Macrocyclic chelators and methods of synthesis

Abstract

The application discloses a macrocyclic chelator and a synthesis method, and belongs to the field of nuclear medicine chelators. The macrocyclic chelator is named as 6,6'-[3,10-dioxa-6,13-diaza-1,8(2,6)-dipyridinocyclotetradecane-6,13-diyl bis(methylene)]dipyridine-2-carboxylic acid. The macrocyclic chelator is synthesized in eight steps by taking 2,6-pyridine dimethanol as a raw material. The application successfully adopts a new method to realize an important breakthrough in a ring-closing step, and ingeniously introduces an amino group protection in multiple steps which need to be purified, and finally obtains a high-purity crystal Macropa analogue new chelator product. The application provides a new idea for subsequent synthesis of Ac-225 new chelator molecules, and to some extent, makes up for the shortcomings of existing chelator molecules.

Description

Technical Field

[0001] This invention relates to the field of radiopharmaceutical chelating agents, and particularly to a macrocyclic chelating agent and its synthesis method. Background Technology

[0002] Ac-225 is a prominent alpha nuclide and plays a crucial role in the field of radiopharmaceuticals. Compared to beta nuclides, such as Lu-177, it has the following significant advantages:

[0003] (1) Beta rays damage the single strand of tumor cell DNA, and the tumor cells may repair themselves, thus leading to tumor recurrence. However, alpha rays can directly damage the double strand of tumor cell DNA, leading to the permanent killing of tumor cells;

[0004] (2) The linear energy transfer density (LET) of α rays is 100 times higher than that of β rays, and the tumor killing effect is significantly higher than that of β rays;

[0005] (3) Alpha rays have a shorter range, only a few cells, and cause less damage to normal tissues;

[0006] (4) The single dose of α nuclide is about two orders of magnitude lower than that of β nuclide, and the radioactive hazard and harm to humans before reaching the target are minimal.

[0007] Currently, there are over 50 Ac-225 radiopharmaceutical development pipelines worldwide, with broad indications covering various tumor types including acute myeloid leukemia, prostate cancer, glioblastoma, neuroendocrine tumors, and solid tumors. Clinical studies show that... 225 Ac-PSMA-617 achieved an objective response rate of 78.6% in treating castration-resistant prostate cancer, with a median survival of 17 months, and showed significant efficacy, especially in patients resistant to β-scans (such as Lu-177).

[0008] Ac-225 requires combination with a suitable chelating agent to exert its therapeutic effect on tumors more efficiently and safely. Existing chelating agents generally suffer from the following technical drawbacks: poor thermodynamic stability and slow kinetics in coordination with larger metal ions; and susceptibility to small metal impurities (such as Ca). 2+ The effects of high ligand concentrations and heating conditions are necessary to achieve sufficient radiolabeled yields. Specifically, regarding chelating agents already in clinical trials: DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) can form complexes with Ac-225 and also readily complexes with small metal ions such as Fe, Ca, and Mg in vivo, resulting in insufficient selectivity; while Macropa can effectively complex Ac-225 and exhibits good in vivo stability, it still suffers from significant off-target effects, leading to high hepatic uptake and poor systemic clearance. 225Taking Ac-PSMA-617 as an example, the incidence of toxic reactions such as dry mouth and anemia after treatment is higher than that of β-radioactive therapy. The fundamental reason is that existing chelating agents have insufficient chelating ability for Ac-225 and its decay products, leading to the accumulation of free radionuclides in non-target organs. Therefore, the development of novel chelating agents is imperative.

[0009] Despite the aforementioned drawbacks such as off-target effects, Macropa's molecular structure (containing an 18-crown-6 backbone and two pyridine-like hanging arms) tends to bind larger metal ions, and it is still considered a lead structure with potential for improvement. Macropa chelators and their analogs exhibit superior complexing properties and in vivo stability. Subsequent studies have developed several analogs based on Macropa, such as py2-macrodipa, with some success. The typical synthetic route for py2-macrodipa is as follows:

[0010]

[0011] This route represents one type of non-fully symmetrical analogue, significantly reducing the difficulty of synthesis. However, current research on chelating agents is relatively limited. A major limiting factor is that the structures of highly effective chelating agents are unique, making their synthesis difficult, and successfully obtaining gram-scale molecules remains a challenge.

[0012] In summary, the synthesis and research of Macropa analogs are becoming increasingly important, and related progress is expected to bring new breakthroughs to the field of chelating agent development. However, the current number of synthesized analogs is still far from meeting the demand, and new synthetic methods are urgently needed. Summary of the Invention

[0013] In order to solve the above-mentioned technical problems, the present invention provides a novel macrocyclic chelating agent with a parent nucleus and a method for its synthesis.

[0014] In a first aspect, the present invention provides a macrocyclic chelating agent, which is achieved by the following technical solution.

[0015] A macrocyclic chelating agent, named 6,6'-[3,10-dioxa-6,13-diaza-1,8(2,6)-dipyridinacyclotetradecaphane-6,13-diylbis(methylene)]dipyridinic acid [6,6'-(3,10-dioxa-6,13-diaza-1,8(2,6)-dipyridinacyclotetradecaphane-6,13-diylbis(methylene))dipicolinic acid] (hereinafter referred to as P-py-18C6dipa), has the following structural formula:

[0016] .

[0017] Furthermore, in the above structural formula, the pyridine ring can be replaced by phenyl, naphthyl, pyridyl, pyrimidinyl, thiazolyl, indolyl, quinolinyl, pyrrole, or pyrazine; the carboxyl group can be replaced by a phosphate group.

[0018] Secondly, the present invention provides a method for preparing a macrocyclic chelating agent, which is achieved by the following technical solution.

[0019] The present invention, P-py-18C6dipa, is synthesized from 2,6-pyridinediethanol via an eight-step process. The synthetic route is as follows:

[0020]

[0021] Specifically, a method for preparing a macrocyclic chelating agent includes the following steps:

[0022] S1. Under nitrogen protection and at 0-10℃, 2,6-pyridinediethanol is dissolved in tetrahydrofuran, and then sodium hydride is added in portions. The temperature is raised to 40-70℃, and bromoacetonitrile is added dropwise. The molar ratio of bromoacetonitrile to 2,6-pyridinediethanol is (1.1-1.5):1. After reacting for 1-4 hours, the temperature is lowered to 15-25℃, and the reaction is quenched by adding glacial acetic acid and methanol. The mixture is extracted with ethyl acetate and subjected to column chromatography to obtain intermediate 1. This step is a typical substitution reaction, and strict control of anhydrous and oxygen-free conditions is required during the process. The reaction flask, raw materials, and reagents must all be kept dry.

[0023] S2. Dissolve intermediate 1 in 1,4-dioxane, then add manganese dioxide, heat the system to 80-90℃, keep the reaction at this temperature for 3-5 hours, then cool to 15-25℃, filter, and concentrate to dryness to obtain intermediate 2; this step is the reaction of hydroxyl oxidation to aldehyde, and manganese dioxide is used as the oxidant, and the reaction effect is good.

[0024] S3. Mix ammonia-methanol and intermediate 1, then add Raney nickel, pressurize with hydrogen to 0.5-2.0 MPa, heat to 40-50℃, maintain the temperature for 3-4 hours, then cool to 15-25℃, filter under nitrogen protection, concentrate the filtrate to dryness to obtain intermediate 3; this step is a typical hydrogen reduction reaction, reducing cyano to amine, and attention should be paid to nitrogen protection during the post-processing to prevent the Raney nickel from burning.

[0025] S4. Under nitrogen protection, intermediates 2 and 3 were added sequentially to methanol at a mass ratio of 1:(1.02-1.05). Glacial acetic acid was then added, and sodium triacetoxyborohydride was added in batches after stirring. The reaction was carried out at 15-25℃ for 3-6 hours. Then, diisopropylethylamine and ditert-butyl dicarbonate were added at a molar ratio of (2-4):(1.5-3):1 to intermediate 2. The reaction was maintained at this temperature for 1-2 hours, concentrated to dryness, extracted with methyl tert-butyl ether, concentrated again, and separated by column chromatography to obtain intermediate 5. This step is a reductive amination reaction of aldehyde and amine. Intermediates 2 and 3 first form an imine, which is then reduced to an amine. The amine is then protected with a protecting group.

[0026] S5. Dissolve intermediate 5 in ammonia-methanol, then add Raney nickel, pressurize with hydrogen to 0.5-2.0 MPa, heat the system to 40-50℃ and react for 3-4 hours, cool to 15-25℃, filter, and concentrate the filtrate to dryness to obtain intermediate 6; this step is a hydrogen reduction reaction, and attention should be paid to the flammability of Raney nickel during the process.

[0027] S6. Under nitrogen protection, intermediate 6 was dissolved in 1,4-dioxane, and then activated manganese dioxide (purchased from Anaiji Chemical, product number: E060064, batch number: 00SURUGH) was added. The temperature was raised to 80-90℃, and the reaction was carried out for 3-5 hours. The temperature was then lowered to 15-25℃, and the mixture was filtered. Methanol and glacial acetic acid were added, and the temperature was controlled at 15-25℃. Sodium triacetoxyborohydride was added in batches, and the reaction was carried out at 15-25℃ for 2-3 hours. Then, diisopropylethylamine and di-tert-butyl dicarbonate were added. The mass ratio of intermediate 6 to intermediate 9 was (1.5-3):(1.5-3):1. The reaction was carried out for 1-2 hours, followed by concentration, extraction with methyl tert-butyl ether, concentration, and column chromatography to obtain intermediate 9. This step involves the oxidation of hydroxyl groups to aldehydes, followed by ring closure to form a macrocyclic structure through reductive amination. This step is crucial, as ring closure is difficult using other methods. Successfully solving this step is key to the successful synthesis of this molecule. The introduction of the protecting group reduces the purification difficulty of intermediate 9, allowing for the acquisition of intermediate 9 with higher purity for the next step.

[0028] S7. Add intermediate 9 to dichloromethane, add trifluoroacetic acid dropwise, react at 15-25℃ for 3-5 h, concentrate, then add N,N-dimethylformamide, followed by potassium iodide, sodium carbonate and methyl 6-(chloromethyl)pyridinecarboxylate. The mass ratio of potassium iodide, sodium carbonate, methyl 6-(chloromethyl)pyridinecarboxylate to intermediate 9 is (0.05-0.2):(2-4):(1.0-1.5):1. The system is heated to 40-45℃ and reacted for 10-15 h. The mixture is concentrated to dryness, and the crude product is separated by column chromatography to obtain intermediate 11. This step first removes the amine protecting group, and then achieves docking through a substitution reaction.

[0029] S8. Intermediate 11 was added to hydrochloric acid, the system was heated to 90-100℃, and the reaction was maintained for 6-7 hours. The mixture was then concentrated to dryness, and the crude product was purified by high-performance liquid chromatography to obtain the macrocyclic chelating agent product. This step successfully yielded the carboxyl group by hydrolyzing the ester group under acidic conditions, thus obtaining the corresponding product.

[0030] Furthermore, in step S1, the solid-liquid ratio of 2,6-pyridinediethanol and tetrahydrofuran is 1:(20-50).

[0031] Furthermore, in step S1, the molar ratio of sodium hydride to 2,6-pyridinediethanol is (1.1-1.5):1.

[0032] Furthermore, in step S2, the solid-liquid ratio of intermediate 1 and 1,4-dioxane is 1:(5-20).

[0033] Furthermore, in step S2, the mass ratio of manganese dioxide to intermediate 1 is (2-4):1.

[0034] Furthermore, in step S3, the solid-liquid ratio of intermediate 1 to ammonia methanol is 1:(5-20), wherein the ammonia methanol is a methanol solution of ammonia with a concentration of 7 mol / L.

[0035] Furthermore, in step S3, the mass ratio of Raney nickel to intermediate 1 is 1:(2-4).

[0036] Furthermore, in step S4, the mass ratio of intermediate 2 to methanol is 1:(10-30).

[0037] Furthermore, in step S4, the mass ratio of glacial acetic acid to intermediate 2 is (1-1.5):1.

[0038] Furthermore, in step S4, the molar ratio of sodium triacetoxyborohydride to intermediate 2 is (3-6):1.

[0039] Furthermore, in step S5, the solid-liquid ratio of intermediate 5 and ammonia methanol is 1:(10-30), wherein the ammonia methanol is a methanol solution of ammonia with a concentration of 7 mol / L.

[0040] Furthermore, in step S5, the mass ratio of Raney nickel to intermediate 5 is 1:(2-5).

[0041] Furthermore, in step S6, the solid-liquid ratio of intermediate 6 and 1,4-dioxane is 1:(5-20).

[0042] Furthermore, in step S6, the mass ratio of manganese dioxide to intermediate 6 is (2-4):1.

[0043] Furthermore, in step S6, the liquid-solid ratio of methanol to intermediate 6 is (3-5):1.

[0044] Furthermore, in step S6, the mass ratio of glacial acetic acid to intermediate 6 is (1-2):1.

[0045] Furthermore, in step S6, the mass ratio of sodium triacetoxyborohydride to intermediate 6 is (1.5-3):1.

[0046] Furthermore, in step S7, the solid-liquid ratio of intermediate 9 to dichloromethane is 1:(5-20).

[0047] Furthermore, in step S7, the liquid-to-solid ratio of trifluoroacetic acid to intermediate 9 is (3-6):1.

[0048] Furthermore, in step S7, the solid-liquid ratio of intermediate 9 to N,N-dimethylformamide is 1:(5-20).

[0049] Furthermore, in step S8, the solid-liquid ratio of intermediate 11 to hydrochloric acid is 1:(5-20), wherein the concentration of hydrochloric acid is 35-37%.

[0050] It should be noted that the solid-liquid ratio mentioned above in this application refers to the following: if 1g of solid dissolves in 1mL of liquid, the solid-liquid ratio is 1:1; the liquid-solid ratio has the same meaning as the solid-liquid ratio.

[0051] This application has the following beneficial effects:

[0052] This invention successfully utilizes a novel method, achieving a significant breakthrough in the ring-closing step. It cleverly protects the amine groups in several purification steps, thereby obtaining pure intermediates and ultimately a novel chelating agent product of high-purity crystalline Macropa analogs. The method of this invention uses readily available and simple raw materials and reagents, is relatively straightforward to operate, and yields a considerable reaction rate. It can conveniently produce gram-scale molecules and has been successfully applied to the complexation studies of corresponding ions, providing new ideas for the subsequent synthesis of novel Ac-225 chelating agents and, to some extent, filling some gaps in existing chelating agent molecules. Attached Figure Description

[0053] Figure 1 This is a high-resolution mass spectrum of P-py-18C6dipa prepared according to an embodiment of the present invention;

[0054] Figure 2 This is the 1H NMR spectrum of P-py-18C6dipa prepared in the embodiments of the present invention;

[0055] Figure 3 This is the carbon NMR spectrum of P-py-18C6dipa prepared in an embodiment of the present invention. Detailed Implementation

[0056] The present invention will be further described below with reference to embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials used in the preparation process in the following embodiments have not undergone further processing and are all commercially available.

[0057] Example

[0058] Step 1:

[0059]

[0060] 1. Under nitrogen protection, add 4000 ml of tetrahydrofuran and 100 g of 2,6-pyridinediethanol to the reaction flask, and cool to 10 °C;

[0061] 2. Add 31.6g of 60% sodium hydride in batches, and keep warm for 30 minutes after the addition is complete;

[0062] 3. Heat the system to 70℃, add 103.4g of bromoacetonitrile dropwise, and maintain the temperature for 2 hours after the addition is complete;

[0063] 4. Stop the reaction, cool the system to 20°C, add 45g of glacial acetic acid and 100ml of methanol to quench the reaction, concentrate the system to remove tetrahydrofuran, add 800ml of saturated sodium bicarbonate aqueous solution, extract three times with ethyl acetate, using 500ml each time, combine the organic phases, add 100g of anhydrous magnesium sulfate and dry for 1h, concentrate to dryness at 50°C.

[0064] 5. Column chromatography: Mix 100g of silica gel (100-200 mesh) with the sample, pack 400g of silica gel (100-200 mesh) into the column, eluent: petroleum ether / ethyl acetate = 5 / 1;

[0065] Results: 71.6 g of yellowish-brown oily substance (intermediate 1) was obtained, with a purity of 95% and a yield of 56%;

[0066] Step 2:

[0067]

[0068] 1. Under nitrogen protection, add 188 ml of 1,4-dioxane, 18.8 g of intermediate 1, and 55.0 g of activated manganese dioxide to the reaction flask;

[0069] 2. Heat the system to 90℃ and maintain the temperature for 5 hours;

[0070] 3. Stop the reaction, cool the system to 25°C, filter, wash the filter cake with 100ml of 1,4-dioxane, combine the filtrates, and concentrate to dryness at 50°C;

[0071] Results: 16.0 g of brown oily substance (intermediate 2) was obtained, with a purity of 74% and a yield of 86.4%;

[0072] Detection: MS (M+1): 177.3;

[0073] Step 3:

[0074]

[0075] 1. Add 255ml of ammonia-methanol, 17g of intermediate 1, and 6.8g of Raney nickel to a 500ml autoclave;

[0076] 2. Close the kettle lid, pressurize the hydrogen to 2.0 MPa, raise the system temperature to 50°C, and maintain the temperature for 3 hours;

[0077] 3. Close the hydrogen valve, release the hydrogen from the reactor, stop the reaction, cool the system to 25°C, filter the system under nitrogen protection, rinse the filter cake with 100ml of methanol, dry it, combine the filtrates, and concentrate it to dryness at 50°C.

[0078] Results: 16.6 g of colorless oil (intermediate 3) was obtained, with a purity of 88.3% and a yield of 96%.

[0079] Detection: MS (M+1): 183.3;

[0080] Step 4:

[0081]

[0082] 1. Under nitrogen protection, add 300 mL of methanol, 16.0 g of intermediate 2, 16.6 g of intermediate 3 and 16.4 g of glacial acetic acid to a 2 L three-necked flask in sequence;

[0083] 2. The system temperature was controlled at 25℃. 25g of sodium triacetoxyborohydride was added in batches. After the addition was complete, the reaction was kept at this temperature for 4 hours.

[0084] 3. Add 35.3g of diisopropylethylamine and 39.8g of ditert-butyl dicarbonate. After the addition is complete, keep the mixture warm for 2 hours.

[0085] 4. Concentrate the system to dryness at 50℃, add 300ml of water, extract three times with methyl tert-butyl ether (150ml each time), combine the organic phases, and concentrate to dryness.

[0086] 5. Column chromatography: Mix 55g of silica gel (100-200 mesh) with sample, pack 200g of silica gel (100-200 mesh) into the column, eluent: petroleum ether / ethyl acetate = 2 / 1;

[0087] Results: 26.1g of light yellow oily substance was obtained, with a purity of 86% and a yield of 64.8%.

[0088] Detection: MS (M+1): 443.7 (intermediate 5); 1H NMR result for intermediate 5 is as follows: 1 ¹H NMR (DMSO, 400 MHz) δ: 7.81–7.77 (m, 2H), 7.37–7.17 (m, 4H), 5.39–5.36 (t, 1H), 4.64–4.49 (m, 10H), 3.62 (s, 2H), 3.52–3.32 (m, 2H), 1.43–1.26 (m, 9H). The structure matches that of the target product.

[0089] Step 5:

[0090]

[0091] 1. Add 520ml of ammonia-methanol, 26g of intermediate 5, and 10.4g of Raney nickel to a 1000ml autoclave;

[0092] 2. Close the kettle lid, pressurize the hydrogen to 2.0 MPa, raise the system temperature to 50°C, and maintain the temperature for 4 hours;

[0093] 3. Close the hydrogen valve, and hydrogen will be discharged from the reactor. Stop the reaction, cool the system to 25°C, filter the system under nitrogen protection, rinse the filter cake with 200ml of methanol, dry it, combine the filtrates, and concentrate it to dryness at 50°C.

[0094] Results: 25.6 g of colorless oil (intermediate 6) was obtained, with a purity of 82% and a yield of 97.7%.

[0095] Detection: MS (M+1): 447.7;

[0096] Step 6:

[0097]

[0098] 1. Under nitrogen protection, add 1536 ml of 1,4-dioxane, 25.6 g of intermediate 6 and 54.8 g of active manganese dioxide to the reaction flask;

[0099] 2. Heat the system to 85℃ and maintain the temperature for 4 hours;

[0100] 3. Stop the reaction, cool the system to 25°C, filter, wash the filter cake with 200 ml of 1,4-dioxane, and combine the filtrates;

[0101] 4. Under nitrogen protection, transfer the above filtrate to a reaction flask, add 100 ml of methanol and 25.6 g of glacial acetic acid, control the temperature at 25°C, add 52 g of sodium triacetoxyborohydride in batches, and keep the reaction at this temperature for 3 h.

[0102] 5. Add 29.6 g of diisopropylethylamine and 50.0 g of ditert-butyl dicarbonate. After the addition is complete, keep the mixture at 25 °C for 2 h.

[0103] 6. Concentrate the system to dryness at 50℃, add 200ml of water, extract twice with methyl tert-butyl ether (MTBE), using 200ml each time, combine the organic phases, and concentrate to dryness;

[0104] 7. For column chromatography: Mix 50g of silica gel (100-200 mesh) with sample, pack 300g of silica gel (100-200 mesh) into the column, and use petroleum ether / ethyl acetate as eluent (1 / 1).

[0105] Results: 7.35 g of white solid was obtained, with a purity of 89.4% and a yield of 23.3%.

[0106] Detection: MS (M+1): 429.8 (intermediate 8), 529.8 (intermediate 9). The 1H NMR result for intermediate 9 is as follows: 1 ¹H NMR (DMSO, 400 MHz) δ: 7.72–7.66 (m, 2H), 7.15–7.08 (m, 4H), 4.46 (s, 4H), 4.27–4.24 (d, 4H), 3.46–3.40 (m, 8H), 1.43–1.32 (m, 18H). The structure matches that of the target product.

[0107] Step 7:

[0108]

[0109] 1. Under nitrogen protection, add 73.5 ml of dichloromethane, 7.35 g of intermediate 9, and 36.7 ml of trifluoroacetic acid to the reaction flask;

[0110] 2. The system temperature was controlled at 25℃, and the reaction was maintained at this temperature for 3 hours;

[0111] 3. Concentrate the system to dryness at 50°C, then remove it once with 50 ml of acetonitrile;

[0112] 4. Under nitrogen protection, add 73.5 ml DMF, 0.74 g potassium iodide, 22.1 g sodium carbonate and 7.7 g methyl 6-(chloromethyl)pyridinecarboxylate to the system in sequence;

[0113] 5. Heat the system to 45℃ and maintain the temperature for 15 hours;

[0114] 6. Concentrate the system to dryness at a controlled temperature of 60℃;

[0115] 7. For column chromatography: Mix 15g of silica gel (100-200 mesh) with sample, pack 70g of silica gel (100-200 mesh) into the column, and use dichloromethane / methanol = 30 / 1 as eluent.

[0116] 8. Concentrate the product through column chromatography to dryness, then recrystallize it with 100ml of ethyl acetate, filter, and dry.

[0117] Results: 7.5 g of off-white solid was obtained with a purity of 98.6% and a yield of 86%.

[0118] Detection: MS (M+1): 329.6 (intermediate 10), 627.8 (intermediate 11).

[0119] Step 8:

[0120]

[0121] 1. Add 75 ml of hydrochloric acid (35%) and 7.5 g of intermediate 11 to the reaction flask;

[0122] 2. Heat the system to 100℃ and maintain the temperature for 7 hours;

[0123] 3. Concentrate the system to dryness at 60℃, then rinse twice with purified water, 30ml each time;

[0124] 4. Crude product was purified by high-pressure chromatography (C8 column, mobile phase H2O:ACN from 0%-0% to 0%-80%), and the product was collected and lyophilized. It was then recrystallized using water as the solvent.

[0125] Results: 6.5 g of white crystalline solid was obtained, named P-py-18C6dipa, with a purity of 99.1% and a yield of 90.3%.

[0126] Test result: MS (M-1): 597.3.

[0127] HRMS(ESI)m / z: Calcd for C 32 H 35 N6O6[M+1] + , 599.2613, Found, 599.2606 (see also) Figure 1 ).

[0128]

[0129] 1HNMR (400 MHz, D2O): δ: 3.7348-3.7571 (t, J =4.6Hz, 4H, H-16, 25); 3.9885-4.0108 (t, J =4.6Hz, 4H, H-15, 24); 4.5898 (s, 4H, H-8, 17); 4.7373(s, 4H, H-7, 26); 4.8714 (s, 4H, H-14, 23); 7.4110-7.4308 (d, 2H, J =8.0Hz, H-10, 19); 7.5968-7.6152 (d, 2H, J =8.0Hz, H-12, 21); 7.6822-7.7014 (d, 2H, J=8.0Hz, H-5, 28); 7.8823-7.9005 (d, 2H, J =8.0Hz, H-3, 30); 7.9171-7.9554 (t,2H, J =8.0Hz, H-11, 20); 8.0133-8.0526 (t, 2H, J =8.0Hz, H-4, 29) (see Figure 2 It conforms to the target product structure.

[0130] 13 CNMR (400 MHz, D2O): δ: 166.4; 155.6; 150.1; 146.9; 146.4; 142.5; 128.1; 126.6; 125.3; 124.2; 70.7; 64.3; 57.9; 57.7; 56.1 (see also...) Figure 3 ).

[0131] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a macrocyclic chelating agent, characterized in that: The macrocyclic chelating agent is named 6,6'-[3,10-dioxa-6,13-diaza-1,8(2,6)-dipyridinylcyclotetradecane-6,13-diylbis(methylene)]dipyridin-2-carboxylic acid, with the following structural formula: ； The preparation method of macrocyclic chelating agents includes the following steps: S1. Under nitrogen protection and at 0-10℃, 2,6-pyridinediethanol was dissolved in tetrahydrofuran, and then sodium hydride was added in portions. The temperature was raised to 40-70℃, and bromoacetonitrile was added dropwise. The molar ratio of bromoacetonitrile to 2,6-pyridinediethanol was (1.1-1.5):

1. After reacting for 1-4 hours, the temperature was lowered to 15-25℃, and the reaction was quenched by adding glacial acetic acid and methanol. The mixture was extracted with ethyl acetate and subjected to column chromatography to obtain intermediate 1. The structural formula of intermediate 1 is as follows: ； S2. Dissolve intermediate 1 in 1,4-dioxane, then add manganese dioxide, heat the system to 80-90℃, keep the reaction at this temperature for 3-5 hours, then cool to 15-25℃, filter, concentrate to dryness, and obtain intermediate 2. The structural formula of intermediate 2 is as follows: ； S3. Mix ammonia methanol with intermediate 1, add Raney nickel, pressurize with hydrogen to 0.5-2.0 MPa, heat to 40-50℃, keep the reaction at this temperature for 3-4 hours, then cool to 15-25℃, filter under nitrogen protection, concentrate the filtrate to dryness, and obtain intermediate 3. The structural formula of intermediate 3 is as follows: ； S4. Under nitrogen protection, intermediates 2 and 3 were added to methanol in sequence, with a mass ratio of 1:(1.02-1.05). Glacial acetic acid was then added, and sodium triacetoxyborohydride was added in batches after stirring. The reaction was carried out at 15-25℃ for 3-6 hours. Then, diisopropylethylamine and ditert-butyl dicarbonate were added, with a molar ratio of (2-4):(1.5-3):1 to intermediate 2. The reaction was kept at this temperature for 1-2 hours, concentrated to dryness, extracted with methyl tert-butyl ether, concentrated again, and separated by column chromatography to obtain intermediate 5. The structural formula of intermediate 5 is as follows: ； S5. Dissolve intermediate 5 in ammonia-methanol, then add Raney nickel, pressurize with hydrogen to 0.5-2.0 MPa, heat the system to 40-50℃ and react for 3-4 hours, cool to 15-25℃, filter, concentrate the filtrate to dryness to obtain intermediate 6. The structural formula of intermediate 6 is as follows: ； S6. Under nitrogen protection, intermediate 6 was dissolved in 1,4-dioxane, and then active manganese dioxide was added. The temperature was raised to 80-90℃ and reacted for 3-5 hours. The temperature was then lowered to 15-25℃ and filtered. Methanol and glacial acetic acid were added, and the temperature was controlled at 15-25℃. Sodium triacetoxyborohydride was added in batches and reacted at 15-25℃ for 2-3 hours. Then, diisopropylethylamine and ditert-butyl dicarbonate were added. The mass ratio of diisopropylethylamine, ditert-butyl dicarbonate and intermediate 6 was (1.5-3):(1.5-3):

1. The reaction was carried out for 1-2 hours. Then, the mixture was concentrated, extracted with methyl tert-butyl ether, concentrated, and column chromatography were performed sequentially to obtain intermediate 9. The structural formula of intermediate 9 is as follows: ； S7. Add intermediate 9 to dichloromethane, add trifluoroacetic acid dropwise, react at 15-25℃ for 3-5 h, concentrate, then add N,N-dimethylformamide, followed by potassium iodide, sodium carbonate and methyl 6-(chloromethyl)pyridinecarboxylate. The mass ratio of potassium iodide, sodium carbonate, methyl 6-(chloromethyl)pyridinecarboxylate to intermediate 9 is (0.05-0.2):(2-4):(1.0-1.5):

1. Heat the system to 40-45℃ and react for 10-15 h, concentrate to dryness, and separate the crude product by column chromatography to obtain intermediate 11. The structural formula of intermediate 11 is as follows: ； S8. Add intermediate 11 to hydrochloric acid, heat the system to 90-100℃, keep the reaction at this temperature for 6-7 hours, concentrate to dryness, and purify the crude product using high performance liquid chromatography to obtain the macrocyclic chelating agent product.

2. The preparation method according to claim 1, characterized in that: In step S1, the solid-liquid ratio of 2,6-pyridinediethanol and tetrahydrofuran is 1:(20-50), and the molar ratio of sodium hydride to 2,6-pyridinediethanol is (1.1-1.5):

1.

3. The preparation method according to claim 1, characterized in that: In step S2, the solid-liquid ratio of intermediate 1 and 1,4-dioxane is 1:(5-20), and the mass ratio of manganese dioxide to intermediate 1 is (2-4):1; in step S3, the solid-liquid ratio of intermediate 1 to ammonia-methanol is 1:(5-20), and the mass ratio of Raney nickel to intermediate 1 is 1:(2-4).

4. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of intermediate 2 to methanol is 1:(10-30); the mass ratio of glacial acetic acid to intermediate 2 is (1-1.5):1; and the molar ratio of sodium triacetoxyborohydride to intermediate 2 is (3-6):

1.

5. The preparation method according to claim 1, characterized in that: In step S5, the solid-liquid ratio of intermediate 5 and ammonia-methanol is 1:(10-30); the mass ratio of Raney nickel to intermediate 5 is 1:(2-5).

6. The preparation method according to claim 1, characterized in that: In step S6, the solid-liquid ratio of intermediate 6 and 1,4-dioxane is 1:(5-20); the mass ratio of manganese dioxide to intermediate 6 is (2-4):1; the liquid-solid ratio of methanol to intermediate 6 is (3-5):1; the mass ratio of glacial acetic acid to intermediate 6 is (1-2):1; and the mass ratio of sodium triacetoxyborohydride to intermediate 6 is (1.5-3):

1.

7. The preparation method according to claim 1, characterized in that: In step S7, the solid-liquid ratio of intermediate 9 to dichloromethane is 1:(5-20); the liquid-solid ratio of trifluoroacetic acid to intermediate 9 is (3-6):1; and the solid-liquid ratio of intermediate 9 to N,N-dimethylformamide is 1:(5-20).

8. The preparation method according to claim 1, characterized in that: In step S8, the solid-liquid ratio of intermediate 11 to hydrochloric acid is 1:(5-20).

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