CHROMATOGRAPHIC SEPARATION OF METALS USING DOTA-BASED CHELATORS

Abstract

The present invention relates to use of a chelating compound for chromatographic separation of rare earth elements, actinides, and/or s-, p- and d-block metals, and to a method of 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 method is characterized in that it comprises the following steps: (a) providing a mixture of at least two different metal ions chosen from rare earth metal ions, actinide ions and/or s-, p- and d-block metal ions, (b) contacting metal ions comprised in said mixture to 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, 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 the metal from the at least one separated metal chelate.

Claims

1. A compound of general formula (I): ##STR00013## A is N or C substituted with one of H, halogen (Cl, Br, F), SO.sub.3H, C.sub.1-4 alkyl, aryl, hetaryl, C—O—C.sub.1-16 alkylamino, Z and Z.sup.1 independently are N or C substituted with one of H, halogen (Cl, Br, F), SO.sub.3H, C.sub.1-4 alkyl, aryl, hetaryl, C—O—C.sub.1-16 alkylamino, E=O, S or P; R.sub.1 is independently substituted or unsubstituted C.sub.4-15alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle, or substituted or unsubstituted heteroaryl, wherein the substitution is by one or more moiety(ies) selected from a group consisting of imide, —C(O)(CH.sub.2)0-3CH3, C.sub.2-5carboxyl, —(CH.sub.2).sub.1-3C(O)(CH.sub.2).sub.0-3CH.sub.3, nitro, amino, thiol, succinimide, maleimide, aminooxyl, acetylene, N.sub.3, acetamino, azide, —C(O)O(CH.sub.2).sub.1-3CH.sub.3, —OC(O)(CH.sub.2).sub.0-3CH.sub.3, halogen, C.sub.1-5alkynyl, and NCS; and a=0-5.

2. The compound according to claim 1, wherein R.sub.1 is ##STR00014## wherein R.sub.2 is independently H, —NCS, —OH, —NH.sub.2, —C(O)NH.sub.2, —NO.sub.2, —(CH.sub.2).sub.1-3O(CH.sub.2).sub.1-3CH.sub.3, —C(O)O(CH.sub.2).sub.1-3CH.sub.3, —OC(O)(CH.sub.2).sub.0-3CH.sub.3, halogen, —(CH.sub.2).sub.1-3C(O)(CH.sub.2).sub.0-3CH.sub.3, cyano, C.sub.2-5carboxyl, thiol, —C(O)(CH.sub.2).sub.0-3CH.sub.3, substituted or unsubstituted C.sub.1-15alkyl, substituted or unsubstituted C.sub.1-15alkenyl, substituted or unsubstituted C.sub.1-15alkynyl, substituted or unsubstituted C.sub.4-15alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle, or substituted or unsubstituted heteroaryl, wherein the substitution is by one or more moiety(ies) selected from a group consisting of imide, —C(O)(CH.sub.2).sub.0-3CH.sub.3, C.sub.2-5carboxyl, —(CH.sub.2).sub.1-3C(O)(CH.sub.2).sub.0-3CH.sub.3, nitro, amino, thiol, succinimide, maleimide, aminooxyl, acetylene, N.sub.3, acetamino, azide, —C(O)O(CH.sub.2).sub.1-3CH.sub.3, —OC(O)(CH.sub.2).sub.0-3CH.sub.3, halogen, C.sub.1-5alkynyl, and NCS; ##STR00015## a=1-4, and b=1-4.

3. Use according to claim 2, wherein R.sub.2 is chosen from the group consisting of H, —NCS, —OH, —NH.sub.2, —C(O)NH.sub.2, —NO.sub.2, —(CH.sub.2).sub.1-3O(CH.sub.2).sub.1-3CH.sub.3, —C(O)O(CH.sub.2).sub.1-3CH.sub.3, —OC(O)(CH.sub.2).sub.0-3CH.sub.3, halogen, —(CH.sub.2).sub.1-3C(O)(CH.sub.2).sub.0-3CH.sub.3, cyano, C.sub.2-5carboxyl, thiol, and —C(O)(CH.sub.2).sub.0-3CH.sub.3.

4. The compound according to claim 3, wherein R.sub.2 is —NH.sub.2 or —NCS.

5. The compound according to claim 4, wherein the compound of general formula (I) is ##STR00016##

6. The compound according to claim 5, wherein the compound of general formula (I) is ##STR00017##

7. A method of chromatographic separation of rare earth elements, actinides and/or s-, p- and d-block metals, from a mixture of at least two metal ions, the method comprising: (a) providing a mixture of at least two different metal ions chosen from rare earth metal ions, actinide ions and/or s-, p- and d-block metal ions, (b) forming chelates by contacting metal ions comprised in the mixture with at least one compound of general formula (I): ##STR00018## A is N or C substituted with one of H, halogen (Cl, Br, F), SO.sub.3H, C.sub.1-4 alkyl, aryl, hetaryl, C—O—C.sub.1-16 alkylamino, Z and Z.sup.1 independently are N or C substituted with one of H, halogen (Cl, Br, F), SO.sub.3H, C.sub.1-4 alkyl, aryl, hetaryl, C—O—C.sub.1-16 alkylamino, E=O, S or P; R.sub.1 is independently substituted or unsubstituted C.sub.4-15alkylaryl, substituted or unsubstituted aryl, substituted or unsubstituted heterocycle, or substituted or unsubstituted heteroaryl, wherein the substitution is by one or more moiety(ies) selected from a group consisting of imide, —C(O)(CH.sub.2)0-3CH3, C.sub.2-5carboxyl, —(CH.sub.2).sub.1-3C(O)(CH.sub.2).sub.0-3CH.sub.3, nitro, amino, thiol, succinimide, maleimide, aminooxyl, acetylene, N.sub.3, acetamino, azide, —C(O)O(CH.sub.2).sub.1-3CH.sub.3, —OC(O)(CH.sub.2).sub.0-3CH.sub.3, halogen, C.sub.1-5alkynyl, and NCS; and a=0-5; (c) subjecting the chelates to chromatographic separation, wherein optionally at least one separated metal chelate 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 the metal from the at least one separated metal chelate.

8. The method of chromatographic separation according to claim 7, wherein the mixture of at least two different metal ions to be separated comprises at least one rare earth element.

9. The method of chromatographic separation according to claim 7, wherein the mixture of at least two different metal ions to be separated comprises two neighbouring lanthanides.

10. The method of chromatographic separation according to claim 7, wherein the mixture of at least two different metal ions to be separated comprises Lu and Yb, or Tb and Gd.

11. The method of chromatographic separation according to claim 10, wherein the mixture of at least two different metal ions to be separated comprises 177Lu and 176Yb, or 161Tb and 160Gd.

12. The method of chromatographic separation according to claim 7, wherein the chromatographic separation is with column chromatography, thin layer chromatography and/or high-performance liquid chromatography.

13. The method of chromatographic separation according to claim 7, wherein metal ions are in a form of salts of organic or inorganic acids, oxides, hydroxides and/or carbonates.

14. The method chromatographic separation according to claim 14, wherein metal ions are in a form of salts selected from the group consisting of chloride, bromide, sulfate, nitrate, methanesulfonate, trifluoromethanesulfonate, formate, acetate, lactate, malate, citrate, 2-hydroxyisobutyrate, mandelate, diglycolate, tartarate, oxide, hydroxide and carbonate.

15. The method of chromatographic separation according to claim 7, wherein a solution containing the mixture in the form of metal salts, or a solid phase containing the mixture in the form of metal oxide, hydroxide and/or carbonate, is mixed with a solution of the compound of general formula (I) in molar ratio of metal ions to compound of general formula (I) from 1:0.5 to 1:100.

16. The method of chromatographic separation according to claim 15, further comprising adding organic or inorganic base to the reaction mixture, allowing complexation to occur in the solution.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0072] FIG. 1: Typical chromatograph of Yb/Lu-chelates on HPLC C-18 column.

[0073] FIG. 2A: First injection of Yb/Lu mix.

[0074] FIG. 2B: Reinjection of collected Lu-fraction from 2a

[0075] FIG. 3: First injection of Yb/Lu mix for B401

[0076] FIG. 4: Reinjection of collected Lu-fraction for B401

[0077] FIG. 5: Elution and separation of Lu and Yb using B501

[0078] FIG. 6: Elution and separation of Lu and Yb using B401

[0079] FIG. 7A: Separation of Lu-177 and Yb-175 in two isomers on patient dose basis using B401

[0080] FIG. 7B: Separation of Lu-177 and Yb-175 after reinjection on patient dose basis

[0081] FIG. 8A: Scale up separation of Lu-177 and Yb-175 using B401 (with 20 mg of Yb)

[0082] FIG. 8B: Scale up separation of Lu-177 and Yb-175 using B401 (with 200 mg of Yb)

[0083] FIG. 9: Decomplexation profile

EXAMPLES

Example 1. Separation of Lu from Yb-Bulk

[0084] 39.2 μg of Lu(NO.sub.3).sub.3 enriched in Lu-176 (82%) was irradiated at a neutron flux of 3.7×10.sup.13 n cm.sup.−2 s.sup.−1 for 1 hour, resulting in 21 MBq of Lu-177 after 1 day cooling (Activity Reference Time, ART). The Lu(NO.sub.3).sub.3 was dissolved in 0.04 M HCl to a final Lu-metal concentration of 18.4 μg/g and Lu-177 activity concentration of 7.5 MBq/g. This Lu-177 stock was used to create Lu-177-spiked Yb/Lu mixtures.

[0085] A representative mixture of Yb/Lu was produced by incubating 146 mg of a 91.33 mg/g Yb-stock solution (13.3 mg Yb=75 μmol) with 140.1 mg of the 18.4 μg/g Lu-stock solution (2.6 μg Lu=0.015 μmol), with a final molar ratio of 5000:1. The mixture thus included 1 MBq of Lu-177 at ART for detection purposes.

[0086] The Yb/Lu mixture was then incubated with 450 mg of a 110 mg/g commercially available chelator B501 (p-NH2-Bn-Oxo-DO3A, Macrocyclics) solution in water (86 μmol), thereby creating a small excess of chelator over total lanthanides of 1:1.1. The pH was raised to 8 by adding 385 μl of NaOH (1 M) and the mixture was incubated for 20 minutes at room temperature, to a final volume of 1.0 gram (1 ml).

[0087] Subsequently, different amounts of the reaction mixture were subjected to a Waters RP-HPLC (Acquity) equipped with a Waters C-18 column (4.6×250 mm, 5 μm particles), a UV-detector, gamma detector and automated fraction collector (analytical scale). The chromatography was performed at a 1 ml/min flow rate and isocratic elution with 0.1% TFA in deionized water. Desired fractions were collected for analysis.

[0088] FIG. 1 shows a typical injection of 2.7 μl of the reaction mixture, containing 40 μg total Yb/Lu. Upon chelation, Lu and Yb form two region-isomers in a stable ratio of 15% (first isomer Yb-1)-85% (second isomer Yb-2). The chromatograph shows baseline separation of the Yb (UV) and Lu (radioactivity) of both isomers (Yb-1 and Yb-2).

Example 2. Purification

[0089] To show the potential of the chelator for separation purposes, a 1-column purification was conducted. FIG. 2A shows the injection of 7.5 μl of the reaction mixture as stated in example 1, this time containing 0.1 mg total Yb/Lu. Both 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 (FIG. 2B). From the UV-absorbance (210 nm) a 500-fold removal of Yb over the first column was calculated.

Example 3. Retention Times of Lanthanides with Different Chelators

[0090] Cold and/or spiked Tb/Gd or Yb/Lu mixes were prepared and subjected to HPLC essentially as described in example 1. The retention times of these lanthanide-chelates (1.sup.st and 2.sup.nd isomer) were then determined by Acquity software. From the differences in retention times, it is clear that both B501(p-NH.sub.2—Bn-oxo-DO3A, 1-Oxa-4,7,10-tetraazacyclododecane-5-S-(4-aminobenzyl)-4,7,10-triacetic acid, Macrocyclics) and B505 (p-SCN-Bn-oxo-DO3A, 1-Oxa-4,7,10-tetraazacyclododecane-5-S-(4-isothiocyantobenzyl)-4,7,10-triacetic acid, Macrocyclics), differ only by the functional group placed at the benzyl, provide different retention times for at least the 2.sup.nd isomer of the metal-chelates.

Example 4

[0091] A chelate containing a pyridine in the ring structure, B401 (p-NH2-Bn-PCTA, 3,6,9,15-Tetraazabicyclo[9.3.1] pentadeca-1(15), 11,13-triene-4-S-(4-aminobenzyl)-3,6,9-triacetic acid, Macrocyclics) was used in analogous experiments. Upon chelation, Lu and Yb form two region-isomers in a stable ratio of 65% (first isomer Yb-1)-35% (second isomer Yb-2). Retention times were determined with injection of 0.1 mg Yb and injection with 0.1% TFA in water, followed by elution with 0.5% EtOH for 15′ followed by 1.5% EtOH. FIG. 3 shows the elution profile and the start of the purification FIG. 4. shows the 2.sup.nd column in which the 1.sup.st and 2.sup.nd isomer are reinjected. Both Lu-177 isomers were collected with a total recovery of 90%. Subsequently, the total Lu-177 (1) fraction (0.9 ml) was reinjected under the same HPLC conditions, followed by the injection of the Lu-177 (2) fraction (0.8 ml). Due to the 7′ time difference between the first and second injection, the Lu-177 (1) isomer elutes at 6′ (FIG. 3). From the UV-absorbance (210 nm) a >500-fold removal of Yb over the first column was calculated for both isomers. B405, the p-NCS analogue of B401 provides similar results.

TABLE-US-00001 TABLE 1 B501 B501 B505 B505 B401 B401 Lanthanide-chelate 1.sup.st isomer 2.sup.nd isomer 1.sup.nd isomer 2.sup.nd isomer 1.sup.nd isomer 2.sup.nd isomer Gd ND ND 9.3 21.1 Tb ND ND 9.3 22.2 Yb 8.3 20.7 8.4 22.0 Lu 8.0 19.6 7.8 19.4 Yb (1% EtOH)*  5.5*  9.1*  5.5*  9.5* Lu (1% EtOH)*  5.0*  8.5*  5.0*  8.7* Yb (0.5%-1.5%)** 16.1** 29.5** Lu (0.5%-1.5%)** 13.1** 27.5** Retention times of *mobile phase = 0.1% TFA in water with 1% EtOH. **0.1% TFA with 0.5%-1.5% EtOH-gradient. All other runs with mobile phase 0.1% TFA in water (without EtOH).

Example 5

[0092] Irradiated enriched Yb (enriched in Yb176, 99.3%) after irradiation Lu177 en Yb175 are formed. The mix of Lu and Yb is chelated with Oxo-chelator (B501). Both isotopes are visible at the same moment on the radiodetector (FIG. 5, bottom), Lu first, followed by Yb for both isomers. Due to the large excess of Yb, the UV detectors (FIG. 5 top) only shows the Yb-chelate (in the two isomers (1 and 2)). 1/100 part of the mixture was brought on the HPLC column. Top: UV detection (only bulk Yb visible); Bottom: Lu177 and Yb-175 visible. It is evident that Lu-177-oxo (B501) for both isomers elutes first followed by the corresponding Yb isomers. Radio detection and UV measurements are taking place at the same time, the two graphs hence represent the same separation.

Example 6

[0093] Irradiated enriched Yb (enriched in Yb176, 99.3%) after irradiation Lu177 en Yb175 are formed. The mix of Lu and Yb is chelated with PTCA-chelator (B401). Both isotopes are visible at the same moment on the radiodetector (FIG. 6, Top), Lu first, followed by Yb for both isomers. Due to the large excess of Yb, the UV detector only shows the Yb-chelate (in the two isomers (1 and 2)). 1/1000 part of the mixture was brought on the HPLC column 4.6×250 mm column. Top: UV detection (only bulk Yb visible); Bottom: Lu177 and Yb175 visible. It is evident that Lu-177-PCTA (B401) for both isomers elutes first followed by the corresponding Yb-PCTA isomers. Radio detection and UV measurements are taking place at the same time, the two graphs hence represent the same separation.

[0094] Polasek demonstrates a separation of 0.158 mg Yb on a 10×250 mm column (example 93 of EP3492460 To come to a dose suitable for one patient, 20 mg Yb176 is necessary. A scale up is hence necessary (by a factor 100-1000) to come to a meaningful separation process. Loading higher amount of Yb on a column, by constant column volume, can lead to uncontrolled spread of the Yb chelate over the column, leading to massive peak fronting as well as tailing, whereby the Yb bulk can interfere and mix with Lu177. It is hence advantageous to load as much mass as possible on a column without affecting the effectiveness of the separation.

Example 7

[0095] Purification of 21 mg of irradiated Yb176 (enriched by 99.3% in Yb176) on a 50 mm column using PCTA chelator (B401). Irradiation results in 10.9 GBq Lu177 and 2.5 GBq Yb175. The ratio of Yb:Lu after irradiation is about 5000:1. The mixture is bound to PCTA derivative (B401) and loaded onto a 50×250 mm column.

[0096] FIG. 7A. First column (radio detection). Lu177 fractions were collected for re-injection on a second column (FIG. 7B). After the second column, the overall recovery is 79% Lu177, with the Yb175 reduced to 0.007% after two columns (Yb removal factor 15,000). This demonstrates that the separation can be carried out on large scale. The chromatogram of example 7 is identical to the radiochromatogram in example 6. The process is stable and consistent at different scales

Example 8

[0097] To demonstrate the effect of a scale-up on the separation profile, a PCTA (B401)-chelate mixture of Yb and Lu177 in the ratio 5000:1 was made, with 20 mg of Yb (FIG. 8A) and 200 mg of Yb (FIG. 8B) loaded on a 50×250 mm column. FIG. 8B shows that the 1st Yb isomer moves away from the 1st Lu177 isomer during this 10× upscaling (to the right, slower elution), while the 2nd Yb isomer moves towards the 2nd Lu177 isomer (to the left, faster elution). This upscaling profile for PCTA (LC2; B401) and oxo (LC1; B501)) chelates is advantageous because the existing small baseline separation between the 1st isomers of Yb and Lu improves relatively on upscaling, while the smaller resolution between the 2nd isomers of Yb and Lu has no negative consequences because the resolution between the 2nd isomers of Yb and Lu is very high. By further adjusting the separation parameters, Yb masses>200 mg can be processed on a 50×250 mm column. The oxo (B501) chelators follow the same profile when scaled up.

[0098] This special property, in combination with the Lu—Yb elution sequence, indicates that PCTA (B401) and oxo (B501) chelators are very suitable for upscaling.

Example 9

[0099] Decomplexation and Isomeric Ratio:

[0100] The mix of Lu-PCTA chelate of example 8 was incubated with 1 M HCl, at 70° C., to break the Lu177-chelate complex and produce free Lu177. FIG. 9 shows the amount of 1.sup.st isomer (triangle), 2.sup.nd isomer (circle) and free Lu177 overtime. In less than 10 minutes the 1.sup.st isomer (triangle) is completely decomplexed. At the same time, the second, more stable, isomer remains still 85% intact. By increasing the pH to 8 at a desired time, the decomplexation will stop and the free Lu177 will complex again in the ratio 65% 1.sup.st isomer and 35% 2.sup.nd isomer. By repeating this process, the amount of the 2.sup.nd isomer is increased and the 1.sup.st isomer is decreased. This trans-chelation demonstrates that the isomer ratio can be influenced, for example to increase the most favorable isomer (depending on the resolution of the Lu/Yb chelates, the desired scale-up and the required separation process). The pattern for PCTA (B401) and Oxo (B501) is the same (2 isomers, elution order Lu—Yb and the shift on upscaling), but the isomer ratio and the resolution between the Lu and Yb isomers is different. The isomer ratio for oxo (B501) is 15% of the 1st isomer and 85% of the 2.sup.nd isomer. The isomer ratio for PCTA (B401)-Lu/Yb chelates, is 65% of the 1st isomer and 35% of the 2.sup.nd isomer. The ratio between 1.sup.st and 2.sup.nd isomer can be influenced because there is a difference between the stability of the 1.sup.st and 2.sup.nd isomers in an acidic environment.