Method Article

Radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-Tryptophan using a One-pot, Two-step Protocol

DOI:

10.3791/63025

⸱

September 21st, 2021

 ,  ,  ,  ,  ,  , 
1Diagnostic & Research PET/MRI Center, Nemours/Alfred I. duPont Hospital for Children, 2Department of Radiology, Nemours/Alfred I. duPont Hospital for Children, 3Department of Neurology, Nemours/Alfred I. duPont Hospital for Children, 4Department of Biomedical Research, Nemours/Alfred I. duPont Hospital for Children

In This Article

Summary

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Here, we describe the radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-tryptophan, a positron emission tomography imaging agent for studying tryptophan metabolism, using a one-pot, two-step strategy in a radiochemistry synthesis system with good radiochemical yields, high enantiomeric excess, and high reliability.

Abstract

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The kynurenine pathway (KP) is a primary route for tryptophan metabolism. Evidence strongly suggests that metabolites of the KP play a vital role in tumor proliferation, epilepsy, neurodegenerative diseases, and psychiatric illnesses due to their immune-modulatory, neuro-modulatory, and neurotoxic effects. The most extensively used positron emission tomography (PET) agent for mapping tryptophan metabolism, α-[11C]methyl-L-tryptophan ([11C]AMT), has a short half-life of 20 min with laborious radiosynthesis procedures. An onsite cyclotron is required to radiosynthesize [11C]AMT. Only a limited number of centers produce [11C]AMT for preclinical studies and clinical investigations. Hence, the development of an alternative imaging agent that has a longer half-life, favorable in vivo kinetics, and is easy to automate is urgently needed. The utility and value of 1-(2-[18F]fluoroethyl)-L-tryptophan, a fluorine-18-labeled tryptophan analog, has been reported in preclinical applications in cell line-derived xenografts, patient-derived xenografts, and transgenic tumor models.

This paper presents a protocol for the radiosynthesis of 1-(2-[18F]fluoroethyl)-L-tryptophan using a one-pot, two-step strategy. Using this protocol, the radiotracer can be produced in a 20 ± 5% (decay corrected at the end of synthesis, n > 20) radiochemical yield, with both radiochemical purity and enantiomeric excess of over 95%. The protocol features a small precursor amount with no more than 0.5 mL of reaction solvent in each step, low loading of potentially toxic 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (K222), and an environmentally benign and injectable mobile phase for purification. The protocol can be easily configured to produce 1-(2-[18F]fluoroethyl)-L-tryptophan for clinical investigation in a commercially available module.

Introduction

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In humans, tryptophan is an essential component of the daily diet. Tryptophan is primarily metabolized via the kynurenine pathway (KP). The KP is catalyzed by two rate-limiting enzymes, indoleamine 2, 3-dioxygenase (IDO) and tryptophan 2, 3-dioxygenase (TDO). More than 95% of tryptophan is converted into kynurenine and its downstream metabolites, ultimately generating nicotinamide adenine dinucleotide, which is essential to cellular energy transduction. The KP is a key regulator of the immune system and an important regulator of neuroplasticity and neurotoxic effects1,2. Abnormal tryptophan metabolism is implicated in various neurologic, oncologic, psychiatric, and metabolic disorders; therefore, radiolabeled tryptophan analogs have been extensively used in clinical investigation. The two most common clinically investigated tryptophan radiotracers are 11C-α-methyl-L-tryptophan ([11C]AMT) and 11C-5-hydroxytryptophan (11C-5-HTP)3.

In the 1990s, 11C-5-HTP was used to visualize serotonin-secreting neuroendocrine tumors4 and to diagnose and monitor therapy of metastatic hormone-refractory prostatic adenocarcinoma5. Later, it was used as an imaging tool for the quantification of the serotonergic system in the endocrine pancreas6. 11C-5-HTP has also been a promising tracer for noninvasive detection of viable islets in intraportal islet transplantation and type 2 diabetes7,8. Over the past two decades, many radiolabeled amino acids have advanced to clinical investigation9,10. In particular, the carbon-11-labeled tryptophan analog [11C]AMT has received extensive attention for mapping brain serotonin synthesis11,12,13,14 and for localizing epileptic foci, epileptogenic tumors, tuberous sclerosis complex, gliomas, and breast cancers15,16,17,18,19,20,21,22,23,24,25,26. [11C]AMT also has high uptake in various low- and high-grade tumors in children27. Furthermore, kinetic tracer analysis of [11C]AMT in human subjects has been used to differentiate and grade various tumors and differentiate glioma from radiation-induced tissue injury15. [11C]AMT-guided imaging shows significant clinical benefits in brain disorders3,25. However, due to the short half-life of carbon-11 (20 min) and the laborious radiosynthesis procedures, [11C]AMT use is restricted to the few PET centers with an onsite cyclotron and a radiochemistry facility.

Fluorine-18 has a favorable half-life of 109.8 min, compared with the 20 min half-life of carbon-11. Increasingly, efforts have been focused on the development of fluorine-18-labeled radiotracers for tryptophan metabolism3,28. A total of 15 unique fluorine-18 radiolabeled tryptophan radiotracers have been reported in terms of radiolabeling, transport mechanisms, in vitro and in vivo stability, biodistribution, and tumor uptake in xenografts. However, rapid in vivo defluorination was observed for several tracers, including 4-, 5-, and 6-[18F]fluorotryptophan, precluding further clinical translation29. 5-[18F]Fluoro-α-methyltryptophan (5-[18F]FAMT) and 1-(2-[18F]fluoroethyl)-L-tryptophan (L-[18F]FETrp, also known as (S)-2-amino-3-(1-(2-[18F]fluoroethyl)-1H-indol-3-yl)propanoic acid, molecular weight 249.28 g/mole), are the two most promising radiotracers with favorable in vivo kinetics in animal models and great potential to surpass [11C]AMT for the evaluation of clinical conditions with deregulated tryptophan metabolism28. 5-[18F]FAMT showed high uptake in IDO1-positive tumor xenografts of immunocompromised mice and is more specific to imaging the KP than [11C]AMT28,30. However, the in vivo stability of 5-[18F]FAMT remains a potential concern as no in vivo defluorination data have been reported beyond 30 min post injection of the tracer30.

A preclinical study in a genetically engineered medulloblastoma mouse model showed that when compared with 18F-fluorodeoxyglucose (18F-FDG), L-[18F]FETrp had high accumulation in brain tumors, negligible in vivo defluorination, and low background uptake, demonstrating a superior target-to-nontarget ratio31,32. Radiation dosimetry studies in mice indicated that L-[18F]FETrp had an approximately 20% lower favorable dosimetry exposure than the clinical 18F-FDG PET tracer33. In agreement with other researchers' findings, preclinical study data provide substantial evidence to support the clinical translation of L-[18F]FETrp for the investigation of abnormal tryptophan metabolism in humans with brain disorders such as epilepsy, neuro-oncology, autism, and tuberous sclerosis28,31,32,33,34,35,36. An overall comparison between the three most widely investigated tracers for tryptophan metabolism, 11C-5-HTP, [11C]AMT, and L-[18F]FETrp, is shown in Table 1. Both 11C-5-HTP and [11C]AMT have a short half-life and laborious radiolabeling procedures. A protocol for the radiosynthesis of L-[18F]FETrp using a one-pot, two-step approach is described here. The protocol features the use of a small amount of radiolabeling precursor, a small volume of reaction solvents, low loading of toxic K222, and an environmentally benign and injectable mobile phase for purification and easy formulation.

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Protocol

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CAUTION: The protocol involves radioactive materials. Any additional dose of radioactive materials could lead to a proportional increase in the chance of adverse health effects such as cancer. Researchers must follow the 'as low as reasonably achievable' (ALARA) dose practices to guide the radiosynthesis protocol with adequate protection in the hot cell or lead hood. Minimizing direct contact time, using a lead shield, and keeping maximum distance for any radiation exposure step in the radiosynthesis process are essential. Wear a radiation dosimetry badge and hand monitoring rings throughout the entire experiment, and frequently monitor potentially contaminated surfaces such as gloves, sleeves, and feet. Nuclear Regulatory Commission (NRC), local, and institutional regulations must be followed for the usage, shipping, and disposal of any radioactive materials.

1. Initial preparations

  1. Prepare 10% ethanol in 50 mM sodium acetate/acetic acid mobile phase for semipreparative high-performance liquid chromatography (HPLC).
    1. Place 3 mL of glacial acetic acid in a clean 1000 mL volumetric flask. Add 900 mL of ultrapure water (18 million ohm-cm resistivity at 25 °C) into the volumetric flask; add approximately 8 mL of 6 M sodium hydroxide solution and adjust the pH to 5.5 using a calibrated pH meter and a pH strip. After the solution cools down to room temperature, make up the volume to 1000 mL with ultrapure water to prepare the 50 mM sodium acetate/acetic acid (pH 5.5) solution.
    2. Vacuum-filter the solution through a 0.2 µm membrane filter and transfer the solution to two 500 mL solvent bottles.
    3. Place approximately 250 mL of the above buffer in a 500 mL volumetric flask. Use a graduated cylinder to measure 50 mL of United States Pharmacopeia (USP) ethanol and add the ethanol to the volumetric flask. Make up the volume to 500 mL with 50 mM sodium acetate/acetic acid, and measure the pH value with a pH strip.
  2. Prepare quality control (QC) solutions for a system suitability test.
    1. Refill the HPLC solvent bottles with fresh ultrapure water (solvent A) and ethanol (solvent B). Prime the HPLC pump and load the HPLC program with a flow rate of 1 mL/min consisting of 30% solvent A and 70% solvent B (v/v).
    2. Make a control solution (blank solution) for QC. Add 5 mL of 0.9% sodium chloride into a 20 mL glass vial. Add 0.15 mL of 23.4% sodium chloride into the above solution. Add 6 mL of semipreparative HPLC mobile phase prepared in step 1.1.3 (10% ethanol in 50 mM sodium acetate/acetic acid, pH 5.5) to the glass vial.
    3. Prepare 1 µg/mL of nonradiolabeled L-FETrp and 5 µg/mL of racemic L-FETrp and D-FETrp mixtures (standard solutions).
    4. Build a calibration curve using standard L-FETrp solutions (0.1 µg/mL, 0.5 µg/mL, 1.0 µg/mL, 10 µg/mL, 100 µg/mL).
    5. Set up the HPLC sequence. Ensure that the sequence includes one run of the blank sample solution, two runs of the standard L-FETrp (1 µg/mL), one run of the racemic L-FETrp and D-FETrp mixtures (5 µg/mL), and one run of the final radiopharmaceutical.
    6. Run the partial HPLC sequence to test the system suitability before analyzing the radioactive samples using an analytical HPLC column (250 x 4.6 mm).
      1. Run one blank sample and ensure that the chromatogram of the blank sample shows no or insignificant peaks between the void volume and 10 min of the chromatogram.
      2. Run two replicates of the standard solution (contains 1 µg/mL of L-FETrp). Ensure that the areas of the L-FETrp in the two replicates are within ±5% of the mean value.
      3. Run one sample of the L-FETrp and D-FETrp mixtures (5 µg/mL of L-FETrp and D-EFTrp, respectively). Ensure that L-FETrp and D-FETrp can be identified on the chromatogram and baseline resolved.
  3. Prepare the radiolabeling solutions and other supplies.
    1. Add the following solutions to five 1.5-mL V-shaped vials, respectively. Vial 1: 1 mL of potassium carbonate (K2CO3)/K222 solution (5 mg/mL K222 and 1 mg/mL K2CO3 in a water/acetonitrile solution, 1/99, v/v) for [18F]fluoride elution; Vial 2: 0.4 mL of anhydrous acetonitrile for [18F]fluoride drying; Vial 3: radiolabeling precursor in anhydrous acetonitrile (1-2 mg in 0.5 mL of anhydrous acetonitrile) for [18F]fluoride incorporation; Vial 4: hydrochloric acid (2 M, 0.25 mL) in acetonitrile (0.25 mL) for acidolysis; Vial 5: 2 M sodium hydroxide (0.25 mL) for neutralization of the reaction mixtures.
    2. Activate a quaternary methylammonium (QMA) light cartridge by first passing through 10 mL of saturated sodium bicarbonate solution, followed by 10 mL of ultrapure water, and then flush the cartridge with a nitrogen flow. Condition a light C8 cartridge and a neutral aluminum oxide cartridge by passing through 10 mL of ethanol, followed by 10 mL of ultrapure water.
    3. Add 0.15 mL of 23.4% sodium chloride and 5 mL of 0.9% sodium chloride to a 30 mL sterile formulation vial to adjust the tonicity and dilute the HPLC fraction.
    4. Prepare a solution (1 mL of sodium acetate/acetic acid buffer, 50 mM, pH = 5.5 prepared in step 1.1.1, 1 mL of ethanol, and 0.5 mL of water [total 2.5 mL]) in a syringe for rinsing the reaction vessel; load into a 10 mL sterile vial.

2. Assemble the radiolabeling supplies and radiosynthesize L-[18F]FETrp

  1. Assemble the radiolabeling supplies.
    1. Turn on the module power, carbon dioxide, compressed air, argon lines, and the programmable logic controller (PLC) power. Click the mod_pscf18 button to activate the program of the radiochemistry synthesis system. Initialize the input, output, and formulation MVP, and ensure that the MVPs are at positions 4, 1, 1, respectively.
    2. Ensure that the HPLC loop is in the Inject position and the QMA light cartridge in the [18F]fluoride trapping position.
    3. Install the semipreparative HPLC mobile phase bottle (containing the solution prepared in step 1.1.3). Equilibrate the HPLC system by passing the mobile phase through the chiral HPLC column (250 x 10 mm) and C18 column (100 x 10 mm) at a flow rate of 2 mL/min for at least 30 min, then switch the diversion valve, let the HPLC mobile pass through the chiral HPLC column only, and increase the flow rate to 3 mL/min.
    4. Install the QMA light cartridge in the [18F]fluoride trapping/releasing line. Install the stacked alumina/C8 cartridges between the input MVP position 6 and the intermediate vial, which is a 10 mL V-shaped vial connected to the HPLC sample loop. Install a 10 mL empty vial (venting vial) to the output MVP position 4 with another needle attached to the vial as a vent. Install the reagent vials 1-5 to the input MVP positions 1-5, respectively.
    5. Install the vial containing the rinse solution prepared in step 1.3.4 to the output MVP position 6.
    6. Install a 500 mL waste bottle (to collect the HPLC waste passing through both the chiral and C18 columns) to the formulation MVP position 1. Install another 500 mL waste bottle (to collect HPLC waste passing through the chiral column) to the waste collection end of the four-port two-position valve.
    7. Connect the fraction collection vial (prefilled solution prepared in step 1.3.3) to the formulation MVP position 2. Connect the output MVP position 3 (gas line) and final product delivery line to the formulation MVP position 2 vials to recover the final formulated product. Install a 10 mL empty sterile vial in formulation MVP position 3, which will be used as the backup vial for the target fraction collection.
    8. Install the C18 short column between the four-port, two-position diversion valve and the formulation MVP.
      NOTE: During the installation of the reagent and formulation vials, ensure the argon supply in the control panel is off, and the argon pressure is zero to avoid any unexpected liquid transfer during the vial assembly. Double-check all needle connections, vial positions, and MVP positions for reproducible radiosynthesis.
  2. Radiosynthesis of L-[18F]FETrp
    1. Receive and survey [18F]fluoride.
      1. When receiving the [18F]fluoride solution (15 ± 3 gigabecquerel (GBq) at the start of synthesis, see the Table of Materials), survey the lead box on the surface and at 1 m to record the maximum radiation exposure rates. Do a wipe test to ensure the shipping box is not contaminated. Record the [18F]fluoride dose and time.
    2. Transfer [18F]fluoride.
      1. Transfer the radioactivity to the radiochemistry synthesis system.
      2. Connect the argon line with a short needle and the [18F]fluoride transfer line with a long needle to the [18F]fluoride vial. Close the hot-cell glass door and lead door.
        CAUTION: Use a long clamp to push down both needles; ensure the long needle tip sits in the bottom of the [18F]fluoride vial so that all [18F]fluoride can be transferred out. Typically, a V-shaped vial is requested for the [18F]fluoride delivery.
    3. Trap, elute, and azeotropically dry [18F]fluoride.
      1. Click Ar Supply to turn on the argon supply line, increase argon pressure, turn on the [18F]fluoride pushing line, and push the aqueous [18F]fluoride through the QMA light cartridge. After all the radioactivity is trapped in the QMA light cartridge, and the radioactivity detector reading is steady, increase the argon pressure and blow argon through the cartridge for another 5 min to remove excess water.
      2. Turn off the [18F]fluoride pushing line, decrease the argon pressure to zero, switch the six-port two-position valve from the [18F]fluoride trapping position to the elution position. Open the reaction vial, turn on the input MVP position 1 argon line, push the K222/K2CO3 solution into the input MVP position 1 vial through the QMA light cartridge to elute out the radioactivity into the reaction vial. Switch the [18F]fluoride elution position to the trapping position.
      3. Click the Heat button to heat the reactor at 110 °C, turn on the output MVP position 4 argon line (sweeping line) that connects to the reactor, and evaporate the solvent into the output MVP position 4 vial.
      4. Click the Cool button to cool down the reactor to room temperature with compressed carbon dioxide, turn off the sweeping line, switch the input MVP position 1 to position 2, and add the anhydrous acetonitrile in the vial 2. Turn on the sweeping line and heater to azeotropically dry [18F]fluoride at 110 °C.
    4. Add the radiolabeling precursor and incorporate [18F]fluoride.
      1. Cool down the reactor to room temperature, turn off the sweeping line, switch the input MVP position 2 to position 3, and add the tosylate radiolabeling precursor in vial 3. Close the reactor, and heat the reaction mixtures at 100 °C for 10 min.
    5. Evaporate the reaction solvent and acidolyse.
      1. Cool down and open the reactor, turn on the sweeping line, and evaporate the reaction solvent at 100 °C.
      2. Cool down the reactor, turn off the sweeping line, switch the input MVP position 3 to position 4, and add the hydrochloric acid/acetonitrile mixture (0.5 mL, 1/1, v/v). Heat the reaction at 100 °C for 10 min to deprotect the tert-butyl and tert-butyloxycarbonyl-protecting groups in the radiolabeling precursor.
    6. Neutralize the reaction.
      1. Cool down the reactor to room temperature, and switch the input MVP position 4 to position 5 to add 2 M sodium hydroxide to neutralize the reaction mixture. Turn off the input MVP argon line.
    7. Transfer the reaction mixture to the intermediate vial.
      1. Click the F button in the output MVP to switch the output MVP from the venting position 4 to position 5, and then click the F button in the input MVP to switch the input MVP from position 5 to position 6. Turn on the output MVP argon line. Push the reaction mixture through the stacked neutral aluminum oxide and C8 cartridges to the intermediate vial installed before the HPLC sample loop.
    8. Rinse the reactor and transfer the solution.
      1. Switch the output MVP position 5 to position 6, push the rinse solution in the vial of output MVP position 6 through the reaction vial, and cartridges to the intermediate vial, successively. Note that the volume of the combined mixture is approximately 3.5 mL. Close the reaction vessel.
    9. Load the combined mixture to the HPLC loop and purify the mixture.
      1. Switch the HPLC loop from injection position to load position, turn on the input MVP argon line, and load the mixtures to the 5 mL HPLC loop. When the load is complete, switch the load button to inject, and click Inject HPLC to start the HPLC chromatogram at a flow rate of 3 mL/min. Click the HPLC monitor button to access the real-time HPLC chromatogram.
    10. Divert the target fraction to the C18 column.
      1. Click the diversion MVP button to divert the target HPLC fraction to the short C18 column at approximately 12 min.
    11. Flush the chiral HPLC column and purify the fraction in the C18 column.
      1. After the target radioactivity is collected in the C18 column (and the HPLC mobile phase flows into the formulation MVP position 1 waste bottle), switch the four-port two-position diversion valve to the waste collection position. Flush the chiral column at 4 mL/min for 6 min to remove the minor D-[18F]FETrp enantiomer and other ultraviolet (UV) impurities.
      2. Click the diversion MVP button to divert the HPLC mobile phase back to the formulation MVP position 1 at a flow rate of 3 mL/min. Observe that the mobile phase passes through the chiral column and C18 column to purify L-[18F]FETrp retained in the C18 column.
    12. Collect the target fraction.
      1. Collect the eluent at approximately 32-34 min into the formulation MVP position 2 vial.
        NOTE: Typically, a 2 min HPLC fraction is collected, and the total volume plus the prefilled sodium chloride solution is 8-15 mL.
    13. Deliver the dose to a sterile final product vial.
      1. Push the solution in the formulation MVP position 2 vial through the delivery line and sterile filter into the final dose vial (via the preinstalled sterile venting filter needle).
        NOTE: Protocol steps 2.2.9-2.2.13 are steps used for the HPLC purification of L-[18F]FETrp.
    14. Assay the radioactivity and dose volume.
      1. Remove the sterile filter and assay the final dose activity and volume.
      2. Flush the system with ultrapure water followed by ethanol at 4 mL/min for at least 15 min each. Turn off the HPLC pump and PLC box; close the program; shut down the compressed air line, argon line, and carbon dioxide line; and shut down the main power of the module.
    15. Withdraw the QC dose and run the QC samples.
      1. Withdraw approximately 0.1 mL of the final dose into a 0.2 mL insert of a QC vial. Run the hot sample as the "partial sequence" program following the system suitability test described in step 1.2.6 .
    16. Analyze the QC data and release the dose.
      1. Calculate the chemical and radiochemical purities, enantiomeric excess value, and molar activity; determine the pH value.
      2. Release the dose if all testing results pass the acceptable range.

3. Post-run system clean

  1. Survey the radiolabeling module using a Geiger-Mueller (GM) survey meter to ensure that the radioactivity is adequately decayed (at least 24 h) before the system clean.
  2. Turn on the radiolabeling module power and PLC box power; activate the program of the radiochemistry synthesis system; and initialize the input MVP, output MVP, and formulation MVP. Switch the column selector to the bypass position.
  3. Detach the QMA light, alumina, and C8 cartridges.
  4. Flush all vials and lines with ultrapure water first, followed by ethanol. Dry the vials and lines with high-purity argon.
  5. Seal each line vent using a sterile needle with a cap. Replace the reagent vials and reaction vessel with oven-burned vials and reaction vessel, respectively.
  6. Turn off the HPLC pump and PLC box; close the program; shut down the compressed air line, argon line, and carbon dioxide line; and shut down the main power of the module.

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Results

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The reaction scheme is shown in Figure 1. The radiolabeling includes the following two steps: 1) reaction of the tosylate radiolabeling precursor with [18F]fluoride provides the 18F-labeled intermediate, and 2) deprotection of the tert-butyloxycarbonyl and tert-butyl-protecting groups in the intermediate affords the final product L-[18F]FETrp. Both reaction steps continue at 100 °C for 10 min.

Before receiving [

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Discussion

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Tryptophan is an essential amino acid for humans. It plays an important role in the regulation of mood, cognitive function, and behavior. Radiolabeled tryptophan derivatives, particularly the carbon-11-labeled [11C]AMT, have been extensively studied due to their unique role in mapping serotonin synthesis38,39, detecting and grading tumors40, guiding epilepsy surgery41,42...

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Disclosures

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The authors declare that no competing financial interests exist.

Acknowledgements

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This work was supported by the Diagnostic & Research PET/MRI Center, and by the Departments of Biomedical Research and Radiology at Nemours/Alfred I. duPont Hospital for Children.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
[18F]Fluoride in [18O]H2OPETNET Solutions Inc.N/A
4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosaneACROS291950010Kryptofix 222 or K222, 98%
Acetic acidACROS22214250099.8%
AcetonitrileSigma-Aldrich271004anhydrous, 99.8%
Agilent 1260 HPLC systemAgilent TechnologiesAgilent 1260Agilent 1260 series
Analytcial chiral HPLC columnSigma-Aldrich12024ASTAstec CHIROBIOTIC T, 25 cm × 4.6 mm
Carbon dioxide, 60 LBSAirgasREFR744R200S99.99%
D-FETrp standard referenceAffinity Research Chemicals IncN/ACustom synthesis
Empty sterile vialJubilant HollisterStier751520 mm closure, 10 mL
EthanolDecon Labs2716200 proof, USP grade. ≥99.9%
Fisherbrand 13 mm Syringe Filter, 0.22 µm, PVDF, sterileFisher Scientific09-720-3
Hydrochloric acidSigma-Aldrich30721≥37%
IsopropanolDecon Labs831670%, sterile
L-[18F]FETrp radiolabeling precursorAffinity Research Chemicals IncN/ACustom synthesis
L-FETrp standard referenceAffinity Research Chemicals IncN/ACustom synthesis
Light C8 cartridgeWatersWAT036770Sep-Pak  C8 plus light cartridge
Needle, 20 G x 1Becton-Dickinson & Co.305175
Needle, 20 G x 1 ½Becton-Dickinson & Co.305176
Needle, 21 G x 2Becton-Dickinson & Co.305129
Neutral aluminum oxideWatersWAT023561Sep-Pak alumina N plus light
Nylon membrane (0.20 µm )MilliPoreGNWP0470047 mm
Pall Acrodisc 25 mm syringe sterile filterPall Corporation4907
PETCHEM radiochemistry synthesis systemPETCHEM Solutions Inc. Pinckney, MIN/ARadiosynthesizer
pH strips 2.0 - 9.0EMD Millipore1.09584.0001
Potassium carbonateSigma-Aldrich36787799.995%
Quaternary methylammonium light cartridgeWaters186004051Sep-Pak QMA light
Semi-preparative C18 HPLC columnPhenomenex00D-4253-N0100 × 10 mm
Semi-preparative chiral HPLC columnSigma-Aldrich12034ASTAstec CHIROBIOTIC T, 25 cm × 10 mm
Sodium chloride injection 23.4%APP Pharmaceutical, LLC18730USP grade
Sodium chloridei injection 0.9%HospiraNDC 0409-4888-10USP grade
Sodium hydroxideHoneywell30657699.99%
Spinal needle, 20 G x 3 ½Becton-Dickinson & Co.405182
Sterile alcohol prep padsBioMed Resource Inc.PC661
Sterile empty vials, 2 mLHollister Stier7505ZA13 mm closure
Sterile empty vials, 30 mLJubilant HollisterStier7520ZA20 mm closure
Syringe PP/PE, 3 mL, Luer LockAir-Tite4020-X00V0
Syringe PP/PE, 5 mL, Luer LockBecton-Dickinson & Co.309646
Syringe,  PP/PE, 10 mL, NORM-JECTAir-Tite4100-000V0
Syringe, 1 mL, Luer SlipBecton-Dickinson & Co.309659
Syringe, 3 mL, Luer-LockBecton-Dickinson & Co.309657
Ultra high purity argonAirgasAR UHP30099.999%
Ultrapure waterMilliporeSigmaZRQSVP300Direct-Q 3 tap to pure and ultrapure water purification system

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Radiosynthesis ProtocolTryptophan Metabolism ImagingKynurenine PathwayF18 RadiolabelingOne Pot SynthesisHPLC PurificationChiral ColumnRadiochemical PurityNeuroimaging Tracer

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