N-substituted pyridine fluoroborate inner salt reagent, its preparation method and application in preparation of F-18 nuclear medicine

Abstract

This invention discloses an N-substituted pyridine fluoroborate inner salt reagent, its preparation method, and its application in the preparation of F-18 radiopharmaceuticals. The N-substituted pyridine fluoroborate inner salt reagent is obtained by reacting protonated pyridine fluoroborate of Formula I with a compound of Formula II in the presence of a solvent. This inner salt reagent, through a substituted alkyl group linked to the pyridine N-phase, can undergo a coupling reaction with molecules containing specific groups (including drug molecules or their derivatives) to generate F-18 radiopharmaceutical precursors. Further isotope exchange reactions yield the F-18 radiopharmaceutical. By adjusting the types of substituents in the substituted alkyl group, this invention can achieve the construction of structurally diverse F-18 radiopharmaceutical precursors with different drug molecules or their derivatives. Furthermore, the prepared F-18 radiopharmaceutical precursors exhibit good stability in aqueous phase and can undergo efficient reactions in aqueous buffer solutions. 18 F- 19 The F isotope exchange reaction avoids the time-consuming dehydration process in the traditional F-18 radiopharmaceutical synthesis, greatly shortening the synthesis time and thus effectively improving the efficiency of F-18 radiopharmaceutical synthesis. 18 F-labeling rate.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, specifically to an N-substituted pyridine fluoroborate inner salt reagent, its preparation method, and its application in the preparation of PET tracers. Background Technology

[0002] Positron emission tomography (PET), a powerful molecular imaging technique, has played a crucial role in preclinical target validation and clinical tumor diagnosis. The core of this technology lies in the use of PET tracers labeled with radioactive isotopes that emit positrons. Among these, fluorine-18 (… 18 F) is one of the most ideal and widely used radionuclides due to its suitable decay characteristics (half-life of 110 minutes and high positron yield). However, 18 The synthesis of F-PET tracers faces severe challenges. On the one hand, 18 F has an extremely short half-life, requiring all radiolabeling steps to be rapid and efficient; on the other hand, the radiolabeling produced by cyclotron accelerators... 18 F is usually hydrated 18 F-ions exist in aqueous solution, have low reactivity, and are conventionally introduced... 18 The labeling methods for F often require strictly anhydrous conditions, which undoubtedly increases the complexity and time cost of the synthesis. Therefore, ideally... 18 The F-labeling strategy urgently needs to develop a method that can directly label F-labeled ... 18 A method for introducing F negative ions into functionalized precursor molecules.

[0003] based on 18 F- 19 The strategy of F isotope exchange reaction offers a new solution to the aforementioned challenges. Organofluoroborates, due to their ability to undergo rapid isotope exchange, have shown great potential in the simplified preparation of PET tracers. However, traditional trifluoroborates exhibit poor stability under aqueous or biological conditions and are prone to hydrolysis, leading to the rapid decomposition of their conjugates with drug molecules, limiting their in vivo applications. To overcome this deficiency, researchers have developed trifluoroborates based on quaternary ammonium salts, quaternary phosphonium salts, and imidazole salts. These structures significantly enhance the stability of the fluoroboron skeleton in the aqueous phase by introducing a positive charge and have been successfully used in the preparation of various PET tracers. Nevertheless, the synthesis of these existing reagents typically involves numerous steps and is difficult to modify structurally, making it challenging to efficiently adjust their physicochemical properties to suit different drug molecules.

[0004] Therefore, there is an urgent need for a water-stable fluoroborate inner salt reagent with a novel framework, which can conveniently incorporate groups with different structures and physicochemical properties, easily couple with drug molecules to form precursors, and react with [the drug] in the aqueous phase. 18 F negative ions undergo rapid isotope exchange, thereby achieving18 The modular and efficient synthesis of F-labeled PET tracers avoids the time-consuming dehydration process in traditional synthesis, shortens the synthesis time, and improves the labeling rate. Summary of the Invention

[0005] Existing methods for preparation 18 The poor water stability of trifluoroborate fluoroborates used as F-PET tracers limits their practical application in vivo. While trifluoroborate fluoroborates based on quaternary ammonium salts, quaternary phosphonium salts, and imidazole salts can improve the water stability of the fluoroboron structure, their synthesis involves numerous steps and structural modification is difficult, making it challenging to efficiently adjust their physicochemical properties to suit different drug molecules. To address these issues, this invention provides an N-substituted pyridine fluoroborate inner salt reagent. By adjusting the type of substituents in the substituted alkyl group, it is possible to construct structurally diverse F-18 radiopharmaceutical precursors with different drug molecules or their derivatives. Furthermore, the prepared F-18 radiopharmaceutical precursors exhibit good stability in aqueous phase and can undergo efficient reaction in aqueous buffer solutions. 18 F- 19 F isotope exchange reaction avoids traditional 18 The time-consuming water removal process in the synthesis of F-type radiopharmaceuticals, thereby achieving 18 Modular and efficient synthesis of F-labeled PET tracers effectively improves 18 F-labeling rate.

[0006] Specifically, the present invention provides the following technical solutions: The first aspect of this invention provides an N-substituted pyridine fluoroborate inner salt reagent, the structure of which is shown below: , FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; R 1 The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino (e.g., dimethylamino), phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl, or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; n is any integer from 1 to 10.

[0007] Preferably, FG1 is an alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl, styryl, maleamido, or -O(CH2)2O(CH2)2N3; R 1 It can be formed by the combination of hydrogen, F, Cl, methyl, tert-butyl, methoxy, or two adjacent carbon atoms on the pyridine ring to form a benzene ring.

[0008] Furthermore, the N-substituted pyridine fluoroborate inner salt reagent comprises compounds with the following structures: .

[0009] A second aspect of the present invention provides a method for preparing the N-substituted pyridine fluoroborate inner salt reagent described in the first aspect, comprising the following steps: The protonated pyridine fluoroborate of Formula I is reacted with the compound of Formula II in the presence of a solvent to obtain the N-substituted pyridine fluoroborate inner salt reagent. The structures of Equations I and II above are shown below: , Among them, R 1The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino, phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; X is a halogen, methanesulfonyloxy, p-toluenesulfonyloxy, trifluoromethanesulfonyloxy, acetoxy, or trifluoroacetoxy; n is any integer from 1 to 10.

[0010] Furthermore, the molar ratio of the protonated pyridine fluoroborate shown in Formula I to the compound shown in Formula II is preferably 1:(1-3), for example 1:2, etc.

[0011] Furthermore, the ratio of the amount of protonated pyridine fluoroborate shown in Formula I to the volume of the solvent is preferably (0.1-5) mol: 1 L.

[0012] Furthermore, the solvent is selected from one or more of alcohol solvents, ketone solvents, ester solvents, hydrocarbon solvents, ether solvents, and halogenated hydrocarbon solvents, such as ethanol, methanol, isopropanol, acetone, butanone, ethyl acetate, butyl acetate, benzene, toluene, hexane, dichloromethane, chloroform, diethyl ether, tetrahydrofuran, etc.

[0013] Furthermore, the reaction can be carried out directly in the air without relying on special conditions such as anhydrous and oxygen-free environments. The reaction temperature is 0-100 °C and the time is 5 min-24 h.

[0014] A third aspect of this invention provides a method for preparing F-18 radiopharmaceuticals, comprising the following steps: S1. The N-substituted pyridine fluoroborate inner salt reagent described in the first aspect is coupled with the compound shown in Formula III in the presence of a catalyst and a solvent to obtain the PET tracer precursor shown in Formula IV. S2, mix the PET tracer precursor with... 18 The F anion undergoes an isotope exchange reaction in an acidic buffer solution or an organic solvent containing Lewis acid to obtain the product shown in formula V. 18 F-PET tracer; The structures of equations III, IV, and V above are as follows: , Among them, R 1 The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino, phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; R 2 It is selected from C1-C6 alkyl, C1-C6 alkoxy, substituted or unsubstituted aryl, drug molecules or their derivatives; the substituents of the substituted aryl group are selected from one or more of the following groups: halogen, cyano, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 alkenyl, C1-C6 alkenoxy, C1-C6 alkynyl, C1-C6 alkynoxy, C1-C6 ester, halo-C1-C6 alkyl, halo-C1-C6 alkoxy; The drug molecules include indomethacin, amlodipine, zidovudine, peptides, linezolid, aminoglutethimide, afatinib intermediate, sulfamethoxazole, prostate-specific membrane antigen (PMSA), and fibroblast activating protein inhibitor (FAPI). FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; FG2 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; and the group FG1 and the group FG2 form a reaction pair capable of undergoing a specific coupling reaction; n is any integer from 1 to 10.

[0015] Further, FG1 is alkynyl and FG2 is azide; or, FG1 is azide and FG2 is alkynyl; or, FG1 is carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride or sulfonyl fluoride and FG2 is amino or hydroxyl; or, FG1 is amino or hydroxyl and FG2 is carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride or sulfonyl fluoride; or, FG1 is mercapto and FG2 is alkenyl; or, FG1 is alkenyl and FG2 is mercapto.

[0016] Further, in step S1, when FG1 is alkynyl and FG2 is azide, the catalyst is a copper salt, which can be selected from one or more of copper sulfate pentahydrate, cuprous chloride, cuprous bromide, cuprous iodide, and tetraethyl copper hexafluorophosphate; the solvent is selected from one or more of ethanol, methanol, isopropanol, acetone, butanone, ethyl acetate, butyl acetate benzene, toluene, hexane, dichloromethane, chloroform, diethyl ether, and tetrahydrofuran; the molar ratio of the N-substituted pyridine fluoroborate inner salt reagent to the compound shown in Formula III is 1:(1.1-2); the ratio of the amount of the N-substituted pyridine fluoroborate inner salt reagent to the volume of the solvent is (0.2-0.4) mol:1 L; the coupling reaction can be carried out directly in air without relying on special conditions such as anhydrous and oxygen-free conditions, the reaction temperature is 0-100 ℃, and the time is 1 min-24 h.

[0017] Furthermore, in step S2, the pH of the acidic buffer solution is 0-7.

[0018] Further, in step S2, the Lewis acid is selected from one or more of boron trifluoride, boron trichloride, aluminum trifluoride, aluminum trichloride, zinc chloride, tin tetrachloride, ferric chloride, antimony pentafluoride, niobium chloride, silver chloride, gold chloride, copper trifluoromethanesulfonate, indium trifluoromethanesulfonate, hafnium trifluoromethanesulfonate, silver trifluoromethanesulfonate, and gold trifluoromethanesulfonate.

[0019] Furthermore, in step S2, the isotope exchange reaction can be carried out directly in the air without relying on special conditions such as anhydrous and oxygen-free environments. The reaction temperature is 25-150 °C and the time is 1-120 min.

[0020] The fourth aspect of this invention provides an F-18 radiopharmaceutical, prepared by the preparation method described in the third aspect.

[0021] Furthermore, the F-18 radiopharmaceutical includes, but is not limited to, compounds with the following structures: , , , .

[0022] The fifth aspect of this invention provides the application of the F-18 radiopharmaceutical described in the fourth aspect in the preparation of PET tracers.

[0023] Furthermore, the F-18 nuclear warhead includes, but is not limited to: , .

[0024] In this invention, the term "alkyl" refers to a fully saturated straight-chain or branched alkane group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, etc.

[0025] In this invention, the term "halogen" or "halogenated" refers to chlorine, bromine, fluorine, or iodine.

[0026] In this invention, the term "aryl" refers to a monovalent group formed by removing a hydrogen atom from an aromatic ring molecule, including but not limited to phenyl, naphthyl, biphenyl aryl, fluorenyl, furanyl, thiophene, pyridyl, benzofuranyl, benzothiophene, quinolinyl, etc.

[0027] The beneficial effects of this invention are: This invention provides an N-substituted pyridine fluoroborate inner salt reagent, obtained by reacting a protonated pyridine fluoroborate inner salt with an alkyl bromide. The preparation method is simple, easy to operate, and operates under mild reaction conditions with high yields, making it suitable for large-scale synthesis and application. Furthermore, the method is applicable not only to unsubstituted protonated pyridine fluoroborate inner salt substrates but also to protonated pyridine fluoroborate inner salt substrates with different positions and types of substituents, all of which can prepare the corresponding N-substituted pyridine fluoroborate inner salt reagents in high yields, demonstrating broad substrate applicability. More importantly, by adjusting the type of alkyl substituent, this reagent can be used to construct structurally diverse F-18 radiopharmaceutical prodrugs with different drug molecules or their derivatives.

[0028] This invention also provides a method for preparing F-18 radiopharmaceuticals, which utilizes an N-substituted pyridine fluoroborate inner salt reagent to couple with a drug molecule or its derivative to generate an F-18 radiopharmaceutical precursor, followed by a further isotope exchange reaction to obtain the F-18 radiopharmaceutical. The above method is simple to operate, and the prepared F-18 radiopharmaceutical precursor exhibits good stability in aqueous solution and can undergo efficient reactions in aqueous buffer solutions. 18 F- 19 F isotope exchange reaction avoids traditional 18 The time-consuming water removal process in the synthesis of F radiopharmaceuticals has been greatly shortened. 18 The synthesis time of F radiopharmaceuticals was reduced, thus effectively improving the efficiency. 18 F labeling rate. Furthermore, animal experiments showed that the F-18 radiopharmaceutical prepared from the above-mentioned N-substituted pyridine fluoroborate inner salt reagent exhibited high in vivo stability and showed promising application prospects in the preparation of PET tracers. Attached Figure Description

[0029] Figure 1 Water stability test of N-substituted pyridine fluoroborate inner salt reagent prepared in Example 1 for NMR spectroscopy 19 F-spectrum; Figure 2Water stability test of N-substituted pyridine fluoroborate inner salt reagent prepared in Example 2 for NMR spectroscopy 19 F-spectrum; Figure 3 Water stability test of N-substituted pyridine fluoroborate inner salt reagent prepared in Example 3 for NMR spectroscopy 19 F-spectrum; Figure 4 The radioactive high-performance liquid chromatography (HPLC) spectrum of the preparation of F-18 radiopharmaceutical in Example 9, Experiment 9-1; Figure 5 The radioactive high-performance liquid chromatography (HPLC) spectrum of the preparation of F-18 radiopharmaceutical in Example 9, Experiment 9-2; Figure 6 The radioactive high-performance liquid chromatography (HPLC) spectrum of the preparation of F-18 radiopharmaceutical in Example 9, Experiment 9-3; Figure 7 The radioactive high-performance liquid chromatography (HPLC) spectrum of the preparation of F-18 radiopharmaceutical in Example 9, Experiment 9-4; Figure 8 This is a graph showing the in vivo stability test of the F-18 radiopharmaceutical. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0032] In the following examples, (pyridin-1-onthium-2-yl)trifluoroborate, (pyridin-1-onthium-3-yl)trifluoroborate, (pyridin-1-onthium-4-yl)trifluoroborate, and (4-methoxypyridin-1-onthium-2-yl)trifluoroborate were all synthesized using methods previously reported in the work (W. Li, Y. Chen, R. Yuan, X. Jia, Y. Yao, L. Zhang. Water-Stable 2-Pyridylboron Reagents: Pd-Catalyzed 2-Pyridylation Reaction of ArylHalides. Angew. Chem. Int. Ed. 2025, 64, (e202500315.) Alkyl bromides were purchased from Shanghai Titan Technology Co., Ltd., with a purity >98%; acetonitrile was purchased from Shanghai Titan Technology Co., Ltd., with a purity >99.9%; sodium L-ascorbate and copper sulfate pentahydrate were purchased from Shanghai Titan Technology Co., Ltd., with a purity >99.0%; tert-butanol was purchased from Shanghai Titan Technology Co., Ltd., with a purity >99.5%; other azide substrates were synthesized using methods reported in the literature.

[0033] In the following examples: Me represents methyl, t Bu represents tert-butyl, OMe represents methoxy, CF3 represents trifluoromethyl, and NMR represents nuclear magnetic resonance.

[0034] This invention employs the following preparation method to prepare N-substituted pyridine fluoroborate inner salt reagent, F-18 radiopharmaceutical precursor, and F-18 radiopharmaceutical, the reaction process of which is shown below:

[0035]

[0036]

[0037] (1) Preparation of N-substituted pyridine fluoroborate inner salt reagent: Add a magnetic stir bar to a 4 mL sample vial, add protonated pyridine fluoroborate (0.500 mmol) and potassium carbonate (0.500 mmol), add a small amount of solvent (e.g., 2.5 mL acetonitrile), and then add an alkyl halide (0.500-1.500 mmol). Seal the sample vial with a diaphragm cap and stir in a stirrer at room temperature for 5 minutes to 1.5 hours. After the reaction is complete, directly concentrate under vacuum, and then purify the crude product by recrystallization or column chromatography to obtain the desired N-substituted pyridine fluoroborate inner salt reagent.

[0038] (2) Preparation of F-18 radiopharmaceutical precursor: Under an air atmosphere, azide (0.450 mmol) was added to...t The mixture was prepared in a BuOH:H2O (1:1) solution and then transferred to a 4 mL sample vial equipped with a magnetic stir bar. Copper sulfate pentahydrate (20 mol%-40 mol%) and sodium ascorbate (40 mol%-60 mol%) were then added to the vial, followed by the N-substituted pyridine fluoroborate inner salt reagent (0.300 mmol) prepared in step (1). The sample vial was sealed with a diaphragm-sealed cap and stirred in a stirrer at room temperature for 9-15 hours. After the reaction was complete, the reaction vessel was opened in air, and the resulting mixture was quenched with saturated NaHCO3 (10 mL) and then extracted into ethyl acetate (3 × 10 mL). The combined organic phases were washed with brine, dried over anhydrous Na2SO4, concentrated by rotary evaporation, and purified by column chromatography to obtain the desired F-18 radiopharmaceutical precursor.

[0039] (3) Preparation of F-18 radionuclide: First, an anion exchange column (QMA column) was used to prepare the carrier-free radionuclide. 18 F-ions were captured and then eluted into an EP tube with 1 mL of physiological saline. 1 mL of anhydrous acetonitrile was added to the tube, and the tube was dried under a nitrogen stream at 105 °C, repeated twice. After thorough drying, 60 μL of physiological saline, 40 μL of pyrazine-hydrochloric acid buffer (pH=2.0), and 20 μL of DMF were added to the EP tube. 18 The F-type radiopharmaceutical precursor mixture was heated at 90 °C for 15 minutes. The reaction was then quenched with 500 μL of PBS (pH=8) and further diluted with 3 mL of water.

[0040] Furthermore, a portion of the solution was transferred for radioactive HPLC analysis, and the radiochemical conversion rate was determined by product identification.

[0041] Furthermore, by loading the reaction mixture from step (3) onto a C18 separation column washed with 3 mL of water, and eluting the radiochemically pure product into a glass bottle containing 10-12 mCi tracer with 1.0 mL of ethanol for a total time not exceeding 30 min, pure F-18 radiopharmaceutical is obtained, which can be used for PET imaging research.

[0042] Example 1: This example relates to the preparation of an N-substituted pyridine fluoroborate inner salt reagent at position 2, and the reaction formula is as follows:

[0043] Under normal pressure, (pyridin-1-onthiol-2-yl)trifluoroborate (73.5 mg, 0.5 mmol), K₂CO₃ (69.0 mg, 0.5 mmol), and 2.5 mL of acetonitrile (0.2 M) were added to a 4 mL sample vial, followed by the addition of 3-bromopropyne (119 mg, 1.0 mmol). The vial was sealed with a diaphragm cap and stirred on a stirrer at room temperature for 1.5 h. After the reaction was complete, the mixture was concentrated and then purified by column chromatography (DCM:CH₃OH = 100:1-50:1) to obtain a yellow solid (84.0 mg, 91%). 1 H NMR (400 MHz, CD3CN, 25 °C, δ): 8.81 (d, J = 6.3 Hz, 1H), 8.26 (t, J =7.7 Hz, 1H), 8.11 (d, J = 7.8 Hz, 1H), 7.80 (t, J = 6.8 Hz, 1H), 5.51 (d, J =2.6 Hz, 2H), 3.04 (t, J = 2.6 Hz, 1H).

[0044] Scale-up experiment: Under normal pressure, (pyridin-1-onthiol-2-yl)trifluoroborate (1.47 g, 10.0 mmol), K2CO3 (1.38 g, 10.0 mmol), and 50 mL of acetonitrile (0.2 M) were added to a 100 mL round-bottom flask, followed by the addition of 3-bromopropyne (2.38 g, 20.0 mmol). The mixture was stirred for 1.5 h at room temperature. After the reaction was completed, the mixture was concentrated and then purified by column chromatography (DCM:CH3OH = 100:1-50:1) to obtain a yellow solid (1.68 g, 91%).

[0045] Example 2: This example relates to the preparation of a 3-position N-substituted pyridine fluoroborate inner salt reagent, and the reaction formula is as follows:

[0046] Under normal pressure, (pyridin-1-onthiol-3-yl)trifluoroborate (441 mg, 3.0 mmol), K₂CO₃ (290 mg, 2.10 mmol), and 15 mL of acetonitrile (0.2 M) were added to a 20 mL sample vial, followed by the addition of 3-bromopropyne (714 mg, 6.00 mmol). After solvation, 10 mL of diethyl ether was added, and the mixture was sonicated, washed with diethyl ether, and then recrystallized with 2 mL of methanol and 98 mL of diethyl ether. After sonication, 359 mg (65% yield) of a pale yellow solid was obtained. 1H NMR (400MHz, CD3CN, 25 °C, δ): 8.68 (s, 1H), 8.60 (dt, J = 6.2, 1.6 Hz, 1H), 8.55 (d,J = 7.5 Hz, 1H), 7.88 (t, J = 6.8 Hz, 1H), 5.33 (d, J = 2.6 Hz, 2H), 3.19 (t,J = 2.6 Hz, 1H).

[0047] Example 3: This example relates to the preparation of an N-substituted pyridine fluoroborate inner salt reagent at position 4, and the reaction formula is as follows:

[0048] Under normal pressure, (pyridin-1-onthium-4-yl)trifluoroborate (73.5 mg, 0.5 mmol), K₂CO₃ (69.0 mg, 0.5 mmol), and 2.5 mL of acetonitrile (0.2 M) were added to a 4 mL sample vial, followed by the addition of 3-bromopropyne (119 mg, 1.0 mmol). The vial was sealed with a diaphragm cap and stirred on a stirrer at room temperature for 1.5 h. After the reaction was complete, the mixture was concentrated and then purified by column chromatography (DCM:CH₃OH = 100:1) to obtain a pale yellow solid (72.3 mg, 78%). 1 H NMR (400 MHz, CD3CN, 25 °C, δ): 8.54 (d, J = 6.1 Hz, 2H), 8.06 (d, J = 5.9Hz, 2H), 5.30 (d, J = 2.6 Hz, 2H), 3.19 (t, J = 2.6 Hz, 1H).

[0049] Example 4: This example involves the preparation of a series of N-substituted pyridine fluoroborate inner salt reagents. The only difference from Example 1 is the type of protonated pyridine fluoroborate; all other conditions are the same. The corresponding N-substituted pyridine fluoroborate inner salt reagents were prepared. Details are shown in the table below:

[0050]

[0051] .

[0052] Example 5: This example relates to the preparation of a series of N-substituted pyridine fluoroborate inner salt reagents. The only difference from Example 1 is the type of protonated pyridine fluoroborate and alkyl halide; all other conditions are the same. The corresponding N-substituted pyridine fluoroborate inner salt reagents were prepared. Details are shown in the table below:

[0053] Example 6: Taking the N-substituted pyridine fluoroborate inner salt reagent prepared in Examples 1-3 as an example, the water stability of the N-substituted pyridine fluoroborate inner salt reagent was tested. The specific test method is as follows: N-propargyl-substituted pyridine fluoroborate internal salt reagent (18.5 mg, 0.100 mmol) was dissolved in a mixture of 0.2 mL PBS buffer and 0.5 mL acetonitrile. After standing for a certain period of time, 1.0 mL of deuterium water and 18.5 mg of sodium trifluoroacetate internal standard were added. Finally, 0.5 mL of the mixture was used for... 19 F nuclear magnetic resonance measurement.

[0054] Test results are as follows Figure 1-3 And as shown in the table below:

[0055] Depend on Figure 1-3 As shown in Table 1 above, the N-substituted pyridine fluoroborate inner salt reagents prepared in Examples 1-3 all have excellent water stability. In particular, the N-substituted pyridine fluoroborate inner salt reagent at position 2 showed almost no change in content after standing in PBS buffer for 12 days.

[0056] Example 7: This example relates to the preparation of a series of F-18 radiopharmaceutical precursors. Taking the N-substituted pyridine fluoroborate inner salt reagent at position 2 prepared in Example 1 as an example, the types of compounds shown in Formula III were changed to prepare the corresponding F-18 radiopharmaceutical precursors.

[0057] Taking the compound represented by Formula III as benzyl azide as an example, the specific preparation process is as follows: Under air atmosphere, benzyl azide (59.5 mg, 0.450 mmol) was added to a 1.5 mL mixture of tert-butanol and water (1:1, 0.2 M), and then transferred to a 4 mL sample vial equipped with a magnetic stir bar. Copper sulfate pentahydrate (15 mg, 0.06 mmol, 20 mol%) and sodium ascorbate (23.8 mg, 0.12 mmol, 40 mol%) were added to the vial, followed by the addition of the 2-position N-propynepyridine fluoroborate inner salt reagent (55.5 mg, 0.300 mmol). The sample vial was sealed with a septum-sealed cap and stirred at room temperature for 12 hours. After the reaction was complete, air was purged into the reaction vessel, and the resulting mixture was quenched with saturated NaHCO3 (10 mL) and then extracted into ethyl acetate (3 × 10 mL). The combined organic phases were washed with brine, dried over anhydrous Na2SO4, concentrated by rotary evaporation, and purified by column chromatography (DCM:CH3OH = 100:1-50:1) to give a pale yellow solid (85.1 mg, 89%). 1 H NMR (400 MHz, CDCl3, 25 °C, δ): 8.86 (d, J = 6.2 Hz, 1H), 8.24 (d, J = 7.6 Hz, 1H), 8.09 (t, J = 7.7 Hz, 1H), 7.93 (s, 1H), 7.64(ddd, J = 7.8, 6.3, 1.8 Hz, 1H), 7.37 – 7.31 (m, 3H), 7.29 – 7.22 (m, 2H), 5.94 (s, 2H), 5.47 (s, 2H).

[0058] The structures and yields of F-18 radiopharmaceutical precursors prepared from different substrates are summarized in the table below:

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] Example 8: This example relates to the preparation of an F-18 radiopharmaceutical precursor, differing from Example 7 only in that it uses the N-substituted pyridine fluoroborate inner salt reagent containing an azide group prepared in Experiment 5-1 of Example 5. Using 4-phenyl-1-butyne as a raw material, and with all other conditions being the same, the corresponding F-18 radiopharmaceutical precursor was prepared. The yield was 87%.

[0065] Example 9: This example relates to the preparation of an F-18 radiodrug. Taking the F-18 radiodrug precursors prepared in experiments 7-2, 7-3, 7-23, and 7-24 of Example 7 as examples, the preparation is carried out... 18 F- 19 The corresponding F-18 radionuclide was synthesized via an F isotope exchange reaction. The specific synthesis method is as follows: First, an anion exchange column was used to process the carrier-free material. 18 F-ions were captured and then eluted into an EP tube with 1 mL of physiological saline. 1 mL of anhydrous acetonitrile was added to the tube, and the tube was dried under a nitrogen stream at 105 °C, repeated twice. After thorough drying, 60 μL of physiological saline, 40 μL of pyrazine-hydrochloric acid buffer (pH=2.0), and 20 μL of DMF were added to the EP tube. 18 F-PET tracer precursor 300 (nmol) was mixed and heated at 90 °C for 10 min. Then, 500 μL of PBS (pH=8) was added to quench the reaction, and the mixture was further diluted with 3 mL of water. Finally, a portion of the solution was transferred for radioactive HPLC analysis. The product was identified as having a radiochemical conversion rate as shown in the figure. Figure 4-7 And as shown in the table below:

[0066] Depend on Figure 4-7 As shown in the table above, the F-18 radiopharmaceutical precursor prepared by this invention... 18 F- 19 The synthesis of F-18 radiopharmaceuticals via F isotope exchange reaction can effectively shorten the synthesis time of F-18 radiopharmaceuticals, with a total time not exceeding 30 minutes, significantly improving efficiency. 18 With an F labeling rate, the radioactivity of the isolated pure product is approximately 10⁻¹² mCi, which can be used for PET imaging.

[0067] Example 10: Taking the F-18 radiopharmaceutical prepared in experiments 9-3 and 9-4 of Example 9 as an example, the in vivo stability of this type of F-18 radiopharmaceutical as a PET tracer was further studied. The specific operation is as follows: Under 2.0% isoflurane anesthesia, the distribution of radioactive probes (F-18 radionuclides prepared in Experiments 9-3 and 9-4 of Example 9) in healthy mice was assessed using a microPET / MR system (Bruker BioSpec 94 / 30 USR + PET plug-in). The F-18 radionuclides prepared in Experiments 9-3 and 9-4 (approximately 7.4 MBq, 0.20 mL, 10% ethanol / saline solution) were administered via tail vein injection. Static microPET / MR imaging was performed at 1 h and 2 h post-injection. The obtained images were reconstructed and analyzed using PMOD 4.3 software.

[0068] The results are as follows Figure 8 As shown, the two F-18 nuclear drugs were significantly enriched in the gallbladder and excretion pathway of mice, and no bone uptake was observed 2 h after injection, which further indicates that these tracers have high in vivo stability.

[0069] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. An N-substituted pyridine fluoroborate inner salt reagent, characterized in that, The structure of the N-substituted pyridine fluoroborate inner salt reagent is shown below: ， FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; R 1 The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino, phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; n is any integer from 1 to 10.

2. The N-substituted pyridine fluoroboronic acid inner salt reagent according to claim 1, characterized in that, The FG1 is an alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl, styryl, maleamido, or -O(CH2)2O(CH2)2N3; R 1 It can be formed by the combination of hydrogen, F, Cl, methyl, tert-butyl, methoxy, or two adjacent carbon atoms on the pyridine ring to form a benzene ring.

3. The N-substituted pyridine fluoroboronic acid inner salt reagent according to claim 1, characterized in that, The N-substituted pyridine fluoroborate inner salt reagent includes compounds with the following structures: 。 4. A method for preparing an N-substituted pyridine fluoroborate inner salt reagent as described in any one of claims 1-3, characterized in that, Includes the following steps: The protonated pyridine fluoroborate of Formula I is reacted with the compound of Formula II in the presence of a solvent to obtain the N-substituted pyridine fluoroborate inner salt reagent. The structures of Equations I and II above are shown below: ， Among them, R 1 The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino, phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; X is a halogen, methanesulfonyloxy, p-toluenesulfonyloxy, trifluoromethanesulfonyloxy, acetoxy, or trifluoroacetoxy; n is any integer from 1 to 10.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the protonated pyridine fluoroborate shown in Formula I to the compound shown in Formula II is 1:(1-3). And / or, the ratio of the amount of protonated pyridine fluoroborate shown in Formula I to the volume of the solvent is (0.1-5) mol: 1 L; And / or, the solvent is selected from one or more of alcohol solvents, ketone solvents, ester solvents, hydrocarbon solvents, ether solvents, and halocarbon solvents; And / or, the reaction is carried out at a temperature of 0-100 °C for a time of 5 min-24 h.

6. A method for preparing an F-18 radiopharmaceutical, characterized in that, Includes the following steps: S1. The N-substituted pyridine fluoroborate inner salt reagent according to any one of claims 1-3 is coupled with the compound shown in Formula III in the presence of a catalyst and a solvent to obtain the F-18 radiopharmaceutical precursor shown in Formula IV. S2, mix the PET tracer precursor with... 18 The F anion undergoes an isotope exchange reaction in an acidic buffer solution or an organic solvent containing Lewis acid to obtain the F-18 nuclear drug shown in Formula V. The structures of equations III, IV, and V above are as follows: ， Among them, R 1 The benzene ring may be hydrogen, halogen, C1-C6 alkyl, halo-C1-C6 alkyl, C1-C6 alkoxy, halo-C1-C6 alkoxy, C1-C6 alkyl-substituted amino, phenyl, halophenyl, C1-C6 alkyl-substituted phenyl, C1-C6 alkoxy-substituted phenyl or halo-C1-C6 alkoxy-substituted phenyl, or cyclized with two adjacent carbon atoms on the pyridine ring to form a substituted or unsubstituted benzene ring; the substituents of the substituted benzene ring are selected from one or more of the following groups: halogen, C1-C6 alkyl, C1-C6 alkoxy; R 2 It is selected from C1-C6 alkyl, C1-C6 alkoxy, substituted or unsubstituted aryl, drug molecules or their derivatives; the substituents of the substituted aryl group are selected from one or more of the following groups: halogen, cyano, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 alkenyl, C1-C6 alkenoxy, C1-C6 alkynyl, C1-C6 alkynoxy, C1-C6 ester, halo-C1-C6 alkyl, halo-C1-C6 alkoxy; The drug molecules include indomethacin, amlodipine, zidovudine, polypeptide, linezolid, aminoglutethimide, afatinib intermediate, sulfamethoxazole, prostate-specific membrane antigen, and fibroblast activation protein inhibitor. FG1 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; FG2 contains at least one of the following groups: alkynyl, azide, carboxyl, acyl chloride, acyl fluoride, sulfonic acid, sulfonyl chloride, sulfonyl fluoride, amino, hydroxyl, mercapto, alkenyl; and the group FG1 and the group FG2 form a reaction pair capable of undergoing a specific coupling reaction; n is any integer from 1 to 10.

7. The preparation method according to claim 6, characterized in that, In step S1, when FG1 is alkynyl and FG2 is azide, the catalyst is selected from one or more of copper sulfate pentahydrate, cuprous chloride, cuprous bromide, cuprous iodide, and copper tetraethyl cyanophosphate. And / or, the molar ratio of the N-substituted pyridine fluoroborate inner salt reagent to the compound shown in Formula III is 1:(1.1-2). And / or, the coupling reaction is carried out at a temperature of 0-100 °C for a time of 1 min-24 h.

8. The preparation method according to claim 6, characterized in that, In step S2, the pH of the acidic buffer solution is 0-7; And / or, the Lewis acid is selected from one or more of boron trifluoride, boron trichloride, aluminum trifluoride, aluminum trichloride, zinc chloride, tin tetrachloride, ferric chloride, antimony pentafluoride, niobium chloride, silver chloride, gold chloride, copper trifluoromethanesulfonate, indium trifluoromethanesulfonate, hafnium trifluoromethanesulfonate, silver trifluoromethanesulfonate, and gold trifluoromethanesulfonate; And / or, the isotope exchange reaction is carried out at a temperature of 25-150 °C for a time of 1-120 min.

9. An F-18 nuclear warhead, characterized in that, It is prepared by the preparation method according to any one of claims 6-8.

10. The use of the F-18 radiopharmaceutical of claim 9 in the preparation of a PET tracer.

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