[¹¹C]methylation of the phenolic precursor with [¹¹C]methyl triflate and purified with a semi-preparative HPLC method in 50–60% radiochemical yield, decay corrected to end of bombardment (EOB), based on [¹¹C]CO₂, and 370±185 GBq/μmol specific radioactivity at EOB. [¹⁸F]Fallypride ([¹⁸F]10) was prepared by nucleophilic substitution of the tosylated precursor with K[¹⁸F]F/Kryptofix 2.2.2 and HPLC combined with solid-phase extraction (SPE) purification in variable (up to 50%) decay corrected radiochemical yield from K[¹⁸F]F and 111–222 GBq/μmol specific activity at EOB.     

No-carrier-added carbon-11-labeled sn-1,2- and sn-1,3-diacylglycerols by [11C]propyl ketene method

This article describes the preparation of sn-1,2-[11C]diacylglycerols and sn-1,3-[11C]diacylglycerols by a no-carrier-added reaction based on a labeling method using [1-11C]propyl ketene, which is one of the most potent acylating agents. [1-11C]Propyl ketene was produced by pyrolytic decomposition of [1-11C]butyric acid and was trapped in pyridine containing L-alpha-palmitoyl-lysophosphatidylcholine, producing L-alpha-palmitoyl-2-[1-11C]butyryl-sn-glycero-3-phosphorylcholine. We adopted an enzymatic reaction to remove the phosphorylcholine, in which L-alpha-palmitoyl-2-[1-11C]butyryl-sn-glycero-3-phosphorylcholine was incubated with phospholipase C, hydrolyzing to produce 1-palmitoyl-sn-2-[1-11C]butyrylglycerol. Total synthesis time was about 50 minutes and the specific activity was estimated at 93 GBq/mumol (2.5 Ci/mumol) at end of synthesis. Radiochemical yield was 3.8% based on the trapped 11CO2. sn-1,3-[11C]Diacylglycerol was also synthesized by [1-11C]propyl ketene reaction with 1-palmitoyl-sn-glycerol in a single procedure. The regional brain tissue radioactivities obtained in sn-1,2-[11C]diacylglycerol were higher than those of sn-1,3-[11C]diacylglycerol, and the regional values varied widely. In autoradiography of brain slices from conscious rats, sn-1,2-[11C]diacylglycerol incorporation sites were discretely localized, especially in the amygdala, cerebral cortex, and hippocampus, suggesting that intensive neuronal processing occurred in these areas on the basis of phosphatidylinositol turnover.     

Synthesis and radiolabeling of N-[4-[4-(2-[11C]methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide -- a potential radiotracer for D3 receptor imaging with PET

FAUC346 (N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide), an in vitro D(3)-selective ligand, and its normethyl derivative have been synthesized from commercially available 1-(2-substituted-phenyl)piperazines. FAUC346 has been labeled using [(11)C]methyl triflate in acetone containing aqueous NaOH (5 Eq) at -10 degrees C for 1 min, purified on semipreparative reverse-phase high-performance liquid chromatography (HPLC) and formulated as an intravenous injectable solution using a Sep-Pak Plus C(18) device. Up to 5.5 GBq of [(11)C]FAUC346 (N-[4-[4-(2-[methyl-(11)C]methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide), with a specific radioactivity of 45-75 GBq/micromol, could be obtained in 30-35 min, including HPLC purification and formulation starting from 44.4 GBq of [(11)C]carbon dioxide. Preliminary pharmacological evaluation of [(11)C]FAUC346 in rat brain clearly demonstrated in vivo selectivity for D(3) receptors and the absence of radiolabeled metabolite within the brain. These encouraging results, however, could not be confirmed in nonhuman primates; therefore, this radioligand does not appear to have the required pharmacological profile for a positron emission tomography probe for imaging D(3) receptors.     

Synthesis procedure for routine production of [carbonyl-11C]desmethyl-WAY-100635.

An improved one-pot synthesis procedure for routine production of [carbonyl-(11)C]desmethyl-WAY-100635 ([(11)C]DWAY) is described. An efficient purification of the crude product has also been developed and was accomplished by C-18 reversed-phase semi-preparative HPLC using 55/45 EtOH-NaH(2)PO(4) buffer (20 mM, pH=6.5) as the eluent. The desired product fraction was collected in a 2.0-2.5 mL volume and formulated with 11 mL of 0.9% saline. The radioligand was ready for human use in 45 min (EOB). The product was obtained with a radiochemical yield of 11.1+/-1.8% (EOB, n=15) with a radiochemical purity of >99%. Specific activity was 133.2-185.0 GBq/micromol (3.6-5.0 Ci/micromol, EOS, n=2) when ca. 37.0 GBq (ca. 1.0 Ci) of starting [(11)C]CO(2) was used. Unlabeled mass of [(11)C]DWAY was found to be 0.15-0.24 microg/mL and the precursor was present in less than 50 ng/mL in final production solution.     

Automatic synthesis of L-[beta-11C]amino acids using an immobilized enzyme column.

We have developed a system for the automatic synthesis of L-[beta-11C]amino acids for i.v. injection by means of enzyme-mediated reactions from 11CO2 via 11CH3I and D,L-[beta-11C]alanine as labeled intermediates. This system, which incorporates an ultrafilter cartridge sterilized by electron beam irradiation and a column packed with immobilized enzymes, was effective for eliminating enzymes and endotoxins that may contaminate the product. Using this system, 1.3 +/- 0.5 GBq of 5-hydroxy-L-[beta-11C]tryptophan with a radiochemical purity of 97.1 +/- 0.6% and a specific activity of 39.6 +/- 8 GBq/mumol a pH value of 4 could be obtained in about 32 min (n = 3, at EOS). No endotoxin, enzyme, or bacteria was detected in the product. L-[beta-11C]dihydroxyphenylalanine (L-[beta-11C]DOPA) was also synthesized using this system.     

Synthesis of "no-carrier-added" carbon-11 SarCNU: the sarcosinamide analog of the chemotherapeutic agent BCNU

Carbon-11-labeled SarCNU [N-(2-chloroethyl)-N-nitroso-N'-(carboxamidomethylene)-N'-(methyl) - [11C]-urea], a potential chemotherapeutic agent, has been prepared by the nitrosation of the corresponding urea, N-(2-chloroethyl)-N'-(carboxamidomethylene)-N'-(methyl) [11C]urea (SarCU). SarCU was prepared by reacting sarcosinamide with [11C]-2-chloroethylisocyanate, which was itself prepared by reacting [11C]-phosgene with 2-chloroethylamine hydrochloride suspended in dioxane. The synthesis yielded [11C]SarCNU with an average radiochemical purity of 95% in an average overall radiochemical yield of 18% relative to the activity measured at the end of [11C]phosgene introduction.