A gadolinium complex, and a preparation method and application thereof

Abstract

The present application relates to the technical field of contrast agents, in particular to a gadolinium complex, a preparation method and application thereof. The gadolinium complex provided by the present application takes PAMAM as a ligand, PAMAM has good biocompatibility and controllable in-vivo metabolic behavior, can prolong the circulation time of the contrast agent and reduce the systemic toxicity; in addition, PAMAM has a regular spherical structure and an internal cavity, and can realize efficient loading of Gd ions; the gadolinium complex provided by the present application integrates multiple gadolinium ions in one molecule, forms a local and high-density 'gadolinium atom group', has high contrast efficiency, and can provide a stronger X-ray attenuation signal than a conventional gadolinium complex (such as gadoterate) under the same dosage (mass or molar concentration), thereby realizing high-definition imaging under a lower dosage or obtaining a stronger contrast under a conventional dosage, which is particularly valuable for the display of fine structures such as blood vessels and tumors.

Description

Technical Field

[0001] This invention relates to the field of contrast agent technology, and in particular to a gadolinium complex, its preparation method, and its application. Background Technology

[0002] CT imaging is indispensable in clinical practice due to its fast scanning speed, high spatial resolution, and relatively low cost. Currently, commercially available CT contrast agents are mainly small-molecule iodine compounds (such as iohexol). However, iodine-based contrast agents have problems such as nonspecific distribution in vivo, short blood circulation time, nephrotoxicity risk, and relatively insufficient X-ray attenuation coefficient under high kilovolt (kVp) conditions.

[0003] Gadolinium (Gd, atomic number 64) has a K absorption edge of 50 keV, higher than iodine (33 keV). This means that under clinically common high-kilovolt (e.g., 100~140 kVp) CT scanning conditions, Gd can provide more effective X-ray attenuation than iodine, theoretically possessing the potential to become an excellent CT contrast agent. Furthermore, Gd... 3+ Gadolinium is the core ion of T1-weighted contrast agents widely used in magnetic resonance imaging (MRI). Therefore, the development of gadolinium-based contrast agents holds promise for enabling multimodal CT / MRI imaging and providing complementary diagnostic information.

[0004] However, free Gd 3+ Due to its toxicity, it must be used in the form of stable chelates (such as Gd-DTPA, Gd-DOTA, and gadolinium ether). Existing Gd chelates have limited gadolinium ion loading efficiency, insufficient X-ray attenuation capability, and imaging performance still needs improvement. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a gadolinium complex, its preparation method, and its application. The gadolinium complex provided by this invention, as a contrast agent, can achieve significant CT imaging even at low concentrations.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a gadolinium complex having the structure shown in any one of formulas 1 to 3: Formula 1; Formula 2; Formula 3.

[0007] This invention provides a method for preparing the gadolinium complex described above. When the gadolinium complex has the structure shown in Formula 3, the preparation method includes the following steps: Compound A-6, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 3. Compound A-6; When the gadolinium complex has the structure shown in Formula 1, the preparation method includes the following steps: Compound B-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 1. Compound B-2; When the gadolinium complex has the structure shown in Formula 2, the following steps are included: Compound C-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 2. Compound C-2.

[0008] Preferably, the preparation method of compound A-6 includes the following steps: Compound A-4, HATU, DIPEA, and a polar organic solvent were mixed to obtain an activated solution; GO-PAMAM was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound A-5; Compound A-5 was subjected to an acidic deprotection reaction to obtain compound A-6; Compound A-4; G0-PAMAM; Compound A-5.

[0009] Preferably, the preparation method of compound B-2 includes: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound B-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound B-1; Compound B-1 was subjected to an acidic deprotection reaction to obtain compound B-2; Compound B-6; Compound B-1.

[0010] Preferably, the preparation method of compound B-6 includes: mixing palladium on carbon catalyst with an organic solution containing compound B-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound B-6; Compound B-5.

[0011] Preferably, the preparation method of compound B-5 includes: dissolving compound B-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound B-5; Compound B-4.

[0012] Preferably, the preparation method of compound C-2 includes: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound C-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound C-1; Compound C-1 was subjected to an acidic deprotection reaction to obtain compound C-2; Compound A-4; Compound C-6; Compound C-1.

[0013] Preferably, the preparation method of compound C-6 includes the following steps: mixing palladium on carbon catalyst with an organic solution containing compound C-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound C-6; Compound C-5.

[0014] Preferably, the preparation method of compound C-5 includes the following steps: dissolving compound C-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound C-5; Compound C-4.

[0015] This invention provides the application of the gadolinium complex described in the above-described scheme or the gadolinium complex prepared by the preparation method described in the above-described scheme in the preparation of CT or MRI contrast agents.

[0016] This invention provides a gadolinium complex using polyamide-amine dendritic polymer (PAMAM) as a ligand. PAMAM exhibits good biocompatibility and tunable in vivo metabolic behavior, which can prolong the contrast agent circulation time and reduce systemic toxicity. Furthermore, PAMAM possesses a regular spherical structure and internal cavity, enabling efficient loading of Gd ions. The gadolinium complex provided by this invention integrates multiple gadolinium ions within a single molecule, forming localized, high-density "gadolinium clusters," resulting in high contrast efficiency. At the same dosage (mass or molar concentration), the gadolinium complex provided by this invention provides a stronger X-ray attenuation signal than conventional gadolinium complexes (such as gadolinium alcohol), thereby achieving high-definition imaging at lower doses or obtaining stronger contrast at conventional doses. This is particularly valuable for displaying fine structures such as blood vessels and tumors.

[0017] The gadolinium complex provided by this invention combines high relaxation rate, stability and biocompatibility, breaking through the bottleneck of traditional contrast agents in clinical application.

[0018] This invention provides a method for preparing the gadolinium complex described above. The preparation method of this invention has the advantages of low cost, simple and easy operation, relatively mild reaction conditions, low safety risks, and ideal yield. Attached Figure Description

[0019] Figure 1 Here is an NMR image of compound A-4 obtained in Example 5; Figure 2 Here is an NMR image of compound A-6 obtained in Example 7; Figure 3 The image shows the NMR image of compound B-2 obtained in Example 13; Figure 4 The image shows the NMR image of compound C-2 obtained in Example 19; Figure 5 Standard curve for commercial contrast agents; Figure 6 The standard curve for the two-arm contrast agent; Figure 7 The standard curve for the three-arm contrast agent; Figure 8 The standard curve for the contrast agent in the four arms; Figure 9 The images show the imaging effects of different concentrations of various contrast agents. The first row on the left shows three-arm contrast agents, the second row on the left shows commercial contrast agents, the third row on the left shows two-arm contrast agents, the first five on the right show four-arm contrast agents, and the last one is 0.9% saline. Detailed Implementation

[0020] This invention provides a gadolinium complex having the structure shown in any one of formulas 1 to 3: Formula 1; Formula 2; Formula 3.

[0021] In this invention, the gadolinium complex shown in Formula 1 is a two-arm gadolinium complex; the gadolinium complex shown in Formula 2 is a three-arm gadolinium complex; and the gadolinium complex shown in Formula 3 is a four-arm gadolinium complex.

[0022] This invention provides a method for preparing the gadolinium complex described above. Unless otherwise specified, all raw materials used are commercially available products well-known in the art.

[0023] The preparation method of the gadolinium complex with the structure shown in Equation 3 will be explained below.

[0024] The preparation method of the gadolinium complex with the structure shown in Formula 3 includes the following steps: Compound A-6, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction, thereby obtaining the gadolinium complex having the structure shown in Formula 3.

[0025] Compound A-6.

[0026] In this invention, the soluble inorganic gadolinium salt is preferably gadolinium triacetate tetrahydrate or gadolinium chloride. The amount of water used is not particularly important, as long as it is sufficient to completely dissolve the soluble inorganic gadolinium salt. In embodiments of this invention, the mass ratio of the soluble inorganic gadolinium salt to the volume ratio of water is preferably 1 g:20 mL. In this invention, the molar ratio of compound A-6 to the soluble inorganic gadolinium salt is preferably 1:(4.4~4.8), and in specific embodiments it can be 1:4.5, 1:4.6, or 1:4.7. In this invention, the mixing preferably includes dissolving compound A-6 in water before adding the soluble inorganic gadolinium salt. In this invention, the mixing temperature is preferably the same as the complexation reaction temperature; in this invention, the complexation reaction temperature is preferably 70~90℃, and in specific embodiments it can be 70, 75, 80, 85, or 90℃. In this invention, the mixing is preferably carried out under stirring conditions, and the mixing time is preferably 1~2 hours.

[0027] In this invention, an aqueous sodium hydroxide solution is preferably used to adjust the pH of the reaction system to 4-6. In specific embodiments, the pH can be adjusted to 4, 4.5, 5, 5.5, or 6. The concentration of the aqueous sodium hydroxide solution is preferably 2 mol / L. Adjusting the pH to 4-6 promotes the dissociation of carboxyl groups, forming a stable complex with gadolinium ions. The complexation reaction time is preferably 48-72 hours, and in specific embodiments, it can be 48, 56, 64, or 72 hours; the complexation reaction is preferably carried out under stirring conditions.

[0028] After the complexation reaction is completed, the present invention preferably transfers the obtained solution into a 2.5 kDa dialysis membrane for dialyzing, and freeze-dries the final osmotic residue to obtain a gadolinium complex having the structure shown in Formula 3.

[0029] In this invention, the preparation method of compound A-6 preferably includes the following steps: Compound A-4, HATU, DIPEA, and a polar organic solvent were mixed to obtain an activated solution; GO-PAMAM was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound A-5; Compound A-5 was subjected to an acidic deprotection reaction to obtain compound A-6; Compound A-4; G0-PAMAM; Compound A-5.

[0030] In this invention, compound A-4, HATU, DIPEA and a polar organic solvent (denoted as the first polar organic solvent) are mixed to obtain an activated solution.

[0031] In this invention, the compound A-4 can be obtained by purchasing or by preparing it using methods well known in the art. In the embodiments of this invention, it is prepared in-house, and the preparation method is detailed in Examples 3 and 4.

[0032] In this invention, the first polar organic solvent preferably includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO); the mass ratio of compound A-4 to the volume ratio of the first polar organic solvent is preferably 1 g: (3~5) mL; the molar ratio of HATU (2-(7-azabenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate) to DIPEA (N,N-diisopropylethylamine) is preferably 1:1; the molar ratio of compound A-4 to HATU is preferably 1:(1.1~1.2). In this invention, the mixing preferably includes: dissolving compound A-4 in the first polar organic solvent, adding HATU and DIPEA to the resulting solution, and stirring at room temperature and atmospheric pressure for 20~30 minutes. In this invention, HATU acts as a condensation reagent, its function being to activate the carboxyl group, making it more susceptible to nucleophilic attack by amines. DIPEA, as an organic base, has two functions: first, to neutralize the acid produced in the reaction and promote the forward reaction; and second, to assist HATU in activating carboxylic acids.

[0033] In this invention, GO-PAMAM is dispersed in a polar organic solvent (denoted as the second polar organic solvent) to obtain a suspension.

[0034] In this invention, the GO-PAMAM can be purchased or prepared using methods well-known in the art (e.g., Example 2 discloses one method for preparing GO-PAMAM). In this invention, the type of the second polar organic solvent is the same as that of the first polar organic solvent, and will not be repeated here. In this invention, the molar ratio of GO-PAMAM to compound A-4 is preferably 1:(8~12), and in specific embodiments it can be 1:8, 1:9, 1:10, 1:11, or 1:12. In this invention, the mass ratio of GO-PAMAM to the volume ratio of the second polar organic solvent is preferably 1 g:(10~30) mL.

[0035] After obtaining the activated solution and the suspension, the present invention adds the suspension to the activated solution to carry out an amidation reaction to obtain compound A-5.

[0036] In this invention, the suspension is preferably added dropwise. In this invention, the temperature of the amidation reaction is preferably 50-60°C; the time of the amidation reaction is preferably 12-18 hours; and the amidation reaction is preferably carried out under stirring conditions.

[0037] After the amidation reaction is completed, the present invention preferably uses rotary evaporation to remove the solvent, and then purifies the crude product using an alkaline alumina silica gel column. In the present invention, the purification is preferably performed by first eluting with ethyl acetate, and then by gradient elution with a mixed solvent of ethyl acetate / methanol to obtain the purified compound A-5. In the present invention, during the gradient elution with the mixed solvent of ethyl acetate / methanol, the volume ratio of ethyl acetate to methanol preferably changes sequentially from 20:1 to 15:1 and then to 10:1.

[0038] After obtaining compound A-5, the present invention performs an acidic deprotection reaction on compound A-5 to obtain compound A-6.

[0039] In this invention, the acidic deprotection reaction preferably comprises: mixing compound A-5 with trifluoroacetic acid (TFA) and stirring at room temperature and atmospheric pressure. In this invention, the preferred mass-to-volume ratio of compound A-5 to TFA is 1 g:(80~120) mL. This invention does not impose special requirements on the time of the acidic deprotection reaction; complete deprotection is sufficient. In the embodiments of this invention, stirring is carried out overnight.

[0040] After completing the acidic deprotection reaction, the present invention concentrates the resulting reaction mixture under reduced pressure, dissolves the resulting residue in water, and freeze-dries it to obtain compound A-6.

[0041] The preparation method of the gadolinium complex with the structure shown in Formula 1 will be described below.

[0042] When the gadolinium complex has the structure shown in Formula 1, the method for preparing the gadolinium complex preferably includes the following steps: Compound B-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 1. Compound B-2.

[0043] In this invention, the molar ratio of compound B-2 to soluble inorganic gadolinium salt is preferably 1:(2.2~2.4), and the preparation method of gadolinium complex with the same structure as shown in Formula 3 is not described here.

[0044] After the complexation reaction is completed, the present invention preferably transfers the obtained solution into a 1 kDa dialysis membrane for dialyzing and freeze-dries the final osmotic residue to obtain a gadolinium complex having the structure shown in Formula 1.

[0045] In this invention, the preparation method of compound B-2 preferably includes the following steps: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound B-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound B-1; Compound B-1 was subjected to an acidic deprotection reaction to obtain compound B-2; Compound B-6; Compound B-1.

[0046] In this invention, compound A-4, HATU, DIPEA and a polar organic solvent (denoted as the third polar organic solvent) are mixed to obtain an activated solution.

[0047] In this invention, the third polar organic solvent preferably includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO); the mass ratio of compound A-4 to the volume ratio of the third polar organic solvent is preferably 1 g:(3~5) mL; the molar ratio of HATU to DIPEA is preferably 1:1; and the molar ratio of compound A-4 to HATU is preferably 1:(1.1~1.2). In this invention, the mixing preferably includes: dissolving compound A-4 in the third polar organic solvent, adding HATU and DIPEA to the resulting solution, and stirring at room temperature and atmospheric pressure for 20~30 minutes.

[0048] In this invention, compound B-6 is dispersed in a polar organic solvent (denoted as the fourth polar organic solvent) to obtain a suspension.

[0049] In this invention, the type of the fourth polar organic solvent is the same as that of the third polar organic solvent, and will not be described again here. In this invention, the preferred mass ratio of compound B-6 to the volume ratio of the fourth polar organic solvent is 1 g: (10~30) mL.

[0050] After obtaining the activated solution and the suspension, the present invention adds the suspension to the activated solution to carry out an amidation reaction to obtain compound B-1.

[0051] In this invention, the suspension is preferably added dropwise. In this invention, the molar ratio of compound B-6 in the suspension to compound A-4 in the activation solution is preferably 1:(4~6), and in specific embodiments it can be 1:4, 1:5, or 1:6. In this invention, the temperature of the amidation reaction is preferably 50~60℃; the time of the amidation reaction is preferably 12~18h; and the amidation reaction is preferably carried out under stirring conditions.

[0052] After the amidation reaction is completed, the present invention preferably removes the solvent by rotary evaporation, and then purifies the crude product using an alkaline alumina silica gel column. In the present invention, the purification is preferably performed by first eluting with ethyl acetate, followed by gradient elution with a mixed solvent of ethyl acetate / methanol to obtain the purified compound B-1. In the present invention, during the gradient elution with the mixed solvent of ethyl acetate / methanol, the volume ratio of ethyl acetate to methanol preferably changes sequentially from 20:1 to 15:1 and then to 10:1.

[0053] After obtaining compound B-1, the present invention performs an acidic deprotection reaction on compound B-1 to obtain compound B-2.

[0054] In this invention, the conditions for the acidic deprotection reaction are the same as those for the acidic deprotection reaction of compound A-5, and will not be repeated here.

[0055] In this invention, compound B-6 is preferably obtained by self-preparation, and the preparation method of compound B-6 preferably includes: mixing palladium on carbon catalyst with an organic solution containing compound B-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound B-6; Compound B-5.

[0056] In this invention, the palladium metal content in the palladium-on-carbon catalyst (Pd / C catalyst) is preferably 10%. In this invention, the organic solution containing compound B-5 is preferably obtained by dissolving compound B-5 in an organic solvent, preferably tetrahydrofuran and / or methanol. When the organic solvent is tetrahydrofuran and methanol, the volume ratio of tetrahydrofuran to methanol is preferably 1:1. In this invention, the mass-to-volume ratio of compound B-5 to the organic solvent is preferably 1 g:(4~4.5) mL; the mass ratio of the palladium-on-carbon catalyst to compound B-5 is preferably 1:(30~50), and in specific embodiments it can be 1:30, 1:35, 1:40, 1:45, or 1:50. In this invention, the pressure of the hydrogen atmosphere is preferably 2~6 MPa, and in specific embodiments it can be 2, 3, 4, 5, or 6 MPa. In this invention, the reduction reaction is preferably carried out under stirring conditions at room temperature; the duration of the reduction reaction is preferably 6 to 12 hours, and in specific embodiments it can be 6, 7, 8, 9, 10, 11 or 12 hours.

[0057] In this invention, compound B-5 is preferably obtained by self-preparation, and the preparation method of compound B-5 preferably includes: dissolving compound B-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound B-5; Compound B-4.

[0058] In this invention, the polar organic solvent is preferably one or more of methanol, ethanol, and tetrahydrofuran; the mass-to-volume ratio of compound B-4 to the polar organic solvent is preferably 1 g:(8~12) mL. In this invention, the ethylenediamine solution is preferably obtained by dissolving ethylenediamine in a solvent, preferably methanol; the mass-to-volume ratio of ethylenediamine to the solvent in the ethylenediamine solution is preferably 1 g:(2~3) mL. In this invention, the molar ratio of compound B-4 to ethylenediamine is preferably 1:(20~30), and in specific embodiments it can be 1:20, 1:23, 1:25, 1:28, or 1:30. In this invention, the solution of compound B-4 is preferably cooled to -10~0℃ before the ethylenediamine solution is added. In this invention, the ethylenediamine solution is preferably added dropwise.

[0059] In this invention, the aminolysis reaction is preferably carried out under atmospheric pressure, room temperature, and stirring conditions. This invention does not impose a specific time limit on the aminolysis reaction; complete reaction is sufficient. In the embodiments of this invention, the reaction time is specifically 3-4 days. After the aminolysis reaction is completed, excess ethylenediamine is initially removed by rotary evaporation at 40°C. A mixed solvent of methanol and toluene (volume ratio 1:9) is added to the resulting residue for azeotropic treatment to completely remove residual ethylenediamine. Finally, the azeotropic solvent is removed by rotary evaporation at 60°C to obtain compound B-5.

[0060] In this invention, compound B-4 is preferably prepared by self-preparation, and the preparation method of compound B-4 preferably includes the following steps: Compound B-3 was dissolved in a polar organic solvent, and a solution of methyl acrylate was added to the resulting solution to carry out an aminolysis reaction to obtain compound B-4. Compound B-3.

[0061] In this invention, the polar organic solvent is preferably one or more of methanol, ethanol, and tetrahydrofuran; the mass-to-volume ratio of compound B-3 to the polar organic solvent is preferably 1 g:(1.5~3) mL. In this invention, the methyl acrylate solution is preferably obtained by dissolving methyl acrylate in a solvent, preferably methanol; the mass-to-volume ratio of methyl acrylate to the solvent in the methyl acrylate solution is preferably 1 g:(2~3) mL. In this invention, the molar ratio of compound B-3 to methyl acrylate is preferably 1:(3~4). In this invention, the solution of compound B-3 is preferably cooled to -10~0℃ before the methyl acrylate solution is added. In this invention, the methyl acrylate solution is preferably added dropwise.

[0062] After the addition is complete, the reaction is preferably carried out at -10~0℃ for 2 hours with stirring. Then, the reaction system is transferred to room temperature under normal pressure and the reaction is continued with stirring for 24 hours. After the reaction is completed, excess methyl acrylate and solvent are removed using a rotary evaporator at 45℃ to obtain compound B-4.

[0063] The preparation method of the gadolinium complex with the structure shown in Formula 2 will be described below.

[0064] When the gadolinium complex has the structure shown in Formula 2, the method for preparing the gadolinium complex preferably includes the following steps: Compound C-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 2. Compound C-2.

[0065] In this invention, the molar ratio of compound C-2 to soluble inorganic gadolinium salt is preferably 1:(2.2~2.4), and the preparation method of gadolinium complex with the same structure as shown in Formula 3 is not described here.

[0066] After the complexation reaction is completed, the present invention preferably transfers the obtained solution into a 1 kDa dialysis membrane for dialyzing and freeze-dries the final osmotic residue to obtain a gadolinium complex having the structure shown in Formula 1.

[0067] In this invention, the preparation method of compound C-2 preferably includes the following steps: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound C-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound C-1; Compound C-1 was subjected to an acidic deprotection reaction to obtain compound C-2; Compound A-4; Compound C-6; Compound C-1.

[0068] In this invention, compound A-4, HATU, DIPEA and a polar organic solvent are mixed to obtain an activated solution.

[0069] In this invention, the reaction conditions are the same as those for preparing the activation solution in the preparation method of compound A-6, and will not be repeated here.

[0070] In this invention, compound C-6 is dispersed in a polar organic solvent to obtain a suspension.

[0071] In this invention, the polar organic solvent is preferably one or more of DMF, DMAC, NMP, and DMSO. In this invention, the molar ratio of compound C-6 in the suspension to compound A-4 in the activation solution is preferably 1:(6~9), and in specific embodiments it can be 1:6, 1:7, 1:8, or 1:9. In this invention, the mass ratio of compound C-6 to the volume ratio of the polar organic solvent is preferably 1 g:(10~30) mL.

[0072] After obtaining the activated solution and the suspension, the present invention adds the suspension to the activated solution to carry out an amidation reaction to obtain compound C-1.

[0073] In this invention, the suspension is preferably added dropwise. In this invention, the temperature of the amidation reaction is preferably 50-60°C; the time of the amidation reaction is preferably 12-18 hours; and the amidation reaction is preferably carried out under stirring conditions.

[0074] After the amidation reaction is completed, the present invention preferably removes the solvent by rotary evaporation, and then purifies the crude product using an alkaline alumina silica gel column. In the present invention, the purification is preferably performed by first eluting with ethyl acetate, followed by gradient elution with a mixed solvent of ethyl acetate / methanol to obtain the purified compound B-1. In the present invention, during the gradient elution with the mixed solvent of ethyl acetate / methanol, the volume ratio of ethyl acetate to methanol is preferably varied from 20:1 to 15:1 or 10:1.

[0075] After obtaining compound C-1, the present invention performs an acidic deprotection reaction on compound C-1 to obtain compound C-2.

[0076] In this invention, the conditions for the acidic deprotection reaction are the same as those for the acidic deprotection reaction of compound A-5, and will not be repeated here.

[0077] In this invention, compound C-6 is preferably prepared by itself; the preparation method of compound C-6 preferably includes the following steps: mixing palladium on carbon catalyst with an organic solution containing compound C-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound C-6; Compound C-5.

[0078] In this invention, the palladium metal content in the palladium-on-carbon catalyst (Pd / C catalyst) is preferably 10%. In this invention, the organic solution containing compound C-5 is preferably obtained by dissolving compound C-5 in an organic solvent, preferably tetrahydrofuran and / or methanol. When the organic solvent is tetrahydrofuran and methanol, the volume ratio of tetrahydrofuran to methanol is preferably 1:1. In this invention, the mass-to-volume ratio of compound C-5 to the organic solvent is preferably 1 g:(4~4.5) mL; the mass ratio of the palladium-on-carbon catalyst to compound C-5 is preferably 1:(30~50), and in specific embodiments, it can be 1:30, 1:35, 1:40, 1:45, or 1:50. In this invention, the pressure of the hydrogen atmosphere is preferably 2~6 MPa, and in specific embodiments, it can be 2, 3, 4, 5, or 6 MPa. In this invention, the reduction reaction is preferably carried out under stirring conditions at room temperature; the duration of the reduction reaction is preferably 6 to 12 hours, and in specific embodiments it can be 6, 7, 8, 9, 10, 11 or 12 hours.

[0079] In this invention, the preparation method of compound C-5 preferably includes the following steps: dissolving compound C-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound C-5; Compound C-4.

[0080] In this invention, the polar organic solvent is preferably one or more of methanol, ethanol, and tetrahydrofuran; the mass-to-volume ratio of compound C-4 to the polar organic solvent is preferably 1 g: (8~12) mL. In this invention, the ethylenediamine solution is preferably obtained by dissolving ethylenediamine in a solvent, preferably methanol; the mass-to-volume ratio of ethylenediamine to the solvent in the ethylenediamine solution is preferably 1 g: (2~3) mL. In this invention, the molar ratio of compound C-4 to ethylenediamine is preferably 1: (30~45), and in specific embodiments it can be 1:30, 1:35, 1:40, or 1:45. In this invention, the solution of compound C-4 is preferably cooled to -10~0℃ before the ethylenediamine solution is added. In this invention, the ethylenediamine solution is preferably added dropwise.

[0081] In this invention, the aminolysis reaction is preferably carried out under atmospheric pressure, room temperature, and stirring conditions. This invention does not impose a specific time limit on the aminolysis reaction; complete reaction is sufficient. In the embodiments of this invention, the reaction time is specifically 3-4 days. After the aminolysis reaction is completed, it is preferred to first use a rotary evaporator at 40-45°C to remove excess ethylenediamine, and then add a mixed solvent of methanol and toluene (volume ratio 1:9) to the resulting residue at 60-70°C for azeotropic treatment to completely remove residual ethylenediamine. Finally, the azeotropic solvent is removed by rotary evaporation at 60°C to obtain compound C-5.

[0082] In this invention, compound C-4 is preferably prepared by self-preparation, and the preparation method of compound C-4 preferably includes the following steps: Compound C-3 was dissolved in a polar organic solvent, and a solution of methyl acrylate was added to the resulting solution to carry out an aminolysis reaction to obtain compound C-4. Compound C-3.

[0083] In this invention, the polar organic solvent is preferably one or more of methanol, ethanol, and tetrahydrofuran; the mass-to-volume ratio of compound C-3 to the polar organic solvent is preferably 1 g : (1.5~3) mL. In this invention, the methyl acrylate solution is preferably obtained by dissolving methyl acrylate in a solvent, preferably methanol; the mass-to-volume ratio of methyl acrylate to the solvent in the methyl acrylate solution is preferably 1 g : (2~3) mL. In this invention, the molar ratio of compound C-3 to methyl acrylate is preferably 1 : (3~4). In this invention, the solution of compound C-3 is preferably cooled to -10~0℃ before the solution of methyl acrylate is added. In this invention, the solution of methyl acrylate is preferably added dropwise.

[0084] After the addition is complete, the reaction is preferably carried out at -10~0℃ for 2 hours with stirring. Then, the reaction system is transferred to room temperature under normal pressure and the reaction is continued with stirring for 24 hours. After the reaction is completed, excess methyl acrylate and solvent are removed using a rotary evaporator at 45℃ to obtain compound C-4.

[0085] In this invention, the English name of compound A-1 is 1,4,7,10-tetraazacyclododecane, the English name of compound A-2 is benzyl2-(1,4,7,10-tetraazacyclododecan-1-yl)acetate, and the English name of compound A-3 is tri-tert-butyl2,2',2''-(10-(2-(benzyloxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1 The English name of compound A-4 is 2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)aceticacid, and the English name of compound A-5 is 1,4,7,10-Tetraazacyclododecane-1,4,7-triaceticacid,10,10′,10′′,10′′′-[1,2-eth anediylbis[nitrilobis[(1-oxo-3,1-propanediyl)imino-2,1-ethanediylimino(2-oxo-2,1-ethanediyl)]]]tetrakis-,1,1′,1′′,1′′′,4,4′,4′′,4′′′,7,7′,7′′,7′′′-dodecakis(1,1-dimethylethyl), the English name of compound A-6 is 1,4,7-Tris(carboxymethy l)-10-[2-[bis(carboxymethyl)amino]ethyl]-1,4,7,10-tetraazacyclododecane,1,1',1'',1''',4,4',4''',7,7',7''',7'''-dodecakis(1,1-dimethylethyl)ester, compound B-3 is named N1,N2-dibenzylethane-1,2-diamine, compound B-4 is named dimethyl 3,3'-(ethane-1,2-diylbis(benzylazanediyl))dipropionate, and compound B-5 is named 3,3'-(ethane-1,2-diylbis(benzylazanediyl))bis(N-(2-aminoethyl)propanamide), the English name of compound B-6 is 3,3'-(ethane-1,2-diylbis(azanediyl))bis(N-(2-aminoethyl)propanamide), the English name of compound B-1 is 1,1',1'',1''',4,4',4'',4 ''',7,7',7''',7'''-Dodeca-tert-butyl10-(1,1',1''',1'''-tetra(tert-butyl)2,2'-((2-(bis(tert-butoxycarbonylmethyl)amino)ethyl)azanediyl)bis(ethane-2,1-diyl)bis(azanediyl))bis(2-o xoethane-2,1-diyl)bis(azanediyl))diacetate)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate, compound B-2 is named 2,2',2''-(10-((Carboxymethyl)(2-((2-((carboxymethyl)(2-((carboxymethyl)amino)ethyl)amino)ethyl)(carboxymethyl)amino)ethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triaceticacid, compound C-3 is named N1-benzylethane-1,2-diamine, and compound C-4 is named dimethyl ,3'-((2-(benzyl(3-methoxy-3-oxopropyl)amino)ethyl)azanediyl)dipropionate, compound C-5 is named 3,3'-((2-((3-((2-aminoethyl)amino)-3-oxopropyl)(benzyl)amino)ethyl)azanediyl)bis(N-(2-aminoethyl)propanamide), compound C-6 is named 3,3'-((2-((3-((2-aminoethyl)amino)-3-oxopropyl)amino)ethyl)azanediyl)bis(N-(2-aminoethyl)propanamide), the English name of compound C-1 is 2',2''-(10-((Carboxymethyl)(2-((2-((carb oxymethyl)(2-((carboxymethyl)amino)ethyl)amino)ethyl)(carboxymethyl)amino)ethyl)amino)ethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triaceticacid, chemical The English name of compound C-2 is 1,1',1'',1''',4,4',4'',4''',7,7',7''',7'''-Dodeca-tert-butyl10-(1,1',1''',1'''-tetra(tert-butyl)2,2'-((2-(bis(tert-butoxycarbonylmethyl)amino )ethyl)azanediyl)bis(ethane-2,1-diyl)bis(azanediyl))bis(2-oxoethane-2,1-diyl)bis(azanediyl))diacetate)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate. ,

[0086] The preparation method provided by this invention is concise and efficient. By optimizing the reaction sequence and conditions, the entire synthetic route is rationally structured, avoiding cumbersome purification processes. The conditions are mild: most reactions are carried out at ambient pressure, room temperature, or moderate temperatures, ensuring high safety and ease of operation. The yields are high: each reaction step yields ideal results, and the final product has good purity. It is easily scaled up: this method is suitable for process scale-up and has industrialization potential.

[0087] This invention provides the application of the gadolinium complex described in the above-described scheme or the gadolinium complex prepared by the preparation method described in the above-described scheme in the preparation of CT or MRI contrast agents.

[0088] The following detailed description of the gadolinium complexes, their preparation methods, and applications provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0089] Example 1: Preparation of Core-PAMAM Under a nitrogen atmosphere, 20.64 g (0.2400 mol) of methyl acrylate was dissolved in 40 mL of methanol, and the resulting solution was cooled to 0 °C in an ice-water bath, denoted as solution A. 2.40 g (0.0399 mol) of ethylenediamine was dissolved in 20 mL of methanol to prepare a methanol solution of ethylenediamine, denoted as solution B. Under continuous stirring and ice-water bath cooling, solution B was slowly added dropwise to solution A using a constant-pressure dropping funnel, with the dropping rate controlled at 1 d / s. After the addition was complete, the reaction was continued with stirring under ice-water bath conditions for 2 h. The reaction system was then transferred to a normal pressure and room temperature environment, and the reaction was continued with stirring for 24 h. After the reaction was completed, excess methyl acrylate and methanol solvent were removed using a rotary evaporator at 45 °C, yielding 14.5 g of a light yellow oily product, with a yield of 90%.

[0090] Core-PAMAM.

[0091] Example 2: Preparation of GO-PAMAM Under a nitrogen atmosphere, 10 g (0.025 mol) of the product from Example 1 was dissolved in 100 mL of methanol, and the resulting solution was cooled to 0°C in an ice-water bath, denoted as solution C. 75 g (1.248 mol) of ethylenediamine was dissolved in 200 mL of methanol to prepare a methanol solution of ethylenediamine, denoted as solution D. Under ice-water bath cooling and continuous stirring, solution D was slowly added dropwise to solution C through a constant-pressure dropping funnel at a dropping rate of 2 drops / s. After the addition was complete, the reaction system was moved to a normal pressure and room temperature environment, and the reaction was continuously stirred for 4 days. After the reaction was completed, excess ethylenediamine was initially removed by rotary evaporation at 40°C. An azeotropic treatment was then performed on the resulting residue using a mixed solvent of methanol and toluene (methanol to toluene volume ratio of 1:9) to completely remove residual ethylenediamine. Finally, the azeotropic solvent was removed by rotary evaporation at 60°C, yielding 12.13 g of the target product in a light yellow oily state, with a yield of 94%.

[0092] Example 3: Synthesis of compound A-2 Under a nitrogen atmosphere, 60 g (0.348 mol) of compound A-1 was dissolved in 20 mL of dichloromethane to prepare solution A. Separately, 40 g (0.174 mol) of benzyl-bromoacetate was dissolved in 100 mL of dichloromethane to prepare solution B. The solutions were added dropwise at a rate of 1 d / s using a constant-pressure dropping funnel. After the addition was complete, the reaction was continued with stirring at room temperature for 4 h. After the reaction was complete, the solid was removed by filtration, and the filtrate was evaporated at 30 °C using a rotary evaporator to remove dichloromethane, yielding the crude product. The crude product was purified by silica gel column chromatography. Gradient elution was performed using a dichloromethane to dichloromethane / methanol (volume ratio 1:1) mixed solvent system, and the eluent containing the target product was collected by thin-layer chromatography. After concentration, the purified final product, compound A-2, was obtained, yielding 32 g (58% yield).

[0093] Compound A-1, Compound A-2.

[0094] Example 4: Synthesis of compound A-3 32 g (0.1 mol) of the product from Example 3 was dissolved in 400 mL of acetonitrile, followed by the addition of 55.28 g (0.4 mol) of potassium carbonate. The mixture was stirred until completely dissolved to prepare mixed solution A. Separately, 78 g (0.4 mol) of tert-butyl bromoacetate was dissolved in 100 mL of acetonitrile to prepare solution B. Solution B was added to mixed solution A at room temperature, and the reaction was allowed to proceed for at least 60 minutes. After the reaction was complete, the acetonitrile solvent was removed using a rotary evaporator. The crude product was purified by silica gel column chromatography. First, impurities were removed with pure dichloromethane, then the elution was performed using a dichloromethane / methanol (9:1 v / v) mixture. The eluent containing the target product was collected by thin-layer chromatography and concentrated to obtain the purified final product compound A-3, yielding 39 g (59% yield).

[0095] Compound A-3.

[0096] Example 5: Synthesis of compound A-4 39 g (0.059 mol) of the product from Example 4 was weighed and dissolved in 160 mL of a mixed solvent of tetrahydrofuran and methanol (volume ratio 1:1). Then, 1 g of 10% Pd / C catalyst was added to the solution. The reaction system was placed under a hydrogen atmosphere and stirred at 6 MPa for 6 h for hydrogenation. After the reaction was complete, the Pd / C catalyst was removed by filtration. The filtrate was collected and the crude product was obtained by rotary evaporation. The crude product was purified by silica gel column chromatography. Gradient elution was performed using a mixed solvent of dichloromethane and methanol (volume ratio 9:1), and the eluent fraction with an Rf value of approximately 0.7 was collected by thin-layer chromatography. After concentration, 5.2 g of purified product (yield 15.4%) was obtained. Figure 1 This is an NMR image of compound A-4 obtained in Example 5. ¹H NMR (400 MHz, DMSO-d6) δ 3.17 (s, 8H), 2.81 (d, J = 63.9 Hz, 16H), 1.44 (ddd, J = 11.4, 9.0, 3.9 Hz, 27H). Figure 1 It is known that the present invention synthesized compound A-4 with the target structure.

[0097] Example 6: Synthesis of compound A-5 Weigh 1 g (1.7 mmol) of the product from Example 5 and dissolve it in 5 mL of DMAC to form a homogeneous solution. Then, add 0.773 g (2.04 mmol) of HATU and 0.263 g (2.04 mmol) of DIPEA sequentially, and stir at room temperature and atmospheric pressure for 20 minutes to complete the pre-activation of the reactants. This solution is designated as organic solvent A. Separately, weigh 0.07315 g (0.1416 mmol) of the product from Example 2, GO-PAMAM, and disperse it in 1.5 mL of DMAC to form a suspension. Slowly add this suspension to organic solvent A. Place the mixed reaction system at 50°C and stir overnight. After the reaction is complete, wash with water and then concentrate using a rotary evaporator to remove the solvent. The crude product was purified by alkaline alumina column chromatography. First, 300 mL of ethyl acetate was used for elution, followed by gradient elution with a mixed solvent of ethyl acetate / methanol. Specifically, 200 mL of ethyl acetate / methanol at a volume ratio of 20:1 was used for elution, then 200 mL of ethyl acetate / methanol at a volume ratio of 15:1 was used, and finally 200 mL of ethyl acetate / methanol at a volume ratio of 10:1 was used. The eluent fraction containing the target product was collected, concentrated, and 0.317 g of purified product was obtained, with a yield of 82%. Figure 2This is an NMR image of compound A-5 obtained in Example 6. 1H NMR (400 MHz, DMSO-d6) δ 7.27(s, 2H), 4.19 – 4.00 (m, 7H), 3.76 (s, 11H), 3.69 (s, 4H), 3.39 (s, 5H), 3.25(d, J = 9.1 Hz, 2H), 3.17 (s, 4H), 3.14 (s, 1H), 2.99 – 2.90 (m, 8H), 2.88 (s, 13H), 2.78 – 2.60 (m, 9H), 2.45 (s, 1H), 2.28 (t, J = 7.3 Hz, 1H), 2.00(d, J = 9.9 Hz, 1H), 1.53 – 1.37 (m, 132H). From Figure 2 It is known that the present invention synthesized compound A-6 with the target structure.

[0098] Example 7: Synthesis of compound A-6 0.317 g of the product from Example 6 was treated with 30 mL of TFA and stirred overnight at room temperature and atmospheric pressure. The reaction mixture was concentrated under reduced pressure, and the resulting residue was dissolved in 10 mL of water and lyophilized to give 0.223 g of the product, with a yield of 91%.

[0099] Example 8: Synthesis of a four-arm gadolinium contrast agent The product of Example 7 was dissolved in 5 mL of water, gadolinium triacetate tetrahydrate was added, and the reaction mixture was stirred at 70 °C for 2 h. The pH of the resulting solution was adjusted to 4.5 by adding an aqueous sodium hydroxide solution (concentration of 2 mol / L), and stirring was continued at 70 °C for 2 days. The resulting solution was transferred to a 2.5 kDa dialysis membrane and dialyzed with water, and the final osmotic residue was lyophilized to obtain a four-arm gadolinium contrast agent (structure of Formula 3).

[0100] Example 9: Synthesis of compound B-4 Under a nitrogen atmosphere, 10.73 g (0.1248 mol) of methyl acrylate was dissolved in 20 mL of methanol, and the resulting solution was cooled to 0 °C in an ice-water bath, denoted as solution A. 10 g (0.0416 mol) of compound B-3 was dissolved in 30 mL of methanol, denoted as solution B. Under continuous stirring and ice-water bath cooling, solution B was slowly added dropwise to solution A using a constant-pressure dropping funnel, with the dropping rate controlled at 1 d / s. After the addition was complete, the reaction was continued under ice-water bath conditions with stirring for 2 h. The reaction system was then transferred to a normal pressure and room temperature environment, and the reaction was continued with stirring for 24 h. After the reaction was completed, excess methyl acrylate and methanol solvent were removed using a rotary evaporator at 45 °C, yielding 15.6 g of a light yellow oily product, with a yield of 91%.

[0101] Example 10: Synthesis of Compound B-5 Under a nitrogen atmosphere, 10 g (0.024 mol) of the product from Example 9 was dissolved in 100 mL of methanol, and the resulting solution was cooled to 0°C in an ice-water bath, denoted as solution C. 36 g (0.6 mol) of ethylenediamine was dissolved in 100 mL of methanol to prepare a methanol solution of ethylenediamine, denoted as solution D. Under ice-water bath cooling and continuous stirring, solution D was slowly added dropwise to solution C through a constant-pressure dropping funnel at a dropping rate of 2 drops / s. After the addition was complete, the reaction system was moved to a normal pressure and room temperature environment, and the reaction was continuously stirred for 4 days. After the reaction was completed, excess ethylenediamine was initially removed by rotary evaporation at 40°C. A mixed solvent of methanol and toluene (volume ratio 1:9) was added to the residue for azeotropic treatment to completely remove residual ethylenediamine. Finally, the azeotropic solvent was removed by rotary evaporation at 60°C, yielding 9.55 g of a light yellow oily product, with a yield of 85%.

[0102] Example 11: Synthesis of compound B-6 Weigh 5 g (0.011 mol) of the product from Example 10 and dissolve it in 20 mL of a mixed solvent of tetrahydrofuran and methanol (volume ratio 1:1). Then, add 0.1 g of 10% Pd / C catalyst to the solution. Place the reaction system under a hydrogen atmosphere and stir at 6 MPa for 6 h to carry out the hydrogenation reaction. After the reaction is complete, separate and remove the Pd / C catalyst by filtration. Collect the filtrate and remove the solvent using a rotary evaporator to obtain 2.89 g of product, with a yield of 91%.

[0103] Example 12: Synthesis of Compound B-1 Weigh 1 g (1.7 mmol) of the product from Example 5 and dissolve it in 5 mL of DMAC to form a homogeneous solution. Then, add 0.773 g (2.04 mmol) of HATU and 0.263 g (2.04 mmol) of DIPEA sequentially and stir at room temperature and atmospheric pressure for 20 minutes to complete the pre-activation of the reactants. This solution is designated as organic solvent A. Separately, weigh 0.0817 g (0.2833 mmol) of the product from Example 11 and disperse it in 2 mL of DMAC to form a suspension. Slowly add this suspension to organic solvent A. Place the mixed reaction system at 50 °C and stir overnight. After the reaction is complete, wash with water and then concentrate using a rotary evaporator to remove the solvent. Purify the crude product using basic alumina column chromatography. First, elute with ethyl acetate, then switch to a gradient elution with a mixed solvent of ethyl acetate / methanol. Collect the eluent containing the target product, concentrate it, and obtain 0.301 g of purified product, with a yield of 76%. Figure 3This is an NMR image of compound B-1 obtained in Example 12. 1 H NMR (400 MHz, DMSO- d 6) δ 5.76 (s, 1H), 4.16 – 4.07 (m, 1H), 2.86 (s, 3H), 2.69 (s, 12H), 1.49 (s, 3H), 1.43 (d, J =2.5 Hz, 69H), 1.22 (dd, J = 12.0, 4.7 Hz, 3H). By Figure 3 It is known that the present invention synthesized compound B-1 with the target structure.

[0104] Example 13: Synthesis of compound B-2 Weigh 0.3 g (0.215 mmol) of the product from Example 12 and treat with 20 mL of TFA. Stir overnight at room temperature and atmospheric pressure. Concentrate the reaction mixture under reduced pressure, dissolve the resulting residue in 10 mL of water, and freeze-dry to give 0.223 g, yield 97%.

[0105] Example 14: Synthesis of a two-arm gadolinium contrast agent The product of Example 13 was dissolved in 5 mL of water. Gadolinium triacetate tetrahydrate was added, and the reaction mixture was stirred at 70 °C for 2 h. The pH of the resulting solution was adjusted to 4.5 by adding an aqueous sodium hydroxide solution (2 mol / L), and stirring was continued at 70 °C for 2 days. The resulting solution was transferred to a 1 kDa dialysis membrane and dialyzed with water. The final osmotic residue was lyophilized to obtain a two-arm gadolinium contrast agent (structure of Formula 1).

[0106] Example 15: Synthesis of compound C-4 Under a nitrogen atmosphere, 26 g (0.3015 mol) of methyl acrylate was dissolved in 40 mL of methanol, and the resulting solution was cooled to 0 °C in an ice-water bath, denoted as solution A. 10 g (0.067 mol) of compound C-3 was dissolved in 30 mL of methanol, denoted as solution B. Under continuous stirring and ice-water bath cooling, solution B was slowly added dropwise to solution A using a constant-pressure dropping funnel, with a dropping rate controlled at 1 d / s. After the addition was complete, the reaction was continued with stirring under ice-water bath conditions for 2 h. The reaction system was then transferred to a normal pressure and room temperature environment, and the reaction was continued with stirring for 24 h. After the reaction was completed, excess methyl acrylate and methanol solvent were removed using a rotary evaporator at 45 °C, yielding 23.5 g of a light yellow oily product, with a yield of 89%.

[0107] Example 16: Synthesis of compound C-5 Under a nitrogen atmosphere, 10 g (0.024 mol) of the product from Example 15 was dissolved in 100 mL of methanol, and the resulting solution was cooled to 0°C in an ice-water bath, denoted as solution C. 54 g (0.9 mol) of ethylenediamine was dissolved in 160 mL of methanol to prepare a methanol solution of ethylenediamine, denoted as solution D. Under ice-water bath cooling and continuous stirring, solution D was slowly added dropwise to solution C through a constant-pressure dropping funnel at a rate of 2 drops / s. After the addition was complete, the reaction system was moved to a normal pressure and room temperature environment, and the reaction was continuously stirred for 4 days. After the reaction was completed, excess ethylenediamine was initially removed by rotary evaporation at 40°C. A mixed solvent of methanol and toluene (volume ratio 1:9) was added to the residue for azeotropic treatment to completely remove residual ethylenediamine. Finally, the azeotropic solvent was removed by rotary evaporation at 60°C, yielding 9.89 g of a light yellow oily product, with a yield of 82%.

[0108] Example 17: Synthesis of compound C-6 Weigh 5 g (0.0102 mol) of the product from Example 16 and dissolve it in 20 mL of a mixed solvent of tetrahydrofuran and methanol (volume ratio 1:1). Then, add 0.1 g of 10% Pd / C catalyst to the solution. Place the reaction system under a hydrogen atmosphere and stir at 6 MPa for 6 h to carry out the hydrogenation reaction. After the reaction is complete, separate and remove the Pd / C catalyst by filtration. Collect the filtrate and remove the solvent using a rotary evaporator to obtain 3.35 g of product, with a yield of 82%.

[0109] Example 18: Synthesis of compound C-1 Weigh 1 g (1.7 mmol) of the product from Example 5 and dissolve it in 5 mL of DMAC to form a homogeneous solution. Then, add 0.773 g (2.04 mmol) of HATU and 0.263 g (2.04 mmol) of DIPEA sequentially and stir at room temperature and atmospheric pressure for 20 minutes to complete the pre-activation of the reactants. This solution is designated as organic solvent A. Separately, weigh 0.076 g (0.188 mmol) of the product from Example 17 and disperse it in 2 mL of DMAC to form a suspension. Slowly add this suspension to organic solvent A. Place the mixed reaction system at 50 °C and stir overnight. After the reaction is complete, wash with water and then concentrate using a rotary evaporator to remove the solvent. Purify the crude product using alkaline alumina column chromatography. First, elute with ethyl acetate, then switch to a gradient elution with a mixed solvent of ethyl acetate / methanol. Collect the eluent containing the target product, concentrate it, and obtain 0.306 g of purified product, with a yield of 79%. Figure 4This is an NMR image of compound C-1 obtained in Example 18. 1H NMR (400 MHz, DMSO-d6) δ 7.27 (s,2H), 4.19 – 4.00 (m, 7H), 3.76 (s, 11H), 3.69 (s, 4H), 3.39 (s, 5H), 3.25 (d,J = 9.1 Hz, 2H), 3.17 (s, 4H), 3.14 (s, 1H), 2.99 – 2.90 (m, 8H), 2.88 (s,13H), 2.78 – 2.60 (m, 9H), 2.45 (s, 1H), 2.28 (t, J = 7.3 Hz, 1H), 2.00 (d, J= 9.9 Hz, 1H), 1.53 – 1.37 (m, 132H). By Figure 3 It is known that the present invention synthesized compound C-1 with the target structure.

[0110] Example 19: Synthesis of compound C-2 0.306 g (0.148 mmol) of the product from Example 18 was weighed and treated with 20 mL of TFA, and stirred overnight at room temperature under normal pressure. The reaction mixture was concentrated under reduced pressure, and the resulting residue was dissolved in 10 mL of water and lyophilized to give 0.222 g of purified product, with a yield of 96%.

[0111] Example 20: Synthesis of a three-arm gadolinium contrast agent The product of Example 19 was dissolved in 5 mL of water. Gadolinium triacetate tetrahydrate was added, and the reaction mixture was stirred at 70 °C for 2 h. The pH of the resulting solution was adjusted to 4.5 by adding an aqueous sodium hydroxide solution (2 mol / L), and stirring was continued at 70 °C for 2 days. The resulting solution was transferred to a 1 kDa dialysis membrane and dialyzed with water. The final osmotic residue was lyophilized to obtain a two-arm gadolinium contrast agent.

[0112] Test Example 1: Contrast-Enhanced CT Imaging Experiment This experiment evaluated the imaging performance of commercial contrast agents (gadolinium) and synthetic contrast agents in CT imaging using Siemens Healthineers NAEOTOM Alpha and United Imaging Healthcare uCT 960+ CT scanners. Key aspects included: establishing standard curves for the commercial contrast agent, comparing the imaging effects of commercial and synthetic contrast agents at low concentrations, and calculating the concentration-efficiency ratio at equivalent CT values.

[0113] CT scanner: Siemens Healthineers NAEOTOM Alpha CT scanner (128 slices, tube voltage 100~140kV, tube current automatically adjusted).

[0114] United Imaging Healthcare uCT 960+ CT scanner (96 slices, tube voltage 80~120kV, spatial resolution 0.3mm).

[0115] Scanning parameters: Axial scan mode, layer thickness 1mm, reconstruction kernel function is standard body algorithm.

[0116] Data Analysis: The standard curve is fitted by linear regression (CT value vs. concentration).

[0117] Imaging effect evaluation: Significant imaging is defined as an increase in CT value >10 HU.

[0118] Concentration efficiency calculation: Under the same CT value (e.g., 300 HU), compare the concentration ratio of commercial contrast agents with that of four-arm contrast agents.

[0119] The results are as follows: Standard curves of commercial contrast agents, such as Figure 5 As shown, by Figure 5 It can be seen that commercially available contrast agents exhibit a good linear relationship within the concentration range (R0). 2 =0.9866), the equation is: CT value (HU) = 6.64 + 1120.97 x. This indicates that the CT value is highly correlated with concentration, making it suitable for quantitative analysis. Imaging results of commercial contrast agents are as follows: Figure 9 As shown in the figure, brightness is highly correlated with concentration. Figure 9 To illustrate the imaging effects of different concentrations of contrast agents, the first row from the left shows three-arm contrast agents, the second row shows commercially available contrast agents, the third row shows two-arm contrast agents, the first five from the right show four-arm contrast agents, and the last is 0.9% saline. Specifically, the contrast agent concentrations in the three rows from left to right are 0.02885, 0.0577, 0.08655, 0.1154, and 0.14425 mmol / mL, respectively. The contrast agent concentrations in the three rows from top to bottom and left to right (excluding the saline group) are 0.02885, 0.0577, 0.08655, 0.1154, and 0.14425 mmol / mL, respectively.

[0120] The standard curve of contrast agent in four arms is as follows: Figure 8 As shown, the horizontal axis represents the contrast agent concentration in mmol / mL, and the vertical axis B represents the CT value (HU). Figure 8 It can be seen that the contrast agents in the four arms exhibit a good linear relationship within the concentration range (R0). 2 =0.99071), the equation is: y = -34.27 + 4109.15 x, where y represents the CT value (HU), and x is the contrast agent concentration (mmol / mL). This indicates a high correlation between CT value and concentration, suitable for quantitative analysis. The imaging results of the four-arm contrast agent are shown below. Figure 9 As shown, by Figure 9 It can be seen that although the concentration of the four-arm contrast agent (0.05 mmol / mL) is low, the imaging is obvious.

[0121] The standard curve of the contrast agent in the two arms is as follows: Figure 6 As shown, y = 7.97 + 191.68 x.

[0122] The standard curve of the contrast agent in the three arms is as follows: Figure 7 As shown, y = 27.87 + 384.40 x.

[0123] Concentration efficiency calculation: At the same CT value of 300, the required concentration of commercial contrast agents is approximately 0.2617 mmol / mL (based on a standard curve), while synthetic four-arm contrast agents require only 0.08135 mmol / mL. Two-arm contrast agents require 1.523 mmol / mL, and three-arm contrast agents require 0.708 mmol / mL.

[0124] Theoretically, increasing the number of gadolinium ions within the molecule should improve CT imaging intensity, but the actual effect is influenced by molecular structure, spatial arrangement, and physicochemical properties. Possible reasons include: (1) Reduced efficiency of individual gadolinium ions: In two- and three-armed molecules, gadolinium ions may be partially shielded by surrounding ligands (such as nitrogen and oxygen atoms), reducing their effective atomic number or electron density under X-rays, thus weakening the imaging contribution of individual gadolinium ions. Commercial contrast agents are optimized, and their single gadolinium ion design may make gadolinium ions more exposed or more easily interact with X-rays, thus resulting in higher gadolinium efficiency. (2) Molecular structure and synergistic effect: The molecular structures of two- and three-armed molecules are relatively simple (symmetrical distribution or linear connection), and gadolinium ions may act independently without synergistic enhancement, or even interfere with each other due to steric hindrance. The four gadolinium ions in a four-armed structure are arranged in a compact, branched manner. This design may produce a synergistic effect, enhancing the overall X-ray absorption capacity and doubling the contribution of each gadolinium ion.

[0125] The calculations show that the concentration of commercial contrast agent / the concentration of four-arm contrast agent is approximately 3.217 times. This indicates that the four-arm contrast agent of this invention can provide higher CT enhancement at a unit concentration, and its efficiency is superior to commercial products.

[0126] The experimental results above demonstrate that by optimizing the contrast agent structure, this invention can achieve effective CT imaging at low concentrations, potentially reducing patient dosage and toxic side effects.

[0127] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gadolinium complex, characterized in that, It has the structure shown in any one of Equations 1 to 3: Formula 1; Formula 2; Formula 3.

2. The method for preparing the gadolinium complex according to claim 1, characterized in that, When the gadolinium complex has the structure shown in Formula 3, the preparation method includes the following steps: Compound A-6, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 3. Compound A-6; When the gadolinium complex has the structure shown in Formula 1, the preparation method includes the following steps: Compound B-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 1. Compound B-2; When the gadolinium complex has the structure shown in Formula 2, the following steps are included: Compound C-2, a soluble inorganic gadolinium salt, and water were mixed, and the pH of the resulting reaction system was adjusted to 4-6 to carry out a complexation reaction to obtain the gadolinium complex having the structure shown in Formula 2. Compound C-2.

3. The preparation method according to claim 2, characterized in that, The preparation method of compound A-6 includes the following steps: Compound A-4, HATU, DIPEA, and a polar organic solvent were mixed to obtain an activated solution; GO-PAMAM was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound A-5; Compound A-5 was subjected to an acidic deprotection reaction to obtain compound A-6; Compound A-4; G0-PAMAM; Compound A-5.

4. The preparation method according to claim 2, characterized in that, The preparation method of compound B-2 includes: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound B-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound B-1; Compound B-1 was subjected to an acidic deprotection reaction to obtain compound B-2; Compound B-6; Compound B-1.

5. The preparation method according to claim 4, characterized in that, The preparation method of compound B-6 includes: mixing palladium on carbon catalyst with an organic solution containing compound B-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound B-6; Compound B-5.

6. The preparation method according to claim 5, characterized in that, The preparation method of compound B-5 includes: dissolving compound B-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound B-5; Compound B-4.

7. The preparation method according to claim 2, characterized in that, The preparation method of compound C-2 includes: mixing compound A-4, HATU, DIPEA and a polar organic solvent to obtain an activated solution; Compound C-6 was dispersed in a polar organic solvent to obtain a suspension; The suspension was added to an activation solution to carry out an amidation reaction, yielding compound C-1; Compound C-1 was subjected to an acidic deprotection reaction to obtain compound C-2; Compound A-4; Compound C-6; Compound C-1.

8. The preparation method according to claim 7, characterized in that, The preparation method of compound C-6 includes the following steps: mixing palladium on carbon catalyst with an organic solution containing compound C-5, and carrying out a reduction reaction under a hydrogen atmosphere to obtain compound C-6; Compound C-5.

9. The preparation method according to claim 8, characterized in that, The preparation method of compound C-5 includes the following steps: dissolving compound C-4 in a polar organic solvent, adding a solution of ethylenediamine to the resulting solution to carry out an aminolysis reaction, thereby obtaining compound C-5; Compound C-4.

10. The use of the gadolinium complex of claim 1 or the gadolinium complex prepared by any one of claims 2 to 9 in the preparation of CT or MRI contrast agents.

Images