Cyclocycline-based compounds and Gd (III) complexes thereof for use as multi-mode PET / MRI contrast agents

Abstract

The present invention relates to the use of cycleanine-based compounds of general formula (I) wherein R is NO2 or F for the preparation of multimode PET / MRI contrast agents; a is independently selected from the group consisting of-CH2COOH; -CH (CH3) COOH; -CH ((CH2) nCH3) COOH, where n is an integer from 1 to 3; and-CH2P (= O) (OH) Ph; z is H or A. The invention also relates to Gd (III) complexes of compounds of general formula (I) wherein R is 18F as multimode PET / MRI contrast agents. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to cyclen-based compounds, their Gd(III) complexes, and their use as multimodal PET / MRI contrast agents, comprising 18 F and Gd 3+ . Background Art

[0002] Magnetic resonance imaging (MRI) and positron emission tomography (PET) are among the most powerful tools in clinical diagnostic imaging. The information provided by these technologies is largely complementary. The latest and most advanced instruments combine the advantages of both methods into a single PET / MRI hybrid technology.

[0003] MRI is appreciated for providing excellent soft tissue anatomical images with high resolution. MRI is based on the nuclear magnetic resonance signal of 1 H nuclei in water molecules, which make up about 60%-70% of body weight. Organs can be easily distinguished in MRI due to different water contents or relaxation rates of the nuclear magnetic resonance (MR) signal. In the case of insufficient native contrast agents, exogenous contrast agents can be injected intravenously. These exogenous contrast agents are mainly based on gadolinium(III) chelates, called gadolinium-based contrast agents (GBCAs). Typical examples are chelates of the macrocyclic ligand DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and chelates of the open-chain ligand DTPA (diethylenetriaminepentaacetic acid). The purpose of paramagnetic Gd(III) ions is to induce the relaxation of nearby 1 H nuclei of water, while the role of the ligand is to mask the toxicity of this metal ion. Generally, macrocyclic DOTA-like chelators are known to provide higher kinetic inertness for Gd(III) chelates compared to acyclic DTPA-like chelators. High kinetic inertness is ideal for in vivo applications because it prevents the escape of toxic Gd(III) ions from the chelate. Therefore, macrocyclic chelators are preferred. Currently used GBCAs are non-specific compounds, i.e., they do not bind to specific molecular targets. However, they provide important diagnostic information based on differences in tissue diffusion and perfusion characteristics, which are usually related to pathological changes. The differences in the biodistribution of GBCAs are visualized in MRI and reveal pathology.

[0004] PET has been of great importance because it provides specific information about molecular targets with very high sensitivity. This technique is based on the administration of tracer molecules labeled with positron-emitting radionuclides. When the radionuclide decays, the emitted positron annihilates with an electron in the vicinity, generating two gamma photons that travel in opposite directions (separated by 180 degrees). An external detector array records the two photons and shows their origin, thus allowing the construction of an image of the tracer molecule in the body. Due to this photon-counting principle, PET is a very sensitive quantitative technique. Detection requires extremely small amounts of tracer molecules, thus allowing the targeting and imaging of low-abundance molecular targets. The drawback is the lack of anatomical images. Therefore, PET is combined with computed tomography (CT) or (more recently) with MRI, both of which provide anatomical images for reference. Many PET tracers have been clinically approved or are under development, using various PET radionuclides such as 11 C, 13 N, 18 F, 64 Cu, 68 Ga, 89 Zr, etc. Among these, 18 F is the most widely used because it is produced in large quantities and cost-effectively by cyclotron irradiation of 18 O water. 18 F has a medium half-life of 110 minutes and is suitable for the synthesis of a wide range of small molecule organic tracer molecules, including the most common clinical PET tracer 18 F]FDG (fluorodeoxyglucose).

[0005] PET / MRI combined instruments have significant advantages compared to separate PET and MRI, as well as other imaging techniques. Primarily, compared to PET / CT, PET / MRI examinations reduce the patient's radiation burden while providing excellent soft tissue anatomical images. Simultaneously obtaining temporally and spatially matched images from both modalities provides opportunities for improving diagnostic accuracy, speed, and discovering new diagnostic imaging markers. However, current PET / MRI examinations involve administering two separate contrast agents: a radioactive tracer for PET and a GBCA for MRI. These contrast agents have completely independent pharmacokinetic behaviors and provide independent diagnostic information. There is no clinically approved reagent that will simultaneously provide PET signals and MRI contrast from a single compound. In fact, to date, only a few such compounds have been reported in the literature. Combining Gd(III) chelates with PET radionuclides into a stable and well-defined molecule presents significant synthetic challenges that impede progress. One of the earliest examples [Frullano, L. et al., Angew. Chem. Int. Ed. 2010, 49(13), 2382-2384] reported a pH-responsive PET / MRI contrast agent based on a Gd(III) chelate that had a 18 F-containing moiety through a click reaction and used a multi-step synthesis with a total yield of only 0.6%. Subsequently, the same group prepared a PET / MRI version of the fibrin-targeted MRI agent EP-2104R by partial dechelation of one of its four Gd(III) chelates followed by complexation 64 with Cu(II) [Uppal, R. et al., Radiology 2011, 258(3), 812-820]. However, due to a lack of control over the dechelation / complexation strategy, a mixture of positional isomers was produced rather than a single well-defined compound. Others have attempted to form dendrimer-like polymetallic structures by modifying a single 68 Ga(III) chelate with multiple Gd(III) chelates, resulting in relatively large and complex molecules [Kumar, A. et al., Bioconjugate Chem. 2015, 26(3), 549-558; Notni, J. et al., Chem. Eur. J. 2013, 19(38), 12602-12606]. Transforming such complex molecules into clinical practice is often hindered by poor synthetic reproducibility.

[0006] Another challenge in preparing PET / MRI dual contrast agents is that the amount of radionuclide required for PET signal is about 9-10 orders of magnitude lower than the Gd(III) chelate required for MRI contrast. To match these conflicting quantitative requirements, a mixture of two isotopically different versions of the reagent can be prepared. The reagent containing the active PET isotope is present only in trace amounts required to obtain the PET signal, while most of the reagent is chemically identical molecules containing stable (non-radioactive) isotopes. This large amount of non-radioactive version is needed to achieve the desired MRI contrast. Since the two versions are chemically identical (differ only in isotopes), they have the same pharmacokinetic properties. However, in the case where the reagent uses a metal PET radionuclide, this means co-administering a relatively large amount of non-radioactive exogenous metal, which poses a significant risk of metal-induced toxicity. From this perspective, using 18 18F is superior to metal PET radionuclides. 18 18F is not only a widely available and inexpensive isotope, but it also forms stable covalent C-F bonds, and fluorinated compounds are generally well tolerated.

[0007] Although 18 18F isotope has good properties, there are still challenges in achieving its rapid and efficient incorporation into PET / MRI reagents, especially in terms of the stability of Gd(III) chelate as the MRI contrast source. To inhibit the loss of 18 18F isotope due to radioactive decay, it is ideally best to attach the 18 18F isotope to the molecule in the final synthesis step. Methods have been developed for pure organic PET tracers to achieve this, but the presence of Gd(III) chelate in PET / MRI reagents is incompatible with many synthesis and purification conditions. For example, Gd(III) chelates are generally poorly soluble in the 18 anhydrous organic solvents required for 18F-labeling chemistry. Gd(III) chelates are also unstable under acidic conditions, while chromatographic or ion-exchange purification of the final product may require acidic conditions. Therefore, the conditions developed for the synthesis of pure organic PET tracers cannot be directly transferred to the chemistry of Gd(III) chelates.

[0008] Therefore, the background art lacks compounds and methods for rapidly and efficiently labeling Gd(III) chelates with 18 18F radionuclide, which will provide well-defined small molecule PET / MRI reagents similar to currently clinically used MRI contrast agents. SUMMARY OF THE INVENTION

[0009] In the background art, a suitable amount of dual-mode PET / MRI reagents have been prepared, and the labeling of PET isotopes is achieved based on rather complex bimetallic compounds or multi-step syntheses. These examples have failed to provide a simple and synthetically accessible molecular PET / MRI reagent similar to the non-specific MRI contrast agents currently in clinical use. In contrast, we have found that macrocyclic Gd(III) chelates bearing pyridine arms equipped with suitable leaving groups can be conveniently labeled with 18 F-fluoride anions by nucleophilic attack. This one-step reaction is rapid and proceeds directly on the pre-formed Gd(III) chelate. Thus, no additional complexation step is required. The macrocyclic chelator molecule is structurally closely related to DOTA, which has a proven long history of safe clinical use as an MRI contrast agent in the form of its Gd(III) chelate. Surprisingly, we have found that 18 F labeling can also be achieved by isotope exchange of 19 F to 18 F on the pyridine moiety of the Gd(III) chelate, but this reaction does not occur at all, or proceeds with a much lower yield, if carried out on the free macrocyclic chelator. This ensures that the Gd(III) chelate is preferentially labeled, thus obtaining a cleaner and more desirable product containing Gd(III) and 18 F for use as a multimodal PET / MRI reagent. Furthermore, this synthetic method allows adjustment of the molar ratio between the (radioactively labeled) version and the non-radioactive version of the PET activity of the reagent to tune the desired PET signal and MRI contrast according to specific PET / MRI instruments and applications. Thus, these compounds and their radiolabeling methods overcome the problems of the above-mentioned background art.

[0010] The object of the present invention is to use the cyclen-based compounds of general formula (I) in pharmacy, preferably to prepare multimodal PET / MRI contrast agents using the cyclen-based compounds of general formula (I):

[0011]

[0012]

[0013] wherein,

[0014] R is NO2 or F;

[0015] A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, wherein n is an integer from 1 to 3; -CH2P(=O)(OH)Ph;

[0016] Z is H or A.

[0017] The compounds of general formula (I) can be synthesized from nitro-pyridine intermediates or fluoro-pyridine intermediates of general formula (II):

[0018]

[0019] wherein,

[0020] R is NO2 or F;

[0021] and X is a halogen, preferably Cl or Br.

[0022] The intermediate of general formula (II) reacts with the cyclen-based intermediate of general formula (III):

[0023]

[0024] wherein,

[0025] A' is A (as defined above), wherein the OH group is protected, preferably protected as methoxy, ethoxy or tert-butoxy;

[0026] and Z' is hydrogen or A'.

[0027] Then the resulting precursor of general formula (IV) is deprotected (removing the protection of the OH group), preferably by using trifluoroacetic acid, to obtain the compound of general formula (I) as defined above,

[0028]

[0029] wherein, Z' and A' are as defined above.

[0030] In a preferred embodiment of the cyclen-based compound of general formula (I), A and Z are the same, preferably selected from -CH2P(=O)(OH)Ph, and -CH(CH3)COOH.

[0031] In a preferred embodiment of the cyclen-based compound of general formula (I), A is the same, preferably selected from -CH2P(=O)(OH)Ph, and -CH(CH3)COOH; and Z is hydrogen.

[0032] In a preferred embodiment, R is in the para position relative to the nitrogen atom of the pyridyl pendant arm. More preferably, R is F.

[0033] In one embodiment, the cyclen-based compounds of general formula (I) are selected from the group comprising:

[0034] 2,2',2”-(10-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 1 )

[0035] 2,2',2”-(10-((6-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 2 )

[0036] 2,2',2”-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 3 )

[0037] 2,2',2”-(10-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 4 )

[0038] 2,2',2”-(10-((5-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 5 )

[0039] 2,2',2”-(10-((6-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 6 )

[0040] 2,2'-(4-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid (L 7 )

[0041] (2S,2'S,2”S)-2,2',2”-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropionic acid (L 8 )

[0042] ((4-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))bis(phenylphosphinic acid) (L 9 )

[0043] 2,2'-(4-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid (L 10 )

[0044] (2S,2'S,2”S)-2,2',2”-(10-((4-fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropionic acid (L 11 )

[0045] (2S,2'S,2”S)-2,2',2”-(10-((4-nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropionic acid (L 12 )。

[0046] An object of the present invention is also a compound of general formula (Ia):

[0047]

[0048] wherein, R is NO2 or F; preferably, R is F;

[0049] A is independently selected from -CH(CH3)COOH; -CH((CH2) n CH3)COOH, wherein, n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; and Z is H or A, preferably, Z is A.

[0050] Preferably, the R substituent is located at the para position relative to the nitrogen atom of the pyridyl pendant arm. More preferably, A is -CH(CH3)COOH.

[0051] In the most preferred embodiment, the compound according to the present invention has the following formula (Va, Vb), wherein, the stereoconfigurations of all -C*H(CH3)COOH groups are the same (either all have the S configuration or all have the R configuration),

[0052]

[0053] Preferably, the R substituent in the compound of formula (Va) or (Vb) is located at the para position relative to the nitrogen atom of the pyridyl pendant arm. More preferably, R is F.

[0054] Another object of the present invention is a coordination compound of Gd(III) ions and a cyclen-based compound of general formula (I) or (Ia) as defined above, and its pharmaceutical use for preparing a multimodal PET / MRI contrast agent. The coordination compound can be obtained by reacting a cyclen-based compound of general formula (I) or (Ia) with Gd 3+It is prepared by reacting with a salt (such as GdCl3), thereby forming a Gd(III) chelate of a compound of general formula (I) or (Ia). Such Gd(III) chelates are contrast agents suitable for MRI imaging because they have high thermodynamic stability, kinetic inertness, and favorable relaxation efficacy characteristics.

[0055] The multimodal PET / MRI contrast agent can be prepared from the coordination compound of the above-mentioned Gd(III) ion and the cyclen-based compound of general formula (I) or (Ia) by 18 radioactively labeling the Gd(III) chelate with 19 F. The radiolabeling can be carried out using 18 isotope exchange of 18 F to 19 F, where R is F, or by using 19 nucleophilic aromatic substitution of 18 F for nitro, where R is NO2. A combination of the two radiolabeling methods can also be used for Gd(III) chelates containing R as NO2, where 18 nucleophilic aromatic substitution of 18 F for nitro is carried out, and then - isotope exchange of

[0056] Therefore, another object of the present invention is a multimodal PET / MRI contrast agent of general formula (VI):

[0057]

[0058] wherein A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, where n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph;

[0059] Z is H or A.

[0060] Preferably, 18 F is located at the para position relative to the nitrogen atom of the pyridyl pendant arm.

[0061] In one embodiment, the multimodal PET / MRI contrast agent has the general formula (VIa):

[0062]

[0063] Wherein, A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, wherein n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; preferably, A is -CH(CH3)COOH or -CH2P(=O)(OH)Ph.

[0064] Preferably, if 18 F is in the para position relative to the nitrogen atom of the pyridyl pendant arm, then A is not -CH2COOH.

[0065] In a preferred embodiment, Z is A, more preferably, A is -CH(CH3)COOH, even more preferably, all the A (-C*H(CH3)COOH) have the same stereoconfiguration (either all the A have the S configuration or all the A have the R configuration). Most preferably, all the A have the same stereoconfiguration, and 18 F is in the para position relative to the nitrogen atom of the pyridyl pendant arm.

[0066] In one embodiment, the multimodal PET / MRI contrast agent has the general formula (VIb):

[0067]

[0068]

[0069] Wherein, A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, wherein n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; preferably, A is -CH(CH3)COOH or -CH2P(=O)(OH)Ph. More preferably, A is -CH(CH3)COOH, even more preferably, the two A (-C*H(CH3)COOH) have the same stereoconfiguration.

[0070] In the most preferred embodiment, the multimodal PET / MRI contrast agent has the general formula (VI), (VIa) or (VIb), wherein, 18 F is in the para position relative to the nitrogen atom of the pyridyl pendant arm.

[0071] An object of the present invention is also a method for preparing a multimodal PET / MRI contrast agent of the general formula (VI) as defined above, the method comprising the following steps:

[0072] a) Provide a cyclen-based compound of general formula (I) as defined above;

[0073] b) Form a Gd(III) chelate of the compound of general formula (I);

[0074] c) Radioactively label the Gd(III) chelate with 18 F.

[0075] In one embodiment, step b) is achieved by reacting a cyclen-based compound of general formula (I) with Gd 3+ ions to form a Gd(III) chelate of the compound of general formula (I).

[0076] Preferably, the conditions for the chelation reaction are as follows:

[0077] A solution containing Gd 3+ ions in salt form (such as chloride, bromide, sulfate, nitrate, methanesulfonate, trifluoromethanesulfonate, formate, acetate, lactate, malate, citrate, 2-hydroxyisobutyrate, mandelate, diethanolate, tartrate) is mixed with a solution of the compound of general formula (I), preferably in a range of 1:0.5 to 1:100, more preferably 1:0.7 to 1:50, even more preferably 1:0.9 to 1:10 of Gd 3+The molar ratio of the ion to the compound of general formula (I). The concentration of the soluble component can be selected from the range of concentrations allowed by the solubility of such compounds in a given solvent at a given temperature, preferably in the concentration range of 0.000001 mol / L to 0.5 mol / L. The solvent can be water, a water-soluble organic solvent such as methanol, ethanol, propanol, isopropanol, acetone, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, or a mixture thereof. An organic or inorganic base (such as LiOH, NaOH, KOH, aqueous NH3, triethylamine, N,N-diisopropylethylamine, or pyridine) is added to the reaction mixture to compensate for the protons released during the complexation process, and the complexation occurs in solution. Preferably, 1 to 10 molar equivalents of the base are added per molecule of the compound of general formula (I). Finally, the reaction can be carried out in a buffer solution. In this case, there is no need to add an organic or inorganic base to the reaction mixture. The mixture is stirred or shaken at room temperature or elevated temperature for up to 24 hours to form a complete complex. Preferably, the mixture is stirred or shaken at 40 °C for 15 minutes. An appropriate excess of the compound of general formula (I) can be used to accelerate the complexation and shift the equilibrium towards the formation of the chelate. The resulting Gd(III) chelate of the compound of general formula (I) can optionally be desalted and purified from the excess compound of general formula (I) and other impurities. For example, purification can be achieved by column chromatography or high-performance liquid chromatography (HPLC). Preferably, chromatography is carried out on a C8, C18, or phenyl-hexyl reverse phase using HPLC. The mobile phase for chromatographic purification can contain water and 3 vol% to 40 vol% of methanol, ethanol, or acetonitrile. Alternatively, a buffer solution of 0.01 mol / L to 0.1 mol / L is used in the mobile phase, where the buffer solution contains ammonium formate pH = 7.0 or ammonium acetate pH = 7.0. The fractions containing the desired metal chelate are collected and evaporated or lyophilized.

[0078] In one embodiment, step c) of radiolabeling the Gd(III) chelate from step b) with 18 F is carried out by using 19 F to 18 F isotope exchange on the pyridine moiety of the Gd(III) chelate, where R is F; or by using 18 F nucleophilic aromatic substitution of the nitro group on the pyridine moiety of the Gd(III) chelate, where R is NO2.

[0079] Preferably, step c) is carried out under the following conditions:

[0080] Dissolve the Gd(III) chelate from step b) in a solvent, which is preferably selected from the group consisting of: acetone, acetonitrile, dichloromethane, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethylpropyleneurea (DMPU), dimethyl sulfoxide (DMSO), sulfolane, ethyl acetate, hexamethylphosphoramide (HMPA), pyridine, tetrahydrofuran (THF), methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone, tert-amyl alcohol, water, or a mixture thereof. Preferably, the final concentration of the Gd(III) chelate in the solvent or solvent mixture is in the range of 10 -12 M to 2M. Optionally, a non-radioactive F - ion source is added to achieve a concentration of 10 -12 M to 2M. The non-radioactive F - ion source can be, for example: tetramethylammonium fluoride, tetraethylammonium fluoride, tetrapropylammonium fluoride, tetrabutylammonium fluoride, tetrahexylammonium fluoride, NaF, KF, RbF, CsF, [Na(15-crown-5) + F - 、[K(18-crown-6) + F - 、[Cs(21-crown-7) + F - 、[Na(cryptand[2.2.1]) + F - 、[K(cryptand[2.2.2]) + F - or [Cs(cryptand[3.2.2]) + F - . Add a non-radioactive F - ion source to effect nucleophilic aromatic substitution of the NO2 group with 19 F. If the Gd(III) chelate from step b) does not contain any NO2 groups, addition of the non-radioactive F - ion can be omitted.

[0081] Similarly, a radioactive 18 F - ion source is added in an amount corresponding to the desired activity. In terms of molar equivalents, this represents only a fraction of the amount of the Gd(III) chelate and / or non-radioactive F - ion. 18 F - ion amount (activity) will be known to those skilled in the art without any inventive activity. The radioactive 18 F - ion source is similar to the non-radioactive F -Ion sources (such as 18 F]tetramethylammonium fluoride, 18 F]tetraethylammonium fluoride, 18 F]tetrapropylammonium fluoride, 18 F]tetrabutylammonium fluoride, 18 F]tetrahexylammonium fluoride, Na 18 F, K 18 F, Rb 18 F, Cs 18 F, [Na(15-crown-5) + 18 F - , [K(18-crown-6) + 18 F - , [Cs(21-crown-7) + 18 F - , [Na(cryptand[2.2.1]) + 18 F - , [K(cryptand[2.2.2]) + 18 F - or [Cs(cryptand[3.2.2]) + 18 F - ). The reaction mixture is then stirred at a temperature in the range from -50 °C to 250 °C, preferably in the range from 5 °C to 200 °C, for at least 0.1 s, preferably for at most 8 h.

[0082] In a more preferred embodiment, step c) is carried out in a solvent selected from acetonitrile, DMF, DMAC, DMPU, DMSO, sulfolane, HMPA, THF, tert-butanol, NMP, 1,3-dimethyl-2-imidazolidinone, tert-amyl alcohol, water, or a mixture thereof. The final concentration of the Gd(III) chelate in the solvent or solvent mixture is in the range from 10 -6 M to 0.5 M. Optionally, a non-radioactive F - ion source is added to achieve a concentration range from 10 -6 M to 0.5 M. The non-radioactive F - ion source is preferably selected from: tetramethylammonium fluoride, tetrabutylammonium fluoride, NaF, KF, CsF, [Na(15-crown-5) + F - , [K(18-crown-6) + F - , [Na(cryptand[2.2.1]) + F - , and [K(cryptand[2.2.2])​​​​​​+ F - 。

[0083] Add a radioactive 18 F - ion source in an amount corresponding to the desired activity. The radioactive 18 F - ion source is similar to the non-radioactive F - ion sources listed above (e.g., 18 F]tetramethylammonium fluoride, 18 F]tetrabutylammonium fluoride, Na 18 F, K 18 F, Cs 18 F, [Na(15-crown-5) + 18 F - 、[K(18-crown-6) + 18 F - 、[Na(cryptand[2.2.1]) + 18 F - 、or [K(cryptand[2.2.2]) + 18 F - )). The reaction mixture is then stirred at a temperature of 25 °C to 200 °C for at least 1 minute, preferably for at most 2 hours.

[0084] Most preferably, the solvent is selected from acetonitrile, DMF, DMSO, or mixtures thereof. The final concentration of the Gd(III) chelate is in the range of 0.1 mM to 100 mM. Optionally, a non-radioactive F - ion source is added to achieve a concentration range of 1 mM to 300 mM. The non-radioactive F - ion source is preferably selected from tetrabutylammonium fluoride, or [K(cryptand[2.2.2]) + F - ). Add a radioactive 18 F - ion source in an amount corresponding to the desired activity. The radioactive 18 F - source is selected from 18 F]tetrabutylammonium fluoride, and [K(cryptand[2.2.2]) + 18 F - ). The reaction mixture is then stirred at a temperature of 25 °C to 150 °C for at least 1 minute, preferably for at most 100 minutes.

[0085] An object of the present invention is also a method for imaging a region of interest in a patient using multimodal PET / MRI imaging, the method comprising:​​​​​

[0086] - Administering to a patient a pharmaceutical preparation comprising a multimodal PET / MRI contrast agent of general formula (VI), (VIa) or (VIb);

[0087] - Detecting the arrival of the multimodal PET / MRI contrast agent present in the preparation at the region of interest by comparing the PET and / or MRI signals in the region of interest during or after administering the pharmaceutical preparation;

[0088] - Collecting PET and MRI image data of the region of interest; and

[0089] - Constructing a multimodal PET / MRI image of the region of interest using the PET and MRI image data, wherein the region of interest appears different from the background tissue.

[0090] The pharmaceutical preparation comprising a multimodal PET / MRI contrast agent of general formula (VI), (VIa) or (VIb) may further comprise pharmaceutically acceptable auxiliary substances conventionally used. The dosage form of the pharmaceutical preparation is a form for injection administration, most commonly a bolus injection or an infusion, preferably intravenous injection. Suitable pharmaceutically acceptable auxiliary substances are preferably selected from the group comprising: solvents (especially aqueous solutions or salt solutions), buffers (especially phosphate buffers, HEPES = 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid), ionization additives, antioxidants, antimicrobial additives. Those skilled in the art will be able to determine which auxiliary substances to select without inventive activity.

[0091] In one embodiment, the pharmaceutical preparation further comprises a coordination compound of Gd(III) ions and a cyclen-based compound of general formula (I) or (Ia) as defined above. The presence of the coordination compound containing Gd(III) and 19 F provides an MRI signal, while the presence of the multimodal PET / MRI contrast agent of general formula (VI), (VIa) or (VIb) bearing 18 F provides PET and MRI signals. Since the amount of the 18 F radionuclide required for the PET signal is about 9 to 10 orders of magnitude lower than the amount of the Gd(III) chelate required for MRI contrast, the MRI contrast of the pharmaceutical preparation is enhanced by the presence of the non-radioactive Gd(III) chelate of the compound of general formula (I) or (Ia) as defined above. If the radioactive Gd(III) chelate and the non-radioactive Gd(III) chelate differ only in the fluorine isotope (which means that the coordination compounds are identical in structure, differing only in bearing 19 F or 18If they differ in terms of F isotopes), they are preferred. The concentration of the non-radioactive Gd(III) chelate should be sufficient to achieve MRI contrast, and the concentration of the PET / MRI contrast agent should be sufficient to achieve PET contrast. A person skilled in the art will know the concentration of the Gd(III) chelate for achieving MRI contrast and the 18 concentration of the F radionuclide. Generally, the molar ratio of the non-radioactive Gd(III) chelate of the compound of general formula (I) or (Ia) to the PET / MRI contrast agent of general formula (VI), (VIa) or (VIb) should preferably be about 1:10 -10 to about 1:10 -8 .

[0092] Another object of the present invention is also the use of the multimodal PET / MRI contrast agent of general formula (VI), (VIa) or (VIb) and / or the pharmaceutical preparation containing the same in medicine, preferably in the combined PET / MRI diagnostic method. Description of the Drawings

[0093] Figure 1 : Chromatogram of the radiolabeling experiment of Example 4 with [Gd(L 1 )] as the precursor. In the UV detector, the product corresponds to the peak at 7.431 minutes. In the gamma detector, the product corresponds to the peak at 7.767 minutes.

[0094] Figure 2 : Chromatogram of the radiolabeling experiment of Example 4 with [Gd(L 4 )] as the precursor. In the UV detector, the product corresponds to the peak at 7.343 minutes. In the gamma detector, the product corresponds to the peak at 7.700 minutes.

[0095] Figure 3 : Chromatogram of the radiolabeling experiment of Example 4 with L 4 as the precursor. It can be seen that there is no radiolabeled product, and the only peak in the gamma detector corresponds to free 18 F - . The main peak in the UV detector corresponds to the unlabeled starting material L 4 .

[0096] Figure 4 : Determination of the relaxation efficacy of [Gd(L 4 )] and [Gd(L 7 )] by the relative longitudinal relaxation rate of the concentrations of [Gd(L 4 )] and [Gd(L 7 )] at 37 °C and 0.47 T through linear regression.

[0097] Figure 5: By measuring the relaxation rate on a relaxometer and comparing the kinetic inertness of [Gd(L 4 )], [Gd(L 7 )], and Magnevist through acid-assisted decomplexation in 0.1 M HCl at 37 °C. The top graph shows the data collected during the first 4 hours of the experiment, and the bottom graph includes the data points after 24 hours. After reaching thermodynamic equilibrium, the R 1p values of all the complexes tested should be the same, but elemental analysis confirmed minor differences in sample concentration (pipetting errors), which explains this discrepancy. Data for an unchelated GdCl3 solution of the same molar concentration are shown for reference. The curves demonstrate the differences in the kinetic inertness of the metal chelates. While Magnevist, which is used clinically, decomplexes almost immediately (<5 minutes), [Gd(L 7 )] takes a longer time to reach complete decomplexation. Finally, the [Gd(L 4 )] chelate is the most inert, and even after 24 hours under these conditions, the curve is far from reaching thermodynamic equilibrium, indicating that most of the chelate remains intact.

[0098] Figure 6 : In vitro simultaneous PET / MRI imaging of radiolabeled [Gd(L 4 )] in the model. (A) Simultaneously acquired T1-weighted MRI and PET images on a batch of vials containing different concentrations of radiolabeled [Gd(L 4 )], different concentrations of Magnevist as a reference, and two samples of pure H2O and PBS (phosphate-buffered saline). The numbers represent the concentration of the contrast agent (in mM). (B) The concentration of [Gd(L 4 )] in the samples of Series A, quantified by ICP-OES (gadolinium content) and gamma counting (radioactivity), shows excellent linear correlation. Quantification of the PET signal in Series A also shows excellent linear correlation with the MRI signal determined from the T1-weighted images (C) and the relaxation rate determined from the T1-mapping (D).

[0099] Figure 7 : Pharmacokinetics of radiolabeled [Gd(L 4 )] in mice (N = 3) from PET / MRI shows rapid renal uptake and clearance. (A) Pharmacokinetic curves obtained from MRI T1-mapping, expressed as the 1 / T1 change, in %. (B) Pharmacokinetic curves obtained from PET images, expressed as % of the injected dose per mL. The right axis pertains to bladder data.

[0100] Figure 8 : Pharmacokinetics of radiolabeled [Gd(L 4)] Biodistribution. (A) Biodistribution based on radioactivity measurement (gamma counter), expressed as % of the injected dose per gram of wet tissue. (B) Biodistribution based on gadolinium measurement (ICP - OES), expressed as % of the injected dose per gram of wet tissue.

[0101] Figure 9 : In vivo simultaneous PET / MRI imaging of radiolabeled [Gd(L 4 )] in mice. Images show time points from left to right: pre - injection image, injection, 10 minutes post - injection, and 60 minutes post - injection. Top row: T1 - weighted dynamic contrast - enhanced (DCE) MRI. Middle row: PET images. Bottom row: merged MRI and PET images. In the PET images, distinct hot spots can be seen in the kidneys, while in the MRI, the same regions are oversaturated and appear darker. Detailed Description of the Invention

[0102] Example

[0103] Example 1: Synthesis of Intermediate

[0104] Synthesis of Intermediate (1): In a 250 mL round - bottom glass flask, 2 - methyl - 4 - nitropyridine N - oxide (5.15 g, 33.4 mmol, 1.0 equiv) was dissolved in DCM (200 mL). A solution of TFAA (14 mL, 101 mmol, 3.0 equiv) in DCM (35 mL) was added dropwise, and the resulting suspension was stirred at room temperature for 96 h. A saturated aqueous solution of K2CO3 (40 mL) was added in four portions over 1 h, and the reaction mixture was stirred until bubbling ceased. The aqueous phase was extracted with DCM (2 × 200 mL), and the solvent was evaporated on a rotary evaporator. The residue was purified by preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized. The resulting white solid was dissolved in DCM (340 mL), then DMF (46 μL, 0.60 mmol, 0.02 equiv) and SOCl2 (5.5 mL, 75.1 mmol, 2.25 equiv) were added dropwise. After stirring at room temperature for 6 h, the reaction mixture was placed in an ice bath and carefully quenched with a saturated aqueous solution of NaHCO3 (200 mL). The phases were separated, and the aqueous phase was extracted with DCM (200 mL). The organic phase was dried over Na2SO4, filtered, and the liquid was evaporated on a rotary evaporator. The residue was purified by column chromatography (SiO2, 100% DCM to DCM solution of 10% MeOH). The fractions containing the product were combined and evaporated to dryness to give the product as a yellow oil. Yield: 2.2 g (38%; 2 steps; based on 2 - methyl - 4 - nitropyridine N - oxide). NMR (CDCl3): 1Hδ H 4.80 (CH2 - aromatic, s, 2H); 7.98 (aromatic, dd, 3 J HH = 5, 4 J HH = 2, 1H); 8.24 (aromatic, d, 4 J HH = 2, 1H); 8.87 (aromatic, d, 3 J HH = 5, 1H); 13 C{ 1 H}δ C 45.8 (CH2 - aromatic, s); 115.6 (aromatic, s); 115.8 (aromatic, s); 151.8 (aromatic, s); 154.8 (aromatic, s); 160.2 (aromatic, s). EI - HRMS: 172.0033 [M] + (theoretical [C6H5O2N2Cl1] + = 172.0034).

[0105] Synthesis of Intermediate (2): In a 50 mL pear - shaped glass flask, 2 - methyl - 6 - nitropyridine (224 mg, 1.62 mmol, 1.0 equiv), NBS (577 mg, 3.24 mmol, 2.0 equiv) and AIBN (42 mg, 0.26 mmol, 0.16 equiv) were dissolved in CCl4 (6 mL). The reaction mixture was heated under reflux for 19 h. The solvent was evaporated on a rotary evaporator. The residue was purified by preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and DCM was added until phase separation occurred. The organic phase was separated and washed with a saturated aqueous solution of NaHCO3. The organic phase was concentrated on a rotary evaporator to give the product as a colorless solid. Yield: 79 mg (23%, 1 step, based on 2 - methyl - 6 - nitropyridine). NMR (CDCl3): 1 Hδ H 4.63 (CH2 - aromatic, s, 2H); 7.87 (aromatic, dd, 2 J HH = 7.6, 3 J HH = 0.9, 1H); 8.07 (aromatic, t, 2 J HH = 7.8, 1H); 8.19 (aromatic, dd, 2 J HH = 8.0, 3 J HH = 0.8, 1H); 13 C{1 H}δ C 31.7 (CH2 - aromatic, s); 117.3 (aromatic, s); 129.3 (aromatic, s); 141.1 (aromatic, s); 156.2 (aromatic, s); 157.5 (aromatic, s). CI - HRMS: 216.9605 [M + H] + (theoretical [C6H6O2Br1N2] + = 216.9607).

[0106] Synthesis of intermediate (3): In a 50 mL round - bottom glass flask, 3 - fluoropicolinic acid (813 mg, 5.76 mmol, 1.0 equiv) was dissolved in MeOH (12 mL), and H2SO4 (300 μL, 5.40 mmol, 0.94 equiv) was added dropwise. The reaction mixture was heated under reflux for 41 h. The reaction mixture was cooled to room temperature and quenched with a saturated aqueous solution of NaHCO3 (1 mL). The reaction mixture was concentrated to about 2 mL on a rotary evaporator and left standing until crystals began to appear. The crystals were washed with H2O (2 × 2 mL) and dried under vacuum. The obtained crystals were dissolved in MeOH (30 mL), and NaBH4 (370 mg, 9.78 mmol, 1.70 equiv) was added in three portions while stirring in an ice - bath. After 30 min, the reaction mixture was allowed to reach room temperature and stirring was continued for 1.5 h. The reaction was quenched with H2O (1 mL), and the liquid was evaporated on a rotary evaporator. The residue was suspended in a saturated aqueous solution of K2CO3 (50 mL) and extracted with DCM (2 × 50 mL). The solvent was evaporated on a rotary evaporator, the residue was dissolved in DCM (7 mL), then DMF (5 μL, 0.06 mmol, 0.01 equiv) and SOCl2 (0.523 mL, 1.17 mmol, 0.20 equiv) were added dropwise. After stirring at room temperature for 1 h, a saturated aqueous solution of NaHCO3 (10 mL) was carefully added to quench the reaction mixture. The phases were separated, and the aqueous phase was extracted with DCM (10 mL). The organic phase was dried over Na2SO4, filtered, and the liquid was evaporated on a rotary evaporator to give the product as a pale yellow oil. Yield: 186 mg (22%; 3 steps; based on 3 - fluoropicolinic acid). NMR (CDCl3): 1 Hδ H 4.68 (CH2 - aromatic, s, 2H); 7.19 - 7.29 (aromatic, m, 1H); 7.32 - 7.42 (aromatic, m, 1H); 8.31 - 8.40 (aromatic, m, 1H); 13 C{ 1 H}δ C 40.6 (CH2 - aromatic, s); 123.9 (aromatic, d, 2 JCF = 18.6 Hz); 125.4 (aromatic, d, 3 J CF = 4.0 Hz); 144.9 (aromatic, d, 2 J CF = 14.2 Hz); 145.5 (aromatic, d, 4 J CF = 5.4 Hz); 157.8 (aromatic, d, 1 J CF = 260.8 Hz). 19 F{ 1 H}δ F -123.2 (s). CI-HRMS: 146.0174 [M + H] + (theoretical [C6H6Cl1N1F1] + = 146.0167).

[0107] Synthesis of Intermediate (4): In a 50 mL round-bottom glass flask, (4-fluoropyridin-2-yl)methanol (227 mg, 1.79 mmol, 1.0 equiv) was dissolved in DCM (35 mL), and DMF (4 μL, 0.05 mmol, 0.01 equiv) was added. The reaction mixture was placed in an ice bath. After being placed in the ice bath for 20 minutes, thionyl chloride (400 μL, 5.36 mmol, 3.0 equiv) was added dropwise, and the reaction mixture was stirred in the ice bath. After 15 minutes, the reaction mixture was allowed to warm to room temperature. After stirring at room temperature for 1 hour, the reaction mixture was placed in an ice bath, and a saturated aqueous solution of NaHCO3 (10 mL) was carefully added to quench the reaction. The phases were separated, and the aqueous phase was extracted with DCM (2 × 40 mL). The organic phase was dried over Na2SO4, filtered, and the liquid was evaporated on a rotary evaporator to obtain the product as a colorless oil. Yield: 217 mg (83%; 1 step; based on (4-fluoropyridin-2-yl)methanol). NMR (CDCl3): 1 H (400.1 MHz, T = 300 K) δ H 4.69 (CH2-aromatic, s, 2H); 7.00 (aromatic, ddd, J = 8, 6, 2 Hz 1H); 7.24 - 7.30 (aromatic, m, 1H); 8.55 (aromatic, dd, J = 8, 6 Hz H). 13 C{ 1 H}(100.6 MHz, T = 300 K) δ C 70.8 (CH2-aromatic, d, 4 J CF = 3 Hz); 110.9 (aromatic, d, 2 J CF= 18 Hz); 111.2 (aromatic, d, 2 J CF = 17 Hz); 151.8 (aromatic, d, 3 J CF = 7 Hz); 160.0 (aromatic, d, 3 J CF = 7 Hz); 169.4 (aromatic, d, 1 J CF = 263 Hz). 19 F{ 1 H}(376.5 MHz, T = 300.0 K) δ F -100.9 (s). ESI-MS: 146.0 [M+H] + (theoretical [C6H6N1F1Cl1] + = 146.0).

[0108] Synthesis of Intermediate (5): Add benzyl l-lactate (900 mg; 4.99 mmol; 1.00 equivalent) and a magnetic stirrer to a pear-shaped glass flask (100 mL), and protect it briefly with argon three times. Then, under a constant argon flow, add dry DCM (20 mL) through the septum, cool the mixture with an ice bath (5 °C), then add dropwise trifluoromethanesulfonic anhydride (0.88 mL; 5.23 mmol; 1.05 equivalent), and then immediately add dropwise dry pyridine (0.42 mL; 5.25 mmol; 1.05 equivalent). Stir the resulting mixture at 5 °C for 30 minutes. Then directly purify the resulting suspension by column chromatography (30 g SiO2, DCM). Evaporate the combined fractions containing the product to dryness and dry briefly under high vacuum to obtain the product as an almost colorless oil in free base form. Yield: 1.12 g (77%; 1 step; based on benzyl l-lactate). NMR (DMSO-d6): 1 H δ H 1.53 (CH3, d, 3H, 3 J HH = 7); 5.27 (CH2, s, 2H); 5.34 (CH, q, 1H, 3 J HH = 7); 7.17 - 7.65 (Ph, m, 5H). 19 F{ 1 H} δ F -77.7 (s). ESI-HRMS: 335.0175 [M+Na] + (theoretical [C 11 H 11 O5F3S1Na1] + = 335.0172).

[0109] Synthesis of Intermediate (6): In a glass vial (20 mL), cyclen (free base; 100 mg; 580 μmol; 1.0 equiv) and K2CO3 (160 mg; 1.16 mmol; 2.0 equiv) were suspended in dry MeCN (6 mL), and then a solution of 5 (362 mg; 1.16 mmol; 2.0 equiv) in dry MeCN (4 mL) was added. The resulting mixture was stirred at 40 °C for 1 h. The solid was filtered off using a syringe microfilter (PTFE), and the filtrate was evaporated to dryness. The residue was purified by preparative HPLC (C18; H2O-MeCN gradient with TFA additive). The fractions containing the product were combined and lyophilized to give the product as a brown honey in the form of the TFA salt. Yield: 106 mg (25%, 1 step, based on cyclen). NMR (CD3CN): 1 Hδ H 1.20 (CH3, d, 3H, 3 J HH = 7 Hz); 1.26 (CH3, d, 6H, 3 J HH = 7 Hz); 2.30 - 2.96 (mc, m, 16H); 3.59 (CHCH3-COOBn, q, 2H, 3 J HH = 7 Hz); 3.77 (CHCH3-COOBn, q, 1H, 3 J HH = 7 Hz); 5.09 (CH2-aromatic, s, 2H); 5.10 (CH2-aromatic, s, 4H); 7.29 - 7.41 (aromatic, m, 15H). ESI-HRMS: 659.3797 [M+H] + (Theoretical [C 38 H 51 N4O6] + = 659.3803). EA (C 38 H 50 N4O6·0.3TFA·2.0H2O, M R = 729.0): C 63.6 (63.0); H 7.5 (6.9); N 7.7 (7.4); F 2.4 (2.2).

[0110] Synthesis of Intermediate (7): In a glass vial (20 mL), Cbz2-cyclen (free base; 242 mg; 549 μmol; 1.0 equiv) was dissolved in MeCN (12 mL), and then solid (CH2O) n(50 mg; 1.67 mmol; 3.0 equiv) and PhP(OMe)2 (350 μL; 2.2 mmol; 4.0 equiv). The resulting suspension was stirred at 80 °C for 24 h. The reaction mixture was then filtered through a syringe microfilter (PTFE), and the filtrate was evaporated to dryness. The residue was purified by preparative HPLC (C18; H2O-MeCN gradient with TFA additive). The fractions containing the product were combined, neutralized with diluted aqueous NaHCO3 and evaporated to dryness. The residue was dissolved in DCM (75 mL) and H2O (75 mL), and transferred to a separatory funnel. After shaking, the bottom layer was separated. The aqueous phase was further extracted with DCM (3 × 25 mL). The combined organic layers were dried over anhydrous Na2SO4, filtered through a glass frit (S3) and evaporated to dryness. The residue was further dried under high vacuum overnight to give the product as an almost colorless oil in free base form. Yield: 259 mg (61%, 1 step, based on Cbz2 cyclanoline). NMR (CD3CN): 1 H δ H 2.30 - 3.38 (mc, CH2-P, m, 16 + 4H); 3.47 (CH3, d, 6H, 3 J HP = 11); 5.00 - 5.12 (CH2-Ph, m, 4H); 7.27 - 7.40 (Ph, m, 10H); 7.40 - 7.51 (Ph, m, 4H); 7.51 - 7.60 (Ph, m, 2H); 7.60 - 7.82 (Ph, m, 4H). 31 P δ P 42.8 (m). ESI-HRMS: 777.3178 [M + H] + (Theoretical for [C 40 H 51 N4O8P2] + = 777.3177).

[0111] Synthesis of intermediate (8): 7 (250 mg; 322 μmol) and a magnetic stirrer were added to a pear-shaped glass flask (50 mL), and purged with argon three times. Then solid Pd@C (50 mg) was added, and then purged with argon again (3 times). Then, under a constant argon flow, MeOH (25 mL) was added via a septum. The argon inlet was then removed, and H2 gas (from a balloon) was bubbled through the mixture at room temperature for 2 h. The catalyst was then filtered off using a syringe microfilter (PTFE; the filter was further washed with MeOH). The filtrate was evaporated to dryness and co-evaporated once with DCM. The residue was further dried under high vacuum overnight to give the product as an almost colorless oil in free base form. Yield: 161 mg (98%; 1 step; based on 8). NMR (CD3CN):1 Hδ H 2.28 - 3.14 (mc, CH2 - P, m, 16 + 4H); 3.53 (CH3, d, 3H, 3 J HP = 11); 3.54 (CH3, d, 3H, 3 J HP = 11); 7.46 - 7.63 (Ph, m, 6H); 7.71 - 7.83 (Ph, m, 4H). 31 Pδ P 43.3 (m). ESI - HRMS: 509.2438[M + H] + (Theoretical [C 24 H 39 N4O4P2] + = 509.2441).

[0112] Synthesis of Intermediate (9): In a 50 mL round - bottom glass flask, methyl 4 - fluoropicolinate (250 mg, 1.61 mmol, 1.0 equiv) was dissolved in MeOH (16 mL), and NaBH4 (180 mg, 4.78 mmol, ~3.0 equiv) was added with stirring. The reaction was stirred at room temperature for 3 h, then H2O (1 mL) was added. The liquid was evaporated on a rotary evaporator, and the residue was suspended in a saturated aqueous solution of K2CO3 (25 mL). The aqueous phase was extracted with DCM (2 × 25 mL), and the solvent was evaporated on a rotary evaporator. The residue was dissolved in DCM (11 mL), and Et3N (280 μL, 2.02 mmol, 1.3 equiv) was added. The reaction mixture was placed in an ice bath. After 20 min in the ice bath, methanesulfonyl chloride (146 μL, 1.88 mmol, 1.23 equiv) was added, and the reaction mixture was stirred on the ice bath. After 15 min, the reaction mixture was warmed to room temperature and then stirred for 1 h. The reaction mixture was diluted with DCM (40 mL) and washed with H2O (2 × 40 mL), brine (40 mL). The organic phase was dried over Na2SO4, filtered, and the liquid was evaporated on a rotary evaporator to give the product as a dark orange oil. Yield: 240 mg (77%; 2 steps; based on methyl 4 - fluoropicolinate). NMR (CDCl3): 1 Hδ H 3.12 (CH3, s, 3H); 5.33 (CH2 - aromatic, s, 2H); 7.04 (aromatic., ddd, J = 8, 6, 3 Hz 1H); 7.24 (aromatic, dd, J = 9, 3 Hz, 1H); 8.58 (aromatic, dd, J = 8, 6 Hz, 1H); 13 C{ 1 H}δ C38.2 (CH3, s); 70.4 (CH2 - aromatic, s); 110.5 (aromatic, d, 2 J CF = 18 Hz); 111.7 (aromatic, d, 2 J CF = 17 Hz); 152 (aromatic, d, 3 J CF = 7 Hz); 157.2 (aromatic, d, 3 J CF = 7 Hz); 169.5 (aromatic, d, 1 J CF = 265 Hz). 19 F{ 1 H}δ F - 99.3 (s). CI - HRMS: 206.0281 [M + H] + (theoretical [C7H9O3N1F1S1] + = 206.0282).

[0113] Synthesis of intermediate (10): In a 50 mL round - bottom glass flask, (5 - fluoropyridin - 2 - yl) methanol (173 mg, 1.36 mmol, 1.0 equiv) was dissolved in DCM (10 mL), and Et3N (250 μL, 1.80 mmol, 1.3 equiv) was added. The reaction mixture was placed in an ice bath. After 20 minutes in the ice bath, methanesulfonyl chloride (142 μL, 1.84 mmol, 1.35 equiv) was added, and the reaction mixture was stirred on the ice bath. After 15 minutes, the reaction mixture was warmed to room temperature and stirred for another 1 hour. The reaction mixture was diluted with DCM (40 mL) and washed with H2O (2 × 40 mL), brine (40 mL). The organic phase was dried over Na2SO4, filtered, and the liquid was evaporated on a rotary evaporator to give the product as an orange solid. Yield: 219 mg (78%; 1 step; based on (5 - fluoropyridin - 2 - yl) methanol). NMR (CDCl3): 1 Hδ H 3.08 (CH3, s, 3H); 5.31 (CH2 - aromatic, s, 2H); 7.42 - 7.53 (aromatic, m, 2H); 8.47 (aromatic, dd, J = 3, 1 Hz, 1H); 13 C{ 1 H}δ C 38.2 (CH3, s); 70.8 (CH2 - aromatic, s); 124.1 (aromatic, d, 3 J CF = 3 Hz); 124.2 (aromatic, d, 2 J CF= 11 Hz); 138 (aromatic, d, 2 J CF = 24 Hz); 149.6 (aromatic, d, 4 J CF = 4 Hz); 159.4 (aromatic, d, 1 J CF = 258 Hz). 19 F{ 1 H}δ F -125.8 (s). CI-HRMS: 206.0284 [M+H] + (theoretical [C7H9O3N1F1S1] + = 206.0282).

[0114] Synthesis of intermediate (11): Ethyl L-lactate (6.70 g; 56.7 mmol; 1.00 equivalent) and a magnetic stirrer were added to a pear-shaped glass flask (500 mL), and the mixture was briefly protected with argon three times. Then, under a constant argon flow, dry DCM (200 mL) was added through a septum, the mixture was cooled with an ice bath (5 °C), then trifluoromethanesulfonic anhydride (10.0 mL; 59.4 mmol; 1.05 equivalents) was added dropwise, and then dry pyridine (4.80 mL; 59.6 mmol; 1.05 equivalents) was immediately added dropwise. Then the ice bath was removed, and the mixture was further stirred at room temperature for 1 hour. Then the resulting suspension was directly purified by column chromatography (250 g SiO2, DCM). The combined fractions containing the product were evaporated to dryness and briefly dried under high vacuum to give the product as a light brown oil. Yield: 12.02 g (85%; 1 step; based on ethyl L-lactate). NMR (DMSO-d6): 1 Hδ H 1.26 (CH3-CH2, t, 3H, 3 J HH = 7); 1.51 (CH3-CH, d, 3H, 3 J HH = 7); 4.19 - 4.31 (CH2, m, 2H); 5.27 (CH, q, 1H, 3 J HH = 7). 19 F{ 1 H}δ F -77.7 (s). CI-HRMS: 251.0193 [M+H] + (theoretical [C6H 10 O5S1F3] + = 251.0196).

[0115] Synthesis of Intermediate (12): In a pear-shaped glass flask (25 mL), cyclen (free base; 200 mg; 1160 μmol; 1.0 equiv) was dissolved in dry DCM (12 mL), and then a solution of tert-butyl 4-nitrophenyl carbonate (278 mg; 1.16 mmol; 1.0 equiv) in dry DCM (4 mL) was added dropwise. The resulting mixture was stirred at room temperature for 30 minutes. The liquid was evaporated, and the residue was purified by preparative HPLC (C18; H2O-MeCN gradient with TFA additive). The fractions containing the product were combined and lyophilized to give the product as a transparent solid in the form of the TFA salt. Yield: 245 mg (42%, 1 step, based on cyclen assuming 12·2TFA). NMR (CD3CN): 1 Hδ H 1.44 (CH3, s, 9H); 3.01 - 3.08 (mc, m, 4H); 3.11 - 3.18 (mc, m, 4H); 3.23 - 3.29 (mc, m, 4H); 3.39 - 3.48 (mc, m, 4H). 13 C{ 1 H}(100.6 MHz, T = 300 K) δC 27.48 (CH3, s); 44.14 (mc, s); 44.70 (mc, s); 47.69 (mc, s); 47.96 (mc, s); 80.57 (C-CH3, s); 155.66 (CO, s). ESI-HRMS: 273.2284 [M+H] + (Theoretical [C 13 H 29 N4O2] + = 273.2285).

[0116] Synthesis of Intermediate (13): In a glass vial (20 mL), Intermediate 12 (100 mg; 200 μmol; 1.0 equiv) and Intermediate 11 (367 mg; 1.47 mmol; 7.4 equiv) were dissolved in dry MeCN (15 mL), and then K2CO3 (254 mg; 1.84 mmol; 9.2 equiv) was added. The resulting mixture was stirred at room temperature for 15 h. The solid was filtered off using a syringe microfilter (PTFE), and the filtrate was evaporated to dryness. The residue was purified by preparative HPLC (C18; H2O-MeCN gradient with FA additive). The fractions containing the pure product in the ethyl ester form were combined and evaporated to dryness. The residue was dissolved in pure TFA (3 mL) and stirred at room temperature for 15 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a clear honey. Yield: 21 mg (20%, 2 steps, based on 12 assuming 13·FA). NMR (DMSO-d6): 1 H δ H 1.17 - 1.24 (CH3, m, 18H); 2.40 (mc, m, 2H); 2.55 (mc, m, 2H); 2.73 - 2.94 (mc, m, 10H); 3.21 (mc, m, 2H); 3.63 (CHCH3-COOEt, q, 2H, 3 J HH = 7 Hz); 3.74 (CHCH3-COOBn, q, 1H, 3 J HH = 7 Hz); 4.07 - 4.13 (O-CH2ZCH3, m, 6H); 8.8 (NH, bs, 1H). 13 C{ 1 H} δ C 14.1 (CH3, s); 14.22 (CH3, s); 14.24 (CH3, s); 15.2 (CH3, s); 44.8, 45.2, 46.6, 50.0 (mc); 54.8 (CCH3HZCOCH2CH3, s); 57.8 (CCH3H-COCH2CH3, s); 60.0 (CCH3H-COCH2CH3, s); 60.04 (CCH3H-COCH2CH3, s); 172.5 (CO, s); 172.8 (CO, s). ESI-HRMS: 473.3329 [M+H] + (Theoretical for [C 23 H 45 N4O6] + = 473.3334).

[0117] Example 2: Synthesis of Ligand

[0118] Synthesis of Ligand L 1 (2,2',2”-(10-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): Solution 1 (168 mg, 0.97 mmol, 1.1 eq) was added to a solution of t-BuDO3A·HBr (527 mg, 0.89 mmol, 1.0 eq) in MeCN (18 mL), and then dry K2CO3 (489 mg, 3.54 mmol, 4.0 eq) was added. The resulting suspension was stirred at room temperature for 24 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). Fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (6 mL) and stirred at room temperature for 16 h. Volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). Fractions containing the product were combined and lyophilized to give the product as a pale yellow solid in the form of the TFA salt. Yield: 342 mg (56%, 2 steps, based on t-BuDO3A·HBr). NMR (D2O): 1 Hδ H 3.09 - 3.70 (mc, CH2-COOH, m, 22H); 4.35 (CH2-aromatic, bs, 2H); 8.14 (aromatic, dd, 1H, 3 J HH = 6 Hz, 4 J HH = 2 Hz); 8.40 (aromatic, d, 1H, 3 J HH = 2 Hz); 8.87 (aromatic, d, 1H, 3 J HH = 6 Hz); 13 C{ 1 H}δ C 49.7 (mc, s); 50.6 (mc, s); 51.0 (mc, s); 54.7 (mc, s); 55.8 (CH2-COOH, s); 57.8 (CH2-aromatic, s); 117.4 (aromatic, s); 118.6 (aromatic, s); 152.0 (aromatic, s); 155.8 (aromatic, s); 173.0 (CO, s); 175.5 (CO, s). ESI-HRMS: 483.2195 [M+H]+ (Theoretical [C 20 H 31 N6O8] + = 483.2198). EA (C 20 H 30 N6O8·1.8TFA·1.0H2O, M R = 687.7): C 41.2 (42.0); H 4.7 (5.2); N 12.2 (12.8); F 14.9 (15.9).

[0119] Synthesis of ligand L 2 (2,2',2”-(10-((6-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): A solution of 2 (74 mg, 0.34 mmol, 1.1 equiv) in MeCN (2 mL) was added to a solution of t-BuDO3A·HBr (185 mg, 0.31 mmol, 1.0 equiv) in MeCN (42 mL), and then dry K2CO3 (215 mg, 1.55 mmol, 5 equiv) was added. The resulting suspension was stirred at room temperature for 24 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (3 mL) and stirred at room temperature for 16 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a pale yellow solid in the form of the FA salt. Yield: 50 mg (31%, 2 steps, based on t-BuDO3A·HBr). NMR (D2O): 1 Hδ H 2.94 - 3.18 (mc, m, 8H); 3.33 - 3.51 (mc, m, 8H); 3.54 (CH2-COOH, s, 2H); 3.61 - 3.82 (CH2-COOH, m, 4H); 4.05 (CH2-aromatic, s, 2H); 8.16 (aromatic, t, 1H, 3 J HH = 8 Hz); 8.24 - 8.33 (aromatic, m, 2H); 13 C{ 1 H}δ C48.6 (mc, s); 51.1 (mc, s); 52.2 (mc, s); 54.1 (CH2-COOH, s); 56.8 (CH2-COOH, s); 58.2 (CH2-aromatic, s); 118.5 (aromatic, s); 132.2 (aromatic, s); 143.6 (aromatic, s); 155.9 (aromatic, s); 157.8 (aromatic, s); 169.9 (CO, s); 175.3 (CO, s). ESI-HRMS: 483.2196 [M+H] + (Theoretical [C 20 H 32 N5O6] + = 483.2198). EA (C 20 H 30 N6O8·0.8FA·0.2H2O, M R = 522.9): C 47.8 (47.8); H 6.2 (6.2); N 16.1 (16.1).

[0120] Synthesis of ligand L 3 (2,2',2”-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): A solution of 3 (106 mg, 0.74 mmol, 1.1 equiv) in MeCN (1 mL) was added to a solution of t-BuDO3A·HBr (400 mg, 0.67 mmol, 1.0 equiv) in MeCN (13.4 mL), and then dry K2CO3 (464 mg, 3.36 mmol, 5.0 equiv) was added. The resulting suspension was stirred at room temperature for 19 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (9 mL) and stirred at room temperature for 19 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the FA / TFA salt. Yield: 273 mg (70%, 2 steps, based on t-BuDO3A·HBr). NMR (referenced to tBuOH) (D2O): 1 Hδ H3.00 - 3.30 (mc, m, 8H); 3.30 - 3.40 (mc, m, 4H); 3.40 - 3.56 (mc, m, 4H); 3.61 (CH2 - COOH, s, 2H); 3.68 (CH2 - COOH, s, 4H); 4.36 (CH2 - aromatic, s, 2H); 7.74 (aromatic, dt, 1H, 3 J HH = 9Hz, 3 J HH = 5Hz); 8.00 (aromatic, t, 1H, 3 J HH = 9Hz); 8.51 - 8.57 (aromatic, m, 1H); 13 C{ 1 H}δ C 49.8 (mc, s); 50.0 (mc, s); 50.6 (mc, s); 50.9 (mc, s); 51.1 (CH2 - aromatic, s); 54.9 (CH2 - COOH, s); 55.9 (CH2 - COOH, s); 127.5 (aromatic, d, 3 J CF = 6Hz); 128.4 (aromatic, d, 2 J CF = 18Hz); 140.7 (aromatic, s); 144.6 (aromatic, s); 158.8 (aromatic, d, 1 J CF = 255Hz); 171.3 (CO, s); 173.4 (CO, s). 19 F{ 1 H}δ F - 122.2 (s). ESI - HRMS: 456.2254 [M + H] + (theoretical [C 20 H 31 N5O6F1] + = 456.2253). EA(C 20 H 30 N5O6F1·0.7TFA·1.1FA, M R = 585.9): C 46.1 (46.4); H 5.7 (5.6); N 12.0 (12.2); F 10.1 (9.7).

[0121] Synthesis of ligand L 4(2,2',2''-(10-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): A solution of 4 (70 mg, 0.48 mmol, 1.02 equiv) in MeCN (0.7 mL) was added to a solution of t-BuDO3A·HBr (281 mg, 0.47 mmol, 1.0 equiv) in MeCN (9 mL), and then dry K2CO3 (266 mg, 1.92 mmol, 4 equiv) was added. The resulting suspension was stirred at room temperature for 24 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (5 mL) and stirred at room temperature for 16 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the TFA salt. Yield: 208 mg (58%, 2 steps, based on t-BuDO3A·HBr). NMR (referenced to tBuOH) (D2O): 1 Hδ H 2.95 - 3.98 (mc, CH2-COOH, m, 22H); 4.20 (CH2-aromatic, bs, 2H); 7.80 (aromatic, m, 1H); 7.96 (aromatic, m, 1H); 8.85 (aromatic, m, 1H); 13 C{ 1 H}δ C 49.1 (mc, s); 50.9 (mc, s); 52.6 (mc, s); 53.6 (mc, s); 54.4 (CH2-aromatic, s); 56.2 (mc, s); 115.9 (aromatic, m); 117.7 (aromatic, m); 148.0 (aromatic, m); 155.6 (aromatic, m); 158.8 (aromatic, d, 1 J CF = 255 Hz); 175.4 (CO, s); 176.1 (CO, s). 19 F{ 1 H}δ F -79.3 (s). ESI-HRMS: 456.2250 [M+H] + (Theoretical [C 20 H 31 N5O6F1] + = 456.2253). EA (C 20 H30 F1N5O6·2.6TFA·0.3H2O, M R = 757.3): C 40.0(39.9); H 4.4(4.5); N 9.3(9.1); F 22.1(22.2).

[0122] Synthesis of ligand L 5 (2,2',2”-(10-((5-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): A solution of 10 (107 mg, 0.52 mmol, 1.1 equiv) in MeCN (2 mL) was added to a solution of t-BuDO3A·HBr (282 mg, 0.47 mmol, 1.0 equiv) in MeCN (9.5 mL), and then dry K2CO3 (327 mg, 2.37 mmol, 5.0 equiv) was added. The resulting suspension was stirred at room temperature for 20 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (6 mL) and stirred at room temperature for 19 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the FA / TFA salt. Yield: 165 mg (63%, 2 steps, based on t-BuDO3A·HBr). NMR (referencing tBuOH) (D2O): 1 H δ H 2.90 - 3.91 (mc, CH2-COOH, m, 22H); 4.30 (CH2-aromatic, s, 2H); 7.67 - 8.05 (aromatic, m, 2H); 8.58 (aromatic, s, 1H); 13 C{ 1 H} δ C 50.0, 50.1, 50.2 (mc); 50.5 (CH2-COOH, s); 55.3 (CH2-COOH, s); 56.7 (CH2-aromatic, s); 127.6 (aromatic, s); 128.5 (aromatic, d, 2 J CF = 17 Hz); 137.1 (aromatic, d, 2 J CF = 28 Hz); 148.4 (aromatic, s); 160.1 (aromatic, d, 1 JCF = 255 Hz); 171.3 (CO, s); 173.4 (CO, s). 19 F{ 1 H}δ F -122.0 (s). ESI-HRMS: 456.2254 [M+H] + (theoretical [C 20 H 31 N5O6F1] + = 456.2253). EA (C 20 H 30 N5O6F1·0.7TFA·1.3FA, M R = 595.1): C 45.8 (45.6); H 5.6 (5.6); N 11.8 (11.7); F 9.9 (10.1).

[0123] Synthesis of ligand L 6 (2,2',2”-(10-((6-fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid): A solution of 2-(chloromethyl)-6-fluoropyridine (81 mg, 0.55 mmol, 1.1 equiv) in MeCN (1 mL) was added to a solution of t-BuDO3A·HBr (300 mg, 0.50 mmol, 1.0 equiv) in MeCN (10 mL), and then dry K2CO3 (278 mg, 2.02 mmol, 4 equiv) was added. The resulting suspension was stirred at room temperature for 16 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (7 mL) and stirred at room temperature for 16 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the FA / TFA salt. Yield: 210 mg (73%, 2 steps, based on t-BuDO3A·HBr). NMR (D2O): 1 Hδ H 3.01 - 3.65 (mc, CH2-COOH, m, 22H); 3.98 (CH2-aromatic, s, 2H); 7.06 (aromatic, m, 1H); 7.58 (aromatic, m, 1H); 7.96 (aromatic, m, 1H); 13 C{ 1H}δ C 48.8 (mc, s); 48.9 (mc, s); 51.2 (mc, s); 51.8 (mc, s); 54.5 (CH2 - COOH, s); 56.8 (CH2 - COOH, s); 58.0 (CH2 - aromatic, s); 109.7 (aromatic, d, 2 J CF = 35 Hz); 123.0 (aromatic, d, 4 J CF = 4 Hz); 144.7 (aromatic, d, 3 J CF = 8 Hz); 154.8 (aromatic, s); 163.3 (aromatic, d, 1 J CF = 239 Hz); 170.2 (CO, s); 174.5 (CO, s). 19 F{ 1 H}δ F - 82.1 (s). ESI - HRMS: 478.2069 [M + Na] + (theoretical [C 20 H 30 N5O6F1Na1] + = 478.2072). EA(C 20 H 30 N5O6F1·0.5TFA·1.4FA, M R = 576.9): C 46.6 (46.9); H 5.8 (5.8); N 12.1 (12.4); F 8.2 (8.0).

[0124] Synthesis of ligand L 7(2,2'-(4-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid): A solution of 4 (127 mg, 0.87 mmol, 1.00 equivalent) in MeCN (1 mL) was added to a solution of t-BuDO2A (350 mg, 0.87 mmol, 1.0 equivalent) in MeCN (44 mL), and then dry K2CO3 (121 mg, 0.87 mmol, 1 equivalent) was added. The resulting suspension was stirred at room temperature for 24 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (5 mL) and stirred at room temperature for 16 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the TFA salt. Yield: 206 mg (36%, 2 steps, based on t-BuDO2A). NMR (D2O): 1 Hδ H 2.96 - 3.60 (mc, CH2-COOH, m, 20H); 4.70 (CH2-aromatic, s, 2H); 7.29 (aromatic, ddd, 1H, 3 J HF = 8 Hz, 3 J HH = 6 Hz, 4 J HH = 3 Hz); 7.34 (aromatic, dd, 1H, 3 J HF = 9 Hz, 4 J HH = 3 Hz); 8.51 (aromatic, dd, 1H, 4 J HF = 8 Hz, 3 J HH = 6 Hz); 13 C{ 1 H}δ C 43.0 (mc, s); 49.2 (mc, s); 50.0 (mc, s); 52.4 (mc, s); 54.5 (CH2-COOH, s); 57.8 (CH2-aromatic, d, 4 J CF = 3 Hz); 112.5 (aromatic, d, 2 J CF= 19 Hz); 113.5 (aromatic, d, 2 J CF = 17 Hz); 152.6 (aromatic, d, 3 J CF = 8 Hz); 153.0 (aromatic, d, 3 J CF = 8 Hz); 170.3 (aromatic, d, 1 J CF = 264 Hz); 174.9 (CO, s). 19 F{ 1 H}δ F -100.1 (s). ESI-HRMS: 398.2197 [M+H] + (theoretical [C 18 H 29 N5O4F1] + = 398.2198). EA (C 18 H 28 F1N5O4·2.2TFA·0.9H2O, M R = 664.5): C 40.0 (39.9); H 4.4 (4.5); N 9.3 (9.1); F 22.1 (22.2).

[0125] Synthesis of ligand L 8((2S,2'S,2”S)-2,2',2”-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid): A solution of 3 (13 mg, 92.2 μmol, 1.5 equiv) was added to a solution of 6 (45 mg, 61.7 μmol, 1.0 equiv) in MeCN (1.2 mL), and then dry K2CO3 (43 mg, 307 μmol, 5 equiv) was added. The resulting suspension was stirred at room temperature for 16 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified by preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in MeOH (3 mL), and then Pd@C catalyst (10%, 10 mg) was added. The flask was briefly flushed with argon, and then H2 gas (from a balloon) was introduced. After 30 min, the catalyst was filtered off, and the mixture was evaporated to dryness. The residue was purified by preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the TFA salt form. Yield: 4.2 mg (13%, 2 steps, based on 6). NMR (D2O): 1 H δ H 1.26 - 1.30 (CH3, m, 3H); δ H 1.49 (CH3, bs, 6H); δ H 2.70 - 3.95 (mc, CH2-COOH, m, 19H); 4.23 - 4.30 (CH2-aromatic, m, 2H); 7.60 (aromatic, m, 1H); 7.84 (aromatic, m, 1H); 8.47 (aromatic, m, 1H); 13 C{ 1 H} δ C 8.6 (CH3, s); 10.3 (CH3, s); 47.7, 47.8 (mc); 50.7 (CH2-aromatic, s); 56.4 (CCH3H-COOH, s); 61.9 (CCH3H-COOH, s); 126.6 (aromatic, d, 3 J CF = 6 Hz); 127.4 (aromatic, d, 2 J CF = 20 Hz); 142.8 (aromatic, d, 2 J CF = 19 Hz); 144.7 (aromatic, d, 4 J CF = 5 Hz); 159.1 (aromatic, d,1 J CF = 254 Hz); 177.2 (CO, s). 19 F{ 1 H}δ F -123.2 (s). ESI-HRMS: 498.2719 [M+H] + (Theoretical [C 23 H 37 N5O6F1] + = 498.2722). EA (C 23 H 36 N5O6F1·0.1TFA·0.6H2O, M R = 519.8): C 53.0 (53.4); H 7.2 (7.0); N 13.5 (13.4); F 4.8 (4.6).

[0126] Synthesis of ligand L 9 (((4-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))bis(phenylphosphonic acid)): A solution of 3 (6 mg, 40.0 μmol, 0.5 equiv) was added to a solution of 8 (41 mg, 80.6 μmol, 1.0 equiv) in MeCN (1 mL), and then dry K2CO3 (11 mg, 80.6 μmol, 1 equiv) was added. The resulting suspension was stirred at room temperature for 16 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the methyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in a mixture of MeOH (1 mL) and H2O (0.2 mL), and then 1 M NaOH (2 mL) was added. After stirring at room temperature for 4 days, the reaction mixture was neutralized with formic acid and the mixture was evaporated to dryness. The residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 9.1 mg (18%, 2 steps, based on 8). NMR (D2O): 1 Hδ H 2.97 - 3.24 (mc, CH2-PhPOOH m, 20H); 4.54 (CH2-aromatic, d, 2H, 5 J HF = 2 Hz,); 7.46 - 7.81 (aromatic, m, 12H); 8.42 - 8.47 (aromatic, m, 1H); 13C{ 1 H}δ C 44.0 (mc), 50.3, 51.6, 51.9, 54.3, 55.1 (mc, CH2-PhPOOH); 52.4 (CH2-aromatic, s); 125.9 (aromatic, d, 2 J CF = 19 Hz); 127.9 (aromatic, d, 3 J CF = 5 Hz); 129.2 (aromatic, d, 2 J CP = 11 Hz); 131.2 (aromatic, d, 2 J CP = 10 Hz); 131.9 (aromatic, d, 4 J CP = 3 Hz); 137.5 (aromatic, d, 2 J CF = 15 Hz); 137.6 (aromatic, d, 1 J CP = 60 Hz); 146.4 (aromatic, d, 4 J CF = 5 Hz); 159.4 (aromatic, d, 1 J CF = 258 Hz); 177.2 (CO, s). 19 F{ 1 H}δ F -122.9 (s); 31 P{ 1 H}δ 30.05. ESI-HRMS: 590.2454 [M + H] + (theoretical [C 28 H 39 N5O4F1P2] + = 590.2456). EA (C 28 H 38 N5O4F1P2·0.1TFA·0.8H2O, M R = 615.4): C 55.0 (55.0); H 6.5 (6.3); N 4.0 (4.1); F 11.4 (11.2).

[0127] Synthesis of ligand L 10(2,2'-(4-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid): A solution of 1 (376 mg, 2.18 mmol, 1.0 equiv) was added to a solution of t-BuDO2A (873 mg, 2.18 mmol, 1.0 equiv) in MeCN (109 mL), and then dry K2CO3 (301 mg, 2.18 mmol, 1.0 equiv) was added. The resulting suspension was stirred at room temperature for 39 h. The solid was filtered off, and the filtrate was concentrated on a rotary evaporator. The resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the pure product in the tert-butyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in pure TFA (6 mL) and stirred at room temperature for 14 h. The volatiles were removed on a rotary evaporator, and the residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a pale yellow solid in the form of the TFA salt. Yield: 358 mg (26%, 2 steps, based on t-BuDO2A). NMR (D2O): 1 H δ H 2.88 - 3.74 (mc, CH2-COOH, m, 20H); 4.91 (CH2-aromatic, s, 2H); 8.21 (aromatic, dd, 1H, 3 J HH = 5 Hz, 4 J HH = 2 Hz); 8.27 (aromatic, dd, 1H, 3 J HH = 2 Hz, 5 J HH = 1 Hz); 8.85 (aromatic, dd, 1H, 3 J HH = 5 Hz, 5 J HH = 1 Hz 13 C{ 1 H} δ C 43.0 (mc, s); 49.1 (mc, s); 50.1 (mc, s); 52.7 (mc, s); 54.5 (CH2-COOH, s); 57.8 (CH2-aromatic, s); 117.3 (aromatic, s); 118.1 (aromatic, s); 152.5 (aromatic, s); 153.1 (aromatic, s); 175.0 (CO, s). ESI-HRMS: 425.2143 [M+H] + (Theoretical [C 18 H29 N6O6] + = 425.2143). EA(C 18 H 28 N6O6·1.7TFA·1.4H2O, M R = 643.5): C 39.9(39.8); H 5.1(4.4); N 13.1(12.4); F 15.1(14.8).

[0128] Synthesis of ligand L 11 ((2S,2'S,2”S)-2,2',2”-(10-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid): Intermediate 9 (18.7 mg, 91.2 μmol, 1.5 equiv) was mixed with intermediate 6 (44.5 mg, 60.8 μmol, 1.0 equiv) in tBuOH (2.4 mL), then DIPEA (53 μl, 304 μmol, 5 equiv) was added, and the resulting solution was stirred at 80 °C for 16 h. The liquid was evaporated on a rotary evaporator and the resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the benzyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in MeOH (3 mL), then AcOH (14 μl, 246 μmol, 4 equiv) and Pd@C catalyst (10%, 5 mg) were added. The flask was briefly flushed with argon and then H2 gas (from a balloon) was introduced. After 30 min, the catalyst was filtered off and the mixture was evaporated to dryness. The residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% TFA in the mobile phase). The fractions containing the product were combined and lyophilized to give the product as a white solid in the form of the TFA salt. Yield: 4.1 mg (13%, 2 steps, based on 6 assumed L 11 ·0.1TFA). NMR (D2O, reference tBuOH): 1 Hδ H 1.11 (CH3, d, 3H, 3 J HH = 7 Hz); 1.22 (CH3, d, 3H, 3 J HH = 7 Hz); 1.46 (CH3, d, 3H, 3 J HH= 7 Hz, ); 2.49 - 2.56 (mc, m, 2H); 2.70 (mc, m, 1H); 2.82 - 3.16 (mc, m, 9H); 3.27 - 3.46 (mc, m, 5H); 3.77 (CHCH3COOH, q, 1H, 3 J HH = 7 Hz); 4.07 (CHCH3COOH, q, 1H, 3 J HH = 8 Hz); 4.13 (m, 1H); 4.50 (CH2 - aromatic, d, 1H, 2 J HH = 13 Hz); 7.10 (aromatic, ddd, 1H, 3 J HF = 8 Hz, 3 J HH = 6 Hz, 4 J HH = 3 Hz); 7.60 (aromatic, dd, 1H, 3 J HF = 8 Hz, 4 J HH = 3 Hz); 8.36 (aromatic, m, 1H); 13 C{ 1 H}δ C 9.0 (CH3, s); 10.5 (CH3, s); 11.0 (CH3, s); 44.0, 46.4, 47.1, 47.4, 47.8, 48.2, 49.0 (mc, s); 58.1 (CH2 - aromatic, s); 57.4 (CCH3H - COOH, s); 61.3 (CCH3H - COOH, s); 62.3 (CCH3H - COOH, s); 112.8 (aromatic, d, 2 J CF = 18 Hz); 115.1 (aromatic, d, 2 J CF = 18 Hz); 150.9 (aromatic, d, 3 J CF = 8 Hz); 160.0 (aromatic, s); 170.8 (aromatic, d, 1 J CF = 266 Hz); 172.0 (CO, s); 174.9 (CO, s); 180.2 (CO, s). 19 F{ 1 H}δ F - 96.4 (s). ESI - HRMS: 498.2724 [M + H] + (theoretical [C 23 H 37 N5O6F1]+ = 498.2722).

[0129] Synthesis of ligand L 12 ((2S,2'S,2”S)-2,2',2”-(10-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid): Intermediate 1 (8.2 mg, 47.6 μmol, 1.6 equiv) was mixed with Intermediate 13 (15.0 mg, 28.9 μmol, 1.0 equiv) in tBuOH (1.3 mL), then DIPEA (28 μl, 158 μmol, 5.5 equiv) was added, and the resulting solution was stirred at 80 °C for 16 h. The liquid was evaporated on a rotary evaporator and the resulting oil was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions containing the pure product in the ethyl ester form were combined, evaporated to dryness, and co-evaporated with MeOH several times to remove MeCN. The residue was dissolved in a mixture of MeCN (500 μl) and H2O (330 μl), then 1 M LiOH solution (296 μl, 296 μmol, 10 equiv) was added. After 47 h, the reaction mixture was quenched with FA (10 μl, 220 μmol, 7.6 equiv) and the mixture was evaporated to dryness. The residue was purified on preparative HPLC (C18, MeCN / H2O gradient, 0.1% FA in the mobile phase). The fractions with the product were pooled and lyophilized to give the product as a pale yellow solid in the form of the FA salt. Yield: 6.0 mg (33%, 2 steps, based on 13). NMR (D2O, reference tBuOH): 1 H δ H 1.24 (CH3, d, 3H, 3 J HH = 7 Hz); 1.25 (CH3, d, 3H, 3 J HH = 7 Hz); 1.59 (CH3, d, 3H, 3 J HH = 7 Hz); 2.60 - 2.64 (mc, m, 2H); 2.83 - 3.05 (mc, CHCH3COOH, m, 6H); 3.10 - 3.31 (mc, m, 5H); 3.41 - 3.55 (mc, CH2-arom, m, 4H); 3.98 (CHCH3COOH, q, 1H, 3 J HH = 7 Hz); 4.20 (CHCH3COOH, q, 1H, 3 J HH= 8 Hz); 4.27 (m, 1H); 4.78 (CH2 - aromatic, m, 1H); 8.07 (aromatic, dd, 1H, 3 J HH = 6 Hz, 4 J HH = 2 Hz); 8.52 (aromatic, d, 1H, 4 J HH = 2 Hz); 8.75 (aromatic, d, 1H, 3 J HH = 6 Hz); 13 C{ 1 H}δ C 8.0 (CH3, s); 10.0 (CH3, s); 10.7 (CH3, s); 43.5, 46.1, 46.9, 47.4, 47.5, 47.8, 48.1, 49.2 (mc, s); 55.7 (CCH3H - COOH, s); 58.2 (CH2 - aromatic, s); 60.9 (CCH3H - COOH, s); 62.1 (CCH3H - COOH, s); 117.2 (aromatic); 120.1 (aromatic); 151. (aromatic); 156.0 (aromatic, s); 160.3 (aromatic); 171.6 (CO, s); 174.7 (CO, s); 177.1 (CO, s). ESI - HRMS: 525.2667 [M + H] + (theoretical [C 23 H 37 N6O8] + = 525.2667). EA (C 23 H 36 N6O8·2.2FA·0.6H2O, M R = 627.4): C 47.5 (47.6); H 6.6 (6.7); N 13.2 (13.1).

[0130] Example 3: Synthesis of Metal Chelates

[0131] Synthesize complex [Gd(L 1 )]: In a glass vial (25 mL), add L 1·1.8 TFA·1.0 H₂O (138 mg, 0.20 mmol, 1.0 equiv) was dissolved in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 2 mL, 6 mmol, 30 equiv), and then an aqueous GdCl₃ solution (100 mM, 2.1 mL, 0.21 mmol, 1.05 equiv) was added. The resulting solution was stirred at room temperature for 15 minutes. The mixture was then purified by preparative HPLC (C18, H₂O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid with a yellowish tint. Yield: 111 mg (81%, 1 step, based on L 1 ·1.8 TFA·1.0 H₂O). ESI-HRMS: 638.1203 [M+H] + (theoretical for [C 20 H 28 N₆O₈Gd] + = 638.1204). EA (C 20 H 27 N₆O₈Gd·2.5H₂O, M R = 687.0): C 35.0 (35.4); H 4.7 (4.4); N 12.2 (11.9); Gd 22.9 (19.4).

[0132] Synthesis of the complex [Gd(L 2 )]: In a glass vial (4 mL), L 2 ·0.8 FA·0.2 H₂O (37.4 mg, 71.5 μmol, 1.0 equiv) was dissolved in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 0.95 mL, 2.85 mmol, 40 equiv), and then an aqueous GdCl₃ solution (100 mM, 0.78 mL, 78 μmol, 1.1 equiv) was added. The resulting solution was stirred at room temperature for 1 hour. The mixture was then purified by preparative HPLC (C18, H₂O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a solid with a yellowish tint. Yield: 33 mg (62%, 1 step, based on L 2 ·0.8 FA·0.2 H₂O). ESI-HRMS: 638.1201 [M+H] + (theoretical for [C 20 H 28 N₆O₈Gd] + = 638.1204). EA (C 20 H 27 N₆O₈Gd·2.1 FA·1.4 H₂O, M R= 758.6): C 35.0 (34.9); H 4.5 (4.4); N 11.1 (11.2); Gd 20.7 (20.8).

[0133] Synthesis of complex [Gd(L 3 )]: In a glass vial (25 mL), L 3 ·0.7TFA·1.1FA (100 mg, 0.17 mmol, 1.0 equiv) was dissolved in MOPS / NaOH buffer aqueous solution (3 M, pH 7.0, 1.7 mL, 5.1 mmol, 30 equiv), and then aqueous GdCl3 solution (100 mM, 1.9 mL, 0.19 mmol, 1.1 equiv) was added. The resulting solution was stirred at room temperature for 1 h. Then the mixture was purified by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 98 mg (88%, 1 step, based on L 3 ·0.7TFA·1.1FA). ESI-HRMS: 611.1257 [M+H] + (theoretical for [C 20 H 28 N5O6Gd1F1] + = 611.1259). EA (C 20 H 27 N5O6Gd1F1·2.5H2O, M R = 654.7): C 36.7 (37.2); H 4.9 (4.9); N 10.7 (10.6); Gd 24.0 (21.4); F 2.9 (2.6).

[0134] Synthesis of complex [Gd(L 4 )]: In a glass vial (25 mL), L 4 ·2.6TFA·0.3H2O (156 mg, 0.21 mmol, 1.0 equiv) was dissolved in MOPS / NaOH buffer aqueous solution (3 M, pH 7.0, 1.9 mL, 5.8 mmol, 28 equiv), and then aqueous GdCl3 solution (100 mM, 2.16 mL, 0.22 mmol, 1.05 equiv) was added. The resulting solution was stirred at room temperature for 15 min. Then the mixture was purified by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 82 mg (59%, 1 step, based on L 4·2.6TFA·0.3H2O). ESI-HRMS: 611.1275 [M+H] + (Theoretical [C 20 H 28 N5O6Gd1F1] + = 611.1259). EA(C 20 H 27 N5O6Gd1F1·2.5H2O, M R = 654.7): C 36.7 (36.2); H 4.9 (5.0); N 10.7 (10.5); Gd 24.0 (19.8); F 2.9 (2.8).

[0135] Synthesis of the complex [Gd(L 5 )]: In a glass vial (25 mL), L 5 ·0.7TFA·1.3FA (100 mg, 0.17 mmol, 1.0 equiv) was dissolved in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 1.7 mL, 5.1 mmol, 30 equiv), and then an aqueous GdCl3 solution (100 mM, 1.9 mL, 0.19 mmol, 1.1 equiv) was added. The resulting solution was stirred at room temperature for 1 h. The mixture was then purified by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 95 mg (82%, 1 step, based on L 5 ·0.7TFA·1.3FA). ESI-HRMS: 611.1257 [M+H] + (Theoretical [C 20 H 28 N5O6Gd1F1] + = 611.1259). EA(C 20 H 27 N5O6Gd1F1·4H2O, M R = 681.8): C 35.2 (35.4); H 5.2 (5.0); N 10.3 (10.1); Gd 23.1 (20.8); F 2.8 (2.4).

[0136] Synthesis of the complex [Gd(L 6 )]: In a glass vial (25 mL), L 6·0.5TFA·1.4FA (150 mg, 0.26 mmol, 1.0 equiv) was dissolved in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 2.6 mL, 7.8 mmol, 30 equiv), and then an aqueous GdCl3 solution (100 mM, 3.1 mL, 0.31 mmol, 1.2 equiv) was added. The resulting solution was stirred at room temperature for 1 h. The mixture was then purified by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 151 mg (86%, 1 step, based on L 6 ·0.5TFA·1.4FA). ESI-HRMS: 611.1256 [M+H] + (theoretical for [C 20 H 28 N5O6Gd1F1] + = 611.1259). EA (C 20 H 27 N5O6Gd1F1·1.5H2O·0.8FA, M R = 673.5): C 37.1 (37.3); H 4.7 (4.6); N 10.4 (10.7); Gd 23.4 (23.4); F 2.8 (2.5).

[0137] (C 20 H 30 N5O6F1·0.5TFA·1.4FA, M R = 576.9)

[0138] Synthesis of complex [Gd(L 7 )]: In a glass vial (25 mL), L 7 ·2.2TFA·0.9H2O (152 mg, 0.22 mmol, 1.0 equiv) was dissolved in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 1.64 mL, 4.9 mmol, 21 equiv), and then an aqueous GdCl3 solution (100 mM, 2.34 mL, 0.23 mmol, 1.05 equiv) was added. The resulting solution was stirred at room temperature for 15 min. The mixture was then purified by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). The fractions containing the product were combined and lyophilized to give the product as a white solid. Yield: 116 mg (77%, 1 step, based on L 7 ·2.2TFA·0.9H2O). ESI-HRMS: 553.1214 [M+H] + (theoretical for [C 18 H26 N5O4Gd1F1] + = 553.1204). EA(C 18 H 26 N5O4Gd1F1·3.1H2O, M R = 681.2): C 33.9(34.5); H 4.7(4.5); N 10.3(9.9); Gd 23.1(19.6); F 7.8(7.4).

[0139] Synthesis of complex [Gd(L 8 )]: In a glass vial (25 mL), dissolve L 8 ·0.1TFA·0.6H2O (4 mg, 8.1 μmol, 1.0 equiv) in an aqueous MOPS / NaOH buffer solution (0.5 M, pH 7.0, 1.00 mL, 0.5 mmol, 62 equiv), then add an aqueous GdCl3 solution (100 mM, 97.0 μL, 9.7 μmol, 1.2 equiv). The resulting solution is stirred at room temperature for 1 h. Then purify the mixture by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). Combine the fractions containing the product and lyophilize to obtain the product as a white solid. Yield: 4.6 mg. ESI-HRMS: 653.1728 [M+H] + (Theoretical for [C 23 H 34 N5O6Gd1F1] + = 653.1729).

[0140] Synthesis of complex [Gd(L 9 )]: In a glass vial (25 mL), dissolve L 9 ·0.1TFA·0.8H2O (6 mg, 9.18 μmol, 1.0 equiv) in an aqueous MOPS / NaOH buffer solution (0.5 M, pH 7.0, 1.00 mL, 0.5 mmol, 51 equiv), then add an aqueous GdCl3 solution (100 mM, 117.0 μL, 11.7 μmol, 1.2 equiv). The resulting solution is stirred at room temperature for 20 h. Then purify the mixture by preparative HPLC (C18, H2O / MeCN gradient with 0.1% AcOH additive). Combine the fractions containing the product and lyophilize to obtain the product as a white solid. Yield: 5.4 mg. ESI-HRMS: 745.1461 [M+H] + (Theoretical for [C 28 H 36 N5O4Gd1F1P2] += 745.1462).

[0141] Synthesis of complex [Gd(L 10 )]: In a glass vial (25 mL), dissolve L 10 ·1.7TFA·1.4H2O (192 mg, 0.20 mmol, 1.0 equiv) in an aqueous MOPS / NaOH buffer solution (3 M, pH 7.0, 2. mL, 8.02 mmol, 40 equiv), then add an aqueous GdCl3 solution (100 mM, 2.2 mL, 0.22 mmol, 1.1 equiv). The resulting solution is stirred at room temperature for 1 h. Then purify the mixture by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). Combine the fractions containing the product and lyophilize to obtain the product as a solid with a yellowish tint. Yield: 92 mg (64%, 1 step, based on L 10 ·1.7TFA·1.4H2O). ESI-HRMS: 580.1152 [M+H] + (Theoretical [C 18 H 26 N6O6Gd1] + = 580.1149). EA (C 18 H 26 N6O6Gd1·3FA, M R = 717.8): C 35.1 (34.9); H 4.5 (4.1); N 11.7 (12.1); Gd 21.9 (19.9).

[0142] Synthesis of complex [Gd(L 11 )]: In a glass vial (4 mL), dissolve L 11 ·0.1TFA (3.1 mg, 6.0 μmol, 1.0 equiv) in an aqueous MOPS / NaOH buffer solution (0.5 M, pH 7.0, 0.738 mL, 369 μmol, 62 equiv), then add an aqueous GdCl3 solution (100 mM, 72.0 μL, 7.2 μmol, 1.2 equiv). The resulting solution is stirred at room temperature for 1 h. Then purify the mixture by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). Combine the fractions containing the product and lyophilize to obtain the product as a white solid. Yield: 3.5 mg. ESI-HRMS: 653.1731 [M+H] + (Theoretical [C 23 H 34 N5O6Gd1F1] + = 653.1729).

[0143] Synthesis of complex [Gd(L 12 )]: In a glass vial (4 mL), dissolve L 12 ·2.2FA·0.6H2O (3 mg, 4.8 μmol, 1.0 equiv) in an aqueous MOPS / NaOH buffer solution (0.5 M, pH 7.0, 0.706 mL, 353 μmol, 73 equiv), then add an aqueous GdCl3 solution (100 mM, 69.0 μL, 6.9 μmol, 1.4 equiv). The resulting solution is stirred at room temperature for 15 minutes. Then purify the mixture by preparative HPLC (C18, H2O / MeCN gradient with 0.1% FA additive). Combine the fractions containing the product and lyophilize to obtain the product as a white solid. Yield: 4.1 mg. ESI-HRMS: 680.1679 [M+H] + (Theoretical for [C 23 H 34 N6O8Gd1] + = 680.1674).

[0144] Radioactive labeling experiment

[0145] Example 4: Radiolabeling with 18 F - anions

[0146] General procedure

[0147] In the CO3 - cycle, absorb the solution containing 18 F - generated on a cyclotron on a QMA column (Sep-Pak, Waters), and elute with 0.8 ml of elution solution (8.3 mg TBAHCO3 in a mixture of 0.4 ml H2O and 0.4 ml MeCN). Transfer the volume containing the desired activity to a preheated 4 ml glass vial with a stir bar at 120 °C and introduce an argon stream. Evaporate the aqueous solution, introduce 300 μl of dry MeCN and evaporate again. This step is performed twice. Introduce 100 μl of a 15 mM radiolabeled material ([Gd(L 1 )], [Gd(L 4 )] or L 4 ) in dry DMSO, then add 4 μl of a THF solution of 1 M TBAF. Transfer the vial to an aluminum heating block preheated to 90 °C and stir the reaction mixture for 5 minutes. Subsequently, analyze the reaction mixture on an HPLC equipped with gamma and UV detectors.

[0148] By nucleophilic aromatic substitution radiolabeling [Gd(L 1 )]

[0149]

[0150] Scheme 1: Schematic diagram of the radiolabeling experiment with [Gd(L 1 )]

[0151] Table 1: Radiolabeling experiments with [Gd(L 1 )] as the precursor. All reactions were carried out in dry solvents.

[0152] The amount of the precursor used was 1 mg.

[0153] Experiment number Radiochemical yield (%) Chemical conversion (%) 1 11 78 2 17 76

[0154] The chromatogram of this radiolabeling experiment is as Figure 1 shown. The radiochemical yield is defined as the amount of activity in the product, expressed as a percentage of the relevant starting activity.

[0155] By 18 F<-> 19 F isotope exchange radiolabeling of [Gd(L 4 )]

[0156]

[0157] Scheme 2: Schematic diagram of the radiolabeling experiment with [Gd(L 18 F<-> 19 F isotope exchange 4 )]

[0158] Table 2: Radiolabeling experiments with [Gd(L 4 )] as the precursor. All reactions were carried out in dry solvents.

[0159] The amount of the precursor used was 1 mg.

[0160] Experiment number Radiochemical yield (%) Chemical conversion (%) 1 17 83 2 17 85 3 13 82

[0161] The chromatogram of this radiolabeling experiment is as Figure 2 shown.

[0162] By 18 F<-> 19 F isotope exchange radiolabels free ligand L 4

[0163] Experiments were carried out using the free ligand L 4 to demonstrate that the chelated metal is crucial for the progress of the radiolabeling reaction. This experiment was carried out under the same conditions as other radiolabeling reactions.

[0164]

[0165] Scheme 3: By 18 F<->19 L carried out by F isotope exchange 4 Schematic diagram of the radiolabeling experiment. The chromatogram of this radiolabeling experiment is as Figure 3 shown.

[0166] Table 3: Radiolabeling experiment with free ligand L 4 as the precursor. All reactions were completed in dry solvents. The amount of precursor used was 1 mg.

[0167] Experiment number Radiochemical yield (%) 1 0 2 0

[0168] Example 5: Relaxivity of [Gd(L 4 )] and [Gd(L 7 )]

[0169] The relaxivity value is proportional to the effectiveness of the compound as an MRI contrast agent. To determine the relaxivity, samples of [Gd(L 4 )] and [Gd(L 7 )] were prepared at concentrations of 0 mM, 0.2 mM, 0.5 mM, 1 mM, and 2 mM in MOPS / NaOH buffer (50 mM, pH 7.0, 150 μL). The samples thus prepared were used to measure the longitudinal relaxation time T1 value on a relaxometer at 37 °C and 0.47 T. From these values, the relaxivity of [Gd(L 4 )] was determined to be 3.43 mM -1 s -1 , and the relaxivity of [Gd(L 7 )] was 5.33 mM -1 s -1 (Table 4). The relaxivity was determined by linear regression of their concentration relative to the longitudinal relaxation rate, as Figure 4 shown. In contrast, under the same conditions, the relaxivity of most clinically used MRI contrast agents is between 3 mM -1 s -1 and 4 mM -1 s -1within the range (Rohrer, M.; Bauer, H.; Mintorovitch, J.; Requardt, M.; Weinmann, H.-J. Comparison of Magnetic Properties of MRI Contrast Media Solutions at Different Magnetic Field Strengths. Investigative Radiology 2005, 40(11), 715 - 724. https: / / doi.org / 10.1097 / 01.rli.0000184756.66360.d3).

[0170] Table 4: Determination of the longitudinal relaxation time T1 values of [Gd(L 4 )] and [Gd(L 7 )]

[0171] Compound <![CDATA[Relaxation efficiency (mM -1 s -1 )]]> <![CDATA[[Gd(L 4 )]]]> 3.43 <![CDATA[[Gd(L 7 )]]]> 5.33

[0172] Example 6: Kinetic inertness of [Gd(L 4 )] and [Gd(L 7 )]

[0173] Acid - assisted decomplexation test of [Gd(L 4 )] and [Gd(L 7 )] using HCl (0.1 M) to determine their kinetic inertness. Gadolinium - DTPA (diethylenetriaminepentaacetic acid), a clinically used contrast agent, was used as a reference, and a solution of GdCl3 (1 mM) in HCl (0.1 M) was used as an example of gadolinium completely released from the chelate. All measured complexes were used in a 1 mM solution with a volume of 150 μL and incubated at 37 °C. During the decomplexation process, gadolinium ions detached from the complex and completely dissolved. During this process, the T1 of the sample decreased because dissolved gadolinium shortened the T1 relaxation time to a greater extent than chelated gadolinium. When the complex was completely decomplexed, the reaction reached equilibrium and all gadolinium was dissolved. In this equilibrium state, the T1 relaxation time no longer decreased. The T1 relaxation time values were determined on a relaxometer at 37 °C and a field strength of 0.47 T. The kinetic inertness was compared in the paramagnetic relaxation rate: R 1p = 1 / T1 - 1 / T 1d . The longitudinal relaxation time of HCl (0.1 M) corresponded to T 1d . During the measurement, a slow increase in the T1 value was observed in the case of [Gd(L 4 )], indicating slow decomplexation of the complex. Within 240 minutes, [Gd(L 4)] The T1 value increased by 12%. The situation of Magnevist is different, and the reaction has reached equilibrium after 6 minutes (Table 5). The R 1p value of the Magnevist sample did not change with time, so it can be assumed that the complex completely dissociates. In the case of [Gd(L 7 )], compared with Magnevist, the increase in R 1p is slower, indicating that [Gd(L 7 )] is more kinetically inert. The measurement shows that [Gd(L 4 )] and [Gd(L 7 )] are more kinetically inert than clinically used Magnevist, and are therefore suitable for in vivo applications. The chart showing the measured values of kinetic inertness is as shown in the figure.

[0174] Table 5: Comparison of the kinetic inertness of [Gd(L 4 )], [Gd(L 7 )], Magnevist, and GdCl3 solution by acid-assisted dissociation in 0.1 M HCl.

[0175]

[0176]

[0177] Example 7: Simultaneous PET / MRI imaging of radiolabeled [Gd(L 4 )]

[0178] In vitro imaging of the model

[0179] Simultaneous PET / MRI was performed on a 7T preclinical PET-MRI scanner (Bruker Clinscan with PET insert). Similar to Example 4, by 19 F isotope exchange with 18 F, a sample of 18 F-radiolabeled [Gd(L 4 )] with an activity of 700 MBq was prepared on an automated radiosynthesis module. Then, a stock solution of 0.5 mM non-radioactive [(Gd(L 4 )] in phosphate buffered saline (PBS) was enriched with 18 F-radiolabeled [Gd(L 4)] to prepare models (sample vials) with concentrations ranging from 0.048 mM to 0.489 mM and activities from 0.033 MBq to 0.490 MBq. Sample vials containing only an aqueous solution of Magnevist ([Gd(DTPA)] complex) with concentrations between 0.1 mM and 0.5 mM were used as reference contrasts for MR images. Simultaneous PET / MRI imaging was performed by acquiring T1-weighted MR images of the models using a 3DFLASH sequence and a 600-second static PET scan ( Figure 6 , Series A). Quantitative analysis of 18 F activity based on gamma counting showed excellent linear correlation with Gd quantification using ICP-OES ( Figure 6 , Series B). Similarly, the radioactivity measured by PET showed excellent linear correlation with the signal obtained from T1-weighted MR images ( Figure 6 , Series C) and the relaxation rate obtained from MRI T1-mapping ( Figure 6 , Series D). Overall, the data confirmed that 18 F-radiolabeled [Gd(L 4 )] provided consistent signals in both imaging modalities and was thus suitable as a dual-mode PET / MRI contrast agent.

[0180] In vivo imaging of mice

[0181] Similar to Example 4, 19 F was prepared by isotope exchange with 18 F on an automated radiosynthesis module to prepare samples of 18 F-radiolabeled [Gd(L 4 )], which were formulated as a saline solution with a molar activity of 518 MBq / μmol. Anesthetized healthy C57BL / 6 mice were injected with 0.09 ± 0.03 mmol / kg of [Gd(L 4 )] with an activity of 0.91 ± 0.16 MBq (N = 6). This dose was administered as a bolus injection via a catheter placed in the tail vein at the start of the PET / MRI scan. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and PET images were acquired simultaneously for 62 minutes to dynamically track the distribution of [Gd(L 4 )] in the MRI and PET modalities (N = 3). Additionally, in another group of N = 3 mice, dynamic T1 mapping was acquired for 55 minutes followed by a 5-minute PET scan. MR signals ( Figure 7 , Series A) and PET signals ( Figure 7, the kinetics of Series B) follow the same pattern, typically with a fast renal excretion rate for small Gd-based agents. This is also confirmed by the biodistribution determined by ex vivo analysis of radioactivity (gamma counter) and gadolinium (ICP-OES), which shows the highest uptake in the kidneys, bladder, and urine ( Figure 8 , for Series A and Series B, respectively). Figure 9 A series of whole-body images of T1-weighted MRI, PET, and their superposition are shown, respectively. These images indicate that the contrast agent provides signals consistently in both modalities. Notably, the advantage of having simultaneous signals from a single agent in both MRI and PET modalities is evident in the renal pelvis, where, due to the high local concentration of the agent in this excretory organ resulting in contrast oversaturation, distinct black spots develop in MRI after injection of the dual-modal agent. These black spots can easily be missed, overlooked, mistaken for imaging artifacts, or wrongly attributed to malignancies (necrosis, poorly perfused areas, etc.). However, the simultaneously acquired PET images undoubtedly confirm the strong accumulation of the tracer in the same regions visible as "hot spots" in PET, thus improving diagnostic accuracy and image interpretation.

Claims

Use of cyclen-based compounds of general formula (I) in pharmacy for the preparation of multimodal PET / MRI contrast agents: wherein, R is NO2 or F; A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, where n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; Z is H or A.

2. The use according to claim 1, wherein A and Z of the cyclen-based compound of general formula (I) are the same and are preferably selected from -CH2P(=O)(OH)Ph, and -CH(CH3)COOH.

3. The use according to claim 1, wherein, All A's of the cyclen-based compound of general formula (I) are the same and are preferably selected from -CH2P(=O)(OH)Ph, and -CH(CH3)COOH; and Z is hydrogen.

4. The use according to claim 1, wherein, R of the cyclen-based compound of general formula (I) is located at the para position relative to the nitrogen atom of the pyridyl pendant arm.

5. Use according to claim 1, wherein, The cyclen-based compound of general formula (I) is selected from the group consisting of: 2,2',2''-(10-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 1 ) 2,2',2''-(10-((6-nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 2 ) 2,2',2''-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 3 ) 2,2',2”-(10-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 4 ) 2,2',2''-(10-((5-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 5 ) 2,2',2”-(10-((6-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (L 6 ) 2,2'-(4-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid (L 7 ) (2S,2'S,2”S)-2,2',2”-(10-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid (L 8 ) ((4-((3-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))bis(phenylphosphinic acid) (L 9 ) 2,2'-(4-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,7-diyl)diacetic acid (L 10 ) (2S,2'S,2”S)-2,2',2”-(10-((4-Fluoropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid (L 11 ) (2S,2'S,2”S)-2,2',2”-(10-((4-Nitropyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tripropanoic acid (L 12 )。 6. Use of a coordination compound of a Gd(III) ion and a cyclen-based compound of general formula (I) as defined in any one of claims 1 to 5 for the preparation of a multimodal PET / MRI contrast agent.

7. A cyclen-based compound of general formula (Ia): wherein, R is NO2 or F; preferably, R is F; A is independently selected from -CH(CH3)COOH; -CH((CH2) n CH3)COOH, where n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; preferably, A is -CH(CH3)COOH; Z is H or A, preferably, Z is A.

8. A cyclen-based compound of general formula (Ia) according to claim 7, wherein, The R substituent is located at the para position relative to the nitrogen atom of the pyridyl pendant arm.

9. A cyclen-based compound of general formula (Ia) according to claim 7 or 8, wherein, Z is A, and all A's are -CH(CH3)COOH having the same stereoconfiguration.

10. A multimodal PET / MRI contrast agent of general formula (VI): Among them, A is independently selected from -CH2COOH; -CH(CH3)COOH; -CH((CH2) n CH3)COOH, wherein n is an integer from 1 to 3; and -CH2P(=O)(OH)Ph; Z is H or A; Preferably, 18 F is in the para position relative to the nitrogen atom of the pyridyl pendant arm.

11. A method for synthesizing a multimodal PET / MRI contrast agent of general formula (VI) as defined in claim 10, the method comprising the following steps: a) providing a cyclen-based compound of general formula (I) as defined in any one of claims 1 to 5; b) React the cyclen-based compound of general formula (I) with Gd 3+ ions to form a Gd(III) chelate of the compound of general formula (I); c) Use 18 radioactive F to label the Gd(III) chelate from step b).

12. The method according to claim 11, wherein, Use 19 F to 18 perform step c) by isotope exchange of F in the pyridine moiety of the Gd(III) chelate, where R is F.

13. The method according to claim 11, wherein, Use 18 F nucleophilic aromatic substitution of the nitro group on the pyridine moiety of the Gd(III) chelate for step c), where R is nitro.

14. A pharmaceutical preparation comprising the multimodal PET / MRI contrast agent of general formula (VI) according to claim 10, the pharmaceutical preparation further comprising at least one pharmaceutically acceptable auxiliary substance commonly used, the pharmaceutically acceptable auxiliary substance being preferably selected from the group consisting of: solvents, buffers, ionization additives, antioxidants, antimicrobial additives.

15. Use of the multimodal PET / MRI contrast agent of general formula (VI) according to claim 10 and / or the pharmaceutical preparation according to claim 14 in medicine, preferably in a multimodal PET / MRI diagnostic method.

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