Synthesis method of zirconium complex

Abstract

The object of the present invention is to synthesize a zirconium complex by reacting a low concentration of DOTA with a radioactive zirconium at a high reaction rate. A solution containing 40% to 95% of an organic substance having water miscibility is mixed with a compound containing a chelating agent represented by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and the like, and finally mixing the zirconium dissolved in the acidic solution into the obtained solution, and heating the obtained mixed solution to a prescribed temperature of 35° C. or more to synthesize the zirconium complex. The acidic solution is hydrochloric acid, and the organic substance is methanol or ethanol.

Description

Technical Field

[0001] The present invention relates to the synthesis 89 A method for synthesizing a zirconium complex of a complex of radioactive zirconium such as Zr and a chelating agent. Background Art

[0002] In the past, it was known that radioactive zirconium ( 89 Zr) is a radioactive isotope that is effective for medical imaging because of its high resolution and moderate half-life of about 78 hours. As a method for producing radioactive zirconium, a method of irradiating a yttrium (Y) target with a proton beam is known. In the production method using a proton beam, a trace amount of radioactive zirconium in the unit of several GBq (tens to hundreds of nanograms (ng) in mass) is generated in the unit of several hundred milligrams (mg) of yttrium by irradiation for several hours.

[0003] On the other hand, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid: DOTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (1,4,7-triazacyclononane-1,4,7-triacetic acid: NOTA), or similar compounds thereof are widely used as chelating agents for labeling of metal radionuclides. DOTA and NOTA are highly versatile chelating agents that form complexes with most metal nuclides such as radioactive copper (Cu), gallium (Ga), yttrium (Y), indium (In), lutetium (Lu), and actinium (Ac). It has been considered difficult to form a complex between DOTA and zirconium (Zr), but it is known that a complex can be formed by reacting them at a high temperature of about 95°C (see Non-Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-123372

[0007] Non-patent literature

[0008] Non-patent document 1: Zirconium tetraazamacrocycle complexes display extraordinary stability and provide a new strategy for zirconium-89-basedradiopharmaceutical development, Chem.Sci.2017,8,2309-2314.

[0009] Non-patent document 2: Evaluation of a chloride-based 89Zr isolation strategy using a tributyl phosphate (TBP)-functionalized extraction resin, Nucl. Bio. and Med., 2018, 64, 1-7. Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, in order to make radioactive zirconium ( 89 In order to react Zr with DOTA while ensuring sufficient radiochemical yield, it is necessary to make the concentration of DOTA higher than 10 -4 mol / L (see Non-Patent Document 2). It should be noted that the radiochemical yield refers to the yield of the target radioactive compound, which is calculated by dividing the radioactivity of the target compound by the radioactivity of the raw material, and is sometimes referred to as the yield. However, according to the disclosure of Non-Patent Document 2, even if the concentration of DOTA is higher than 10 -4 When the concentration of 2-hydroxy-1-nitrogen 2 ...

[0012] In addition, most of the reagents used in PET (Positron Emission Tomography) (hereinafter referred to as PET reagents) are administered in very small amounts of micrograms (μg). -4 10 mol / L -5 It is also considered sufficient to label radioactive zirconium with a reagent of low concentration of DOTA of about 10 mol / L. In this case, it is expected that DOTA and radioactive zirconium will combine at a reaction rate of more than 90%. However, even if the reaction conditions based on the prior art are higher than 10 -5 The concentration of mol / L is 10 -4The problem of the radiochemical yield of about 0% when DOTA is reacted with radioactive zirconium at a concentration of about mol / L is also present. The same problem exists in NOTA.

[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for synthesizing a zirconium complex by which a chelating agent such as DOTA or NOTA can react with radioactive zirconium at a high reaction rate to synthesize a zirconium complex even at a low concentration.

[0014] Means for solving problems

[0015] In order to solve the above-mentioned problems and achieve the purpose, a method for synthesizing a zirconium complex in one embodiment of the present invention is characterized in that a mixed solution is kept at a predetermined temperature or above to synthesize the zirconium complex, wherein the mixed solution is a mixture of: an organic solvent miscible with water; a chelating agent solution in which a chelating agent having a structure represented by the general formula (1) or the general formula (2) is dissolved; and zirconium dissolved in an acidic solution.

[0016]

Chemistry 1

[0017]

[0018] (In the general formula (1), R1, R2, R3, and R4 are each hydrogen (-H) (in this case, there is no further connection between R5 to R 12 ), -CH-, -(CH2) n CH- group, -N(=O)(CH2) n NCH- group, or -(CH2) n NC(=O)N- group. The above n is an integer greater than 0. R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 At least two of the above are selected from carboxylic acid, primary amide, hydroxamic acid, phosphonic acid, phosphoric acid, sulfonic acid, alcohol, amine, phenol, aniline, and esters, secondary amides, hydroxamic acid, and phosphates to which substituents are added, and the remaining substituents are hydrogen, an alkyl chain, a tert-butyl protected carboxylic acid, nitrobenzene, or an alkyl chain to which substituents are added. 20The functional groups contained in can be attached with a PET probe or a functional group that is easily combined with a PET probe. The functional group that is easily combined refers to carboxylic acid, carboxylic acid succinimidyl ester, carboxylic acid tetrafluorophenol ester, alcohol, amine, thiol, isothiocyanate, maleimide, phenol, aniline, benzoic acid, phenylisothiocyanate, or alkyne as a click chemistry reagent, azide, DBCO, BCN, TCO, norbornene, tetrazine, or methyl tetrazine. The above R5 to R 20 It may have a structure with the above-mentioned functional group that is easy to bind, or a condensed structure of the PET probe and the above-mentioned functional group that is easy to bind.)

[0019] (In general formula (2), R 21 , R 22 , R 23 are hydrogen (-H) (in this case, there is no further connection R 24 ~R 29 ), -CH-, -(CH2) n CH- group, -N(=O)(CH2) n NCH- group, or -(CH2) n NC(=O)N- group. The above n is an integer greater than 0. 24 , R 25 , R 26 , R 27 , R 28 , R 29 , R 30 , R 31 , R 32 , R 33 , R 34 , R 35 At least two of the R are selected from carboxylic acid, primary amide, hydroxamic acid, phosphonic acid, phosphoric acid, sulfonic acid, alcohol, amine, phenol, aniline, and esters, secondary amides, hydroxamic acid, and phosphates to which substituents are added, and the remaining substituents are hydrogen, an alkyl chain, a tert-butyl protected carboxylic acid, nitrobenzene, or an alkyl chain to which substituents are added. 24 ~R 35 The functional groups contained in can be attached with a PET probe or a functional group that is easily bound to a PET probe. The functional group that is easily bound refers to the following functional groups. Carboxylic acid, carboxylic acid succinimidyl ester, carboxylic acid tetrafluorophenol ester, alcohol, amine, thiol, isothiocyanate, maleimide, phenol, aniline, benzoic acid, phenylisothiocyanate, or alkyne as a click chemistry reagent, azide, DBCO, BCN, TCO, norbornene, tetrazine, or methyl tetrazine. The above R 24 ~R 35 It may have a structure with the above-mentioned functional group that is easy to bind, or a condensed structure of the PET probe and the above-mentioned functional group that is easy to bind.)

[0020] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the organic substance is methanol or ethanol.

[0021] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the organic substance has a dipole moment of less than 3.0D.

[0022] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the concentration of the organic substance is 40% by volume or more.

[0023] The synthesis method of the zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the oxalic acid concentration is adjusted to 10 -6 mol / L or more 10 -4 mol / L or less.

[0024] A method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the predetermined temperature is 35° C. or higher.

[0025] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the organic solvent is a solvent purified by a metal removing agent.

[0026] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the acidic solution is hydrochloric acid.

[0027] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, the zirconium dissolved in the acidic solution is mixed with a solution obtained by mixing the organic solvent and the chelating agent solution just before heating to the predetermined temperature or above or after the heating.

[0028] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the above invention, R5 to R 20 At least one of or R in the above general formula (2) 24 ~R 35 At least one of them binds to the molecular probe via at least one structure selected from the group consisting of chemical formulae (16) to (21) and (26), or the linker binds to the molecular probe.

[0029]

Chemistry 2

[0030]

[0031] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the configuration, the molecular probe is a protein, a peptide, or a low-molecular organic compound.

[0032] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the structure, the protein or the peptide is composed of natural amino acids, non-natural amino acids, or both the natural amino acids and the non-natural amino acids, and has a linear structure or a cyclic structure.

[0033] The method for synthesizing a zirconium complex according to one embodiment of the present invention is characterized in that, in the configuration, the linker is polyethylene glycol, an alkyl chain, or piperazine, or a complex thereof.

[0034] Effects of the Invention

[0035] According to the method for synthesizing a zirconium complex of the present invention, even a chelating agent such as DOTA or NOTA at a low concentration can react with radioactive zirconium to synthesize a zirconium complex at a high radiochemical yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The effect of oxalic acid on DOTA- 89 A graph showing the effect of Zr on the radiochemical yield.

[0037] Figure 2 The effect of oxalic acid on the 89 Graph showing the effect of Zr-DOTA on the radiochemical yield of the PET probe.

[0038] Figure 3 This is a diagram for explaining an example of a specific method for reacting zirconium and DOTA according to one embodiment of the present invention.

[0039] Figure 4 This is a diagram for explaining a specific method for reacting zirconium and DOTA in the prior art as a comparative example.

[0040] Figure 5 This is a graph showing the organic substance concentration dependence of the radiochemical yield of zirconium according to one embodiment of the present invention.

[0041] Figure 6 This is a graph showing the methanol concentration dependence of the generation rate of a precipitate, the radiochemical purity, and the radiochemical yield in the generation of the zirconium complex according to one embodiment of the present invention.

[0042] Figure 7 This is a graph showing the ethanol concentration dependence of the generation rate of a precipitate, the radiochemical purity, and the radiochemical yield in the generation of the zirconium complex according to one embodiment of the present invention. DETAILED DESCRIPTION

[0043] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the present invention is not limited to the embodiment described below. First, when describing an embodiment of the present invention, in order to facilitate the understanding of the present invention, the experiments and in-depth studies conducted by the inventors to solve the above-mentioned problems will be described.

[0044] First, the present inventors have conducted extensive research on radioactive zirconium (hereinafter also referred to as zirconium, Zr, or 89 The reaction of Zr) with the compound DOTA represented by the following general formula (1) will be described with reference to the problems of the prior art.

[0045] In the past, DOTA represented by the following general formula (1) can easily bind to radioisotopes (RI) of various metals and is therefore widely used as a general chelating agent. In addition, the synthesis methods of DOTA derivatives have been established for many reagents, and DOTA and its derivatives (such as DOTAM and DOTP) are also easy to obtain.

[0046]

Chemistry 3

[0047]

[0048] In the general formula (1), R1, R2, R3, and R4 are each hydrogen (-H) (in this case, there is no further connection with R5 to R 12 ), -CH-, -(CH2) n CH- group, -N(=O)(CH2) n NCH- group, or -(CH2) n NC(=O)N- group. n is an integer greater than 0. R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 At least two of the substituents are selected from carboxylic acid, primary amide, hydroxamic acid, phosphonic acid, phosphoric acid, sulfonic acid, alcohol, amine, phenol, aniline, and esters, secondary amides, hydroxamic acid, and phosphate esters to which substituents are added, and the remaining substituents are hydrogen, an alkyl chain, a tert-butyl protected carboxylic acid, nitrobenzene, or an alkyl chain to which substituents are added. 20The functional groups contained in can be attached with a PET probe or a functional group that is easily bound to a PET probe. The easily bound functional group refers to carboxylic acid, carboxylic acid succinimidyl ester, carboxylic acid tetrafluorophenol ester, alcohol, amine, thiol, isothiocyanate, maleimide, phenol, aniline, benzoic acid, phenylisothiocyanate, or alkyne as a click chemistry reagent, azide, DBCO, BCN, TCO, norbornene, tetrazine, or methyl tetrazine. R5~R 20 It may have a structure with a functional group that is easily bindable, or a condensed structure of a PET probe and a functional group that is easily bindable.

[0049] In addition, other compounds can be further bonded to the above functional groups by means of ester bonds, amide bonds, etc., or the alkyl chain can have a branched chain for holding other compounds. Specifically, cross-linking forming functional groups such as succinimide, isothiocyanate, amine, thiol, carboxylic acid, or functional groups such as azide, olefin, alkyne, tetrazine, etc. that target click chemistry can be cited. In addition, reagents for molecular imaging can be bonded by these cross-linking forming functional groups.

[0050] In addition, R1 to R4 can each be a structure represented by the following general formula (3), and specifically, a structure selected from the structures represented by chemical formulas (3-1) to (3-4). It should be noted that n in chemical formulas (3-2) to (3-4) is an integer greater than 0.

[0051]

Chemistry 4

[0052]

[0053] R5~R 20 Each of the structures selected from the following general formulae (4) to (21) may be used. It should be noted that n in the general formulae (4) to (21) is an integer greater than 0. The general formulae (4) to (21) are functional groups that are easily coordinated and bonded to metals. It should be noted that R5 to R 12 At least two of them are preferably selected from the structures represented by general formulae (4) to (21). 20 Each of the structures selected from the following general formulae (22) to (26) may be used. It should be noted that the structures represented by general formulae (22) to (26) are structures that do not form complexes with metal ions or are difficult to form complexes with metal ions. 16 Any of them can bind to the molecular probe via at least one structure selected from the group of the above chemical formulae (16) to (26), or can bind the linker to the molecular probe.

[0054]

Chemistry 5

[0055]

[0056]

Chemistry 6

[0057]

[0058] In addition, a complex of DOTA or a derivative of DOTA with a reagent such as an antibody, protein, peptide, or low molecular organic compound that is the object of a molecular imaging experiment can also be used. Proteins and peptides are composed of natural amino acids, non-natural amino acids, or both natural amino acids and non-natural amino acids, and substances with a straight chain structure or a cyclic structure can be used. Specifically, a method of amidating a carboxylic acid in the structure of DOTA and cross-linking it with a reagent is also known; a substance obtained by cross-linking a cyclic alkyl chain in the structure of DOTA, etc. DOTA is sometimes also combined with a reagent by an appropriate linker such as polyethylene glycol. Specifically, it is also used for polymer drugs such as antibodies and low molecular drugs such as PSMA-617. The linker is typically polyethylene glycol, an alkyl chain, or piperazine, or a complex of polyethylene glycol, an alkyl chain, or piperazine, but it is not necessarily limited to this. In the present invention, the substance to be combined is not limited to DOTA, but also includes its derivatives and complexes with reagents. That is, in each of the above general formulae (16) to (21) and (26), R may be a structure selected from the structures represented by the following chemical formulae (27) to (47). 89 Zr complexes with DOTA structure and can also make 89 After Zr is complexed, the reagent is combined with R.

[0059]

Chemistry 7

[0060]

[0061]

Chemistry 8

[0062]

[0063] On the other hand, as mentioned above, 89 Zr has a moderate half-life and high resolution, making it an extremely suitable nuclide for medical imaging. 89 As a chelating agent for labeling Zr, for example, deferoxamine (DFO) shown in the following chemical formula (100) is used. DFO has a weak binding force to substances other than Zr and is essentially a chelating agent exclusively for radioactive zirconium. Therefore, it lacks versatility and cannot be used for imaging with other nuclides. Therefore, the complex of DFO and PET probe needs to be used only for 89 In addition, DFO has insufficient binding strength with Zr, and there are problems such as radioactive zirconium being separated from the reagent in vivo in molecular imaging.

[0064]

Chemistry 9

[0065]

[0066] Therefore, the use of DOTA as a chelating agent and 89 Various studies have been conducted on the method of Zr. 89 When Zr is combined with DOTA, the combination itself is strong, so it is not difficult to detect in the human body during medical imaging such as PET. 89 Zr is difficult to be separated from the chelating agent, which has the advantage of improving image quality. 68 The reagents containing DOTA developed for other nuclides such as Ga can be transferred to 89 Zr chelates, so in the label 89 The development of Zr reagents can achieve cost reduction.

[0067] However, the above DOTA and 89 The bonding of Zr is very difficult. Specifically, as described in Non-Patent Document 2, in order to 89 Existing methods of combining Zr with chelating agents make 89 The combination of Zr and DOTA requires the reaction temperature to be above 90°C, preferably above 95°C, the reaction time to be 1 hour, and the DOTA concentration to be 10 -4 mol / L or more. The inventors used 89 The radiochemical yield of Zr reacting with DOTA was verified, and it was found that even if the experiment was conducted according to the method described in Non-Patent Document 2, the reproducibility of the results was sometimes low and the radiochemical yield was also low. 89 When Zr is used in medical imaging, it is hoped that 89 For Zr, the concentration is 10 -5 mol / L of DOTA can also bind. However, the inventors verified the radiochemical yield under this condition, and found that the radiochemical yield was approximately 0%. The inventors conducted experiments and confirmed that the reason for the approximately 0% radiochemical yield is that most of the 89 Zr is attached to reaction vessels such as microtubes. The inventors have studied this and speculated that 89 Zr precipitates in the form of zirconium hydroxide and adheres to the reaction vessel.

[0068] The present inventors have made 89 Various studies have been conducted on the problems and causes of the reaction between Zr and DOTA, and it has been found that in order to 89 To obtain high radiochemical yields in the complexation reaction of Zr and DOTA, it is necessary to increase the reaction rate or inhibit 89Therefore, the present inventors conducted various experiments to increase the reaction rate and inhibit the formation of hydroxides and conducted in-depth research. That is, the present inventors conducted the following experiments: 89 Impurities other than Zr, such as iron ions (Fe 3+ ), titanium ions (Ti 4+ ) and yttrium ions (Y 3+ ) and other metal ions according to the concentration of 10 -2 mol / L of DOTA were mixed in an equimolar concentration and reacted. The results are shown in Table 1. 89 The binding rate of Zr, i.e., the radiochemical yield, is reduced to about 10% to 32%. That is, it is known that DOTA reacts with other metal ions preferentially compared to Zr, and other metal ions do not exchange with Zr after the reaction. Therefore, it is preferred to remove the metal ions that become impurities in this reaction. Specifically, 89 In the buffer solution and organic solvent used in the reaction of Zr and DOTA, it is preferred to remove the metal that will become an impurity by using a metal remover such as a styrene divinylbenzene copolymer containing iminodiacetate ions. It should be noted that the method described in Patent Document 1 can also be used to improve 89 Purity of the purified Zr solution.

[0069]

Table 1

[0070] (Table 1)

[0071] Adding metal ions <![CDATA[ 89 Zr binding rate]]> Not added 92％ <![CDATA[Y 3+ ]]> 10％ <![CDATA[Ti 4+ ]]> 12％ <![CDATA[Fe 3+ ]]> 32％

[0072] In addition, the present inventors have confirmed that adding dimethyl sulfoxide (DMSO) represented by the following chemical formula (200) can make 89 The reaction of Zr with DOTA resulted in a reaction time of about 30 minutes, half of the conventional 1 hour, and a radiochemical yield of 95%. 89 This is a phenomenon in which Zr turns into zirconium hydroxide and adheres to the reaction container.

[0073]

Chemistry 10

[0074]

[0075] According to the research of the inventor, in DOTA and 89 In the mixed solution of Zr, the reaction intermediate complex shown on the left side of the following reaction formula (301a) and (301b) is first generated. Then, the reaction intermediate complex is heated and is believed to be transformed into DOTA- 89 On the other hand, since Zr ions are also strongly bound to water molecules and hydroxide ions, it is also speculated that89 Zr is split from the reaction intermediate complex together with hydration water by heating, and changes into zirconium hydroxide shown on the right side of chemical formula (301b). The reason for the low yield under the existing reaction conditions is that the zirconium hydroxide reacted as in chemical formula (301b) adheres to the reaction container, etc., and the reaction becomes inactive.

[0076]

Chemistry 11

[0077]

[0078] On the other hand, if a highly polar substance such as DMSO is added, it is believed that the reaction intermediate complex 89 The coordination of Zr in organic solvents and water competes. When the concentration of highly polar organic solvents is high enough, it is predicted that the coordination structure shown in the following reaction formula (302) will be formed. In this case, it is believed that, unlike the case of water coordination, the reaction intermediate complex thus generated cannot react to produce zirconium hydroxide, so most of the 89 Zr as DOTA- 89 Zr is generated.

[0079]

Chemistry 12

[0080]

[0081] The inventors have conducted further research based on the above in-depth research. First, the inventors have studied a method for more effectively removing organic solvents. That is, the so-called high-polarity organic solvents such as DMSO mentioned above have a boiling point of about 189°C, so it is extremely difficult to remove the solvent using an evaporator. High-polarity organic solvents usually have high boiling points. For example, the boiling point of N,N-dimethylformamide is 153°C, and the boiling point of N-methylpyrrolidone is 202°C. When using such high-polarity organic solvents, the removal of the solvent often becomes a problem. Therefore, the inventors have also studied the removal of organic solvents by solid phase extraction using C18 columns and the like. However, high concentrations of organic solvents inhibit the hydrophobic interaction between the ligand (ligand) of the chelating agent and reagent complex and the solid phase and hinder retention on the column, so it is difficult to separate the organic solvent by solid phase extraction. By using high performance liquid chromatography (HPLC), high-polarity organic solvents can be removed, but not only does it require a dedicated device, but there is also a problem that separation takes time.

[0082] In addition, the present inventors conducted various experiments and studies on organic solvents other than high-polarity organic solvents and found that 89A method of using an organic solvent with moderate polarity and water miscibility in the reaction of Zr and DOTA. Organic solvents with moderate polarity usually have a low boiling point and can be easily removed by an evaporator. Furthermore, the inventors have found through experiments that the concentration of the organic solvent is preferably 40% to 90% by volume, and the reaction temperature is preferably above 80°C. Thus, the same reactivity as the above-mentioned DMSO is obtained. In addition, the inventors have found that methanol (CH3OH), ethanol (C2H5OH) and the like are preferred as organic solvents with moderate polarity and water miscibility.

[0083] That is, the inventors first studied the reason why the yield of the complex of DOTA and zirconium ions in water is low. As described above, in the reaction of DOTA and metal ions, an intermediate state complex having the structure shown on the left side of reaction formulas (301a) and (301b) is formed. The intermediate state complex is a complex in which two diagonal molecules in the cyclic amine are protonated, four carboxylic acids are coordinated with the metal, and multiple water molecules are coordinated with the metal. In addition, the protons on the amine and the water coordinated with the metal ions are separated by heating, thereby as shown on the right side of reaction formula (301a), 89 Zr is combined with DOTA. However, 89 Zr easily generates hydroxide, so it is believed that 89 Zr is easily released from DOTA to form zirconium hydroxide through the reaction shown in reaction formula (301b), and the radiochemical yield is reduced.

[0084] In addition, the present inventors have studied the reasons why the yield of Zr is improved by mixing a mixed solvent of an organic solvent and water. As described above, the present inventors predict that the water molecules coordinated with zirconium in the intermediate state complex will hinder the reaction of forming the complex. Therefore, the present inventors believe that, as shown in the following reaction formula (302a), by replacing the coordination of water molecules with the coordination of the organic solvent L, the generation of zirconium hydroxide shown in the reaction formula (302b) can be suppressed, and the yield can be increased. Therefore, the present inventors thought of a method of mixing an organic solvent in a reaction solution in the synthesis of zirconium.

[0085]

Chemistry 13

[0086]

[0087] (L is an organic solvent.)

[0088] Based on the above research, the inventors have studied various organic solvents. That is, the inventors compared the yields when DOTA and radioactive zirconium were reacted at a reaction temperature of 100°C and a reaction time of 30 minutes in various organic solvents at a concentration of 50% by volume. As a result, it was found that the yield varied significantly with the type of organic solvent. In addition, it was confirmed that the higher the polarity of the organic solvent, the higher the yield. Therefore, the inventors predict that the stronger the affinity of the organic solvent to zirconium, the easier it is to hinder the hydration of zirconium, and thus the generation of zirconium hydroxide will be suppressed. On the other hand, in the case of an organic solvent with a low degree of polarity, the affinity with zirconium is poor compared to a high-polarity organic solvent, so it is predicted that the effect of hindering the hydration of zirconium is weak and the yield is also poor. It was found that: in the case of highly polar organic solvents such as DMSO, DMF, NMP, etc. with a dipole moment of more than 3.0D, particularly good radiochemical yields can be obtained, but even organic substances with moderate polarity (hereinafter referred to as medium-polar organic solvents) with a dipole moment of less than 3.0D, such as medium-polar organic solvents with a degree of miscibility with water such as methanol or ethanol, relatively good radiochemical yields can be obtained.

[0089] The present inventors have also studied a method for compensating for the low affinity of a medium-polar organic solvent for zirconium by using the concentration, that is, a method for using a medium-polar organic solvent at a high concentration. Figure 5 is a graph showing the relationship between the concentration of the neutral polar organic solvent and the yield. Figure 5 As shown, it was confirmed that the yield was improved by increasing the organic solvent concentration, and the yield of methanol and ethanol was the highest at 60 volume %. Thus, it was shown that the yield can be improved by optimizing the concentration of the medium-polar organic solvent.

[0090] Furthermore, the inventors conducted various experiments and found that DOTA- 89 The radiochemical yield of Zr is based on 89 Specifically, when using Zr prepared by the purification method described in Non-Patent Documents 1 and 2, 89 In the case of Zr solution, the yield is extremely low. 89 In the case of Zr solution, the yield is high.

[0091] Therefore, the inventors conducted in-depth research on the difference in yield and found that the purified 89 The concentration of oxalic acid contained in the Zr solution is the main reason. 89 Zr is first roughly purified by using hydroxamic acid resin in the form of oxalic acid solution, and then replaced by anion exchange resin into hydrochloric acid solution. In the method described in non-patent literature 1 and 2, pure water is used to absorb the adsorbed Zr. 89After the Zr anion exchange resin was washed, it was eluted with 1 mol / L hydrochloric acid. 89 However, according to the analysis conducted by the inventors, in the eluted by the method described in non-patent documents 1 and 2, 89 There is 10 dissolved in Zr solution -3 On the other hand, in the method described in Patent Document 2, it was confirmed that: 89 The anion exchange resin was cleaned with dilute hydrochloric acid before Zr, which could reduce the oxalic acid concentration. Specifically, the dissolved oxalic acid concentration could be reduced to 10 -6 mol / L order of magnitude.

[0092] Next, the inventors studied the effect of oxalic acid concentration on radiochemical yield. It should be noted that DOTA and DOTA-containing PET probes (e.g., trade name PSMA-617) were used as reagents. 89 The Zr solution was prepared by the method described in Patent Document 2, and oxalic acid was further added to adjust the oxalic acid concentration. Figure 1 and Figure 2 middle. Figure 1 The effect of oxalic acid on DOTA- 89 The effect of Zr on the radiochemical yield is shown in the graph. Figure 2 The effect of oxalic acid on the 89 Graph showing the effect of Zr-DOTA on the radiochemical yield of the PET probe.

[0093] The inventors according to Figure 1 and Figure 2 The present inventors have found that there is a preferred oxalic acid concentration among the oxalic acid concentrations. That is, the present inventors have found that, although it depends on the reagent and the solvent, the oxalic acid concentration is typically preferably 10 -5 mol / L or more and less than 10 - 4 mol / L, preferably 10 -5 mol / L or above 5×10 -5 It should be noted that according to the research of the present inventors, under the condition of not adding oxalic acid, 89 Zr is easy to adhere to the container, so it is estimated that zirconium hydroxide is easy to be generated when the oxalic acid concentration is low. On the other hand, it was also found that: when the oxalic acid concentration is high, it is almost not generated. 89 Zr is attached to the container, but the reaction rate is reduced. The reason is believed to be that oxalic acid 89Zr forms a complex, the formation of hydroxide is suppressed, but the formation of a complex with reagents such as DOTA is hindered. Therefore, it is preferred that the concentration of oxalic acid is such that the formation of hydroxide is suppressed while the reaction with DOTA is not hindered. The range of the oxalic acid concentration is 10 -5 mol / L or more and less than 10 -4 mol / L, preferably 10 - 5 mol / L or above 5×10 -5 mol / L or less.

[0094] In addition, in the case of highly polar organic substances such as DMSO or DMF, the radiochemical yield has a low dependence on the oxalic acid concentration, but in the case of intermediate polar organic substances such as methanol (MeOH) or ethanol (EtOH), the dependence on the oxalic acid concentration is large. Furthermore, in the intermediate polar substances, the preferred oxalic acid concentration is a relatively high concentration compared to the highly polar substances. The reason for this is believed to be that the highly polar substances react with oxalic acid in the same manner. 89 Zr coordinated, and the hydroxide formation was suppressed. That is, it was confirmed that radioactive zirconium and DOTA can be reacted with high yield using a medium-polarity organic solvent even by controlling the oxalic acid concentration in the reaction solution.

[0095] The same effect may be obtained with zirconium-binding organic substances (citric acid or ascorbic acid, etc.). In addition, it is believed that the appropriate concentration range varies depending on the substance. In addition, in the above experiment on the dependence of organic solvent concentration, it is assumed that oxalic acid is 10 -6 ~10 -5 It exists at around mol / L.

[0096] In the past, in the complex formation reaction between DOTA and metal ions, it was believed that the deprotonation of the cyclic tertiary amine of DOTA controlled the rate. That is, in the protonated state of the cyclic tertiary amine, even if the intermediate complex shown on the left side of the chemical formula (302), (302a), and (302b) can be formed, the final product shown on the right side cannot be reached. Therefore, the deprotonation reaction of the cyclic tertiary amine controls the rate of the complexation reaction. Assuming this mechanism, it is believed that: due to the decrease in the pKa of the amine, the yield of the radioactive zirconium DOTA complex is increased. Here, generally, the polarity of the organic solvent is lower than that of water, and therefore has the effect of inhibiting the ionization of the organic compound, that is, the protonation of the amino group or the deprotonation of the carboxylic acid. Therefore, it is possible to reduce the acid dissociation constant pKa of the protonated amino group of the reaction intermediate complex and promote the reaction to change into the target complex. That is, the inventors assume that: if 89When Zr is hydrated, the generation of zirconium hydroxide takes precedence over the reaction with DOTA. According to this hypothesis, highly polar organic solvents coordinate with zirconium in preference to water, inhibiting hydration, thereby increasing the yield. On the other hand, the inventors further discovered that: the ability of medium polar organic solvents to coordinate with zirconium is low, but by increasing the concentration, they can coordinate with zirconium in preference to water, inhibiting hydration, thereby increasing the yield. In addition, it is believed that: the fact that the yield of the target complex is increased by adding a small amount of a substance such as oxalic acid that has a strong coordination ability with zirconium also indicates that the inhibition of zirconium hydration helps promote the reaction of DOTA with radioactive zirconium. The present invention and one embodiment thereof described below were conceived through the above-mentioned in-depth research of the inventors.

[0097] In addition, as an alternative to the above-mentioned DOTA, a three-membered ring such as NOTA represented by the following general formula (2) can be used. That is, the above-mentioned inventors' intensive research has shown that the same discussion can be conducted even if DOTA is replaced by NOTA.

[0098]

Chemistry 14

[0099]

[0100] In the general formula (2), R 21 , R 22 , R 23 are hydrogen (-H) (in this case, there is no further connection R 24 ~R 29 ), -CH-, -(CH2) n CH- group, -N(=O)(CH2) n NCH- group, or -(CH2) n NC(=O)N- group. n is an integer greater than 0. R 24 , R 25 , R 26 , R 27 , R 28 , R 29 , R 30 , R 31 , R 32 , R 33 , R 34 , R 35 At least two of the R are selected from carboxylic acid, primary amide, hydroxamic acid, phosphonic acid, phosphoric acid, sulfonic acid, alcohol, amine, phenol, aniline, and esters, secondary amides, hydroxamic acid, and phosphates to which substituents are added, and the remaining substituents are hydrogen, an alkyl chain, a tert-butyl protected carboxylic acid, nitrobenzene, or an alkyl chain to which substituents are added. 24 ~R 35A PET probe or a functional group that can easily bind to a PET probe can be attached to the functional group contained in. The functional group that can easily bind refers to the following functional groups. Carboxylic acid, carboxylic acid succinimidyl ester, carboxylic acid tetrafluorophenol ester, alcohol, amine, thiol, isothiocyanate, maleimide, phenol, aniline, benzoic acid, phenylisothiocyanate, or alkyne as a click chemistry reagent, azide, DBCO, BCN, TCO, norbornene, tetrazine, or methyl tetrazine. R 24 ~R 35 It may have a structure with a functional group that is easily bindable, or a condensed structure of a PET probe and a functional group that is easily bindable.

[0101] In addition, other compounds can be further bonded to the above functional groups by means of ester bonds, amide bonds, etc., or the alkyl chain can have a branched chain for holding other compounds. Specifically, cross-linking forming functional groups such as succinimide, isothiocyanate, amine, thiol, carboxylic acid, or functional groups such as azide, olefin, alkyne, tetrazine, etc. that target click chemistry can be cited. In addition, reagents for molecular imaging can be bonded by these cross-linking forming functional groups.

[0102] In addition, R 21 ~R 23 Each of them can adopt the structure represented by the following general formula (3), and specifically, can adopt a structure selected from the structures represented by chemical formulas (3-1) to (3-4). In addition, n in chemical formulas (3-2) to (3-4) is an integer greater than or equal to 0.

[0103]

Chemistry 15

[0104]

[0105] R 24 ~R 29 Each of them can be a structure selected from the structures represented by the following general formulae (4) to (21). It should be noted that n in the general formulae (4) to (21) is an integer greater than or equal to 0. 20 The structures selected from the following general formulae (22) to (26) can be used. It should be noted that the structures represented by general formulae (22) to (26) are structures that do not form complexes with metal ions or are difficult to form complexes with metal ions. 24 ~R 35 Any of them can bind to the molecular probe via at least one structure selected from the group consisting of chemical formulae (16) to (21) and (26), or can bind the linker to the molecular probe.

[0106]

Chemistry 16

[0107]

[0108] In addition, a complex of NOTA or a derivative of NOTA with a reagent such as an antibody, protein, peptide, or low molecular organic compound that is the object of a molecular imaging experiment can also be used. Proteins and peptides are composed of natural amino acids, non-natural amino acids, or both natural amino acids and non-natural amino acids, and substances with a straight chain structure or a cyclic structure can be used. Specifically, a method of amidating a carboxylic acid in the structure of NOTA and cross-linking it with a reagent is also known; a substance obtained by cross-linking a cyclic alkyl chain in the structure of NOTA, etc. Sometimes NOTA and the reagent are combined by an appropriate linker such as polyethylene glycol. Specifically, it is also used for high molecular drugs such as antibodies and low molecular drugs such as PSMA-617. The linker is typically polyethylene glycol, an alkyl chain, or piperazine, or a complex of polyethylene glycol, an alkyl chain, or piperazine, but it is not necessarily limited to this. In the present invention, the substance to be combined is not limited to NOTA, but also includes its derivatives and complexes with reagents. That is, in each of the above general formulae (16) to (21) and (26), R may be a structure selected from the structures represented by the following chemical formulae (27) to (47). 89 Zr complexes with NOTA structure and can also make 89 After Zr is complexed, the reagent is combined with R.

[0109]

Chemistry 18

[0110]

[0111]

Chemistry 19

[0112]

[0113] In the above general formulae (1) and (2), R5 to R 20 Any one of, R in the general formula (2) 24 ~R 35 Any of them can bind to a molecular probe having a structure represented by the following chemical formulas (61) to (64), or a linker having a structure represented by the following chemical formulas (71) to (74) can be bound to a molecular probe.

[0114]

Chemistry 20

[0115]

[0116]

Chemistry 21

[0117]

[0118] Regarding DOTA represented by the general formula (1), a structure formed by reactions as shown in the following reaction formulas (1-1) to (1-13) can also be adopted. In reaction formulas (1-1) to (1-13), from the left are DOTA derivatives, substances to be bound (indicated on the arrow), and the condensed structure. It should be noted that regarding reaction formulas (1-11) to (1-13), they are binding methods targeting click chemistry.

[0119]

Chemical Formula 22

[0120]

[0121]

Chemical Formula 23

[0122]

[0123]

Chemical Formula 24

[0124]

[0125] Regarding NOTA represented by the general formula (2), a structure formed by reactions as shown in the following reaction formulas (2-1) to (2-13) can also be adopted. In reaction formulas (2-1) to (2-13), from the left are NOTA derivatives, substances to be bound (indicated on the arrow), and the condensed structure. It should be noted that regarding reaction formulas (2-11) to (2-13), they are binding methods targeting click chemistry.

[0126]

Chemical Formula 25

[0127]

[0128]

Chemical Formula 26

[0129]

[0130]

Chemical Formula 27

[0131]

[0132] (Embodiment)

[0133] Next, a method for synthesizing a zirconium complex according to an embodiment of the present invention will be described. Figure 3 It is a diagram showing an example of a specific method for reacting zirconium with DOTA in this embodiment.

[0134] As Figure 3As shown, first, a DOTA solution is introduced into a microtube as a reaction container as a chelating agent solution of a predetermined concentration, wherein a compound containing DOTA is dissolved in the DOTA solution. Here, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid is used as the DOTA chelating agent. The concentration of the DOTA solution is 10 -7 mol / L or more and less than 10 -4 In this embodiment, the final concentration of the DOTA solution is, for example, 10 -5 mol / L, the amount of introduction is, for example, at a concentration of 10 -2 Next, a roughly neutral buffer solution is introduced into the microtube. As the final buffer solution, for example, HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) with a concentration of about 0.25 mol / L and a pH of 7.0 is used. The amount of introduction is, for example, 449 μL in the case of a 0.5 mol / L solution. It should be noted that the buffer solution used in this embodiment is prepared by removing metal ions in advance using a metal remover. 89 This can reduce the amount of Fe ions mixed in as impurities in the final mixed reaction solution. 3+ 、Ti 4+ , Y 3+ The possibility of metal ions.

[0135] Next, an organic solvent containing a water-miscible organic substance is introduced into the microtube. Specifically, in this embodiment, an organic solvent containing, for example, methanol or ethanol as the organic substance is used. Here, the relationship between the concentration of the organic solvent containing methanol or ethanol and the zirconium radiochemical yield is described. Figure 5 is a graph showing the concentration dependence of the radiochemical yield of zirconium on organic solvents including methanol and ethanol.

[0136] Depend on Figure 5 It is known that by making the organic solvent concentration greater than 0 volume % and 1 volume % or more, the radiochemical yield can be increased compared to the case where no organic solvent is mixed. Figure 5 It can be seen that 89 The radiochemical yield of Zr reaches its peak when the concentration is 60 volume %. Figure 5 It is known that in order to 89 The radiochemical yield of Zr is, for example, 50% or more, preferably 20% by volume or more when the organic solvent is methanol, and preferably 40% by volume or more when the organic solvent is ethanol. Figure 5 ,according to 89The radiochemical yield required in Zr can be selected by the concentration of the organic substance in the organic solvent. That is, from the aspect of obtaining the effect of improving the radiochemical yield, the concentration of the organic substance with water miscibility in the organic solvent is preferably more than 40 volume %, more preferably more than 50 volume %. On the other hand, if the organic substance exceeds 95 volume %, the reaction rate decreases, so the concentration of the organic substance is preferably less than 95 volume %, if the radiochemical yield is considered, it is more preferably less than 80 volume %, further preferably less than 70 volume %. The amount of organic solvent introduced is, for example, 600 μL in the case of an organic solvent with a final concentration of 60 volume %. The order in which the above-mentioned DOTA solution, buffer solution and organic solvent are introduced into the microtube is not limited to the above order, and can be introduced in various orders.

[0137] After the DOTA solution, buffer solution and organic solvent are introduced into the microtube, the reaction solution in the microtube is introduced with 89 Acidic solution of Zr (containing 89 Here, in this embodiment, the acidic solution is preferably a strong acid solution, specifically hydrochloric acid (HCl). However, the acidic solution is not necessarily limited to a strong acid solution such as hydrochloric acid. 89 The amount of the Zr acid solution introduced is, for example, 50 μL.

[0138] In addition, although it also depends on the purification method, 89 There may be a trace amount of oxalic acid remaining in the acidic solution of Zr. In this case, the yield can be further improved by controlling the concentration of the residual oxalic acid. Specifically, for example, 89 A method of adjusting the mixing ratio of the Zr acid solution with a reaction solvent such as a mixed solution of a HEPES buffer solution and an organic solvent by adjusting the oxalic acid concentration of the Zr acid solution; a method of adding an oxalic acid solution; etc.

[0139] Figure 6 and Figure 7 The graphs are respectively showing the methanol concentration dependence and the ethanol concentration dependence of the precipitate generation rate, radiochemical purity and radiochemical yield in the generation of zirconium complex. That is, when methanol is used as the organic substance having water miscibility, it is possible to Figure 6 The methanol concentration of the organic solvent is selected based on the curve shown in FIG. 1 . In addition, when ethanol is used as the organic substance having water miscibility, the methanol concentration of the organic solvent can be selected based on Figure 7 In these cases, the concentration of the organic substance in the organic solvent can be selected so that the formation rate of precipitates attached to microtubes etc. is less than the desired level, or the radiochemical purity is the desired level.

[0140] Back to Figure 3DOTA solution, buffer solution, organic solvent and 89 After mixing with the acidic solution of Zr, the mixture is heated to a predetermined temperature and maintained for a predetermined time. 89 It should be noted that in this embodiment, the 89 The acidic Zr solution is preferably introduced into the microtube just before the mixed solution is heated. This is because 89 When Zr is left at room temperature under neutral conditions, it will also undergo hydration, and the reaction with DOTA will become inactive. It should be noted that zirconium hydroxide is a stable compound, and even if the temperature rises later, 89 The reaction between Zr and DOTA will not proceed. 89 Zr is then quickly heated to a predetermined temperature and reacts rapidly with DOTA. 89 After Zr complexes with DOTA, 89 Zr does not undergo hydroxide formation.

[0141] In the present embodiment, the prescribed temperature is preferably above 35°C, as long as the substance bonded to DOTA is a high temperature resistant substance, and may be, for example, above 70°C, more specifically, 80°C. It should be noted that when the heating temperature is set to above 80°C, for example, the boiling point of methanol is 68°C, and therefore the temperature may exceed the boiling point of the organic substance contained in the organic solvent. In this case, as the microtube, it is preferred to use a highly sealed container such as a microtube with a screw cap. In addition, the prescribed time is, for example, about 30 minutes. Thus, 89 The reaction of Zr and DOTA is terminated according to the following reaction formula (401), and DOTA and 89 Zr-bound zirconium complex.

[0142]

Chemistry 28

[0143]

[0144] contain 89 The acidic solution of Zr is strongly acidic, and if it is added to the reaction vessel, the pH may change significantly. Therefore, a high concentration buffer solution is added to the microtube. 89 After the acid solution containing Zr is added, it is also necessary to adjust the pH range to be within the desired range. 89 After adding Zr-containing acidic solution, check the pH with a pH meter or pH test paper. 89 After adding alkaline solution to the acidic solution of Zr, 89Zr may undergo hydroxidation in a short time and become inactive in the reaction with DOTA. Therefore, it is preferable to avoid the neutralization operation using an alkaline solution. Here, as the pH range, it is preferably 4 or more and 9 or less, more preferably 5 or more and 9 or less, and further preferably 6 or more and 8 or less.

[0145] In addition, after the complexation reaction between DOTA and 89 Zr, post-treatment is carried out as needed. For example, the organic solvent and buffer solution are removed and replaced with physiological saline or an ethanol / physiological saline mixed solution. In this case, by using an organic substance such as methanol or ethanol, good reactivity is shown, and it is also easy to remove the organic solvent by evaporation to dryness. It should be noted that methods such as solid-phase extraction using an ion-exchange resin, a C18 column, or a graphite carbon column, and fractionation using a liquid chromatography device are also considered, and a method suitable for each reagent is adopted. It should be noted that in the case of applying solid-phase extraction, it is desirable to remove the organic solvent as much as possible in advance using an evaporator.

[0146] (Comparative Example)

[0147] For comparison with the above-described embodiments, as a comparative example, a method for synthesizing a zirconium complex of the prior art will be described. Figure 4 It is a diagram showing a specific method for reacting zirconium with DOTA of the prior art.

[0148] As Figure 4 shown, first, a DOTA solution with a concentration of 10 -4 mol / L or more is introduced into a microtube as a reaction vessel. Next, an acidic solution containing 89 Zr is introduced into the microtube. Next, HEPES with a pH of 7.0 is introduced into the microtube as a substantially neutral buffer solution. Thereafter, it is reacted at a temperature of 70 °C or more and 80 °C for about 1 hour, whereby DOTA and 89 Zr are reacted according to the following reaction formula (402). Thus, a zirconium complex in which DOTA and 89 Zr are combined is obtained.

[0149] [Chemical Formula 29]

[0150]

[0151] When a zirconium complex is produced by the synthesis method of the zirconium complex of the comparative example, it is confirmed that more than 90% of the dissolved 89 Zr adheres to the microtube. In addition, it is confirmed that about 95% of the 89 Zr dissolved in the reaction solution other than the 89 Zr adhering to the microtube has reacted. That is, it can be seen that in the comparative example, relative to the initial 89The amount of Zr was ((1-0.9)×0.95×100=) a radiochemical yield of about 9.5%. In contrast, when a zirconium complex was produced by the synthesis method of a zirconium complex according to one embodiment of the present invention, it was confirmed that the zirconium complex attached to the microtubules 89 Zr is dissolved 89 In addition, it was confirmed that in addition to the 89 Other than Zr, dissolved in the reaction solution 89 Of the Zr, about 92% reacted. That is, it can be seen that: 89 The amount of Zr is ((1-0.09)×0.92×100=) a radiochemical yield of about 83.7%, which can ensure a radiochemical yield of about 8.8 times that of the comparative example. It is also known that the reaction proceeds within a short reaction time even at a low concentration of DOTA.

[0152] As described above, according to one embodiment of the present invention, even if 10 -7 ~10 -4 Even at low concentrations of about mol / L, DOTA can react with 89 Zr reacts to synthesize zirconium complex.

[0153] Above, an embodiment of the present invention is specifically described, but the present invention is not limited to the above embodiment, and various modifications can be made based on the technical idea of ​​the present invention. For example, the values ​​and materials listed in the above embodiment are always examples, and different values ​​and materials can be used as needed, and the present invention is not limited by the records and drawings that constitute a part of the content of the present invention of this embodiment.

[0154] For example, in one embodiment, hydrochloric acid (HCl) is used as the acidic solution, but other acidic solutions may be used. In addition, in one embodiment, methanol and ethanol are used as organic substances having water miscibility, but they are not necessarily limited to methanol and ethanol, and aqueous solutions of various organic substances having water miscibility such as various alcohols may be used.

[0155] Industrial Applicability

[0156] The synthesis method of the zirconium complex of the present invention can be suitably used in medical imaging.

Claims

1. A method for synthesizing a zirconium complex, which comprises subjecting a mixed solution to a predetermined temperature or higher to synthesize the zirconium complex, wherein the mixed solution is mixed with: Organic solvents containing water-miscible organic substances; a chelating agent solution in which a chelating agent is dissolved; and Zirconium dissolved in acidic solution, It is characterized in that The organic substance is methanol or ethanol, and the concentration of the organic substance is 40% by volume or more, Adjust the oxalic acid concentration to 10 -6 mol / L or more 10 -4 mol / L or less, The organic solvent is a solvent purified by a metal removing agent. The chelating agent is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, namely DOTA, or 1,4,7-triazacyclononane-1,4,7-triacetic acid, namely NOTA.

2. The method for synthesizing the zirconium complex according to claim 1, characterized in that: The predetermined temperature is 35° C. or higher.

3. The method for synthesizing the zirconium complex according to claim 1 or 2, characterized in that: The acidic solution is hydrochloric acid.

4. The method for synthesizing the zirconium complex according to claim 1 or 2, characterized in that: Immediately before heating to the predetermined temperature or higher or after the heating, the zirconium dissolved in the acidic solution is mixed with the solution in which the organic solvent and the chelating agent solution are mixed.

5. The method for synthesizing the zirconium complex according to claim 1 or 2, characterized in that: At least one carboxylic acid in the DOTA or at least one carboxylic acid in the NOTA binds to the molecular probe via at least one structure selected from the group consisting of chemical formulas (27) to (47), or binds the linker to the molecular probe.

6. The method for synthesizing the zirconium complex according to claim 5, characterized in that: The molecular probe is a protein or a peptide.

7. The method for synthesizing the zirconium complex according to claim 6, characterized in that: The protein or the peptide is composed of natural amino acids, non-natural amino acids, or both the natural amino acids and the non-natural amino acids, and has a linear structure or a cyclic structure.

8. The method for synthesizing the zirconium complex according to claim 5, characterized in that: The linker is polyethylene glycol, an alkyl chain, or piperazine, or a complex thereof.

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