Separation of Metals Using Chelating Agent Chromatography Based on DOAT

Abstract

The present invention relates to the use of chelate compounds (I) for the chromatographic separation of rare earth elements, actinides and / or s-, p- and d-block metals, and to a process for the chromatographic separation of chelates of rare earth elements, actinides and / or s-, p- and d-block metals from a mixture of at least two metal ions. The process is characterized in that it comprises the following steps: (a) providing a mixture of at least two different metal ions selected from rare earth metal ions, actinide ions and / or s-, p- and d-block metal ions, (b) contacting the metal ions comprised in the mixture with at least one compound of general formula (I) as defined in any one of the preceding claims to form chelates; (c) subjecting the chelates from step (b) to chromatographic separation, where optionally at least one of the separated metal chelates obtained in step (c) is subjected to at least one further chromatographic separation in order to increase the purity of at least one of the separated metal chelates; and optionally, (d) obtaining the metal from at least one of the separated metal chelates. (I)

Description

Technical Field

[0001] The present invention relates to the use of chelating compounds for the chromatographic separation of rare earth elements, actinides and / or s-, p- and d-block metals, and to a method for chromatographically separating chelates of rare earth elements, actinides and / or s-, p- and d-block metals. Background Art

[0002] For decades, radionuclides have been successfully used in diagnostic applications. In the past decade, new compounds have been developed that can target diseases, such as cancer, very specifically. By binding these compounds to radionuclides, diseases such as cancer can be imaged, enabling accurate diagnosis and serving as the basis for optimal treatment. The targeting precision of these compounds has now reached such a level that radionuclides with therapeutic effects by locally destroying tissues and cells can be used, with little harm to healthy tissues and cells to a large extent. With the development of more and more specific targeting compounds, the combination of radionuclide imaging and therapy (theranostics) will surely expand, benefiting patients from more personalized treatment possibilities that combine efficacy with fewer side effects.

[0003] For therapeutic applications, radionuclides with appropriate properties and specifications are required, especially radionuclides with high nuclear purity, high chemical purity and high specific activity. One possible way to produce radionuclides is by neutron activation of non-radioactive elements to produce radionuclides of the same element. Since the target radionuclide and the product radionuclide have the same chemical properties, they cannot be chemically separated, and thus this mixture is called "carrier-added" (CA).

[0004] Even better properties can be achieved by neutron activation of an element that is usually rich in one isotope, resulting in a part of the atoms being converted into another isotope of another chemical element, which is then (chemically) extracted after irradiation. Compared with the CA route, this so-called "non-carrier-added" (NCA) or "carrier-free" production route produces products with the highest purity and the highest specific activity. However, the chemical separation of radioactive products from the irradiated target is extremely complex:

[0005] The elements to be separated can be very similar in chemical properties, such as adjacent elements from the lanthanide series, which makes it difficult to separate them effectively.

[0006] Only very small amounts of the desired isotope are produced in the source material by activation. Extracting these trace amounts of the desired isotope from a large amount of source material with sufficient efficiency is challenging.

[0007] The material decays rapidly, so separation needs to be carried out as quickly as possible to maintain the required high specific activity.

[0008] The material is radioactive, which can affect the infrastructure required for the safe handling of the material and the stability and efficiency of the separation process.

[0009] To meet the growing demand for high-quality radionuclides in therapy, a robust, fast, safe, and efficient separation of (radioactive) elements is required.

[0010] For the complex separation of rare earth elements, especially lanthanides, a variety of methods and techniques have been developed. The most commonly used method at present is to use (catalytic) ion exchange chromatography columns, such as those disclosed in EP2546839 (US2014294700, ITG) or US6716535 (Batelle). In the latter case, ytterbium is first eluted from the chromatography column containing LN-resin with medium-concentration hydrochloric acid, and then 177Lu is obtained with higher-concentration hydrochloric acid. In this case, a microamount of 177Lu is separated from a macroamount of ytterbium. The disadvantage of this prior art method is that there is a huge excess of the first-eluted macrocomponent, and due to the tailing of the macrocomponent, the separation of the later-eluted microamount of 177Lu becomes complicated. This requires a repeated separation process.

[0011] Other possibilities are solvent-solvent extraction, taking advantage of the slight differences in extractability from solvents, liquid membrane extraction (under development), and electrochemical separation by selective reduction and (Hg) cathode deposition. These methods have all been developed to varying degrees. However, despite the variety of potential separation methods, each of these methods still requires a great deal of development and scale-up efforts, and the feasibility of these methods to provide a fast, efficient, and robust production process remains to be seen. Similar problems are encountered when separating actinides and / or s-, p-, and d-block metals.

[0012] A chelator-based separation method was recently disclosed in EP3492460 (Polasek), in which complexed metal elements can be separated by chromatographic separation. For this method, DOTA-based chelators are used. Although this method has advantages over the above methods, the chelators used are not yet optimal in terms of separation potential. WO20071014035 discloses polyaza macrocyclic chelators with a shared asymmetric structure, but their use as metal chelators for chromatographic separation is not mentioned.

[0013] It is well known that DOTA-based chelators form highly stable complexes with metals, especially lanthanide elements such as Lu, Yb, Gd, and Tb. The success of DOTA and its derivatives is largely due to their ability to form complexes with these metal ions that have high thermodynamic stability and extraordinary kinetic inertness. Although the formation of highly stable complexes is crucial for bifunctional chelators used in clinical or in vivo settings, this stability is a drawback when the chelator is used in chromatographic separation processes where the chelator needs to be removed after the separation.

[0014] In addition, DOTA derivatives have been reported to form complexes slowly under mild conditions, requiring radiolabeling reactions to be carried out at elevated temperatures.

[0015] Ideally, the chelator used in the chromatographic separation process of metal elements shows a rapid complexation rate under mild conditions (i.e., room temperature, mild pH, low molar excess), has a rapid dissociation rate upon mild acidification, but is stable under separation conditions. In addition to the separation quality (i.e., the chromatographic resolution of the metal elements to be separated) and initial scalability, these qualities will increase the speed and simplicity of the method, thus increasing the potential for industrial application and scale-up.

[0016] The object of the present invention is to overcome one or more of the above problems, or at least to provide a useful alternative. Another object of the present invention is to provide a separation method that is suitable for rapid complexation and subsequent separation of radioactive isotopes from radioactive source materials with great chemical similarity, such as separating 177Lu from 176Yb, or separating 161Tb from 160Gd, and subsequent rapid dissociation of the isotope from the chelator. Summary of the Invention

[0017] It has now surprisingly been found that another class of chelators is very advantageous for the separation of chemical elements, especially the separation of very similar elements. Compared with DOTA, these chelators form stable complexes with metal elements very quickly, while their stability in vivo is lower than that of DOTA derivatives. For (scaled-up) separation processes, the rapid complexation and convenient dissociation of this class of chelators compared with DOTA is an advantage, while the in vivo stability does not affect this application.

[0018] Chelating agents of this type show different residence times on the chromatographic column, and this is also true for elements with very similar chemical properties, such as ytterbium and lutetium, as well as terbium and gadolinium. Chelating agents of this type also show a favorable reversal of the elution order: trace amounts of the (desired) element are eluted first, followed by the major element. This is an unexpected finding given the similarity between the chelating agents of the present invention and known chelating agents (DOTA, EP3492460). In addition, it has been found that chelating agents of this type according to the present invention are capable of forming isomeric complexes. Although this initially seems disadvantageous because the presence of two isomers is likely to complicate the separation process, it has unexpectedly been found that this is advantageous in the separation process because the loading of the chromatographic column can be increased to a higher level compared to chelating agents in the art that do not form isomeric complexes.

[0019] Therefore, chelating agents of this type according to the present invention can be advantageously used for the chromatographic separation of radioactive metals.

[0020] In particular, the present invention discloses the use of compounds of formula (I) for the chromatographic separation of rare earth elements, actinides and / or s-, p- and d-block metals,

[0021]

[0022] wherein

[0023]

[0024] A is N or C substituted by one of H, halogen (Cl, Br, F), SO3H, C 1-4 alkyl, aryl, heteroaryl, C-O-C 1-16 alkylamino,

[0025] Z and Z 1 independently are N or C substituted by one of H, halogen (Cl, Br, F), SO3H, C 1-4 alkyl, aryl, heteroaryl, C-O-C 1-16 alkylamino,

[0026] E = O, S or P;

[0027] R1 independently is substituted or unsubstituted C 4-15 alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle or substituted or unsubstituted heteroaryl, wherein the substitution is carried out by one or more moieties selected from the group consisting of imide, -C(O)(CH2) 0-3 CH3, C 2-5 carboxyl, -(CH2) 1-3 C(O)(CH2) 0-3CH3, nitro, amino, thiol, succinimide, maleimide, aminooxy, acetylene, N3, acetamido, azide, -C(O)O(CH2) 1- 3CH3, -OC(O)(CH2) 0-3 CH3, halogen, C 1-5 alkynyl and NCS; and

[0028] a = 0 - 5.

[0029] The present invention further discloses a method for chromatographically separating rare earth elements, actinides and / or s-, p- and d-block metals from a mixture of at least two metal ions, characterized in that the method comprises the following steps:

[0030] (a) providing a mixture of at least two different metal ions selected from rare earth metal ions, actinide ions and / or s-, p- and d-block metal ions,

[0031] (b) contacting the metal ions comprised in the mixture with at least one compound of general formula (I) according to any one of the preceding claims to form chelates;

[0032] (c) subjecting the chelates from step (b) to chromatographic separation, wherein optionally, at least one of the separated metal chelates obtained in step (c) can be subjected to at least one further chromatographic separation in order to increase the purity of at least one of the separated metal chelates; and optionally,

[0033] (d) obtaining the metal from at least one of the separated metal chelates.

[0034] The advantage of chromatographic separation using the specific class of chelating agents represented by general formula (I) is that the complexation and separation processes are very fast and the (de)complexation is very easy. In addition, the desired (minor) elements are eluted first compared to the major elements.

[0035] These aspects greatly facilitate large-scale separation processes to produce carrier-free radionuclides.

[0036] Chelating agents of general formula (I) can be used to separate mixtures of at least two elements, which are rare earth elements, actinides and / or s-, p- and d-block metals. For example, the chelating agent can be used to separate isotopes of an element with atomic number n + 1 from a radioactive sample of isotopes of an element with atomic number n (also known as adjacent elements, i.e., adjacent in the periodic table), for example, separating Lu-177 from radioactive Yb-176. In the latter example, after irradiating Yb-176 with neutrons in a nuclear reactor, a small amount of a mixture of radioactive Lu-177 is formed in the Yb matrix in an initial ratio of approximately 5000:1. In addition to the extremely similar chemical and physical properties of the adjacent elements (in this case, the lanthanides Yb and Lu), this large ratio makes it very difficult to separate the radioactive element from the matrix.

[0037] The method proposed by the present invention is comparable to the method described in EP3492460. However, the chelating agent of the present invention produces different metal chelate complexes, which have excellent chelating properties in terms of, for example, speed and temperature, as well as enhanced separation potential, favorable elution order (eluting the desired product first), and an enlarged difference in residence time. The acidification for decomplexation is rapid, and only a small amount of acid is required for decomplexation and removal of the chelating agent. Detailed Description

[0038] In the present invention, compounds of general formula (I) are used for chromatographic separation of rare earth elements, actinides and / or s-, p- and d-block metals:

[0039]

[0040] where

[0041]

[0042] A is N or C substituted by one of H, halogen (Cl, Br, F), SO3H, C 1-4 alkyl, aryl, heteroaryl, C-O-C 1-16 alkylamino,

[0043] Z and Z 1 independently are N or C substituted by one of H, halogen (Cl, Br, F), SO3H, C 1-4 alkyl, aryl, heteroaryl, C-O-C 1-16 alkylamino,

[0044] E = O, S or P;

[0045] R1 independently is substituted or unsubstituted C 4-15An alkylaryl, a substituted or unsubstituted aryl, a substituted or unsubstituted heterocycle, or a substituted or unsubstituted heteroaryl, wherein the substitution is effected by one or more moieties selected from the group consisting of: imide, -C(O)(CH2) 0-3 CH3, C 2-5 carboxyl, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, nitro, amino, thiol, succinimide, maleimide, aminooxy, acetylene, N3, acetamido, azide, -C(O)O(CH2) 1- 3CH3, -OC(O)(CH2) 0-3 CH3, halogen, C 1-5 alkynyl, and NCS; and

[0046] a = 0 - 5.

[0047] The principle of chromatographic separation using the chelating compounds of the present invention provides a simplified operation for the treatment and purification of rare earth elements, actinides, and s-, p-, and d-block metal radionuclides in solution. The speed and simplicity of this method are crucial for the treatment of radionuclides undergoing radioactive decay. When combined with rare earth metal ions, actinide ions, and / or s-, p-, or d-block metal ions, the chelating agents of the present invention respond to even very small differences in the metal ion radius through a significant difference in the polarity of the respective resulting chelates. Due to the different polarities, the chelates can be separated on a normal or reverse phase by conventional chromatography. The metals are thus separated in the form of chelates. Importantly, the chelating agents disclosed in the present invention form chelates that are kinetically inert on the time scale of the separation process. The kinetic inertness effectively protects the radionuclides from additional contamination by other metals, since the radionuclides cannot escape from the chelates and cannot be replaced by another metal ion during the chromatographic process. Importantly, this property allows the use of conventional chromatographic columns and instruments composed of metal components. The separation method of the present invention can be used to separate elements regardless of the specific isotopes of the elements involved.

[0048] Rare earth elements, as well as actinides and s-, p-, and d-block metals, provide a wide selection of radionuclides for medical applications and are thus an object of the present invention.

[0049] The rare earth elements are the elements consisting of scandium - Sc, yttrium - Y, and the lanthanide series: lanthanum - La, cerium - Ce, praseodymium - Pr, neodymium - Nd, promethium - Pm, samarium - Sm, europium - Eu, gadolinium - Gd, terbium - Tb, dysprosium - Dy, holmium - Ho, erbium - Er, thulium - Tm, ytterbium - Yb, and lutetium - Lu.

[0050] The actinides are actinium - Ac, thorium - Th, protactinium - Pa, uranium - U, neptunium - Np, plutonium - Pu, americium - Am, curium - Cm, berkelium - Bk, californium - Cf, einsteinium - Es, fermium - Fm, mendelevium - Md, nobelium - No, and lawrencium - Lr.

[0051] The s -, p -, and d - block metals are preferably Group II.A, III.A, IV.A, V.A metals and transition metals, more preferably Group II.A, III.A (Al, Ga, In, Ti), IV.A (Sn, Pb), V.A (Bi), I.B, II.B, and VIII.B group metals, and most preferably selected from Ca 2+ , Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Al 3+ , Pb 2+ , Bi 3+ .

[0052] The general formula (I) of the present invention means including all isomers, enantiomers, and diastereoisomers.

[0053] The R1 group in the general formula (I) provides the hydrophobicity required for retention and thus also provides retention differences between different elements on a column (e.g., a C18 column). In addition, the R1 group provides UV visibility, enabling easy localization of non - radioactive components during HPLC purification.

[0054] R1 is preferably

[0055]

[0056] wherein R2 is independently

[0057] H, - NCS, - OH, - NH2, - C(O)NH2, - NO2, -(CH2) 1-3 O(CH2) 1-3 CH3, - C(O)O(CH2) 1-3 CH3, - OC(O)(CH2) 0-3 CH3, halogen, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, cyano, C 2-5 carboxyl, thiol, - C(O)(CH2) 0-3 CH3, substituted or unsubstituted C 1-15 alkyl, substituted or unsubstituted C 1-15 alkenyl, substituted or unsubstituted C 1-15Alkynyl, substituted or unsubstituted C 4-15 Alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle, or substituted or unsubstituted heteroaryl, wherein the substitution is carried out by one or more moieties selected from the group consisting of: imide, -C(O)(CH2) 0-3 CH3, C 2-5 Carboxyl, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, nitro, amino, thiol, succinimide, maleimide, aminooxy, acetylene, N3, acetamido, azide, -C(O)O(CH2) 1-3 CH3, -OC(O)(CH2) 0-3 CH3, halogen, C 1-5 Alkynyl and NCS; and

[0058] b = 1 - 4.

[0059] M is preferably

[0060] R1 is preferably located at the following positions on the macrocycle:

[0061]

[0062] R2 is preferably selected from the group consisting of: H, -NCS, -OH, -NH2, -C(O)NH2, -NO2, -(CH2) 1-3 O(CH2) 1-3 CH3, -C(O)O(CH2) 1-3 CH3, -OC(O)(CH2) 0-3 CH3, halogen, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, cyano, C 2-5 Carboxyl, thiol and -C(O)(CH2) 0-3 CH3.

[0063] More preferably, R2 is -NH2 or -NCS.

[0064] Preferably a = 1 - 4, more preferably a = 1 - 3, even more preferably a = 1 - 2, and most preferably a = 1.

[0065] Preferably b = 1 - 3, more preferably b = 1 - 2, and most preferably b = 1.

[0066] In a preferred embodiment, R1 is

[0067]

[0068] wherein R2 is independently H, -NCS, -OH, -NH2, -C(O)NH2, -NO2, -(CH2) 1-3 O(CH2) 1-3 CH3, -C(O)O(CH2) 1-3 CH3, -OC(O)(CH2) 0-3 CH3, halogen, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, cyano, C 2-5 carboxyl, thiol, -C(O)(CH2) 0-3 CH3, substituted or unsubstituted C 1-15 alkyl, substituted or unsubstituted C 1-15 alkenyl, substituted or unsubstituted C 1-15 alkynyl, substituted or unsubstituted C 4-15 alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle or substituted or unsubstituted heteroaryl, wherein the substitution is carried out by one or more moieties selected from the group consisting of: imide, -C(O)(CH2) 0-3 CH3, C 2-5 carboxyl, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, nitro, amino, thiol, succinimide, maleimide, aminooxy, acetylene, N3, acetamido, azide, -C(O)O(CH2) 1-3 CH3, -OC(O)(CH2) 0-3 CH3, halogen, C 1-5 alkynyl and NCS;

[0069] M is preferably

[0070] a = 1 - 4; and

[0071] b = 1 - 4.

[0072] R2 can be located at the ortho (2-), meta (3-), or para or (4-) position of the CH2 group, face to face.

[0073] In one embodiment, R2 is preferably located at the para position of CH2.

[0074] More preferably, the compound of formula (I) is

[0075] And

[0076] Even more preferably is

[0077]

[0078] In another preferred embodiment, the compound of formula (I) is

[0079] and

[0080] even more preferably is

[0081]

[0082] Preferably, R2 is selected from the group consisting of: H, -NCS, -OH, -NH2, -C(O)NH2, -NO2, -(CH2) 1-3 O(CH2) 1-3 CH3, -C(O)O(CH2) 1-3 CH3, -OC(O)(CH2) 0-3 CH3, halogen, -(CH2) 1-3 C(O)(CH2) 0-3 CH3, cyano, C 2-5 carboxyl, thiol and -C(O)(CH2) 0-3 CH3, and more preferably R2 is -NH2 or -NCS.

[0083] Most preferably, the compound of formula (I) is

[0084]

[0085] Preferably, the rare earth elements, actinides and / or s-, p- and d-block metals are rare earth elements, also known as rare earth metals. Rare earth elements are particularly desirable and are especially used in medical applications. More preferably, the rare earth elements are lanthanides. Even more preferably, the lanthanides are two adjacent lanthanides. Even more preferably, the lanthanides are Lu and Yb or Tb and Gd. Most preferably, the lanthanides are Lu and Yb.

[0086] In the method of the present invention, the rare earth elements, actinides and / or s-, p- and d-block metals are separated from a mixture of at least two metal ions, characterized in that the method comprises the following steps:

[0087] (a) providing a mixture of at least two different metal ions selected from rare earth metal ions, actinide ions and / or s-, p- and d-block metal ions,

[0088] (b) contacting the metal ions comprised in the mixture with at least one compound of formula (I) according to any one of the preceding claims to form a chelate;

[0089] (c) subject the chelate obtained from step (b) to chromatography, wherein optionally at least one separated metal chelate obtained in step (c) can be subjected to at least one further chromatography to increase the purity of at least one separated metal chelate; and optionally,

[0090] (d) obtain the metal from at least one separated metal chelate.

[0091] In step (a), a mixture of at least two different metal ions can be dissolved in a strong acid, evaporated and resuspended in dilute hydrochloric acid, such as hydrochloric acid with a concentration of 0.01 - 0.1 M, preferably 0.02 - 0.08 M, more preferably 0.03 - 0.05 M.

[0092] Preferably, the metal ions are in the form of salts, oxides, hydroxides and / or carbonates of organic or inorganic acids, more preferably selected from the group including chlorides, bromides, sulfates, nitrates, methanesulfonates, trifluoromethanesulfonates, formates, acetates, lactates, malates, citrates, 2 - hydroxyisobutyrates, mandelates, diglycolates, tartrates, oxides, hydroxides and / or carbonates.

[0093] Preferably, in step (b), a solution containing the mixture provided in step (a) in the form of a metal salt or a solid phase containing the mixture provided in step (a) in the form of a metal oxide, hydroxide and / or carbonate is mixed with a solution of the compound of general formula (I), and the molar ratio of the metal ion to the compound of general formula (I) is 1:0.5 to 1:100; an organic base or an inorganic base is added to the reaction mixture, and complexation is carried out in solution.

[0094] More preferably, a chelating agent of general formula (I) is added to the mixture, and the molar ratio of the metal ion to the chelating agent is between 1:0.5 and 1:100, even more preferably between 1:1 and 1:2, and most preferably between 1:1.01 - 1:1.5 (slightly in excess).

[0095] For example, at room temperature, the pH value of the mixture can be increased to 5 - 8 by adding dilute NaOH or a buffer solution to form a stable metal - chelating agent complex.

[0096] Preferably, the chromatography in step (c) is column chromatography, thin - layer chromatography and / or high - performance liquid chromatography. The mixture of the obtained metal - chelating agent complexes can be loaded onto a chromatography column, such as RP (reverse - phase) - HPLC, with a C - 8 or C - 18 stationary phase and a mobile phase of water and an organic modifier and / or TFA (if necessary). Due to the slightly different ionic radii between the metals, the resulting metal - chelating agent complexes have different lipophilicities and thus behave differently on the chromatography column.

[0097] The desired metal ion chelate can be collected from the outlet of the chromatographic column using a fraction collector, thereby separating it from other metal chelates.

[0098] If desired, the above chromatographic separation process can be repeated with the collected metal ion chelate, for example, at least twice, to further increase the purity of the product.

[0099] After purification, i.e., in step (d), the metal ion can be decomplexed from the chelating agent by acidification. The chelating agent can then be removed from the metal ion by further chromatographic separation to obtain the final purified product.

[0100] Thus, in the chromatographic separation method according to the present invention, the mixture of at least two different metal ions to be separated contains at least one rare earth element. More preferably, the mixture contains two adjacent lanthanide elements (i.e., adjacent in the periodic table), and more preferably, the mixture contains Lu and Yb, or Tb and Gd, and even more preferably 177Lu and 176Yb, or 161Tb and 160Gd.

[0101] Most preferably, the mixture includes Lu and Yb, especially 177Lu and 176Yb. The method of the present invention is particularly suitable for separating Lu and Yb. Upon chelation, Lu and Yb form two regioisomers in a stable ratio of 10 - 90 w% to 40 - 60% (depending on the structure of the chelating agent). Although this may initially seem like a disadvantage, the isomerization can be an advantageous condition in the first round of separation to remove most of the Yb, as the difference in retention times between the isomers is large enough.

[0102] For example, step (c) can be carried out at least twice. When this multi-column strategy is used to remove Yb from Lu, the two collected Lu isomer fractions can be combined and reinjected into the next column. This will again produce two Lu isomers, which can be separated from the Yb isomers.

[0103] Optionally, the first isomer collected can be decomplexed by acidification and immediately followed by recomplexation by increasing the pH value. By doing so, 85% of the first Lu isomer can be converted into the second isomer. The combined Lu fractions can consist almost entirely of the second Lu-isomer (98%). This strategy can facilitate fraction collection in subsequent columns.

[0104] In a preferred embodiment of the method of the present invention, the method comprises the step of enriching the chelate-metal complex with the desired isomer by decoordinating a partially isomerized mixture, for example by changing the pH value (raising or lowering), whereby the less stable chelate isomers will decoordinate, providing free metal ions. By reversing the pH value in the opposite direction (down or up), the free metal ions are re-coordinated. The free metal ions will re-coordinate in the ratio of the preferred isomers, thereby increasing the relative amount of the more stable chelate. Thus, in a preferred embodiment, the method further comprises one or more decoordination-recoordination cycles, preferably by pH cycling, resulting in isomer enrichment of the metal chelate complex.

[0105] Typically, the Lu complex elutes before the Yb complex. This will minimize the tailing of Yb into the Lu fraction. In other words, the Lu complex can be collected first while reducing the risk of collecting any Yb complex remaining on the column. In the case where the Yb complex detaches from the column first, due to the large amount of Yb complex, when the desired Lu fraction (much less material) starts to elute, a portion of the Yb complex will still elute from the column, thus contaminating the Lu fraction. Therefore, the method according to the present invention provides a particularly optimized separation result for this pair of adjacent lanthanides by effectively removing most of the undesired isotopes or elements in each pass, while collecting the desired isotope in high yield. This is particularly beneficial in large-scale production scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 : Typical chromatogram of Yb / Lu-chelate on an HPLC C-18 column;

[0107] Figure 2A : First injection of Yb / Lu mixture;

[0108] Figure 2B : Re-injection of the Lu fraction collected from 2a;

[0109] Figure 3 : First injection of Yb / Lu mixture for B401;

[0110] Figure 4 : Re-injection of the collected Lu fraction of B401;

[0111] Figure 5 : Elution using B501 and separation of Lu and Yb;

[0112] Figure 6 : Elution using B401 and separation of Lu and Yb;

[0113] Figure 7A: Separating Lu-177 and Yb-175 in two isomers based on patient dose using B401;

[0114] Figure 7B : Separating Lu-177 and Yb-175 after re-injection based on patient dose;

[0115] Figure 8: Amplifying the separation of Lu-177 and Yb-175 using B401;

[0116] Figure 9 : Dissociation complex curve.

[0117] Examples

[0118] Example 1: Separating Lu from Yb matrix

[0119] 39.2 μg of Lu(NO3)3 enriched with Lu-176 (82%) was irradiated with a neutron flux of 3.7×10 13 n cm -2 s -1 for 1 hour, and 21 MBq of Lu-177 (activity reference time, ART) was obtained after 1-day cooling. Lu(NO3)3 was dissolved in 0.04 M HCl to make the final Lu-metal concentration 18.4 μg / g and the Lu-177 activity concentration 7.5 MBq / g. This Lu-177 stock solution was used to produce a Yb / Lu mixture doped with Lu-177.

[0120] A representative mixture of Yb / Lu was prepared by incubating 146 mg of a 91.33 mg / g Yb stock solution (13.3 mg Yb = 75 μmol) with 140.1 mg of an 18.4 μg / g Lu stock solution (2.6 μg Lu = 0.015 μmol), with a final molar ratio of 5000:1. Thus, the ART mixture included 1 MBq of Lu-177 for detection purposes.

[0121] Then, the Yb / Lu mixture was incubated with an aqueous solution (86 μmol) of 450 mg of a commercially available chelating agent B501 (p-NH2-Bn-Oxo-DO3A, Macrocyclics) at 110 mg / g, thus producing a slight excess of chelating agent relative to the total lanthanide elements of 1:1.1. The pH was raised to 8 by adding 385 μl of NaOH (1 M) and the mixture was incubated at room temperature for 20 minutes to a final volume of 1.0 g (1 ml).

[0122] Subsequently, different amounts of the reaction mixture were subjected to Waters RP-HPLC (Acquity) equipped with a Waters C-18 column (4.6 x 250 mm, 5 μm particles), a UV-detector, a γ-detector, and an automatic fraction collector (analytical scale). Chromatography was carried out at a flow rate of 1 ml / min, and isocratic elution was performed with 0.1% TFA in deionized water. The desired fractions were collected for analysis.

[0123] Figure 1 A typical injection of 2.7 μl of the reaction mixture containing 40 μg total Yb / Lu is shown. Upon chelation, Lu and Yb form two regioisomers in a stable ratio of 15% (first isomer Yb-1) - 85% (second isomer Yb-2). Chromatography shows baseline separation of Yb (UV) and Lu (radioactivity) of the two isomers (Yb-1 and Yb-2).

[0124] Example 2, Purification

[0125] To demonstrate the potential of the chelating agent for separation purposes, 1-column purification was carried out. Figure 2A An injection of 7.5 μl of the reaction mixture as described in Example 1 is shown, this time containing 0.1 mg total Yb / Lu. Two Lu-177 isomers were collected with a total recovery of 90%. Subsequently, the total Lu-177 fraction (1 ml) of the second isomer was reinjected under the same HPLC conditions ( Figure 2B ). A 500-fold removal rate of Yb on the first column was calculated from the ultraviolet absorbance (210 nm).

[0126] Example 3, Residence Time of Lanthanides with Different Chelating Agents

[0127] Essentially as described in Example 1, cold and / or doped Tb / Gd or Yb / Lu mixtures were prepared and subjected to HPLC. Then the residence times of these lanthanide-chelates (first and second isomers) were determined by Acquity software. From the difference in residence times, it is clear that the difference between B501 (p-NH2-Bn-oxa-DO3A, 1-oxa-4,7,10-triazacyclododecane-5-S-(4-aminobenzyl)-4,7,10-triacetic acid, macrocyclic compound) and B505 (p-SCN-Bn-oxa-DO3A, 1-oxa-4,7,10-triazacyclododecane-5-S-(4-isothiocyanatobenzyl)-4,7,10-triacetic acid, macrocyclic compound) lies only in the functional group located on the benzyl group, providing different residence times for at least the second isomer of the metal chelate.

[0128] Example 4

[0129] In a similar experiment, the chelate B401 (p-NH2-Bn-PCTA, 3,6,9,15-tetraazabicyclo[9.3.1]pentadec-1(15),11,13-triene-4-S-(4-aminobenzyl)-3,6,9-triacetic acid, macrocyclic compound) containing pyridine in the macrocyclic structure was used. After chelation, Lu and Yb formed two regioisomers in a stable ratio of 65% (first isomer Yb-1) - 35% (second isomer Yb-2). The residence time was determined by injecting 0.1 mg of Yb and injecting an aqueous solution of 0.1% TFA, followed by elution with 0.5% EtOH for 15 minutes and then with 1.5% ethanol. Figure 3 Shows the elution curve and the start of purification. Figure 4 Shows the second column with re-injection of the 1st and 2nd isomers. Two Lu-177 isomers were collected with a total recovery of 90%. Subsequently, the total Lu-177(1) fraction (0.9 ml) was re-injected under the same HPLC conditions, followed by injection of the Lu-177(2) fraction (0.8 ml). Due to the 7-minute time difference between the first and second injections, the Lu-177(1) isomer eluted at 6 minutes ( Figure 3 ). A >500-fold removal rate of Yb on the first column for the two isomers was calculated from the UV absorbance (210 nm). The p-NCS analogue B405 of B401 provided similar results.

[0130]

[0131] Table 1. *Residence time of the mobile phase = aqueous solution of 0.1% TFA with 1% ethanol. **0.1% TFA, with a gradient of 0.5% - 1.5% EtOH. All other tests used an aqueous solution of 0.1% TFA (without ethanol) as the mobile phase.

[0132] Example 5

[0133] After irradiation of Lu177 and Yb175, irradiated enriched Yb (rich in Yb176, 99.3%) was formed. The mixture of Lu and Yb was chelated with an oxo chelator (B501). Both isotopes were simultaneously visible on the detector ( Figure 5 , lower figure below), first Lu, and then Yb of the two isomers. Due to the large excess of Yb, the UV detector ( Figure 5 , upper figure above) showed only the Yb chelate (in both isomers (1 and 2)). One-hundredth part of the mixture was loaded onto an HPLC column. Upper figure: UV detection (only the main Yb is visible); lower figure: Lu177 and Yb-175 are visible. It is clear that the two isomers of Lu-177-oxo (B501) eluted first, followed by the corresponding Yb isomers. Wireless detection and UV measurement were carried out simultaneously, so the two figures represent the same separation.

[0134] Example 6

[0135] After irradiation with Lu177 en Yb175, an irradiated enriched Yb (rich in Yb176, 99.3%) is formed. The mixture of Lu and Yb is chelated with PTCA-chelator (B401). Both isotopes are simultaneously visible on the detector ( Figure 6 , upper figure), first Lu, then Yb of the two isomers. Due to the large excess of Yb, the UV detector only shows the Yb chelate (in both isomers (1 and 2)). 1 / 1000 part of the mixture is loaded onto a HPLC column 4.6×250 mm column. Upper figure: UV detection (only the main Yb is visible); lower figure: Lu177 and Yb-175 are visible. It is obvious that the two isomers of Lu-177-PCTA (B401) are eluted first, followed by the corresponding Yb-PCTA isomers. Wireless detection and UV measurement are carried out simultaneously, so these two figures represent the same separation.

[0136] Polasek showed the separation of 0.158 mg Yb on a 10×250 mm column (Example 93 of EP 3492460). To obtain a dose suitable for one patient, 20 mg of Yb176 is required. Therefore, it is necessary to scale up (100 - 1000 times) to achieve a meaningful separation process. By keeping the column volume constant and loading a higher amount of Yb on the column, uncontrolled diffusion of the Yb chelate on the column can occur, resulting in a large amount of peak fronting and tailing, whereby the main Yb can interfere with Lu177 and mix with Lu177. Therefore, it is advantageous to load as much mass as possible on the column without affecting the separation effect.

[0137] Example 7

[0138] 21 mg of irradiated Yb 176 (rich in 99.3% Yb176) is purified on a 50 mm column using the PCTA chelator (B401). The irradiation produces 10.9 GBq of Lu177 and 2.5 GBq of Yb175. The ratio of Yb:Lu after irradiation is approximately 5000:1. The mixture is combined with the PCTA derivative (B401) and loaded onto a 50×250 mm column.

[0139] Figure 7A , the first column (wireless detection). The Lu177 fraction is collected for reinjection onto a second column ( Figure 7B ). After the second column, the total recovery rate of Lu177 is 79%, and after two columns, Yb175 is reduced to 0.007% (Yb removal factor is 15,000). This shows that the separation can be carried out on a large scale. The chromatogram of Example 7 is the same as the radiochromatogram of Example 6. The process is stable and consistent at different scales.

[0140] Example 8

[0141] To demonstrate the effect of scale-up on the separation curve, a mixture of PCTA(B401)-chelates of Yb and Lu177 in a ratio of 5000:1 was prepared, where 20 mg of Yb( Figure 8A ) and 200 mg of Yb( Figure 8B ) were loaded onto a 50×250 mm column. Figure 8B It was shown that during 10-fold scale-up, the first Yb isomer moved away from the first Lu177 isomer (to the right, slower elution), while the second Yb isomer moved towards the second Lu177 isomer (to the left, faster elution). The PCTA(LC2; B401) and oxo(LC1; B501) chelates are advantageous because the existing small baseline separation between the first isomers of Yb and Lu is relatively improved upon scale-up, while the smaller separation between the second isomers of Yb and Lu has no adverse consequences because the separation between the second isomers of Yb and Lu is very high. By further adjusting the separation parameters, a Yb mass greater than 200 mg can be processed on a 50×250 mm chromatography column. When scaled up, the oxo(B501) chelating agent follows the same curve.

[0142] This particular property, combined with the Lu-Yb elution sequence, indicates that the PCTA(B401) and oxo(B501) chelating agents are very suitable for scale-up.

[0143] Example 9

[0144] Dissociation and isomerization ratio:

[0145] The mixture of Lu-PCTA chelates from Example 8 was incubated with 1 M HCl at 70 °C to break the Lu177-chelates complex and generate free Lu177. Figure 9Shows the variation of the content of the 1st isomer (triangle), the 2nd isomer (circle) and free Lu177 over time. In less than 10 minutes, the 1st isomer (triangle) is completely decomplexed. At the same time, the second, more stable isomer remains 85% intact. By increasing the pH to 8 at the desired time, the decomplexation will stop and the free Lu177 will complex again in a ratio of 65% of the 1st isomer and 35% of the 2nd isomer. By repeating this process, the amount of the 2nd isomer increases while the amount of the 1st isomer decreases. This trans-chelation demonstrates that the isomer ratio can be affected, for example, by increasing the most favorable isomer (depending on the resolution of the Lu / Yb chelate, the desired magnification and the desired separation process). The patterns of PCTA (B401) and oxo (B501) are the same (two isomers, elution order Lu-Yb and shift upon magnification), but the isomer ratios and the separation between the Lu and Yb isomers are different. The isomer ratio of oxo (B501) is 15% of the 1st isomer and 85% of the 2nd isomer. The isomer ratio of the PCTA (B401)-Lu / Yb chelate is 65% of the 1st isomer and 35% of the 2nd isomer. The ratio between the 1st and 2nd isomers can be affected because the 1st and 2nd isomers have different stabilities in an acidic environment.

Claims

1. Use of a compound of the following general formula for chromatographic separation of rare earth elements, wherein A is C substituted by one of H and C 1-4 alkyl, Z and Z 1 are independently C substituted by one of H and C 1-4 alkyl, E = O or S; R1 is wherein R2 is selected from the group consisting of: H, -NCS, -OH, thiol group, -NH2, -NO2, halogen and cyano group, a = 1, and b = 1.

2. The use according to claim 1, wherein 3. The use according to claim 1, wherein R2 is -NH2 or -NCS.

4. The use according to claim 3, wherein the compound of the general formula is 5. The use according to claim 4, wherein the compound of the general formula is 6. The use according to claim 1 for chromatographic separation of two adjacent lanthanide elements.

7. The use according to claim 1 for chromatographic separation of Lu and Yb, or Tb and Gd.

8. The use according to claim 1 for chromatographic separation of 177Lu and 176Yb, or 161Tb and 160Gd.

9. A method for chromatographic separation of lanthanide elements from a mixture of at least two metal ions, characterized in that the method comprises the following steps: (a) Providing a mixture of at least two different metal ions selected from lanthanide element ions, (b) Contacting the metal ions comprised in the mixture with at least one compound of the general formula used in the use according to any one of claims 1 to 8 to form a chelate; (c) Subjecting the chelate obtained from step (b) to chromatographic separation, wherein optionally, at least one separated metal chelate obtained in step (c) can be subjected to at least one further chromatographic separation in order to increase the purity of the at least one separated metal chelate; and optionally, (d) Obtaining a metal from the at least one separated metal chelate.

10. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the mixture of the at least two different metal ions to be separated comprises two adjacent lanthanides.

11. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the mixture of the at least two different metal ions to be separated comprises Lu and Yb, or Tb and Gd.

12. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the mixture of the at least two different metal ions to be separated comprises 177Lu and 176Yb, or 161Tb and 160Gd.

13. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the chromatography in step (c) is column chromatography and / or thin-layer chromatography.

14. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the chromatography in step (c) is high performance liquid chromatography.

15. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the metal ions are in the form of salts, oxides and / or hydroxides of organic acids or inorganic acids.

16. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein the metal ions are in a form selected from the group consisting of chlorides, bromides, sulfates, nitrates, methanesulfonates, trifluoromethanesulfonates, formates, acetates, lactates, malates, citrates, 2-hydroxyisobutyrates, mandelates, diglycolates, tartrates, oxides, hydroxides and / or carbonates.

17. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 9, wherein in step (b), a solution containing the mixture provided in step (a) in the form of a metal salt or a solid phase containing the mixture provided in step (a) in the form of a metal oxide and / or hydroxide is mixed with a solution of the compound of the general formula, and the molar ratio of the metal ion to the compound of the general formula is from 1:0.5 to 1:100; an organic base or an inorganic base is added to the reaction mixture, and complexation is carried out in the solution.

18. The method for chromatographically separating lanthanides from a mixture of at least two metal ions according to claim 17, wherein the metal salt is a carbonate.

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