Manganese complex Mn (1, 4-Et4DO2A) as well as synthesis method and application thereof

Abstract

The invention provides a manganese complex Mn (1, 4-Et4DO2A) as well as a synthesis method and application thereof, and belongs to the technical field of synthesis of manganese complexes. The manganese (II) complex Mn (1, 4-DO2A) is subjected to structural modification, so that the stability and the inertia of the manganese (II) complex Mn (1, 4-DO2A) are improved; in the tested hexadentate manganese (II) complex, the manganese (II) complex Mn (1, 4-Et4DO2A) containing four chiral ethyl groups shows the highest stability, and the inertia of the manganese (II) complex Mn (1, 4-Et4DO2A) is doubled by introducing a rigid phenyl analogue through a side arm. Compared with the manganese (II) complex Mn (1, 4-DO2A), the longitudinal relaxation rate of the manganese (II) complex Mn (1, 4-Et4DO2A) at 25 DEG C and 20 MHz is improved by 50%; mouse experiment results show that the manganese complex Mn (1, 4-Et4DO2A) is expected to become an MRI diagnostic tool for replacing a gadolinium-based contrast agent, including detection of in-situ liver cancer.

Description

Technical Field

[0001] The present invention relates to the technical field of synthesis of manganese complexes, and in particular to a manganese complex Mn(1,4-Et4DO2A) and a synthesis method and application thereof. Background Art

[0002] Over the past 40 years, gadolinium(III)-based contrast agents (GBCAs) have been widely used in clinical magnetic resonance imaging (MRI) to enhance the diagnosis of soft tissue diseases. However, gadolinium(III) deposition in organs and tissues has been found in patients undergoing multiple enhanced MRI scans. Therefore, the search for viable alternatives to GBCAs has become a research hotspot.

[0003] Manganese(II) is considered a potential candidate for developing safer and more biocompatible alternatives to GBCAs due to its high-spin electronic configuration (S=5 / 2) and rapid water exchange properties. However, unlike GBCAs, manganese(II) complexes generally exhibit low thermodynamic stability and kinetic inertness, which is related to their low charge-to-radius ratio and lack of ligand-field stabilization energy. Although manganese(II) is an essential element for the human body, its release from contrast agents (CAs) must be avoided for the following reasons: First, manganese(II) release may cause acute toxicity, as the dose of CAs in a single scan is typically high to ensure effective contrast enhancement; second, free manganese(II) and its adducts with proteins (such as human serum albumin (HSA)) have higher longitudinal relaxation rates than most small-molecule manganese(II) complexes, potentially causing off-target signals or unexpected background noise; finally, excessive exposure to free manganese(II) may lead to clinical symptoms associated with Parkinson's disease.

[0004] Macrocyclic ligands generally provide higher stability and inertness than linear ligands when chelating metal ions (Clough, JT, Jiang L., Wong K.-L., et al. Ligand design strategies to increasestability of gadolinium-based magnetic resonance imaging contrast agents [J]. Nature Communications, 2019, 10 (1): 1420. DOI: 10.1038 / s41467-019-09342-3). Mn-NOTA is one of the most stable manganese (II) complexes, but its relaxivity is low due to the lack of coordinated water molecules. In contrast, the hexadentate ligand 1,4-DO2A can accommodate manganese (II) while retaining one coordinated water molecule, thereby achieving a reasonable relaxivity. Moreover, the thermodynamic stability constants of Mn (1,4-DO2A) and Mn-NOTA are similar (logKML 16.1 and 16.3, respectively), so Mn(1,4-DO2A) is considered to be an ideal candidate for designing highly efficient inert MRI contrast agents (Garda, Z., Forgács, A., Do, QN, et al. Physico-chemical properties of Mn II complexes formed with cis-and trans-DO2A: thermodynamic, electrochemical and kinetic studies. Journal of Inorganic Biochemistry, 2016, 163, 206–213. DOI: 10.1016 / j.jinorgbio.2016.07.018).

[0005] Numerous studies on Gd-DOTA-type complexes have shown that the inertness of these complexes can be significantly enhanced by introducing chiral groups into the macrocycle and sidearms. For example, Gd-Et4DOTA, containing four S-ethyl groups, significantly outperforms Gd-DOTA in both kinetic inertness and horizontal exchange rate. Introducing a phenyl group into one of the side arms of Gd-DOTA significantly enhances its kinetic inertness, while introducing an R-ethyl group into the macrocycle further stabilizes the complex; kinetic studies in 1M HCl show that the complex remains almost unchanged after being placed at room temperature for nearly two years (Xu, W., Lu, Y., Xu, J., et al. Rational Design of Gd-DOTA-Type Contrast Agents for Hepatobiliary Magnetic Resonance Imaging[J]. Journal of Medicinal Chemistry, 2023, 66(13), 8993-9005. DOI: 10.1021 / acs.jmedchem.3c00579; Xu, W., Ye, X., Wu, M., et al. Chiral Gd-DOTA as a Versatile Platform for Hepatobiliary and Tumor Targeting MRI Contrast Agents[J]. Journal of Medicinal Chemistry, 2023, 66(21):14669-14682.DOI:10.1021 / acs.jmedchem.3c01183.).

[0006] Therefore, it is necessary to modify 1,4-DO2A using chiral strategies and construct a more stable and inert manganese(II) complex for use as a contrast agent in clinical magnetic resonance imaging to avoid the safety risks of current gadolinium(III) contrast agents. Summary of the Invention

[0007] The object of the present invention is to provide a manganese complex Mn (1,4-Et4DO2A) and its synthesis method and application, wherein the manganese complex Mn (1,4-Et4DO2A) has stronger stability and inertness, and its longitudinal relaxation rate (r1 = 3.1mM -1 s -1 ) is 50% higher than that of the manganese complex Mn(1,4-DO2A); the manganese complex Mn(1,4-Et4DO2A) is expected to become an MRI diagnostic tool to replace gadolinium-based contrast agents, including the detection of HCC.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a manganese complex Mn(1,4-Et4DO2A), wherein the structural formula of the manganese complex Mn(1,4-Et4DO2A) is as follows:

[0010]

[0011] The present invention also provides a method for synthesizing the manganese complex Mn(1,4-Et4DO2A), comprising the following steps:

[0012] (1) Tetraethylcyclorotaxane was mixed with potassium carbonate and acetonitrile, and then an acetonitrile solution containing benzyl bromide was added, and the mixture was concentrated and purified to obtain compound 1;

[0013] (2) Compound 1 was mixed with potassium carbonate, acetonitrile, and tert-butyl bromoacetate, concentrated, added with ethyl acetate, extracted, dried, and concentrated to obtain compound 2;

[0014] (3) Compound 2 was mixed with ethanol, a catalyst was added, and the mixture was evaporated under reduced pressure to obtain compound 3;

[0015] (4) Compound 3 is mixed with hydrochloric acid and evaporated to obtain the ligand 1,4-Et4DO2A;

[0016] (5) Mixing the ligand 1,4-Et4DO2A with MnCl2 and water, adjusting the pH, and obtaining the manganese complex Mn(1,4-Et4DO2A).

[0017] Preferably, in step (1), the mass volume ratio of the tetraethylcyclorotaxane, potassium carbonate, and acetonitrile is 2.5-3.5 g:2.5-3.5 g:25-35 ml; the molar ratio of the tetraethylcyclorotaxane to potassium carbonate is 10-11:21-22; and the acetonitrile solution containing benzyl bromide is prepared by adding 3-4 g of benzyl bromide and 21-22 mmol of benzyl bromide to 15-25 ml of acetonitrile solution.

[0018] Further preferably, the concentration method in step (1) is rotary evaporation under reduced pressure, the concentration temperature is 25-35° C., and the concentration time is 20-30 min; the purification method is silica gel column chromatography, and the solvents used in the purification are petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is 1.5-2.5:1.

[0019] Preferably, in step (2), the mass volume ratio of compound 1, potassium carbonate, acetonitrile, and tert-butyl bromoacetate is 0.8-1.2 g: 0.5-1 g: 15-25 ml: 0.8-1.2 g; the amount of substance ratio of compound 1, potassium carbonate, and tert-butyl bromoacetate is 2.0-2.5: 4.0-4.5: 5.0-5.5; the concentration method is reduced pressure rotary evaporation, the concentration temperature is 25-35 ° C, and the concentration time is 20-30 min; the mass volume ratio of ethyl acetate to compound 1 is preferably 0.8-1.2 g: 25-35 ml; the extraction solvent is hydrochloric acid, the concentration of hydrochloric acid is 1-1.5 M, and the number of extractions is 2-3 times; the temperature of the drying and concentration is 20-30 ° C, and the drying and concentration time is 0.5-1.5 h.

[0020] Preferably, in step (3), the mass volume ratio of the compound 2 to ethanol is 0.5-1.5 g: 25-35 ml; the catalyst is Pd / C; the mass ratio of the compound 2 to the catalyst is 0.5-1.5: 0.2-0.4; the temperature of the reduced pressure steaming is 25-35° C., and the time of the reduced pressure steaming is 20-30 min.

[0021] Preferably, in step (4), the mass volume ratio of the compound 3 to hydrochloric acid is 0.5-1.5 g:15-25 ml; the steaming temperature is 35-45° C., and the steaming time is 30-50 min.

[0022] Preferably, in step (5), the molar ratio of the ligand 1,4-Et4DO2A to MnCl2 is 1-1.05:0.95-1.0.

[0023] The present invention also provides use of the manganese complex Mn(1,4-Et4DO2A) as a contrast agent.

[0024] The present invention also provides the use of the manganese complex Mn(1,4-Et4DO2A) in preparing products for clinical magnetic resonance imaging or for detecting hepatocellular carcinoma.

[0025] The beneficial effects of the present invention compared with the prior art are:

[0026] The present invention improves the stability and inertness of the manganese (II) complex Mn (1,4-DO2A) by modifying its structure. Among the hexadentate manganese (II) complexes tested, the manganese (II) complex Mn (1,4-Et4DO2A) containing four chiral ethyl groups exhibits the highest stability constant (logK MnL ), and the introduction of a rigid phenyl analogue by the side arm can double its inertness. At 25 ° C and 20 MHz, the longitudinal relaxation rate of Mn (1,4-Et4DO2A) (r1 = 3.1mM -1 s -1 ) was 50% higher than that of the manganese(II) complex Mn(1,4-DO2A). In the Zn(II) challenge experiment at pH 6.0 and 37°C, the half-lives of Mn(1,4-DO2A) and Mn(1,4-Et4DO2A) were 0.5 and 12h, respectively, indicating a significant contribution of chiral modification to the enhanced inertness. After further introduction of a phenyl analogue on one side arm, the half-lives of Mn-L1 and Mn-L2 were extended to approximately 1 and 22h, respectively. The performance of manganese(II) complexes in mice was evaluated by 3.0T clinical MRI scanning, and the manganese(II) complex Mn(1,4-Et4DO2A) showed potential for liver MRI, with more than 23% of the injected dose excreted through the hepatobiliary pathway. Its potential for diagnosing liver disease was further validated in an orthotopic mouse model of hepatocellular carcinoma (HCC). In summary, the manganese(II) complex Mn(1,4-Et4DO2A) has the potential to become an alternative MRI diagnostic tool to gadolinium-based contrast agents, including the detection of HCC, due to its high stability and inertness. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 The synthetic route of manganese(II) complex Mn(1,4-Et4DO2A) is shown below;

[0029] Figure 2 The synthetic route of the manganese(II) complex Mn-L1 is shown;

[0030] Figure 3 The synthetic route of manganese(II) complex Mn(1,7-Et4DO2A) is shown below;

[0031] Figure 4 The synthetic route of the manganese(II) complex Mn-L2 is shown in FIG.

[0032] Figure 5 The in vitro toxicity of different manganese (II) complexes on human hepatic stellate cell line LX-2 cells;

[0033] Figure 6 Magnetic resonance imaging images of normal mice after tail vein injection of different manganese (II) complexes, where a, b, and c represent Mn-L1, Mn(1,4-Et4DO2A), and Mn-L2, respectively;

[0034] Figure 7 These are the magnetic resonance imaging results of model mice after tail vein injection of manganese (II) complex Mn(1,4-Et4DO2A) 1 week and 2 weeks after HCC modeling. DETAILED DESCRIPTION

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0037] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0038] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0039] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0040] The present invention provides a manganese complex Mn(1,4-Et4DO2A), wherein the structural formula of the manganese complex Mn(1,4-Et4DO2A) is as follows:

[0041]

[0042] The present invention also provides a method for synthesizing the manganese complex Mn(1,4-Et4DO2A), comprising the following steps:

[0043] (1) Tetraethylcyclorotaxane was mixed with potassium carbonate and acetonitrile, and then an acetonitrile solution containing benzyl bromide was added, and the mixture was concentrated and purified to obtain compound 1;

[0044] (2) Compound 1 was mixed with potassium carbonate, acetonitrile, and tert-butyl bromoacetate, concentrated, added with ethyl acetate, extracted, dried, and concentrated to obtain compound 2;

[0045] (3) Compound 2 was mixed with ethanol, a catalyst was added, and the mixture was evaporated under reduced pressure to obtain compound 3;

[0046] (4) Compound 3 was mixed with hydrochloric acid and evaporated to obtain the ligand 1,4-Et4DO2A;

[0047] (5) Mixing the ligand 1,4-Et4DO2A with MnCl2 and water, adjusting the pH, and obtaining the manganese complex Mn(1,4-Et4DO2A).

[0048] In the present invention, the synthesis method of the tetraethylcyclorotaxane in step (1) is based on the article "Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications" (Dai, L., Jones, CM, Chan, WTK, et al. Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications. Nature Communications, 2018, 9(1), 857.DOI:10.1038 / s41467-018-03315-8); the mass volume ratio of the tetraethylcyclorotaxane, potassium carbonate and acetonitrile is preferably 2.5-3.5 g: 2.5-3.5 g: 25-35 ml, more preferably 2.8-3.2 g: 2.8-3.2 g: 28-32 ml, and further preferably 3.0 g: 3.0 g: 30 ml; the amount of substance ratio of the tetraethylcyclorotaxane and potassium carbonate is preferably 10-11: 21-22, more preferably 10.2-10.8: 21.2-21.8, further preferably 10.4-10.6: 21.4-21.6, and further preferably 10.5: 21.5; the method of adding the acetonitrile solution containing benzyl bromide is preferably dropwise addition, and the frequency of the dropwise addition is preferably 3 0-90 drops / min, more preferably 40-80 drops / min, more preferably 50-70 drops / min, and even more preferably 60 drops / min; the dropwise addition time is preferably 0.5-1h, more preferably 0.6-0.8h, and even more preferably 0.7h; the preparation method of the acetonitrile solution containing benzyl bromide is preferably: adding 3-4g of benzyl bromide with an amount of 21-22mmol to 15-25ml of acetonitrile solution, more preferably adding 3.2-3.8g of benzyl bromide with an amount of 21.2-21.8mmol to 18-24ml of acetonitrile solution, more preferably adding 3.4-3.6g of benzyl bromide with an amount of 21.4-21.6mmol to 20-22ml of acetonitrile solution, and even more preferably adding 3.5g of benzyl bromide with an amount of 21.5 mmol of benzyl bromide is added to 21 ml of acetonitrile solution; after the dropwise addition, stirring is preferably performed, and the stirring temperature is preferably 20-30°C, more preferably 22-28°C, more preferably 24-26°C, and further preferably 25°C; the stirring time is preferably 8-12 hours, more preferably 9-11 hours, and further preferably 10 hours; after the stirring, filtration is preferably performed, and the filtration method is preferably vacuum filtration, and the number of filtrations is preferably 1; the concentration method is preferably vacuum rotary evaporation; the concentration temperature is preferably 25-35°C, more preferably 28-32°C, and further preferably 30°C; the concentration time is preferably 20-30 minutes, more preferably 22-28 minutes, more preferably 24-26 minutes, and further preferably 25 minutes; the purification method is preferably silica gel column chromatography, and the solvents used in the purification are preferably petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is preferably 1.5-2.5:1, more preferably 1.8-2.2:1, and further preferably 2.0:1.

[0049] In the present invention, the mass volume ratio of the compound 1, potassium carbonate, acetonitrile and tert-butyl bromoacetate in step (2) is preferably 0.8-1.2 g: 0.5-1 g: 15-25 ml: 0.8-1.2 g, more preferably 0.9-1.1 g: 0.6-0.8 g: 18-22 ml: 0.9-1.1 g, and further preferably 1.0 g: 0.7 g: 20 ml: 1.0 g; the amount ratio of the compound 1, potassium carbonate and tert-butyl bromoacetate is preferably 2.0-2.5: 4.0-4.5: 5.0-5.5, and further preferably 2.2-2. 4:4.2-4.4:5.2-5.4, more preferably 2.3:4.3:5.3; after the mixing, the mixture is preferably stirred, and the stirring temperature is preferably 20-30°C, more preferably 22-28°C, more preferably 24-26°C, and further preferably 25°C; the stirring time is preferably 8-12h, more preferably 9-11h, and further preferably 10h; after the stirring, the mixture is preferably filtered, and the filtration method is preferably vacuum filtration, and the number of filtrations is preferably 1; the concentration method is preferably vacuum rotary evaporation; The concentration temperature is preferably 25-35°C, more preferably 28-32°C, and more preferably 30°C; the concentration time is preferably 20-30 min, more preferably 22-28 min, more preferably 24-26 min, and even more preferably 25 min; the mass volume ratio of ethyl acetate to compound 1 is preferably 0.8-1.2 g: 25-35 ml; the extraction solvent is preferably hydrochloric acid, and the concentration of hydrochloric acid is preferably 1-1.5 M, more preferably 1.2-1.4 M, and even more preferably 1.3 M; the number of extractions is preferably The extraction is preferably performed 2 to 3 times; after the extraction, an aqueous phase and an organic phase are preferably obtained, the aqueous phase is preferably neutralized with potassium carbonate and then extracted with dichloromethane to obtain an organic phase; the organic phase is preferably dried and concentrated to obtain compound 2; anhydrous sodium sulfate is preferably used as a drying agent during the drying and concentration; the drying and concentration temperature is preferably 20 to 30°C, more preferably 22 to 28°C, more preferably 24 to 26°C, and further preferably 25°C; the drying and concentration time is preferably 0.5 to 1.5h, more preferably 0.8 to 1.2h, and further preferably 1h.

[0050] In the present invention, the mass volume ratio of the compound 2 to ethanol in step (3) is preferably 0.5-1.5 g: 25-35 ml, more preferably 0.6-1.4 g: 26-34 ml, more preferably 0.8-1.2 g: 28-32 ml, and further preferably 1.0 g: 30 ml; the amount of the compound 2 is preferably 1.2-1.5 mmol, more preferably 1.3-1.4 mmol; the catalyst is Pd / C, and the mass fraction of the Pd / C is preferably 8-12%, more preferably 9-11%, and further preferably 10%; the mass ratio of the compound 2 to the catalyst is preferably 0.5-1.5: 0.2-0.4, more preferably 0.6-1.4: 0.3, more preferably 0.8-1.2: 0.3, and further preferably 1.0: 0.3; the addition of the catalyst The mixture is then preferably stirred in a hydrogen environment, and the hydrogen content in the hydrogen environment is preferably 100%; the stirring temperature is preferably 65-75°C, more preferably 66-74°C, more preferably 68-72°C, and further preferably 70°C; the stirring time is preferably 8-12h, more preferably 9-11h, and further preferably 10h; after the stirring, it is preferably filtered, and the filtering method is preferably vacuum filtration, and the number of filtrations is preferably 1; the reduced pressure steaming method is preferably reduced pressure rotary evaporation; the reduced pressure steaming temperature is preferably 25-35°C, more preferably 28-32°C, and further preferably 30°C; the reduced pressure steaming time is preferably 20-30min, more preferably 22-28min, more preferably 24-26min, and further preferably 25min.

[0051] In the present invention, the mass volume ratio of the compound 3 to hydrochloric acid in step (4) is preferably 0.5-1.5 g:15-25 ml, more preferably 0.6-1.4 g:16-24 ml, more preferably 0.8-1.2 g:18-22 ml, and further preferably 1.0 g:20 ml; the amount of the compound 3 is preferably 1.5-2.5 mmol, more preferably 1.8-2.2 mmol, and further preferably 2.0 mmol; the concentration of the hydrochloric acid is preferably 5-7 M, and further preferably 6 M; It is preferred to perform stirring treatment before steaming, and the stirring temperature is preferably 55-65°C, more preferably 56-64°C, more preferably 58-62°C, and further preferably 60°C; the stirring time is preferably 8-12h, more preferably 9-11h, and further preferably 10h; the steaming temperature is preferably 35-45°C, more preferably 38-42°C, and further preferably 40°C; the steaming time is preferably 30-50min, more preferably 35-45min, and further preferably 40min.

[0052] In the present invention, the molar ratio of the ligand 1,4-Et4DO2A to MnCl2 in step (5) is preferably 1-1.05:0.95-1.0, more preferably 1.02-1.04:0.96-0.98, and more preferably 1.03:0.97; the mixing is preferably performed after stirring, and the stirring time is preferably 8-10 hours, and more preferably 9 hours; the stirring temperature is preferably 22-28°C, more preferably 24-26°C, and more preferably 25°C; the manganese complex Mn(1,4-Et4DO2A) is preferably a manganese (II) complex Mn(1,4-Et4DO2A).

[0053] The present invention also provides use of the manganese complex Mn(1,4-Et4DO2A) as a contrast agent.

[0054] The present invention also provides the use of the manganese complex Mn(1,4-Et4DO2A) in preparing products for clinical magnetic resonance imaging or for detecting hepatocellular carcinoma.

[0055] General Information: All chemicals were purchased from commercial suppliers, including Anaiji Chemical (Shanghai, China), Shanghai MacLean Biochemical Technology Co., Ltd., and Shanghai Aladdin Biochemical Technology Co., Ltd., and were used without further purification. 1 H and 13C nuclear magnetic resonance (NMR) spectra were measured using a QUANTUM-I-400 MHz NMR spectrometer (purchased from Wuhan Zhongke Oxford Spectroscopy Technology Co., Ltd.). Deuterated solvents included CDCl3, D3O, and DMSO-d6 (purchased from Shanghai MacLean Biochemical Technology Co., Ltd.). Standard hydrochloric acid (1 M) and potassium hydroxide (2 M) solutions were purchased from Shenzhen Bolinda Technology Co., Ltd. Ultrapure water (Milli-Q, 18.2 MΩ·cm) was used for titration studies. -1 ) before use. The Mn(II) complex was characterized using an Agilent ultra-performance liquid chromatography (UPLC) system (1290 InfinityIH-6135MS) equipped with a diode array (DAD) and electrospray ionization (ESI)-mass spectrometry (MS) detector. Quantitative analysis of Mn(II) was performed using an Agilent 7850 inductively coupled plasma mass spectrometer (ICP-MS). A calibration curve was prepared using a Mn(II) standard (purchased from National Standards (Beijing) Inspection and Certification Co., Ltd.) in 2% nitric acid, with 1 ppb of Tb(III) used as an internal standard.

[0056] Samples were analyzed using a Waters Alliance e2695 reversed-phase high-performance liquid chromatography (RP-HPLC) system equipped with a photodiode array (PDA) detector and a Waters C18 column (5 μm, 4.6 × 150 mm). Initial conditions were: a solution containing 0.05% trifluoroacetic acid (TFA) (phase A, 90%) and acetonitrile (phase B, 10%) at a flow rate of 1 mL / min. The proportion of phase B was then increased to 100% over 10 minutes and then returned to 10% over the next 2 minutes. The column was flushed for an additional 3 minutes before the next injection.

[0057] Preparative separations of the compounds were performed using a Waters semi-preparative HPLC system equipped with a PDA detector and a Waters C18 column (5 μm, 19 × 250 mm). Mobile phase A consisted of 0.05% TFA in water, and mobile phase B consisted of acetonitrile. The acetonitrile ratio was linearly increased from 10% to 50% over 20 minutes, then returned to 10% over 2 minutes. The flow rate was maintained at 7 mL / min, and the next injection was performed after a 3-minute rinse.

[0058] Example 1

[0059] A method for synthesizing the manganese (II) complex 1,4-Et4DO2A comprises the following steps:

[0060] (1) Tetraethylcyclorotaxane (Et4cyclen, the tetraethylcyclorotaxane is 3b in Fig. 1: R=Et) was synthesized according to the synthesis method described in the article "Chiral DOTAchelators as an improved platform for biomedical imaging and therapy applications". 3.0 g of the synthesized tetraethylcyclorotaxane (10.5 mmol) was mixed with 2.9 g of potassium carbonate (21.1 mmol) and 30 ml of acetonitrile. An acetonitrile solution containing benzyl bromide (preparation method: adding 3.6 g of benzyl bromide (21.1 mmol) to 20 ml of acetonitrile solution) was slowly added dropwise at 60 drops / min. The mixture was added dropwise for 1 hour, stirred at 25°C for 10 hours, filtered under reduced pressure once, concentrated at 30°C for 25 minutes, and purified by silica gel column chromatography for 6 hours using petroleum ether and ethyl acetate (volume ratio: 2:1) as solvent to obtain compound 1. Compound 1 was tested as follows:

[0061] 1 H NMR (400MHz, CDCl3, δppm): 0.83(t,J=7.52Hz,3H),0.99(m,9H),1.09(m,2H),1.29(m,1H),1.73(m,4H),2.10(t,J=11.72Hz,1H),2.45(m,4H),2.76 (m,7H),2.90(m,2H),3.04(d,J=13.32Hz,1H),3.44(d,J=13.16Hz,1H),3 .91(d,J=13.20Hz,1H),6.94(s,2H),7.18(m,6H),7.39(d,J=7.24Hz,2H).

[0062] 13 C NMR (100MHz, CDCl3, δppm): 10.18, 10.98, 12.19, 12.97, 17.43, 18.60, 24.61, 50.19, 52.8 3,55.16,56.99,57.98,126.68,126.97,128.08,128.31,129.23,129.66,139.75,139.91.

[0063] ESI-MS m / z: [M+H]+ calculated value 465.4, found value 465.4.

[0064] (2) 1.0 g, 2.1 mmol of compound 1 was mixed with 0.6 g, 4.3 mmol of potassium carbonate, 20 ml of acetonitrile, and 1.0 g, 5.2 mmol of tert-butyl bromoacetate. The mixture was stirred at 25°C for 10 h, filtered once under reduced pressure, concentrated at 30°C for 25 min, and 30 ml of ethyl acetate was added. The mixture was extracted three times with 1 M hydrochloric acid to obtain an aqueous phase and an organic phase. The aqueous phase was neutralized with potassium carbonate and extracted three times with 30 ml of dichloromethane to obtain an organic phase. The organic phase was dried and concentrated with anhydrous sodium sulfate at 25°C for 1 h to obtain compound 2. Compound 2 was tested as follows:

[0065] 1 H NMR (400MHz, CDCl3, δppm): 0.88 (t, J = 7.28Hz, 3H), 0.99 (m, 9H), 1.13 (m, 1H), 1.30 ( m,3H),1.44(s,9H),1.51(s,9H),1.67(m,3H),1.87(m,3H),2.12(m,2H),2.31(dd,J1 =9.04Hz, J2=12.44Hz,1H),2.80(m,2H),3.01(m,5H),3.14(m,3H),3.23(d,J=13.92H z, 1H), 3.30 (m, 2H), 3.68 (d, J = 13.80Hz, 1H), 3.91 (d, J = 13.88Hz, 1H), 7.27 (m, 10H).

[0066] 13 C NMR (100MHz, CDCl3, δppm): 11.53, 11.90, 23.04, 23.14, 23.53, 28.13, 28.18, 47.96, 48.06, 49.85, 52.26, 52.64 ,55.66,56.29,80.30,80.42,126.53,126.56,128.05,128.11,128.68,128.72,140.75,141.06,171.91,172.10.

[0067] ESI-MS m / z: [M+H] + Calculated value 693.5, measured value 693.6.

[0068] (3) 1.0 g, 1.4 mmol of compound 2 was mixed with 30 ml of ethanol, and 0.3 g of a 10% mass fraction of Pd / C catalyst was added. The mixture was stirred at 70°C for 10 h in an environment with a hydrogen content of 100%, filtered once under reduced pressure, and rotary evaporated at 30°C under reduced pressure for 25 min to obtain compound 3. Compound 3 was tested as follows:

[0069] 1 H NMR (400MHz, CDCl3, δppm): 0.90 (m, 12H), 1.13 (s, 1H), 1.24 (m, 1H), 1.44 (s, 18H), 1.63 (m, 5H), 2.57 (m, 5H), 2.88 (s, 4H), 3.36 (m, 4H).

[0070] 13 C NMR (100MHz, CDCl3, δppm): 10.46, 10.63, 11.70, 12.43, 19.78, 20.78, 23.52, 25.33, 2 8.09,28.13,29.70,43.97,44.02,50.43,52.57,54.78,60.90,81.18,171.41,171.53.

[0071] ESI-MS m / z: [M+H] + Calculated value 513.4, measured value 513.4

[0072] (4) 1.0 g, 2.0 mmol of compound 3 was mixed with 20 ml, 6 M hydrochloric acid, stirred at 60°C for 10 h, and steamed at 40°C for 40 min to obtain the ligand 1,4-Et4DO2A. The ligand 1,4-Et4DO2A was tested as follows:

[0073] 1 H NMR (400MHz, CDCl3, δppm): 1.07 (m, 12H), 1.57 (m, 4H), 1.80 (m, 1H), 1.96 (m, 3H), 2.65 (t, J = 13.16Hz, 0.5H), 2.88 (m, 0. 5H), 3.22 (m, 10H), 3.35 (d, J = 14.48Hz, 1H), 3.45 (d, J = 16.48Hz, 1H), 3.57 (d, J = 17.00Hz, 2H), 3.80 (d, J = 16.44Hz, 1H).

[0074] 13 C NMR (100MHz, CDCl3, δppm): 9.05, 9.15, 9.28, 9.37, 10.24, 10.34, 10.91, 18.30, 18.73, 21.07, 23.95,43.42,45.65,50.48,51.37,52.41,54.20,54.59,55.36,56.92,62.05,171.60,176.28.

[0075] ESI-MS m / z: [M+H]+ calculated value 401.3, found value 401.2.

[0076] (5) 0.8 g, 2.0 mmol, of the ligand 1,4-Et4DO2A and 0.24 g, 1.9 mmol, of MnCl2 were dissolved in 30 ml of aqueous solution (pH 7.4) and stirred at 25°C for 10 h under a nitrogen atmosphere to obtain the manganese (II) complex Mn(1,4-Et4DO2A). The manganese (II) complex Mn(1,4-Et4DO2A) was tested as follows:

[0077] ESI-MS m / z: [M+H]+ calculated value 454.2, found value 454.3.

[0078] Example 2

[0079] A method for synthesizing the manganese (II) complex 1,4-Et4DO2A comprises the following steps:

[0080] (1) Tetraethylcyclorotaxane was synthesized according to the synthesis method described in the article "Chiral DOTAchelators as an improved platform for biomedical imaging and therapy applications". 2.5 g of the synthesized tetraethylcyclorotaxane (10 mmol) was mixed with 2.5 g of potassium carbonate (21 mmol) and 25 ml of acetonitrile. An acetonitrile solution containing benzyl bromide (preparation method: add 3 g of benzyl bromide (21 mmol) to 15 ml of acetonitrile solution) was slowly added dropwise at 90 drops / min for 0.5 h. The mixture was stirred at 20° C. for 12 h, filtered under reduced pressure once, and rotary evaporated under reduced pressure at 35° C. for 20 min. The mixture was purified by silica gel column chromatography for 6 h using petroleum ether and ethyl acetate (volume ratio: 1.5:1) as solvent to obtain compound 1.

[0081] (2) 0.8 g, 2.0 mmol of compound 1 was mixed with 0.5 g, 4.0 mmol of potassium carbonate, 15 ml of acetonitrile, and 0.8 g, 5.0 mmol of tert-butyl bromoacetate, stirred at 20°C for 12 h, filtered once under reduced pressure, and rotary evaporated at 35°C for 20 min. 25 ml of ethyl acetate was added, and the mixture was extracted twice with 1.2 M hydrochloric acid to obtain an aqueous phase and an organic phase. The aqueous phase was neutralized with potassium carbonate and extracted with dichloromethane to obtain an organic phase. The organic phase was dried and concentrated with anhydrous sodium sulfate at 30°C for 0.5 h to obtain compound 2.

[0082] (3) 0.5 g, 1.2 mmol of compound 2 was mixed with 25 ml of ethanol, and 0.2 g of 8% Pd / C catalyst was added. The mixture was stirred at 65°C for 12 h in an environment with 100% hydrogen content, filtered under reduced pressure once, and rotary evaporated at 35°C under reduced pressure for 20 min to obtain compound 3.

[0083] (4) 0.5 g, 1.5 mmol of compound 3 was mixed with 15 ml, 5 M hydrochloric acid, stirred at 55 °C for 12 h, and steamed at 45 °C for 30 min to obtain the ligand 1,4-Et4DO2A.

[0084] (5) 0.8 g, 2.0 mmol, of the ligand 1,4-Et4DO2A and 0.24 g, 1.9 mmol, of MnCl2 were dissolved in 30 ml of aqueous solution (pH 7.4) and stirred at 28°C for 8 h under a nitrogen atmosphere to obtain the manganese (II) complex Mn(1,4-Et4DO2A).

[0085] Example 3

[0086] A method for synthesizing the manganese (II) complex 1,4-Et4DO2A comprises the following steps:

[0087] (1) Tetraethylcyclorotaxane was synthesized according to the synthesis method described in the article "Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications". 3.5 g of the synthesized tetraethylcyclorotaxane (11 mmol) was mixed with 3.5 g of potassium carbonate (22 mmol) and 35 ml of acetonitrile. An acetonitrile solution containing benzyl bromide (preparation method: 4 g of benzyl bromide (22 mmol) was added to 25 ml of acetonitrile solution) at a rate of 30 drops / min. The mixture was added dropwise for 0.7 h, stirred at 30° C. for 8 h, filtered under reduced pressure once, and rotary evaporated under reduced pressure at 25° C. for 30 min. The mixture was purified by silica gel column chromatography for 6 h using petroleum ether and ethyl acetate (volume ratio: 2.5:1) as solvent to obtain compound 1.

[0088] (2) 1.2 g, 2.5 mmol of compound 1 was mixed with 1 g, 4.5 mmol of potassium carbonate, 25 ml of acetonitrile, and 1.2 g, 5.5 mmol of tert-butyl bromoacetate, stirred at 30°C for 8 h, filtered once under reduced pressure, and rotary evaporated at 25°C for 30 min. 35 ml of ethyl acetate was added, and the mixture was extracted three times with 1.5 M hydrochloric acid to obtain an aqueous phase and an organic phase. The aqueous phase was neutralized with potassium carbonate and then extracted with dichloromethane to obtain an organic phase. The organic phase was dried and concentrated with anhydrous sodium sulfate at 20°C for 1.5 h to obtain compound 2.

[0089] (3) 1.5 g, 1.5 mmol of compound 2 was mixed with 35 ml of ethanol, and 0.4 g of 12% Pd / C catalyst was added. The mixture was stirred at 75°C for 8 h in a hydrogen atmosphere with a 100% hydrogen content. The mixture was filtered under reduced pressure once and rotary evaporated at 25°C for 30 min to obtain compound 3.

[0090] (4) 1.5 g, 2.5 mmol of compound 3 was mixed with 25 ml, 7 M hydrochloric acid, stirred at 65 °C for 8 h, and steamed at 35 °C for 50 min to obtain the ligand 1,4-Et4DO2A.

[0091] (5) 0.8 g, 2.0 mmol, of the ligand 1,4-Et4DO2A and 0.24 g, 1.9 mmol, of MnCl2 were dissolved in 30 ml of aqueous solution (pH 7.4) and stirred at 22°C for 9 h under a nitrogen atmosphere to obtain the manganese (II) complex Mn(1,4-Et4DO2A).

[0092] Comparative Example 1 Synthesis of Manganese (II) Complex Mn-L1

[0093] 4b' in Table 1 was prepared according to the method described in "cis-diprotected cyclams and cyclens: A new route to symmetrically or asymmetrically 1,4-disubstituted tetraazamacrocycles and to asymmetrically tetrasubstituted derivatives" (Bellouard, F., Chuburu, F., Kervarec, N., et al. cis-diprotected cyclams and cyclens: A new route to symmetrically or asymmetrically 1,4-disubstituted tetraazamacrocycles and to asymmetrically tetrasubstituted derivatives [J]. Journal of the Chemical Society, Perkin Transactions 1, 1999, 23, 3499-3505. DOI: 10.1002 / chin.200019138.), and the structural formula of compound 4 is as follows: Figure 2 As shown by “4” in .

[0094] 2.0 g, 5.6 mmol of compound 4 and 1.9 g, 6.7 mmol of 4-(1-bromo-2-methoxy-2-oxoethyl)benzoate were dissolved in 30 mL of acetonitrile and stirred at room temperature overnight under a nitrogen atmosphere. The mixture was concentrated and dissolved in 30 mL of ethyl acetate and extracted three times with 30 mL of 1 M HCl solution. The aqueous phase was neutralized with K2CO3 and extracted three times with 30 mL of DCM. The solvent was evaporated to obtain compound 5. Compound 5 was tested as follows:

[0095] 1 H NMR (400MHz, CDCl3, δppm): 2.71 (s, 4H), 2.90 (br, 4H), 3.05 (s, 4H), 3.16 (br, 2H), 3.33 (d, J = 15.68Hz, 2H), 3.77 (d, J = 3.76Hz, 2H), 3.8 1(s,3H),3.96(s,3H),4.71(s,1H),6.87(s,2H),7.30(m,4H),7.41(m,3H),7.46(m,2H),7.53(d,J=8.08Hz,2H),8.13(d,J=8.12Hz,2H).

[0096] 13 C NMR (100MHz, CDCl3, δppm): 48.61, 49.09, 50.05, 51.14, 52.23, 62.85, 127.62, 128.07, 12 8.51,128.66,129.49,129.70,129.81,130.08,130.68,134.30,138.39,166.30,171.57.

[0097] ESI-MS m / z: [M+H]+ calculated value 559.3, found value 559.1.

[0098] 2.0 g, 3.5 mmol of compound 5 and 0.5 g, 3.5 mmol of K2CO3 were dissolved in 30 mL of acetonitrile, 0.7 g, 4.0 mmol of ethyl bromoacetate were added, and the mixture was stirred at room temperature for 4 h. After filtration, the solution was concentrated under reduced pressure, and the residue was dissolved in 30 mL of ethyl acetate and extracted three times with 30 mL of 1 M HCl solution. The combined aqueous phases were neutralized with K2CO3 and then extracted three times with 30 mL of DCM. The organic phase was dried and concentrated to obtain 1.9 g of compound 6 (yield 86%). Compound 6 was tested as follows:

[0099] 1H NMR (400MHz, CDCl3, δppm): 1.24 (m, 3H), 2.63 (m, 11H), 2.85 (m, 7H), 3.21 (s, 2H), 3.49 (m, 5H), 3.75 (s, 3H), 3.9 5(s,3H),4.13(m,2H),4.63(s,1H),7.29(m,10H),7.39(m,2H),7.52(d,J=5.80Hz,2H),8.01(d,J=5.04Hz,2H).

[0100] 13 C NMR (100MHz, CDCl3, δppm): 14.34, 49.71, 51.53, 52.17, 52.39, 52.56, 52.78, 55.06, 59.93, 60.09, 68.20, 126. 78,128.07,128.12,128.92,129.04,129.09,129.47,129.52,139.71,139.91,142.69,166.93,171.68,172.33.

[0101] ESI-MS m / z: [M+H]+ calculated value 645.4, found value 645.2.

[0102] 1.0 g, 1.5 mmol of compound 10 was dissolved in 30 mL of methanol, and 0.2 g, 6 mmol of NaOH dissolved in 1 mL of water was added. The mixture was stirred at 50°C overnight. The solvent was evaporated to obtain crude compound 7 as its sodium salt. 0.3 g of 10% Pd / C and 30 mL of ethanol were added, and the mixture was heated at 60°C under a hydrogen atmosphere overnight. After evaporation of the solvent, the residue was purified by semi-preparative HPLC to obtain manganese(II) complex L2. Ligand L1 was tested as follows:

[0103] 1 H NMR (400MHz, D2O, δppm): 2.34 (s, 1H), 2.47 (s, 1H), 3.01 (m, 14H), 3.42 (s, 1H), 3.62 (s, 1H), 7.17 (d, J = 8.20Hz, 2H), 7.75 (d, J = 7.76Hz, 2H).

[0104] 13 C NMR (100MHz, D2O, δppm): 41.30, 42.58, 43.22, 45.15, 46.15, 51.18, 52.27, 53.76, 64.88, 130.08, 137.32, 169.33, 171.66, 173.72.

[0105] ESI-MS m / z: [M+H]+ calculated value 409.2, found value 409.3.

[0106] 0.8 g, 2.0 mmol, of ligand L1 and 0.24 g, 1.9 mmol, of MnCl2 were dissolved in 30 ml of aqueous solution (pH 7.4) and stirred at room temperature for 10 h under a nitrogen atmosphere to obtain the manganese (II) complex Mn-L1. The manganese (II) complex Mn-L1 was tested as follows:

[0107] ESI-MS m / z: [M+H]+ calculated value 462.1, found value 462.2.

[0108] Comparative Example 2 Synthesis of Manganese (II) Complex Mn (1,7-Et4DO2A)

[0109] 3.0 g, 4.6 mmol of Et4cyclen-4Bn (the synthesis of Et4cyclen-4Bn is described in the article "Chiral DOTAchelators as an improved platform for biomedical imaging and therapy applications", where Et4cyclen-4Bn is 2b in Fig. 1 described in the article: R = Et) and 0.5 g of Pd / C (10%) were dissolved in 30 mL of acetic acid and stirred at room temperature overnight under a hydrogen atmosphere. After filtration and concentration, the residue was neutralized with K2CO3, and the aqueous phase was extracted three times with 30 mL of DCM and purified by silica gel column chromatography (petroleum ether / ethyl acetate = 2 / 1) to obtain 1.8 g of compound 8 (yield 82%). Compound 8 was tested as follows:

[0110] 1 H NMR (400MHz, CDCl3, δppm): 0.89 (m, 12H), 1.28 (d, J = 5.68Hz, 1H), 1.58 (s, 2H), 1.78 (s, 2H), 2.26 (m, 2H) ,2.71(m,11H),2.87(s,2H),3.01(d,J=13.32Hz,2H),3.89(d,J=13.36Hz,2H),7.28(m,2H),7.37(m,8H).

[0111] 13 C NMR (100MHz, CDCl3, δppm): 10.47, 12.65, 17.23, 25.52, 44.22, 52.25, 52.72, 53.66, 56.92, 127.13, 128.38, 129.19, 140.00.

[0112] ESI-MS m / z: [M+H] + Calculated value 465.4, measured value 465.3.

[0113] 1.0 g, 2.1 mmol of compound 8, 0.6 g, 4.2 mmol of K2CO3, 1.0 g, 5.2 mmol of tert-butyl bromoacetate were dissolved in 30 mL of acetonitrile and stirred at room temperature overnight. After filtration and concentration, the residue was dissolved in 30 mL of ethyl acetate and extracted three times with 30 mL of 1 M HCl solution. After the aqueous phase was neutralized, it was extracted three times with 30 mL of DCM to obtain compound 9. Compound 9 was tested as follows:

[0114] 1 H NMR (400MHz, CDCl3, δppm): 0.90 (t, J = 7.24Hz, 6H), 1.09 (t, J = 7.32Hz, 6H), 1.43 (s, 18H), 1.66 ( m,3H),1.86(m,2H),1.98(dd,J1=12.4Hz,J2=9.04Hz,2H),2.21(dd,J1=12.4Hz,J2=8.88Hz,2H) ,2.76(d,J=15.84Hz,2H),2.90(d,J=11.36Hz,2H),3.03(s,4H),3.13(d,J=15.88Hz,2H),3.18( d,J=13.80Hz,2H),3.27(d,J=11.32Hz,2H),3.91(d,J=13.80Hz,2H),7.25(m,2H),7.35(m,8H).

[0115] 13 C NMR (100MHz, CDCl3, δppm):11.37,11.98,22.96,23.32,28.11,47.81,49.54, 52.25,52.79,55.70,56.06,80.31,126.61,128.12,128.67,140.82,171.93.

[0116] ESI-MS m / z: [M+H] + Calculated value 693.5, measured value 693.5.

[0117] 1.0 g, 1.4 mmol of compound 9 and 0.3 g of Pd / C (10%) were mixed in 30 mL of ethanol and heated at 70° C. under a hydrogen atmosphere to obtain compound 10. Compound 10 was tested as follows:

[0118] 1H NMR (400MHz, CDCl3, δppm): 0.86 (m, 12H), 1.02 (s, 2H), 1.18 (m, 2H), 1.41 ( s,18H),1.48(m,2H),1.66(s,2H),2.51(m,10H),3.16(m,2H),3.26(m,4H).

[0119] 13 C NMR (100MHz, CDCl3, δppm): 10.10, 12.36, 20.08, 24.39, 28.13, 44.51, 51.60, 53.63, 57.18, 80.40, 171.85.

[0120] ESI-MS m / z: [M+H] + Calculated value 513.4, measured value 513.3.

[0121] Compound 10 was dissolved in 6M HCl solution and stirred at 60°C overnight to obtain the ligand 1,7-Et4DO2A. The ligand 1,7-Et4DO2A was tested as follows:

[0122] 1 H NMR (400MHz, D2O, δppm): 0.87 (m, 12H), 1.06 (m, 2H), 1.21 (br, 2H), 1.56 (br, 2H), 1.72 (s, 2H), 2.52 (m, 10H), 2.99 (s, 2H), 3.19 (d, J = 15.6Hz, 2H).

[0123] 13 C NMR (100MHz, D2O, δppm): 10.29, 12.12, 12.16, 18.89, 23.34, 39.43, 43.30, 46.65, 53.39, 56.85, 58.71, 64.90, 181.25.

[0124] ESI-MS m / z: [M+H] + Calculated value 401.3, measured value 401.3.

[0125] 0.8 g, 2.0 mmol, of the ligand 1,7-Et4DO2A was dissolved with 0.24 g, 1.9 mmol, of MnCl2 in 30 ml of a pH 7.4 aqueous solution and stirred at room temperature under a nitrogen atmosphere for 10 h to obtain the manganese (II) complex Mn(1,7-Et4DO2A). The manganese (II) complex Mn(1,7-Et4DO2A) was tested as follows:

[0126] ESI-MS m / z: [M+H]+ Calculated value 454.2, measured value 454.3.

[0127] Comparative Example 3 Synthesis of Manganese (II) Complex Mn-L2

[0128] Et4cyclen-4Bn was dissolved in acetic acid and reacted in a hydrogen atmosphere under the catalysis of Pd / C to obtain Et4cyclen-3Bn. Et4cyclen-3Bn was tested as follows:

[0129] 1 H NMR (400MHz, CDCl3, δppm): 0.91 (m, 12H), 1.08 (m, 3H), 1.62 (m, 3H), 1.76 (m, 1H), 1.91 (s, 2H), 2.15 (d, J = 8.56Hz, 1H), 2.26 (d, J = 7.68Hz, 1H), 2.85 (br, 10H), 3.18 (m, 2H), 3.33 (s, 1H), 3.43 (s, 1H), 3.63 (d, J = 13.68Hz, 1H), 3.83 (s, 1H), 7.11 (s, 4H), 7.30 (m, 9H), 7.44 (s, 2H).

[0130] ESI-MS m / z: [M+H] + Calculated value 555.4, measured value 555.4.

[0131] 2.0 g, 3.6 mmol of Et4cyclen-3Bn, 0.5 g, 3.6 mmol of K2CO3, and 0.8 g, 4.3 mmol of tert-butyl bromoacetate were dissolved in 30 mL of acetonitrile and stirred at room temperature for 4 h. After filtration, the solid was washed with acetonitrile and water, and dried at 50°C to obtain 2.0 g of compound 11 (yield 83%). Compound 11 was tested as follows:

[0132] 1H NMR (400MHz, CDCl3, δppm): 0.91 (t, J = 7.28Hz, 3H), 1.01 (m, 6H), 1.09 (t, J = 7.32Hz, 3H), 1.29 (m,2H),1.44(s,9H),1.54(m,11H),1.72(m,3H),1.89(m,2H),2.07(m,2H),2.25(dd,J1=9.04 Hz,J2=12.52Hz,1H),2.78(d,J=15.84Hz,1H),2.91(d,J=12.48Hz,1H),3.04(m,9H),3.23(d, J=13.96Hz,1H),3.33(d,J=12.84Hz,1H),3.70(m,2H),3.94(d,J=13.96Hz,1H),7.30(m,15H).

[0133] 13 C NMR (100MHz, CDCl3, δppm):11.43,11.87,11.93,11.99,22.86,23.06,23.29,28.12,47.67,47.81,52.31,52.65, 52.75,55.77,80.34,126.49,126.53,126.59,128.06,128.15,128.63,128.67,140.78,140.94,141.00,172.01.

[0134] ESI-MS m / z: [M+H]+ calculated value 669.5, found value 669.5.

[0135] 2.0 g, 3.0 mmol of compound 11 and 0.3 g of Pd / C (10%) were dissolved in 30 mL of ethanol and stirred at 80°C overnight under a hydrogen atmosphere. After filtration, the solvent was evaporated to obtain compound 12. Compound 12 was tested as follows:

[0136] 1 H NMR (400MHz, CDCl3, δppm): 0.88 (m, 12H), 1.20 (m, 3H), 1.44 (s, 9H), 1.55 (m, 4H), 2.16 (t, J = 11.20Hz, 1H), 2.4 3(m,5H),2.65(m,3H),2.80(d,J=9.96Hz,1H),2.89(d,J=15.84Hz,1H),3.29(d,J=16.56Hz,1H),3.34(br,1H).

[0137] 13C NMR (100MHz, CDCl3, δppm):10.12,10.34,10.46,12.36,19.00,24.65,25.05,25.24,2 5.32,28.16,44.85,44.88,49.29,51.57,53.52,54.58,56.57,57.59,80.75,171.60.

[0138] ESI-MS m / z: [M+H]+ calculated value 399.4, found value 399.3.

[0139] 1.0 g, 2.5 mmol, of compound 12 and 0.9 g, 3.0 mmol, of methyl 4-(1-bromo-2-methoxy-2-oxoethyl)benzoate were dissolved in 30 mL of acetonitrile and reacted at 50°C for 2 days under a nitrogen atmosphere. The solvent was evaporated to yield compound 13, which was dissolved in 30 mL of methanol. 0.4 g, 10.0 mmol, of NaOH dissolved in 2 mL of water were added, and the mixture was stirred at 50°C overnight. The mixture was purified by reverse-phase HPLC to yield ligand L2. Ligand L2 was tested as follows:

[0140] 1 H NMR (400MHz, D2O, δppm): -0.02(m,1H),0.35(t,J=7.24Hz,3H),0.68(m,2H),0.82(t,J=7.32H z,3H),0.88(t,J=7.48Hz,3H),0.99(t,J=7.40Hz,3H),1.28(m,1H),1.49(m,4H),1.90(m,1H), 2.46(t,J=12.68Hz,1H),2.83(m,7H),2.99(m,2H),3.31(m,1H),3.86(m,1H),4.02(d,J=18.04 Hz, 1H), 4.19 (d, J = 18.16Hz, 1H), 4.82 (s, 1H), 7.27 (d, J = 7.88Hz, 2H), 7.90 (d, J = 8.40Hz, 2H).

[0141] 13 C NMR(100MHz,D2O,δppm):9.73,10.11,10.19,10.29,19.41,20.67,21.01,21.99,37.64,38.17,42.31,50 .70,51.67,55.12,57.45,57.60,62.87,64.28,129.52,130.12,130.20,138.90,169.60,169.78,174.54.

[0142] ESI-MS m / z: [M+H]+ calculated value 521.3, found value 521.2.

[0143] 1.0 g, 2.0 mmol of ligand L2 and 0.24 g, 1.9 mmol of MnCl2 were dissolved in 30 ml of aqueous solution (pH 7.4) and stirred at room temperature for 10 h under a nitrogen atmosphere to obtain the manganese (II) complex Mn-L2. The manganese (II) complex Mn-L2 was tested as follows:

[0144] ESI-MS m / z: [M+H]+ calculated value 574.3, found value 574.3.

[0145] Comparative Example 4 Preparation of ligand 1,4-DO2A

[0146] 1,4-DO2A was prepared according to the method described in "Bellouard, F., Chuburu, F., Kervarec, N., et al. cis-diprotected cyclams and cyclens: A new route to symmetrically or asymmetrically 1,4-disubstituted tetraazamacrocycles and to asymmetrically tetrasubstituted derivatives [J]. Journal of the Chemical Society, Perkin Transactions 1, 1999, 23, 3499-3505. DOI: 10.1002 / chin.200019138.", wherein the 1,4-DO2A is 8b' in Table 2 described in the article.

[0147] Comparative Example 5 Preparation of ligand 1,7-DO2A

[0148] 1,7-DO2A was prepared according to the method described in "Kovacs, Z. and Sherry, AD. A general synthesis of 1,7-disubstituted 1,4,7,10-tetraazacyclododecanes [J]. Cheminform, 1995, 26(24): 185-186. DOI: 10.1002 / chin.199524157.", wherein the 1,7-DO2A is 4a in Table 2 described in the article.

[0149] Comparative Example 6 Preparation of Manganese (II) Complexes Mn (1,4-DO2A) and Mn (1,7-DO2A)

[0150] 0.6 g (2.0 mmol) of the ligand 1,4-DO2A prepared in Comparative Example 4 and 0.24 g (1.9 mmol) of MnCl2 were dissolved in 30 ml of a pH 7.4 aqueous solution and stirred at room temperature under a nitrogen atmosphere for 10 hours to obtain the manganese (II) complex Mn(1,4-DO2A). The manganese (II) complex Mn(1,4-DO2A) was tested as follows:

[0151] ESI-MS m / z: [M+H]+ calculated value 342.1, found value 342.1.

[0152] The structural formula of the manganese (II) complex Mn (1,4-DO2A) is as follows:

[0153]

[0154] 0.6 g (2.0 mmol) of the ligand 1,7-DO2A prepared in Comparative Example 5 and 0.24 g (1.9 mmol) of MnCl2 were dissolved in 30 ml of a pH 7.4 aqueous solution and stirred at room temperature under a nitrogen atmosphere for 10 hours to obtain the manganese (II) complex Mn(1,7-DO2A). The manganese (II) complex Mn(1,7-DO2A) was tested as follows:

[0155] ESI-MS m / z: [M+H]+ calculated value 342.1, found value 342.1.

[0156] The structural formula of the manganese (II) complex Mn (1,7-DO2A) is as follows:

[0157]

[0158] Test Example 1 Calculation of hydrophobic parameter (logP)

[0159] The logP of the manganese (II) complexes prepared in Example 1 and Comparative Examples 1-3 were determined and calculated according to the high performance liquid chromatography (HPLC) method described in the article "Chiral Gd-DOTA as a Versatile Platform for Hepatobiliary and Tumor Targeting MRI Contrast Agents" (Xu, W., Ye, X., Wu, M., et al. Chiral Gd-DOTA as a Versatile Platform for Hepatobiliary and Tumor Targeting MRI Contrast Agents [J]. Journal of Medicinal Chemistry, 2023, 66 (21): 14669-14682, DOI: 10.1021 / acs.jmedchem.3c01183). The results are shown in Table 1.

[0160] Table 1. LogP values ​​of manganese(II) complexes.

[0161] Manganese(II) complexes Mn(1,4-Et4DO2A) <![CDATA[Mn-L1]]> Mn(1,7-Et4DO2A) <![CDATA[Mn-L2]]> LogP 1.00 0.58 0.99 0.96

[0162] As can be seen from Table 1, the log P value of the manganese (II) complex Mn (1,4-Et4DO2A) is 1.00, the log P value of the manganese (II) complex Mn-L1 is 0.58, the log P value of the manganese (II) complex Mn (1,7-Et4DO2A) is 0.99, and the log P value of the manganese (II) complex Mn-L2 is 0.96.

[0163] Test Example 2 Determination of protonation constant and thermodynamic stability constant

[0164] pH-potentiometric titrations of ligands 1,4-Et4DO2A, L1, 1,7-Et4DO2A, and L2 were performed at 25°C using a Metrohm Eco automated potentiometric titrator (purchased from Metrohm, China). A Mn(II) stock solution was prepared by dissolving MnCl2·4H2O in ultrapure water and adjusting to pH 6 with 1 M HCl. Its concentration was calibrated by ICP-MS. Ligand content was determined by stepwise titration of Mn(II) solutions of known concentration and plotting a 1 / T2 curve. 3 mM ligand was dissolved in 0.1 M KCl solution and adjusted to pH 1.7 in a total volume of 10 mL. Under nitrogen, the solution was titrated to pH 12.0 with 0.5 M KOH solution in 10 μL steps. Volume-pH data were recorded. The data were fitted using Hyperquad 2013 to obtain the protonation constant.

[0165] To determine the stability constants of the manganese(II) complexes prepared in Example 1, Comparative Examples 1-3, and Comparative Example 6, the ligands prepared in Example 1 and Comparative Examples 1-3, 1,4-DO2A prepared in Comparative Example 4, and 1,7-DO2A prepared in Comparative Example 5 were dissolved in 0.1M KCl solution at a molar ratio of 1.05:1. The mixture was then titrated to pH 12.0 with 0.5M NaOH under nitrogen. Hyperquad 2013 was used to calculate the stability constants. The results are shown in Table 2.

[0166] Table 2 Test results of the protonation constants of the ligands and the stability constants of their manganese complexes.

[0167]

[0168] The results show that the stability constants (logK MnL ) is significantly higher than that of traditional manganese (II) complexes Mn (1,4-DO2A) and Mn (1,7-DO2A), among which the stability of the manganese (II) complex Mn (1,4-Et4DO2A) is the highest among the currently reported hexadentate macrocyclic manganese (II) complexes.

[0169] Experimental Example 3: Comparison of dissociation kinetics and inertness

[0170] The kinetic inertness of the Mn(II) complexes prepared in Example 1, Comparative Examples 1-3, and Comparative Example 6 was evaluated using a Zn(II) competition assay. Specifically, 25 mM ZnCl2 was dissolved in MES solution (containing 50 mM 2-(N-morpholino)ethanesulfonic acid and 0.1 M potassium chloride) to prepare a working buffer, and the pH was adjusted to 6.0 with 6 M hydrochloric acid. 1 mM Mn(II) complex was dissolved in the working buffer and incubated at 37°C. The transverse relaxation time (T2) was recorded at different time points. The dissociation rate constant (K) was calculated by fitting the incubation time and relaxation rate (1 / T2) with the formula I provided in the article "Garda, Z., Forgács, A., Do QN, et al. Physico-chemical properties of MnII complexes formed with cis- and trans-DO2A: thermodynamic, electrochemical and kinetic studies [J]. Journal of Inorganic Biochemistry, 2016, 163, 206-213. DOI: 10.1016 / j.jinorgbio.2016.07.018."d ) and half-life (T 1 / 2 ).

[0171]

[0172] T 1 / 2 =ln2 / K d Formula II;

[0173] Among them, X0, X t 、X e The results are shown in Table 3.

[0174] Table 3 Dissociation rate K of the manganese (II) complexes d and half-life time t 1 / 2

[0175]

[0176] The results showed that the half-lives (t 1 / 2 ) are 35 and 39 min, respectively. It is worth noting that the t 1 / 2 The inertness of the manganese (II) complex Mn(1,7-Et4DO2A) is nearly 10 times higher than that of Mn(1,7-DO2A) (t 1 / 2 =352min). The manganese(II) complexes Mn-L1 and Mn-L2 with benzoic acid groups introduced into the side arms showed higher inertness. 1 / 2 60 and 1305 minutes respectively.

[0177] Test Example 4: Determination of longitudinal relaxation rate r1

[0178] The longitudinal relaxation rates r1 of the manganese (II) complexes prepared in Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 6 were measured using an HTS-1103T high-temperature superconducting variable-field nuclear magnetic relaxation analyzer (purchased from Micro, Germany) at 25°C and 20 MHz. The results are shown in Table 4.

[0179] Table 4 Longitudinal relaxation rate r1 of the manganese (II) complexes

[0180] Manganese(II) complexes Mn(1,4-Et4DO2A) <![CDATA[Mn-L1]]> <![CDATA[Mn-L2]]> Mn(1,4-DO2A) <![CDATA[r1(mM -1 s -1 )]]> 3.1 2.8 2.5 2.1

[0181] The results showed that the longitudinal relaxation rate r1 of the manganese (II) complex Mn (1,4-Et4DO2A) was 3.1 mM -1 s-1 The longitudinal relaxation rate r1 of the manganese (II) complex Mn-L1 is 2.8 mM -1 s -1 The longitudinal relaxation rate r1 of the manganese (II) complex Mn-L2 is 2.5 mM -1 s -1 The longitudinal relaxation rate r1 of the manganese (II) complex Mn (1,4-DO2A) is 2.1 mM -1 s -1 .

[0182] Test Example 5 Cytotoxicity Experiment

[0183] The manganese (II) complex Mn (1,4-Et4DO2A) prepared in Example 1, the manganese (II) complex Mn-L1 prepared in Comparative Example 1, the manganese (II) complex Mn-L2 prepared in Comparative Example 3, and the Mn (II) complex Mn (1,4-DO2A) prepared in Comparative Example 6 were used as experimental materials.

[0184] Human hepatic stellate cell line LX-2 (purchased from Shanghai Yubo Biotechnology Co., Ltd.) was co-incubated with the Mn(II) complex to assess its cytotoxicity. Specifically, the Mn(II) complex was dissolved in 100 μL of DMEM to obtain culture media with Mn(II) complex concentrations of 0.05, 0.1, 0.3, 0.5, and 1 mM. Human hepatic stellate cell line LX-2 cells were seeded at a density of 5,000 cells per well in 96-well plates. 100 μL of DMEM culture medium (purchased from Guangdong Huankai Biotechnology Co., Ltd.) was added to each well and pre-incubated at 37°C, 5% CO2, and saturated humidity for 24 hours. The original culture medium was removed and culture medium containing the Mn(II) complex was added. The cells were incubated under standard conditions for another 24 hours. Subsequently, 10 μL of CCK-8 solution (purchased from Wuhan Lianxing Biotechnology Co., Ltd.) was added to each well. After incubation for 4 hours, the absorbance at 450 nm was recorded using a microplate reader. The control group was treated with medical saline instead of the culture medium containing manganese (II) complex. Cell viability is expressed as a percentage of the control group. The experiment was repeated three times. The in vitro toxicity of manganese (II) complex on human hepatic stellate cells (LX-2) was evaluated by CCK-8 assay. The results are shown in Figure 3. Figure 5 shown.

[0185] Depend on Figure 5 It can be seen that all manganese (II) complexes still maintained cell viability comparable to that of the saline control group at a concentration of 1 mM, indicating that manganese (II) complexes have little toxicity to human hepatic stellate cells LX-2.

[0186] Experimental Example 6 Preparation and MRI Imaging of Mouse Orthotopic Hepatocellular Carcinoma (HCC) Model

[0187] All animal experiments followed the ethical guidelines of the Institutional Animal Care and Use Committee (IACUC) of Wenzhou Institute (University of Chinese Academy of Sciences). The HCC model was established by selecting male BALB / c mice (weighing 25 ± 3 g, purchased from Beijing Weitonglihua Laboratory Animal Technology Co., Ltd.) and acclimating them to the environment for 1 week before the operation. They were fasted for 12 hours before the experiment (with free access to water). During the experiment, the mice were anesthetized by intraperitoneal injection of tribromoethanol (0.6 mL / 20 g). After disinfection with iodine, a concentration of 1 × 10 7 10 μL of an H22 cell suspension (purchased from Bohui Biotechnology (Guangzhou) Co., Ltd., mixed with Matrigel (purchased from Shanghai Xinchao Biotechnology Co., Ltd.) at a ratio of 1:1) was injected into the right lobe of the liver. The liver was repositioned and the incision sutured, and antibiotics were administered postoperatively to prevent infection. Mice were placed in a warming cage to recover and were used for MRI studies one week after inoculation.

[0188] MRI imaging was performed on normal mice and the HCC model mice obtained above. The specific operation method was as follows: male BALB / c mice (25±3g) were anesthetized with tribromoethanol (0.6mL / 20g) and fixed in a 3.0T clinical magnetic resonance imaging machine (Philips Ingenia elition) dedicated mouse coil. Before the injection of manganese (II) complex, background scans were performed using T1 and T2 weighted sequences (coronal and cross-sectional), respectively. Subsequently, manganese (II) complex was injected into the tail vein at a dose of 0.05mmol / kg, and the scan was completed within approximately 30 minutes after injection. Scans of tumor-bearing mice required pre-scanning using T1 and T2 weighted sequences before injection. The details are as follows:

[0189] Scan parameters:

[0190] T1-weighted sequence: TE = 9.7 ms, TR = 191.1 ms, flip angle (FA) = 50°, field of view (FOV) = 50 × 50 mm, matrix size = 200 × 135, number of slices = 12, slice thickness = 1.5 mm, inter-slice distance = 0.15 mm.

[0191] T2-weighted sequence: TE = 120 ms, TR = 4000 ms, FA = 90°, FOV = 50 × 50 mm, matrix size = 200 × 168, number of slices = 12, slice thickness = 1.5 mm, inter-slice spacing = 0.15 mm.

[0192] The acquired MR images were processed using MicroDicomViewer to compare the signal intensity (SI) at the same anatomical location before and after injection, and the relative enhancement (RE) of the liver and kidney signal changes was calculated.

[0193] RE=(SI post -SI pre) / SI pre ×100% Formula III;

[0194] Among them, SI pre Indicates the signal intensity before injection, SI post represents the signal intensity after injection.

[0195] The contrast between the liver and the tumor is expressed as the contrast-to-noise ratio (CNR), which is calculated as follows:

[0196] CNR=SI liver -SI tumor / SD air Formula IV;

[0197] Among them, SD air The standard deviation of the signal in the air area surrounding the mouse, SI liver Indicates the signal intensity of normal liver, SI tumor Indicates the signal intensity of the liver cancer area.

[0198] The performance of manganese (II) complexes in normal BALB / c mice was evaluated using a 3.0T clinical MRI scanner. The results are shown in Tables 5 to 6 and Figures 6 and 7 shown.

[0199] Table 5 MRI relative enhancement (RE) of liver and kidney of normal mice

[0200]

[0201]

[0202] Table 6 Contrast-to-noise ratio (CNR) of the liver and tumor regions in magnetic resonance imaging of mice injected with the manganese (II) complex Mn(1,4-Et4DO2A) 1 week and 2 weeks after HCC modeling

[0203]

[0204] T1-weighted images revealed that the manganese(II) complex Mn-L1 is primarily excreted via the kidneys, while the R-ethyl modification significantly favors hepatobiliary uptake of the manganese(II) complex Mn(1,4-Et4DO2A). Following intravenous injection, the hepatic signal intensity increased by 76% at 18 minutes, followed by rapid excretion via the gallbladder into the small intestine. In contrast, the p-benzoyl-modified manganese(II) complex Mn-L2 exhibited diminished hepatic uptake (peak enhancement of only 37%), likely due to its rapid renal clearance.

[0205] The diagnostic potential of the manganese(II) complex Mn(1,4-Et4DO2A) in an orthotopic model of hepatocellular carcinoma (HCC) was demonstrated using T2-weighted imaging. Twelve minutes after injection, a one-week tumor (3.0 × 2.3 mm) exhibited high contrast (CNR = 43.8) on T1-weighted images. A two-week tumor (6.5 × 3.5 mm) exhibited a CNR of 56.8 after enhancement due to its increased size, clearly distinguishing tumor from normal tissue.

[0206] As can be seen from the above examples, the present invention provides a manganese complex Mn(1,4-Et4DO2A) and its synthesis method and application. The present invention improves the stability and inertness of the manganese(II) complex Mn(1,4-DO2A) by structurally modifying the manganese(II) complex Mn(1,4-DO2A); among the hexadentate manganese(II) complexes tested, the manganese(II) complex Mn(1,4-Et4DO2A) containing four chiral ethyl groups exhibits the highest stability, and its inertness can be doubled by introducing a rigid phenyl analogue into the side arm. At 25°C and 20MHz, the longitudinal relaxation rate (r1=3.1mM) of the manganese(II) complex Mn(1,4-Et4DO2A) is -1 s -1 ) is 50% higher than that of the manganese (II) complex Mn (1,4-DO2A); the results of mouse experiments show that the manganese (II) complex Mn (1,4-Et4DO2A) is expected to become an MRI diagnostic tool to replace gadolinium-based contrast agents.

[0207] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A manganese complex Mn(1,4-Et4DO2A), characterized in that The structural formula of the manganese complex Mn(1,4-Et4DO2A) is as follows: 。 2. A method for synthesizing the manganese complex Mn(1,4-Et4DO2A) according to claim 1, characterized in that: The steps include: (1) Tetraethylcyclorotaxane was mixed with potassium carbonate and acetonitrile, and then an acetonitrile solution containing benzyl bromide was added, and the mixture was concentrated and purified to obtain compound 1; (2) Compound 1 was mixed with potassium carbonate, acetonitrile, and tert-butyl bromoacetate, concentrated, added with ethyl acetate, extracted, dried, and concentrated to obtain compound 2; (3) Compound 2 was mixed with ethanol, a catalyst was added, and the mixture was evaporated under reduced pressure to obtain compound 3; (4) Compound 3 was mixed with hydrochloric acid and evaporated to obtain the ligand 1,4-Et4DO2A; (5) The ligand 1,4-Et4DO2A is mixed with MnCl2 and water, and the pH is adjusted to obtain the manganese complex Mn(1,4-Et4DO2A).

3. The synthesis method according to claim 2, characterized in that In step (1), the mass volume ratio of the tetraethylcyclorotaxane, potassium carbonate, and acetonitrile is 2.5-3.5 g:2.5-3.5 g:25-35 ml; the molar ratio of the tetraethylcyclorotaxane to potassium carbonate is 10-11:21-22; and the acetonitrile solution containing benzyl bromide is prepared by adding 3-4 g of benzyl bromide with an amount of 21-22 mmol to 15-25 ml of acetonitrile solution.

4. The synthesis method according to claim 3, characterized in that The concentration method in step (1) is reduced pressure rotary evaporation, the concentration temperature is 25-35° C., and the concentration time is 20-30 min; the purification method is silica gel column chromatography, and the solvents used in the purification are petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is 1.5-2.5:

1.

5. The synthesis method according to claim 2, characterized in that In step (2), the mass volume ratio of compound 1, potassium carbonate, acetonitrile, and tert-butyl bromoacetate is 0.8~1.2g:0.5~1g:15~25ml:0.8~1.2g; the amount of substance ratio of compound 1, potassium carbonate, and tert-butyl bromoacetate is 2.0~2.5:4.0~4.5:5.0~5.5; the concentration method is reduced pressure rotary evaporation, the concentration temperature is 25~35°C, and the concentration time is 20~30min; the mass volume ratio of ethyl acetate to compound 1 is preferably 0.8~1.2g:25~35ml; the extraction solvent is hydrochloric acid, the concentration of hydrochloric acid is 1~1.5M, and the number of extractions is 2~3 times; the drying and concentration temperature is 20~30°C, and the drying and concentration time is 0.5~1.5h.

6. The synthesis method according to claim 2, characterized in that In step (3), the mass volume ratio of the compound 2 to ethanol is 0.5-1.5 g: 25-35 ml; the catalyst is Pd / C; the mass ratio of the compound 2 to the catalyst is 0.5-1.5: 0.2-0.4; the temperature of the reduced pressure steaming is 25-35° C., and the time of the reduced pressure steaming is 20-30 min.

7. The synthesis method according to claim 2, characterized in that In step (4), the mass volume ratio of the compound 3 to hydrochloric acid is 0.5-1.5 g:15-25 ml; the steaming temperature is 35-45° C., and the steaming time is 30-50 min.

8. The synthesis method according to claim 2, characterized in that In step (5), the molar ratio of the ligand 1,4-Et4DO2A to MnCl2 is 1-1.05:0.95-1.

0.

9. Use of the manganese complex Mn(1,4-Et4DO2A) according to claim 1 as a contrast agent.

10. Use of the manganese complex Mn(1,4-Et4DO2A) according to claim 1 in the preparation of products for clinical magnetic resonance imaging or for detecting hepatocellular carcinoma.

Images