Fluorine-containing wheel-shaped molecules, methods for their preparation and use

Abstract

The application belongs to the technical field of molecular machines, and particularly relates to a fluorine-containing rotaxane molecule and a preparation method and application thereof. The fluorine-containing rotaxane molecule of the application takes fluorine-containing crown ether as a cyclic molecule, and is also a fluorine-19 magnetic resonance signal source; takes a chain molecule containing a secondary ammonium salt cation as an axle, and can control the relaxation property of fluorine through the interaction with the fluorine-containing crown ether; and takes 3,5-substituted benzene derivatives as end-capping groups to prevent the fluorine-containing crown ether from falling off from the axle. The molecule can be used as a fluorine-19 magnetic resonance contrast agent, and based on the structure characteristics of the rotaxane, the motion of the molecule is limited to improve the sensitivity of magnetic resonance imaging, a paramagnetic metal is not needed, the fluorine signal is single and strong, and the structure is convenient for subsequent functionalization, so that a high-performance 19 F MRI contrast agent is provided.

Description

Technical Field

[0001] This invention belongs to the field of molecular machine technology, specifically relating to a fluorinated rotaxane molecule, its preparation method, and its application. Background Technology

[0002] Magnetic resonance imaging (MRI) technology, compared to other medical imaging techniques, has advantages such as being non-invasive, non-ionizing, producing no ionizing radiation, offering high soft tissue contrast, good tissue penetration, and rich image information. Protons ( 1 H) is the most abundant observable nucleus in the human body via magnetic resonance imaging, and it has the highest gyromagnetic ratio. Therefore... 1 H MRI is a commonly used diagnostic technique in clinical practice. However, traditional 1 HMRI has strong background signal interference, and approximately 30% of MRI examinations require the use of magnetic resonance imaging contrast agents. In recent years, other atoms that can generate magnetic resonance imaging signals have been continuously studied and explored. Among them, fluorine-19 (… 19 F) is a stable isotope with 100% natural abundance, and its sensitivity is second only to 1 H (equivalent to) 1 H (which makes up 83% of the body's total hydrogen content) is a trace element in the human body, mainly distributed in bones and teeth. Its transverse relaxation time (T2) is extremely short, making it difficult to detect by MRI machines. Furthermore, it does not have background signal interference. 19 The fMRI signal comes entirely from fluorinated contrast agents, exhibiting the characteristics of "hot spot" imaging, and has promising application prospects in the field of biomedical research.

[0003] at present, 19 MRI contrast agents are mainly divided into: 1) small molecule compounds. For example, perfluorocarbons, taking perfluorooctyl bromide (PFOB), a straight-chain alkyl bromide in which all hydrogen atoms are replaced by fluorine atoms, as an example [Magnetic Resonance in Medicine, 2010, 5(6): 548-554.]. This compound has good stability and biocompatibility. It is generally used for downstream applications by adding surfactants to form a stable emulsion. However, due to the structure of PFOB molecules... 19 F is an asymmetric distribution. 19F NMR signal splitting limits its application to some extent. Other perfluorinated carbon small molecule compounds with symmetrical fluorine atoms, such as perfluorodecyl crown ether and perfluorobenzene, are difficult to modify. 2) Polymers and branched polymers. In order to improve the sensitivity of contrast agents, introducing more fluorine atoms into their structure is one of the effective strategies. For example, linear perfluoropolyethers (PFPEs), Ahrens et al. [Nature Biotechnology, 2005, 23(8):983-987] first proposed using PFPEs to label dendritic cells for in vivo cell tracing and quantification. In order to further improve the sensitivity of contrast agents, Kislukhin et al. [Nature Materials, 2016, 15(6):662-668] introduced paramagnetic gadolinium ions or iron ions into PFPEs to improve the longitudinal relaxation rate (T1), but the safety issues brought by paramagnetic metals cannot be ignored. 3) Inorganic fluorides. Because fluorine atoms in inorganic compounds are fixed in the crystal lattice, their T2 is very short, requiring special NMR methods such as ultrashort echo time (UTE) for signal acquisition [Angewandte Chemie-International Edition, 2018, 57(25): 7478-7482].

[0004] Rotaxanes are a class of mechanically interlocked molecules, consisting of an assembly of molecules with one or more cyclic molecules and one or more chain molecules as axes. The chain molecules act as axes, passing through the cavities of the cyclic molecules, and are bound at both ends with large stopper groups to prevent the cyclic molecules from detaching, thus forming a stable rotaxane structure. This invention uses fluorinated crown ethers as cyclic molecules, assembling rotaxanes through crown ethers and secondary ammonium salt cation axes. Due to hydrogen bonding, the free movement of the fluorinated crown ethers is restricted, accelerating their relaxation rate and thus improving sensitivity. This safe and effective improvement... 19 Strategies for improving the sensitivity of fMRI contrast agents have not yet been reported. Summary of the Invention

[0005] In order to improve 19 To improve the sensitivity of MRI contrast agents, this invention utilizes the unique mechanical interlocking structure of rotaxane to restrict the free molecular movement of fluorinated modules, thereby accelerating their longitudinal relaxation rate in nuclear magnetic resonance (NMR). The fluorinated rotaxane molecule of this invention uses a fluorinated crown ether as a cyclic molecule, which is also a fluorine-19 NMR signal source; it uses a chain molecule containing a secondary ammonium salt cation as an axis, and the relaxation properties of fluorine can be modulated through interaction with the fluorinated crown ether; and it uses a 3,5-substituted benzene derivative as a capping group to prevent the fluorinated crown ether from detaching from the axis. This type of... 19fluoropolymer (FFR) contrast agents enhance sensitivity by restricting molecular motion based on the structural properties of rotaxane, eliminating the need for paramagnetic metals. Fluorine provides a single, strong signal, and its structure facilitates subsequent functionalization, making it a high-performance contrast agent. 19 This provides new insights into the development of f MRI contrast agents.

[0006] The main objective of this invention is to provide a highly sensitive 19 In order to achieve this purpose, the present invention utilizes the structural characteristics of rotaxane mechanical interlocking to increase the longitudinal relaxation rate by restricting the movement of fluorinated crown ethers, thereby enhancing sensitivity.

[0007] This invention discloses a fluorinated rotaxane molecule, which has a fluorinated crown ether as a cyclic molecule and is also a fluorine-19 magnetic resonance signal source. It has a chain molecule containing a secondary ammonium salt cation as its axis and 3,5-substituted benzene derivatives as end-capping groups. The specific structural formula of the fluorinated rotaxane molecule is as follows: Formula 1:

[0008]

[0009] Wherein, R1 is selected from any one of tert-butyl, trifluoromethyl, and benzyloxy; R f It is selected from any one of perfluorotert-butoxy, trifluoroethoxy or fluorotolyloxy (preferably, the fluorotolyloxy is p-fluorotolyloxy or difluorotolyloxy), and F is fluorine-19.

[0010] Another object of the present invention is to provide a method for preparing the above-mentioned fluorinated rotaxane molecule, comprising the following steps:

[0011] (a) The synthesis of fluorinated crown ether compounds includes the following steps:

[0012]

[0013] (1-1) Using dibenzo-24-crown ether-8 as raw material, paraformaldehyde and hydrogen bromide were added to carry out tetrabromomethylation reaction. The mixture was heated and stirred until the solid was completely dissolved. After standing until the reaction was complete, the solid was collected, washed and dried to obtain the tetrabromomethylated compound.

[0014] (1-2) The tetrabromomethylated compound and the metal salt of the fluorinated alcohol were dissolved in an organic solvent and stirred at room temperature until the reaction was complete. After extraction and column chromatography purification, the fluorinated crown ether compound was obtained.

[0015] (II) The synthesis of chain-like molecule includes the following steps:

[0016]

[0017] (2-1) Under a protective atmosphere, using p-hydroxybenzylamine and p-hydroxybenzaldehyde as raw materials, in the presence of a catalyst and an organic solvent (preferably anhydrous magnesium sulfate as the catalyst, the amount of catalyst being 1.2 times the molar amount of p-hydroxybenzylamine; preferably anhydrous ethanol as the organic solvent), the mixture is heated to reflux until the reaction is complete, the resulting solid is dispersed in the solvent, and then a reducing agent is slowly added to it at 0°C to obtain compound 4a through a reduction amination reaction;

[0018] (2-2) Compound 4a was dissolved in a solvent, and at 0°C under a protective atmosphere, alkali was added and stirred until homogeneous. Then, di-tert-butyl dicarbonate was added and the reaction was allowed to proceed to completion at room temperature to obtain compound 4b, a secondary amine protected by a tert-butyloxycarbonyl group.

[0019] (2-3) Dissolve the base in the solvent, add compound 4b and 3-bromopropyne to the base solution at 0°C and under a protective atmosphere, and then carry out the Williamson ether synthesis reaction at room temperature to obtain compound 4c modified with alkynyl group;

[0020] (2-4) Removal of the secondary amine protecting group tert-butyloxycarbonyl in the alkynyl-modified compound 4c: Trifluoroacetic acid and a cation scavenger were added to the alkynyl-modified compound 4c, and the mixture was stirred at room temperature until the reaction was complete. After vacuum concentration, an organic solvent (preferably anhydrous methanol) was added to the resulting solid, and then ammonium hexafluorophosphate solution was added and stirred until the reaction was complete to obtain compound 4.

[0021] (III) Synthesis of end-capped molecules: Using benzyl bromide as a raw material, compound 5 was obtained by nucleophilic substitution reaction with sodium azide;

[0022]

[0023] (iv) Synthesis of fluorinated rotaxane molecules: Fluorinated crown ether compounds were dissolved in a solvent, compound 4 was added, and the mixture was stirred until homogeneous. Then, compound 5 and copper tetraethyl cyanophosphate (I) were added sequentially. The mixture was stirred at room temperature until the reaction was complete. The crude product was purified by silica gel column chromatography to obtain fluorinated rotaxane molecules.

[0024]

[0025] Furthermore, in step (1-1) of the preparation method, the tetrabromomethylation reaction temperature is 60-70℃, the hydrogen bromide is added in the form of an acetic acid solution of hydrogen bromide, and the mass fraction of hydrogen bromide in the acetic acid solution of hydrogen bromide is 33%; the molar ratio of dibenzo-24-crown ether-8 to paraformaldehyde is 1:(2.5-3.5).

[0026] Furthermore, in step (1-2) of the preparation method, the organic solvent is N,N-dimethylformamide (DMF) or a mixed solvent of DMF and tetrahydrofuran (THF) in a volume ratio of (1 / 1-1 / 2).

[0027] Furthermore, in step (1-2) of the preparation method, the metal salt of the fluoroalcohol is a potassium or sodium salt of perfluorotert-butanol, trifluoroethanol, or fluorobenzyl alcohol; the molar ratio of the tetrabromomethylated compound to the metal salt of the fluoroalcohol is 1:6.

[0028] Furthermore, in step (2-1) of the preparation method, the reducing agent is sodium borohydride, sodium cyanoborohydride, or sodium triacetoxyborohydride, and the molar ratio of p-hydroxybenzaldehyde, p-hydroxybenzylamine, and the reducing agent is 1:1:4.

[0029] Furthermore, in step (2-1) of the preparation method, the solvent is methanol (MeOH) or a mixed solvent of MeOH and THF with a volume ratio of (1 / 1-5 / 1); in step (2-2) of the preparation method, the solvent is tetrahydrofuran, and the base is triethylamine or 4-dimethylaminopyridine.

[0030] Furthermore, in step (2-2) of the preparation method, the molar ratio of compound 4a, ditert-butyl dicarbonate, and base is 20.5:30.75:26.6.

[0031] Furthermore, in step (2-3) of the preparation method, the solvent is DMF, the alkali is sodium hydride, the ammonium hexafluorophosphate solution is a saturated aqueous solution of ammonium hexafluorophosphate, and the molar ratio of sodium hydride, compound 4b and 3-bromopropyne is 3:1:3.5.

[0032] Furthermore, in step (2-4) of the preparation method, the cation scavenger is anisole, and the molar ratio of trifluoroacetic acid, compound 4c and anisole is 20:1:1.5.

[0033] Furthermore, in step (iii) of the preparation method, the benzyl bromide compound is 3,5-bis(trifluoromethyl)benzyl bromide or 3,5-bis(tert-butyl)benzyl bromide, the temperature of the nucleophilic substitution reaction is 70-80℃ (preferably 80℃), and the molar ratio of the benzyl bromide compound to sodium azide is 1:1.5.

[0034] Furthermore, in step (iv) of the preparation method, the solvent is dichloromethane, and the eluent used for silica gel column chromatography is a mixed solvent of DCM and MeOH with a volume ratio of 50 / 1–20 / 1.

[0035] Furthermore, in step (iv) of the preparation method, the reaction time is 2-3 days.

[0036] Furthermore, in step (iv) of the preparation method, the molar ratio of the fluorinated crown ether compound, compound 4, compound 5 and tetraethyl cyanophosphate (I) is 2:1:3:2.

[0037] The present invention also provides the application of the fluorinated rotaxane molecule or the fluorinated rotaxane molecule obtained by the above preparation method in the preparation of fluorine-19 magnetic resonance contrast agent.

[0038] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0039] 1. The fluorinated rotaxane molecule synthesized in this invention has a suitable relaxation rate and T2 / T1 ratio, which can realize highly sensitive fluorine-19 magnetic resonance imaging.

[0040] 2. The fluorinated rotaxane molecule synthesized in this invention contains 36 magnetically equivalent fluorine-19 atoms, which can generate a single fluorine signal, avoiding the problems of fluorine signal splitting and low fluorine atom utilization.

[0041] 3. In the temperature range of 274-318K, the relaxation rate of the fluorinated rotaxane molecules of the present invention is linearly related to temperature, and has the potential to serve as a temperature probe.

[0042] 4. Within the molecular concentration range of 0.0625-4.0 mM, the fluorine signal intensity of the fluorinated rotaxane molecules of the present invention exhibits a good linear relationship with their concentration: R 2 A linear relationship greater than 0.999 lays the foundation for quantitative imaging applications.

[0043] 5. Under the same conditions, the fluorine-19 magnetic resonance imaging signal intensity of the fluorinated rotaxane molecule of the present invention can be increased by 79% compared with the corresponding fluorinated crown ether, which proves the feasibility and effectiveness of the strategy of enhancing sensitivity based on the structural characteristics of rotaxane molecules of the present invention. Attached Figure Description

[0044] Figure 1 The fluorinated rotaxane molecule 1a prepared in Example 1 1 H NMR;

[0045] Figure 2 The fluorinated rotaxane molecule 1b prepared in Example 2 1 H NMR;

[0046] Figure 3 Linear fitting plots of the longitudinal relaxation rate versus temperature for fluorinated rotaxane molecules 1a and 1b.

[0047] Figure 4 For fluorinated rotaxane molecules 1a and 1b at different concentrations (0.0625-4.0 mM), 19The image shows the MRI results (top) and the linear relationship between the concentration and the corresponding fluorine signal intensity (bottom). Detailed Implementation

[0048] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0049] Example 1: Fluorinated rotaxane molecule 1a, its structural formula is as follows:

[0050]

[0051] The fluorinated rotaxane molecule 1a is prepared by the following method:

[0052] Step 1: Preparation of Compound 2-Tetrabromomethylated Compound

[0053] At room temperature (25°C), 8.0 mL of hydrobromic acid (an acetic acid solution of hydrogen bromide containing 33% hydrogen bromide by mass) was added to a round-bottom flask containing dibenzo-24-crown ether-8 (0.50 g, 1.11 mmol) and paraformaldehyde (0.30 g, 3.34 mmol). The mixture was then heated and stirred at 60°C until the solid was completely dissolved. The mixture was allowed to stand for two days to allow a white precipitate to form. The white precipitate was collected by filtration, washed successively with water, anhydrous ethanol, and anhydrous diethyl ether, and dried at room temperature (25°C) for 5 h to obtain compound 2-tetrabromomethylated compound, which was a white solid (0.78 g, yield 85%). 1 H NMR (400MHz, CDCl3) δ6.82(s,4H),4.59(s,8H),4.15(s,8H),3.91(s,8H),3.80(s,8H).

[0054] Step 2: Preparation of potassium perfluorotert-butoxide

[0055] Dissolve potassium hydroxide (1.20 g, 21.18 mmol) in 25 mL of deionized water, then slowly add it to perfluorotert-butanol (5.0 g, 21.18 mmol), stir the reaction at room temperature for 3 h, and then freeze-dry the reaction solution. The resulting white solid is potassium perfluorotert-butanol (5.8 g, 100% yield). 19 F NMR(471MHz,CD3Cl3)δ-73.56(s).

[0056] Step 3: Preparation of fluorinated crown ether 3

[0057] The structural formula of fluorinated crown ether 3 is shown below:

[0058]

[0059] At room temperature, 10 mL of a DMF / THF mixed solution (DMF / THF volume ratio = 1 / 1) was added to a reaction vessel containing compound 2 (1.22 g, 1.49 mmol) and potassium perfluorotert-butoxide (2.45 g, 8.94 mmol). The mixture was stirred overnight. After the reaction was complete as indicated by thin-layer silica gel chromatography (TLC), 150 mL of deionized water was added to the reaction mixture, followed by extraction twice with 60 mL of ethyl acetate each time. The organic phases from the two extractions were combined, dried over anhydrous sodium sulfate, concentrated under vacuum, and finally purified by silica gel column chromatography (V...). 石油醚(PE) / V 乙酸乙酯(EA) =2 / 1) to obtain compound fluorinated crown ether 3 (1.43 g, yield 67%), which is a white waxy solid. 1 H NMR (500MHz, CD3CN) δ7.01(s,4H),5.11(s,8H),4.13-4.15(m,8H),3.79-3.81(m,8H),3.67(s,8H). 19 F NMR(471MHz,CD3CN)δ-71.32(s). 13 C NMR (126MHz, CD3CN) δ150.4, 127.4, 121.4 (q, J = 289.8Hz), 117.9, 116.5, 80.4-81.1 (m), 71.7, 70.4, 70.0.HRMS (ESI + )m / z:[M+Na] + calcd for C 44 H 36 F 36 NaO 12 + 1463.1524, found1463.1524.

[0060] Preparation of step 4: Axial molecule 4a

[0061] Under nitrogen atmosphere, anhydrous ethanol (120 mL) was added to a two-necked flask containing p-hydroxybenzaldehyde (4.89 g, 40.00 mmol), p-hydroxybenzylamine (4.93 g, 40.00 mmol), and anhydrous magnesium sulfate (5.78 g, 48.00 mmol). The mixture was heated under reflux for 24 hours until the reaction was complete. The solvent was removed under vacuum, and the resulting mixture was redispersed in a mixed solution of THF (60 mL) and MeOH (60 mL). Then, NaBH4 (6.05 g, 160.00 mmol) was slowly added in 10 equal portions at 0 °C. After the addition was complete, the reaction flask was removed and placed at room temperature. It was stirred overnight at room temperature. After TLC showed the reaction was complete, a saturated ammonium chloride solution was added to quench the reaction. The solvent was removed under vacuum, and 200 mL of deionized water was added. The mixture was then extracted three times with anhydrous diethyl ether (450 mL of anhydrous diethyl ether each time). The organic phases from the three extractions were combined, dried over anhydrous sodium sulfate, concentrated under vacuum, and purified by silica gel column chromatography (V...). 石油醚(PE) / V 乙酸乙酯(EA) =1:9) to obtain compound axial molecule 4a (4.79 g, yield 52%), as a yellow solid. 1 H NMR (400MHz, acetone-d6) δ7.17 (d, J = 8.6 Hz, 4H), 6.77 (d, J = 8.6 Hz, 4H), 3.64 (s, 4H).

[0062] Preparation of step 5: Axial molecule 4b

[0063] Triethylamine (3.71 mL, 26.60 mmol) was added to a round-bottom flask containing 100 mL of THF solution containing 4a (4.70 g, 20.50 mmol). The mixture was stirred at this temperature for 10 minutes. Then, di-tert-butyl dicarbonate (6.71 g, 30.75 mmol) was slowly added dropwise to the flask using a syringe. The mixture was then heated to room temperature and stirred. After the reaction was complete, the solvent was removed under vacuum, and the solution was purified by silica gel column chromatography (V...). 石油醚(PE) / V 乙酸乙酯(EA) =2:1) ​​to obtain a compound 4b (4.02 g, 60% yield) of secondary amine protected by tert-butoxycarbonyl group, as a white solid. 1 H NMR (400MHz, acetone-d6) δ8.38 (s, 2H), 7.10 (d, J = 7.3Hz, 4H), 6.80-6.82 (m, 4H), 4.22-4.28 (m, 4H), 1.48 (s, 9H).

[0064] Preparation of 6-axis molecule 4c

[0065] Under nitrogen atmosphere, at 0°C, 50 mL of DMF solution containing 3.30 g (10.00 mmol) of axial molecule 4b and 2.74 mL (35.00 mmol) were added sequentially to a 50 mL round-bottom flask containing a DMF suspension of sodium hydride (0.72 g, 30.00 mmol). The mixture was then heated to room temperature and stirred. After the reaction was complete as indicated by TLC, 30 mL of saturated ammonium chloride solution was added to quench the reaction. The mixture was then extracted three times with 30 mL of ethyl acetate each time. The organic phases from the three extractions were combined, washed with brine, dried over anhydrous sodium sulfate, concentrated under vacuum, and purified by silica gel column chromatography (V...). 石油醚(PE) / V 乙酸乙酯(EA) =10 / 1) yielded alkynyl-modified compound - axial molecule 4c (4.03 g, 99% yield), which was a yellow oily liquid. 1 H NMR (400MHz, CDCl3) δ7.13-7.16 (m, 4H), 6.93 (d, J = 8.7Hz, 4H), 4.69 (d, J = 2.4Hz, 4H), 4.25-4.33 (m, 4H), 2.53 (t, J = 2.4Hz, 2H), 1.50 (s, 9H).

[0066] Step 7: Preparation of Axial Molecule 4

[0067] Removal of the secondary amine protecting group tert-butyloxycarbonyl from compound 4c after alkyne modification: Trifluoroacetic acid (14.75 mL, 198.58 mmol) and anisole (1.62 mL, 14.89 mmol) were added to 50 mL of dichloromethane (DCM) solution containing molecule 4c (4.03 g, 9.93 mmol). The reaction mixture was stirred at room temperature for 12 hours. After TLC showed completion, the reaction mixture was concentrated under vacuum using a rotary evaporator to obtain a pale yellow solid (2.01 g, 66.3% yield), which was used directly in the next synthesis without further purification.

[0068] 9 mL of anhydrous methanol was added to the resulting pale yellow solid (0.50 g, 1.19 mmol), followed by 18 mL of saturated ammonium hexafluorophosphate solution. The mixture was stirred at room temperature for 5 hours. After TLC showed that the reaction was complete, 100 mL of dichloromethane was added to the reaction solution for dilution. The organic phase was collected, and the solvent was evaporated under vacuum to obtain the crude product. The crude product was then subjected to silica gel column chromatography (V... DCM / V MeOH The compound was purified at a ratio of 10:1 to obtain compound axial molecule 4 (0.56 g, yield 76%) as a yellow waxy solid. 1H NMR (400MHz, CDCl3) δ7.27(d,J=8.6Hz,4H),6.94(d,J=8.7Hz,4H),4.68(d,J=2.4Hz,4H),3.74(s,4H),2.52(t,J=2.4Hz,2H). 13 C NMR(101MHz,acetone-d6)δ159.4,132.6,124.8,116.0,79.4,77.3,56.2,51.8.HRMS(ESI + )m / z:[M-PF6 - ] + calcd for C 20 H 20 NO2 + ,306.1489; found,306.1485.

[0069] Step 8: Preparation of end-capped molecule 5a

[0070] The structural formula of the end-capped molecule 5a is shown below.

[0071]

[0072] Under nitrogen atmosphere, sodium azide (0.98 g, 15.00 mmol) was added to a round-bottom flask containing 30 mL of DMF solution containing 3,5-bis(trifluoromethyl)benzyl bromide (3.07 g, 10.00 mmol). The reaction mixture was stirred overnight at 80 °C. After the reaction was complete as shown by TLC, the reaction mixture was cooled to room temperature and diluted with 60 mL of deionized water. It was then extracted twice with anhydrous diethyl ether, 80 mL each time. The organic phases from the two extractions were combined and washed three times with 100 mL of brine each time. The mixture was then dried over anhydrous sodium sulfate and concentrated under vacuum to obtain compound-terminated molecule 5a (2.32 g, 89% yield), which was a pale yellow oily liquid. 1 H NMR (400MHz, CDCl3) δ7.42 (t, J = 1.8 Hz, 1H), 7.16 (d, J = 1.8 Hz, 2H), 4.35 (s, 2H), 1.36 (s, 18H).

[0073] Step 9: Preparation of fluorinated rotaxane molecule 1a

[0074] Under an argon atmosphere, 10 mL of DCM solution containing fluorinated crown ether 3 (255.30 mg, 0.18 mmol) was added to a round-bottom flask containing compound axial molecule 4 (40.00 mg, 0.089 mmol), and the mixture was stirred at room temperature for 0.5 h. Subsequently, end-capping molecule 5a (71.50 mg, 0.27 mmol) and tetraethyl cyanophosphate copper(I) [Cu(CH3CN)4]PF6 (66.10 mg, 0.18 mmol) were added to the flask, and the mixture was stirred at room temperature for another 48 h. After the reaction was complete as indicated by TLC, the solvent was concentrated under vacuum, and the mixture was purified by silica gel column chromatography (V...). DCM / V MeOH =50 / 1) yielded fluorinated rotaxane molecule 1a (97.70 mg, yield 45%), which was a colorless waxy solid. 1 H NMR(500MHz,CD3CN)δ8.00(s,2H),7.90(s,6H),7.29(d,J=8.6Hz,4H),6.86(s,4H),6.74(d,J=8.6Hz,4H),5.71 (s,4H),5.11(s,8H),4.95(s,4H),4.59-4.61(m,4H),4.08(d,J=2.5Hz,8H),3.79(d,J=3.5Hz,8H),3.67(s,8H). 19 F NMR (471MHz, CD3CN) δ-64.00 (s, 12F), -71.32 (s, 36F), -73.29 (d, J = 706.5Hz, 6F). 13 C NMR (126MHz, CD3CN) δ159.8,148.9,144.6,139.7,132.6(q,J=25.2Hz),131.9,129.8,127.4,125.5,125.2,124.4(q,J=277 .2Hz),123.4,121.4(q,J=289.8Hz),115.5,115.0,80.4-81.1(m),71.8,71.0,70.0,69.2,62.3,53.2,52.8.MALDI-ICR-MS m / z:[M-PF6 - ] + calcd for C 82 H 66 F 48 N7O 14 + ,2284.3896; found,2284.3880.

[0075] Example 2: Fluorinated rotaxane molecule 1b, its structural formula is as follows:

[0076]

[0077] The fluorinated rotaxane molecule 1b is prepared by the following method:

[0078] Step 1: Preparation of end-capped molecule 5b

[0079] The structural formula of the end-capped molecule 5b is shown below.

[0080]

[0081] Under nitrogen atmosphere, sodium azide (0.98 g, 15.00 mmol) was added to a round-bottom flask containing 30 mL of DMF solution containing 3,5-bis(trifluoromethyl)benzyl bromide (3.07 g, 10.00 mmol). The reaction solution was stirred overnight at 80 °C. After the reaction solution cooled to room temperature, it was diluted with 60 mL of deionized water and then extracted twice with 80 mL of diethyl ether each time. The organic phases from the two extractions were combined and washed three times with 100 mL of brine each time. The mixture was then dried over anhydrous sodium sulfate and concentrated under vacuum to obtain the terminal molecule 5b (2.52 g, 94% yield), a pale yellow oily liquid. 1 H NMR (400MHz, CDCl3) δ7.86 (s, 1H), 7.79 (s, 2H), 4.56 (s, 2H).

[0082] Step 2: Preparation of fluorinated rotaxane molecule 1b

[0083] Under an argon atmosphere, a DCM solution containing compound fluorinated crown ether 3 (255.30 mg, 0.18 mmol) was added to a round-bottom flask containing compound axial molecule 4 (40.00 mg, 0.089 mmol) and stirred at room temperature for 0.5 hours. Subsequently, compound end-capping molecule 5b (65.20 mg, 0.27 mmol) and [Cu(CH3CN)4]PF6 (66.10 mg, 0.18 mmol) were added to the flask, and stirring continued at room temperature for 48 hours. After the reaction was complete as shown by TLC, the solvent was concentrated under vacuum, and the mixture was purified by silica gel column chromatography (V...). DCM / V MeOH =50 / 1), yielding 1b of fluorinated rotaxane molecules (136.7 mg, yield 65%), which is a colorless waxy solid. 1H NMR (500MHz, CD3CN) δ7.81(s,2H),7.44(t,J=1.8Hz,2H),7.27(d,J=8.7Hz,4H),7.20(d,J=1.8Hz,4H),6.87(s,4H),6.74(d,J=8.7H z,4H),5.50(s,4H),5.14(s,8H),4.93(s,4H),4.57-4.60(m,4H),4.08-4.09(m,8H),3.77-3.78(m,8H),3.65(s,8H),1.27(s,36H). 19 F NMR (471MHz, CD3CN) δ-71.27 (s, 36F), -73.36 (d, J = 706.5Hz, 6F). 13 C NMR(126MHz,CD3CN)δ159.8,152.6,148.9,144.2,136.0,131.9,127.5,125.4,124.6,123.5,123.5,121.4(q, J=289.8Hz),115.6,115.0,80.4-81.1(m),71.8,71.0,70.0,69.2,62.2,55.0,52.8,35.5,31.5.MALDI-ICR-MS m / z:[M-PF6 - ] + calcd for C 94 H 102 F 36 N7O 14 + ,2236.6904; found,2236.6874.

[0084] Test 1: Temperature-relaxation rate relationship of fluorinated rotaxane molecules 1a and 1b

[0085] Step 1: Prepare 1.0 mM acetonitrile solutions of fluorinated rotaxane molecules 1a and 1b respectively, and transfer 0.4 mL of each solution to a 5 mm NMR sample tube for the following test experiments;

[0086] Step 2: Perform field locking, tuning, and shimming in a 500M nuclear magnetic resonance spectrometer;

[0087] Step 3: The longitudinal relaxation time T1 is determined using the inversion recovery method, and the transverse relaxation time T2 is determined using the CPMG method.

[0088] The linear fitting plots of the longitudinal relaxation rates (reciprocals of the longitudinal relaxation times) versus temperature for fluorinated rotaxane molecules 1a and 1b are shown below. Figure 3As shown, it can be seen that the relaxation rates of fluorinated rotaxane molecules 1a and 1b decrease with increasing temperature, and the two show a linear relationship. 2 = 0.9944 (1a of fluorinated rotaxane molecules), R 2 = 0.9868 (fluorinated rotaxane molecule 1b).

[0089] Example 4: In vitro analysis of fluorinated rotaxane molecule 1a and fluorinated crown ether 3 19 f MRI experiment

[0090] Step 1: Prepare acetonitrile solutions of fluorinated rotaxane molecule 1a and fluorinated crown ether 3 at the following concentrations: 4.0, 2.0, 1.0, 0.5, 0.25, 0.125, and 0.0625 mM. Transfer 2 mL of each solution to a 10 mm NMR sample tube for the following tests.

[0091] Step 2: Tuning and shimming are performed in the 400M magnetic resonance imaging spectrometer;

[0092] Step 3, proceed 19 During the fMRI imaging experiment, the RARE sequence was used for data acquisition. The samples were repeated 8 times, the sampling matrix was 32×32, the scan time was 307s, and the other sampling parameters were set as follows: acceleration factor RARE factor = 4, repetition time TR = 600.0ms, echo time TE = 17.5ms.

[0093] Figure 4 For fluorinated rotaxane molecule 1a and fluorinated crown ether 3 at different concentrations (0.0625-4.0 mM) 19 MRI imaging results (top), and linear relationship between fluorine signal intensity and concentration at different fluorine concentrations (bottom). Fluorinated rotaxane molecule 1a at different fluorine concentrations (0.0625-4.0 mM). 19 Even at concentrations as low as 0.0625 mM, fluorine signals were still clearly visible on MRI, with the signal intensity of fluorinated rotaxane molecule 1a being significantly higher than that of fluorinated crown ether 3. A linear relationship was plotted between concentration and corresponding fluorine signal intensity, showing a good linear relationship. 2 =0.9994 (containing fluorinated crown ether 3), R 2 = 0.9997 (fluorinated rotaxane molecule 1a).

Claims

1. A fluorinated rotaxane molecule, wherein the fluorinated rotaxane molecule is a cyclic molecule with a fluorinated crown ether as the cyclic molecule, a chain molecule containing a secondary ammonium salt cation as the axis, and a 3,5-substituted benzene derivative as the end-capping group, wherein the fluorinated crown ether also serves as a fluorine-19 magnetic resonance signal source, and the specific structural formula of the fluorinated rotaxane molecule is as follows: Formula 1: ， in, R1 is selected from either tert-butyl or trifluoromethyl; R f It is selected from either perfluorotert-butoxy or trifluoroethoxy, where F is fluorine-19.

2. The method for preparing the fluorinated rotaxane molecule according to claim 1, comprising the following steps: (a) The synthesis of fluorinated crown ether compounds includes the following steps: (1-1) Using dibenzo-24-crown ether-8 as raw material, paraformaldehyde and hydrogen bromide were added to carry out a tetrabromomethylation reaction. The mixture was heated and stirred until the solid was completely dissolved. After standing for the reaction to be complete, the solid was collected, washed, and dried to obtain the tetrabromomethylated compound. (1-2) The tetrabromomethylated compound and the metal salt of the fluorinated alcohol were dissolved in an organic solvent and stirred at room temperature until complete. After extraction and purification by column chromatography, the fluorinated crown ether compound was obtained. ； The reaction equations for steps (1-1) and (1-2) are as follows: ； (ii) The synthesis of chain-like axon molecules includes the following steps: (2-1) Under a protective atmosphere, p-hydroxybenzylamine and p-hydroxybenzaldehyde were used as raw materials. In the presence of a catalyst and an organic solvent, the mixture was heated to reflux until the reaction was complete. The resulting solid was dispersed in the solvent. Then, a reducing agent was slowly added to the solvent at 0°C to obtain compound 4a through a reduction amination reaction. (2-2) Compound 4a was dissolved in a solvent, and at 0°C under a protective atmosphere, alkali was added and stirred until homogeneous. Then, di-tert-butyl dicarbonate was added and the reaction was allowed to proceed to completion at room temperature to obtain compound 4b, which is a secondary amine protected by a tert-butyloxycarbonyl group. (2-3) Dissolve the base in the solvent, add compound 4b and 3-bromopropyne to the base solution at 0°C and under a protective atmosphere, and then carry out the Williamson ether synthesis reaction at room temperature to obtain the alkynyl-modified compound 4c. (2-4) Removal of the secondary amine protecting group tert-butyloxycarbonyl in the alkynyl-modified compound 4c: Trifluoroacetic acid and a cation scavenger were added to the alkynyl-modified compound 4c, and the mixture was stirred at room temperature until the reaction was complete. After vacuum concentration, an organic solvent was added to the resulting solid, and then ammonium hexafluorophosphate solution was added and stirred until the reaction was complete to obtain compound 4. The reaction equations for steps (2-1), (2-2), (2-3), and (2-4) are as follows: (III) Synthesis of end-capped molecules: Using benzyl bromide as a raw material, compound 5 was obtained by nucleophilic substitution reaction with sodium azide; ； (iv) Synthesis of fluorinated rotaxane molecules: Dissolve the fluorinated crown ether compound in a solvent, add compound 4 to it, stir until homogeneous, then add compound 5 and copper tetraethyl cyanophosphate (I) to it in sequence, stir at room temperature until the reaction is complete, extract and purify the reaction solution, and purify the crude product by silica gel column chromatography to obtain fluorinated rotaxane molecules.

3. The preparation method according to claim 2, characterized in that, In step (1-1) of the preparation method, the tetrabromomethylation reaction temperature is 60-70℃, the hydrogen bromide is added in the form of an acetic acid solution of hydrogen bromide, and the mass fraction of hydrogen bromide in the acetic acid solution of hydrogen bromide is 33%; the molar ratio of dibenzo-24-crown ether-8 to paraformaldehyde is 1:(2.5-3.5).

4. The preparation method according to claim 2, characterized in that, In step (1-2) of the preparation method, the metal salt of the fluoroalcohol is a potassium or sodium salt of perfluorotert-butanol or trifluoroethanol; the molar ratio of the tetrabromomethylated compound to the metal salt of the fluoroalcohol is 1:

6.

5. The preparation method according to claim 2, characterized in that, In step (2-1) of the preparation method, the reducing agent is sodium borohydride, sodium cyanoborohydride, or sodium triacetoxyborohydride, and the molar ratio of p-hydroxybenzaldehyde, p-hydroxybenzylamine, and the reducing agent is 1:1:4; in step (2-2) of the preparation method, the base is triethylamine or 4-dimethylaminopyridine; in step (2-2) of the preparation method, the molar ratio of compound 4a, ditert-butyl dicarbonate, and the base is 20.5:30.75:26.

6.

6. The preparation method according to claim 2, characterized in that, In step (2-3) of the preparation method, the solvent is DMF and the base is sodium hydride; the molar ratio of sodium hydride, compound 4b and 3-bromopropyne is 3:1:3.

5.

7. The preparation method according to claim 2, characterized in that, In step (2-4) of the preparation method, the ammonium hexafluorophosphate solution is a saturated aqueous solution of ammonium hexafluorophosphate, the cation scavenger is anisole, and the molar ratio of trifluoroacetic acid, compound 4c and anisole is 20:1:1.

5.

8. The preparation method according to claim 2, characterized in that, In step (iii) of the preparation method, the benzyl bromide compound is 3,5-bis(trifluoromethyl)benzyl bromide or 3,5-bis(tert-butyl)benzyl bromide, the temperature of the nucleophilic substitution reaction is 70-80℃, and the molar ratio of the benzyl bromide compound to sodium azide is 1:1.

5.

9. The preparation method according to claim 2, characterized in that, In step (iv) of the preparation method, the molar ratio of fluorinated crown ether compound, compound 4, compound 5 and tetraethyl cyanophosphate (I) is 2:1:3:

2.

10. The use of the fluorinated rotaxane molecule of claim 1 or the fluorinated rotaxane molecule prepared by any one of claims 2-8 in the preparation of fluorine-19 magnetic resonance contrast agent.

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