Development of scandium-catalyzed N-[18F]fluoroalkylation of aryl and heteroaryl amines with [18F]epifluorohydrin.

Objectives: [18F]Fluoroalkylation is a useful method for introduction of fluorine-18 into molecules containing NH, OH, and SH-groups. Using various [18F]fluoroalkylating agents, we are routinely producing clinically-useful 18F-radiotracers, such as [18F]FMeNER-d2, [18F]FEDAA1106, [18F]FEDAC, [18F]FE-SPARQ and [18F]FEtPE2I. Recently, we have reported a convenient [18F]fluoroalkylation route for introducing 3-[18F]fluoro-2-hydroxypropyl ([18F]FHP) group into a targeted molecule via ring-opening reaction of [18F]epifluorohydrin ([18F]2) with phenol analogs by using an automated synthesis system [1]. However, despite the usefulness of epifluorohydrin in organic chemistry, the reaction of [18F]2 with low nucleophilic reagents, such as aromatic amine has rarely been reported. To extend application of this technique, in this study, we developed a simple method for introducing [18F]FHP group into aryl or heteroaryl amines in the presence of Sc(OTf)3. Methods: Unlabeled 3a-n were prepared by reactions of aryl or heteroaryl amines with epifluorohydrin in the presence of Sc(OTf)3 at moderate chemical yields (40-84%). [18F]2 was synthesized by the reaction of glycidyl tosylate 1 (10 mg) and [18F]KF/K2.2.2 in 1,2-dichlorobenzene at 130 oC for 2 min and immediately transferred by distillation into a reaction vial including aromatic amine in CCl4. The reaction conditions for the N-[18F]fluoroalkylation of p-anisidine as a model compound with [18F]2 were optimized with regard to solvents, temperatures and times. Under the optimized conditions, [18F]3a-n were synthesized by the reaction of various aryl or heteroaryl amines and [18F]2. Radiochemical conversions (RCCs) were determined by radio-HPLC for these reaction mixtures. Figure 1. Synthesis of [18F]3a–nResults: Firstly, a suitable solvent for N-[18F]fluoroalkylation of p-anisidine with [18F]2 in the presence of Sc(OTf)3 (10 mol%) was examined. In coordinating solvents such as THF and DMF, the reaction did not effectively proceed. On the other hand, the reaction efficiency was significantly increased by the use of nonpolar solvent such as CCl4. Under several temperatures and times investigated, the reaction performed in CCl4 at 50 oC for 20 min was found to give the best [18F]fluoroalkylating result. According to the optimized conditions, [18F]3a was synthesized by reaction of p-anisidine and [18F]2 using an automated synthesis system. By purification for the reaction mixture with semi-preparative HPLC and formulation, [18F]3a was obtained with a synthesis time of 85 ± 3 min and 27% radiochemical yield (isolated-yield based on the cyclotron-produced [18F]F-). To demonstrate suitability of this method, [18F]3b-n were synthesized from various aryl or heteroaryl amines containing halogen, alkyl, acetyl or hydroxyl groups. Radio-HPLC analyses for the reaction mixtures indicated that [18F]3b-l and [18F]3m-n were yielded in 25–69% and 6–16% RCCs, respectively. Using 2,2,2-trifluoroethanol (TFE) as a co-solvent, N-[18F]fluoroalkylation of aryl amines proceeded more effectively to give the corresponding product [18F]3b-l in 30–98% RCCs.Conclusion: Scandium-catalyzed N-[18F]fluoroalkylation with [18F]2 allowed facile introduction of [18F]FHP group into aryl or heteroaryl amines under mild conditions. Next, we will focus on improving efficiency for the N-[18F]fluoroalkylation of heteroaryl amines.References: [1] M. Fujinaga, T. Ohkubo, T. Yamasaki, et al. ChemMedChem. 2018, 13, 1723–1731.ISRS201

Tetrabutylammonium fluoride-promoted alpha-[11C]methylation of alpha-arylesters: a simple and robust method for the preparation of 11C-labeled ibuprofen

Tetrabutylammonium fluoride-promoted alpha-[11C]methylation of alpha-arlylesters was developed. The method was amenable to the remote-controlled synthesis of 11C-labeled ibuprofen

Nitroaldol reaction of nitro[11C]methane to form 2-(hydroxymethyl)-2-nitro[2-11C]-propane-1,3-diol and [11C]Tris

The nitroaldol reaction of nitro[11C]methane and formaldehyde, which yields 2-(hydroxymethyl)-2-nitro[2-11C]propane-1,3-diol, is explored. The fluoride-ion-assisted nitroaldol reaction using (C4H9)4NF was rapid and provided the desired nitrotriol in more than 97% radiochemical conversion (decay-corrected) in 3 min at room temperature. Neither 2-nitro[2-11C]ethanol nor 2-nitro[2-11C]propane-1,3-diol was observed under the reaction conditions. The preparation of 2-amino-2-(hydroxymethyl)-[2-11C]propane-1,3-diol ([11C]Tris) was described, which was followed by the nitro-group reduction using NiCl2 and NaBH4 in aqueous MeOH. The decay-corrected radiochemical conversion to [11C]Tris was 68.0+/-6.5% in two steps

The simultaneous measurement method for the molar radioactivity, radiochemical purity, and chemical impurity of the [11C]choline injection

Background/Aims: [11C]Choline has been extensively used clinically for imaging prostate cancer [1]. [11C]Choline is prepared by 11C-methylation of [11C]methyl iodide and 2-dimethylaminoethanol (DMAE). It is important to determine accurately the quantity of DMAE in the final product. The most common method for the determination of the substance of [11C]choline or DMAE was by co-injection of carrier-choline or DMAE method, and by two separate analysis LC system and gas chromatography [2-4]. The quality control procedures for 11C-labeled radiopharmaceuticals is acquired rapid assessment due to short half-life radionuclide (about 20 min). Thus, we developed a rapid and simultaneous measurement method for the molar radioactivity, radiochemical purity, and chemical impurity of the [11C]choline injection using the radio-HPLC coupled with the corona-charged aerosol detector (CAD). Methods: The molar radioactivity, radiochemical purity, and chemical impurity (DMAE) of the [11C]choline injection was measured using the radio-HPLC-CAD with the post-column method. We also validated the measurement of choline and DMAE using this HPLC, and evaluated these parameters of the accuracy, precision, specificity, quantitation of limit, and linearity. Results: The molar radioactivity, radiochemical purity, and chemical impurity were over 130 GBq/μmol (over 0.1 μg/mL) at end of synthesis (EOS), over 95% at EOS, and less than 0.5 μg/mL of DMAE, respectively. In the validation, the percentages of recovery of choline and DMAE were within 100±5%. The RSD of choline and DMAE were less than 10%. Resolution between obtained choline and DMAE peak was over 1.5. The limit of quantitation of choline and DMAE was 0.1 and 0.5 μg/mL, respectively. The coefficient of correlation (R2) of choline (0.1-50 μg/mL) and DMAE (0.5-50 μg/mL) found to be >0.9999. Conclusions: We developed and optimized the simultaneous measurement method for the molar radioactivity, radiochemical purity, and chemical impurity of the [11C]choline injection using the radio-HPLC-CAD with the post-column method.References: [1] Giovacchini G, et al. Eur J Nucl Med Mol Imaging. 2017;44:1751-76. [2] Mishani E, et al. Nucl Med Biol. 2002;39:359-62. [3] Shao X, et al. Appl Radiat Isot. 2011;69:403-9. [4] Biasiotto G, et al. Med Chem. 2012;8:1182-9.\n(Abstracts are to be no more than 300 words. References, Title and authors details are not included in the word count. Abstracts should not contain bullet points.)12th World Congress of the World Federation of Nuclear Medicine and Biolog

The fully-automated synthesis of [11C]CF3-aryl derivatives with [11C]fluoroform

Objectives: The trifluoromethyl group can improve physicochemical properties, such as metabolic stability, lipophilicity and pharmacokinetics of targeted probes. Radiolabeling by trifluoromethyl group is an attractive method to synthesize a useful PET probe. Recently, Haskali et al. have developed the synthetic method of [11C]fluoroform from [11C]CH4 with a CoF3 column and the application route of [11C]fluoroform for various trifluoromethylation reactions [1]. However, those application reactions were not automated and the synthesis of [11C]CF3-aryl derivatives is difficult because preparation of [11C]CuCF3 as a trifluoromethylation reagent was conducted in a glove box to avoid air and moisture. Herein, we developed a synthetic method of [11C]CF3-aryl derivatives using a fully-automated system equipped with [11C]CuCF3 without glove box.Methods: [11C]Trifluoromethylation of aryl precursor was performed by using a fully-automated synthesis system (Scheme 1). [11C]Fluoroform was produced by passing [11C]CH4 through a column that was precoated with cobalt(III) fluoride (24 g) and heated at 350 oC. CuOtBu was generated by mixing t-BuOK (15 mol) with CuBr (5 mol) in DMF (0.3 mL) in a sealed vial under N2. Preparation of [11C]CuCF3 was performed by bubbling [11C]fluoroform into the CuOtBu solution at -45 oC. After the radioactivity of [11C]fluoroform reached a plateau, the reaction mixture was warmed to room temperature for 2 min and then added Et3N-3HF (0.82 L) in DMF (0.2 mL). The trifluoromethylation was performed by the reaction of [11C]CuCF3 with aryl precursor (10 mg) at room temperature or 130 oC for 5 min. After the preparative HPLC mobile phase (1.0 mL) was added, the reaction mixture was applied to the HPLC system for separation. The HPLC fraction of [11C]1 was directly collected in a vial. The radioactive product was analyzed by HPLC with radioactivity and UV-VIS detectors. Scheme 1. Preparation of [11C]CuCF3 and synthesis of [11C]CF3-aryl derivativesResults: We prepared CuOtBu without a glove box by carefully treating the all reaction reagents under N2. Reaction of aryl precursor and [11C]CuCF3 did not proceed because HF that was produced by the decomposition of CoF3 prevented the [11C]trifluoromethylation reaction. To solve this problem, we tested various Sep-Pak cartridges to trap HF. Of them, silica plus Sep-Pak cartridge completely removed HF. When using aryl boronic acid as a precursor, [11C]1 was synthesized in 3 ± 1% (n = 5) radiochemical yield from [11C]CH4 at the end of irradiation, with > 99% radiochemical purity. The average total synthesis time from the end of bombardment was 35 min.. On the other hand, when using aryl iodide as a precursor, [11C]1 was only obtained in trace amount. The application scope of [11C]trifluoromethylation is under investigation.Conclusions: We succeeded in the [11C]trifluoromethylation of aryl precursors with [11C]CuCF3 using a full-automated system. We are currently optimizing reaction conditions to improve the radiochemical yield of [11C]1.Acknowledgements: This research is supported by QST President’s Strategic Grant Exploratory Research

Scandium triflate-catalyzed N-[18F]Fluoroalkylation of aryl- or heteroaryl-amines with [18F]epifluorohydrin under mild condi-tions

Scandium triflate-catalyzed N-[18F]fluoroalkylation of aryl- or heteroaryl-amines with [18F]epifluorohydrin ([18F]2) was investigated. This reaction is mild and provides one-step access to N-[18F]fluoroalkylated aryl- or heteroaryl-amines, which are used for positron emission tomography imaging. Use of 2,2,2-trifluoroethanol as a cosolvent improved the re-action efficiency. The use of (S)- or (R)-[18F]2 produced the corresponding enantiomeric N-[18F]fluoroalkylated anilines

Identifying antitumor responses of IDO1-targeting combination immunotherapy through 11C-L-1MTrp based PET platform

Background and Objectives: Defining biomarkers that reliably monitor antitumor responses represents a crucial challenge, due to the complexity of continuous crosstalk between tumor cells and host immune system during immunotherapeutic manipulation [1]. Whole-body imaging with a broad view can aid this exploration, and attempt had been started by developing novel PET probes derived from indoleamine-2,3-dioxygenase (IDO1) checkpoint inhibitor [2]. Here, we addressed further this problem by first validating a promising platform imaging biomarker—the 11C-L-1MTrp-PET— in melanoma mice with the presence or absence of antitumor immune responses.Methods: The IDO1-targeting combination immunotherapeutic models were established in immunocompetent C57BL/6J mice by s.c. transplantation of B16F10 melanoma cells, then treated with IDO1 inhibitor L-1MTrp combination with chemotherapeutic agents cyclophosphamide (CPA) or paclitaxel (PTX). Treatment responses were defined through quantifying the specific growth rate (SGR; %/d) of tumors.11C-L-1MTrp with PET/CT, was performed to capture pharmacokinetic imaging during treatment-induced immune editing. Biodistribution, autoradiography, and histopathology were conducted to confirm the results of whole-body PET. Receiver operating characteristic (ROC) curve analysis was performed to define an optimal cutoff for discriminating between responsive and unresponsive immune conditions.Results: The activated antitumor response, a progression-free SGR, was proved in melanoma mice treated with L-1MTrp and CPA, compared with L-1MTrp and PTX. Whole-body PET/CT exhibited a high accumulation of 11C-L-1MTrp in mesenteric lymph nodes (MLN) and epididymis (Fig 1), in the mice with L-1MTrp and CPA therapy(MLN 9.46 ± 0.33 %ID/g; epididymis 11.36 ± 0.43 %ID/g, at 75 min), but not in the placebo mice (mLN 3.55 ± 0.32 %ID/g; epididymis 3.21 ± 0.34 %ID/g) or the unresponsive mice (MLN 4.51 ± 0.41 %ID/g; epididymis 4.92 ± 0.83 %ID/g) with L-1MTrp and PTX therapy. Biodistribution and autoradiography confirmed the unforeseen PET pharmacokinetic imaging. Immunohistochemistry verified same expression pattern of IDO1 in MLN and epididymis. Empirical cutoff in mLN and epididymis were identified that discriminated with 100% sensitivity and specificity between responsive and unresponsive conditions in the two chemo-immunotherapeutical models strategies. Tracking with 11C-L-1MTrp PET the longitudinal efficacy of L-1MTrp and CPA, the cutoff of MLN provided early on-treatment indicator of response with a specificity of 97.92 %, and the cutoff of epididymis resulted in a sensitivity of 100% as a predictive index of immune exhaustion.Conclusion: Immune-checkpoint protein IDO1 combination immunotherapy edited pharmacokinetics of inhibitor L-1MTrp and host immunity in melanoma mice. 11C-L-1MTrp PET as a sensitive platform imaging biomarker, including a primary biomarker of MLN and secondary biomarker of epididymis, may carry out global and reliable identification of the IDO1 targeting antitumor responses, with prospective near-term clinical application.\nReferences: [1]. Pardoll DM. Nature Rev. Cancer. 2012, 12, 252. [2] Xie, L. et al. Sci. Rep.2015, 5,16417.\nFigure1. PET imaging of 11C-L-1MTrp in B16F10 bearing C57BL/6J mice treated with either placebo (+PBS) or L-1MTrp combination with cyclophosphamide (CPA) / paclitaxel (PTX). White circles indicate tumors, blue triangles indicate mesenteric lymph nodes, and green triangles indicate epididymis.2017 World Molecular Imaging Congress(WMIC2017

Radiosynthesis and evaluation of a negative allosteric modulator for the PET imaging of metabotropic glutamate receptor 2 in rat brain

ObjectivesMetabotropic glutamate receptor 2 (mGluR2) is related to a wide variety of brain functions. For this reason, mGluR2 has been appointed as a potential therapeutic target for several neuropsychiatric disorders such as anxiety, schizophrenia, and addiction. So far, several PET tracers targeting mGluR2 have been developed, some of which underwent preclinical imaging in animal studies, but no reliable radiotracer was used for clinical imaging of mGluR2 in human brain. In this study, we aimed to develop a new useful radiotracer for the visualization of mGluR2 in the brain. We established 4‐(2‐fluoro‐4‐methoxyphenyl)‐5‐((2‐methylpyridin‐4‐yl)methoxy)picolinamide (1) as a candidate for mGluR2. Compound 1, an analog of VU6001192,1 is a potent negative allosteric modulator (NAM) and showed high binding affinity for mGluR2 (IC50 = 26nM) than VU6001192 and high brain penetration. Moreover, 1 showed a suitable lipophilicity (cLogD = 3.12). Herein, we performed the chemical syntheses of unlabeled 1 and desmethyl phenol precursor, the radiosynthesis of [11C]1, and the in vitro and vivo specific binding studies in the rodent brain using autoradiography and PET. We also synthesized [11C]VU6001192 and compared its potentials as a PET tracer with [11C]1. Methods[11C]1 and [11C]VU6001192 were synthesized by the reaction of their corresponding desmethy precursors with [11C]methyl iodide. The distribution of radioactivity in mice was measured at different time points after injection of radiotracer. In vitro autoradiography, PET scan, and metabolite analysis were performed on rat brains. Results[11C]1 (7.4 ± 2.8 GBq; n = 8) and [11C]VU6001192 (3.2 ± 1.5 GBq; n = 5) were obtained from [11C]CO2 of 20–22 GBq with >98% radiochemical purity and 70–112 GBq/μmol molar activity. In vitro autoradiography showed that the distribution pattern of [11C]1 radioactivity was heterogeneous with high expression in the cerebral cortex, striatum, hippocampus, and cerebellum. This distribution pattern was consistent with the distribution of mGluR2 in the rat brain. The radioactivity was significantly reduced by self‐ or MNI‐137 (a mGluR2 NAM) blocking. In the mouse brain, the initial uptake of [11C]1 was 1.1%ID/g at 1 min. PET study showed that the uptake of radioactivity peaked at 2 min with a SUV of 0.72 in the cerebral cortex and rapidly decreased afterwards. Self‐blocking with 1 produced a fairly uniform distribution of radioactivity in all brain regions. The PET results suggest that a certain level of in vivo specific binding of [11C]1 could be found in the rat brain. The whole brain uptake increased 74% in Pgp/BCRP‐KO mice, compared to that in wild‐type mice (calculated from the area under curve). Metabolite analysis showed most radioactivity in the brain represented the unchanged [11C]1. On the other hand, PET with [11C]VU6001192 showed a very low brain uptake (SUV < 0.3). ConclusionIn this study, we have synthesized [11C]1 as a new PET tracer with good radiochemical yield, high radiochemical purity, and high molar activity. While [11C]1 has limited potential as a PET tracer for the imaging of brain mGluR2, it can be used to develop new radiotracers with improved in vitro profiles and in vivo behaviors. REFERENCEBollinger K. A., Felts A. S., Brassard C. J., et al. ACS Med. Chem. Lett. 2017, 8, 919–924.ISRS201