Novel l-thyroxine radioiodine label and process for production thereof

Abstract

The present invention relates to a multistage synthesis process proceeding from 3,5-diiodo-L-thyronine for synthesis of an L-thyroxine radiolabelled in the 3 position on the inner ring. The present invention further relates to specific intermediates in the synthesis process of the invention, to the radiolabels obtainable and to the use of the radiolabels in nuclear-medical imaging methods and in in vitro and ex vivo applications.

Description

[0001]Forschungszentrum Jülich GmbH Our reference: FD 45189 / AL ----------------------------------------------------------------------------------------------------------------- Forschungszentrum Jülich GmbH Wilhelm-Johnen-Straße, 52428 Jülich ----------------------------------------------------------------------------------------------------------------- New L-thyroxine radioiodine marker and process for its preparation ----------------------------------------------------------------------------------------------------------------- The present invention relates to a multi-step synthesis process starting from 3,5-diiodo-L-thyronine for the synthesis of an L-thyroxine which is radioiodine-labeled in the 3-position on the inner ring. Furthermore, the present invention relates to specific intermediates in the synthesis process according to the invention, the radiomarkers obtainable according to the invention and the use of the radiomarkers in imaging methods in nuclear medicine or in in vitro applications.Thyroid hormones (THs) are essential for the fetal and postnatal development of the nervous system and also play a key role in maintaining brain function in adulthood. They are essential endocrine signaling molecules that regulate a variety of physiological functions. These include, for example, body temperature, cardiac function, metabolism, and consciousness. Thyroid hormones are metabolized multiple times in the human body and thereby regulate hormonal activity. THs are synthesized by the thyroid gland primarily as a prohormone in the form of 3,5,3',5'-tetraiodo-L-thyronine and released into the bloodstream. Outside the thyroid, 3,5,3',5'-tetraiodo-L-thyronine is deiodinated at the tissue level enzymatically by deiodinases (DIOs) mainly to biologically active 3,3',5-triiodothyronine and other, non-biologically active derivatives.3,3',5-Triiodothyronine is generally considered the biologically active form of the hormone and acts by binding to TH nuclear receptors and regulating the transcription of TH-responsive genes. The activation / deactivation cascade can be represented, for example, by the following scheme: In vivo, the prohormone (topmost link) is reductively deiodinated by iodothyronine deiodinases, whereby predominantly an iodine atom of the outer phenol ring (3' or 5' position) is replaced by a hydrogen atom. The most important deiodinase is DIO2, which is the only enzyme capable of converting the prohormone into the biologically active hormone T3 (solid arrow, left link) by monodeiodination of the outer phenol ring. DIOs 1 and 3 and further enzymatic conversions lead to biologically inactive compounds (dashed arrows, right and bottom link). THs play a crucial role not only in various thyroid diseases. Allan-Herndon-Dudley syndrome (AHDS) – also known as MCT8 deficiency (monocarboxylate transporter 8 deficiency) – is based on a genetic disorder that impairs cognitive abilities,The mobility and general health of a child are severely impaired. In people with ADHD, the active thyroid hormone cannot reach the brain cells due to a specific transporter defect in MCT8 for the active compound. MCT8 is highly expressed in the liver and brain. The syndrome is characterized by congenital hypotonia, which develops into spastic paralysis with severe psychomotor delays. Affected boys also exhibit muscle hypoplasia, general muscle weakness, and impaired speech ability. Radioactively labeled thyroxines have long been used as molecular probes to study the in vivo and in vitro distribution of the biologically active hormone. However, these markers were labeled in the 3',5' position of the outer ring. These positions, however, are unfavorable,because the iodine atoms located in this position are metabolically very labile. In addition, the phenolic hydroxyl group on the outer ring weakens the iodine-carbon bonds in the ortho positions of the outer ring, which under certain conditions leads to an unwanted exchange of iodine atoms. The latter can cause undesirable artifacts in tomographic imaging procedures. The patent literature also contains a wide variety of approaches regarding the use and quantification of thyroxine in different environments and with different testing methods. For example, EP 0257352 A1 describes a method for determining the concentration of the free fraction of an active ingredient present in a biological fluid in the presence of natural binding agents, whereby the free and bound fractions of the active ingredient are in equilibrium with each other.by a) bringing a sample of the liquid into contact with an unlabeled antibody; b) separating the sample from the unlabeled antibody; c) incubating the unlabeled antibody with a labeled substance (tracer) that cross-reacts with it; d) measuring the proportion of the tracer that is bound or unbound to the antibody and calculating the concentration of the free portion of the active ingredient from this, wherein the amount of the unlabeled antibody and / or its affinity for the active ingredient are so small that they do not significantly influence the equilibrium between the free and bound portions of the active ingredient and the tracer has a significantly higher or significantly lower affinity for the antibody than the active ingredient itself, and a test kit suitable for this method. In another patent document, DE 2627455 A1,A method for the radioimmunological in vitro determination of thyroxine in non-extracted blood serum is described. The method is characterized in that a sample of blood serum, the thyroxine content of which is to be determined, is mixed with a reagent consisting essentially of a buffered solution containing radioactive thyroxine and an inhibitor for inhibiting the binding of thyroxine to thyroxine-binding globulin; to the mixture is added an antiserum containing an antibody capable of immunoreactivity with thyroxine and prepared from an immunogen containing a conjugate of the N-acetyl derivative of thyroxine coupled to bovine serum albumin with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide; the resulting mixture is incubated at a temperature and for a sufficient period of time,that the thyroxine bound to the antibody and the unbound thyroxine are brought into practical equilibrium; the unbound thyroxine is separated from the thyroxine bound to the antibody; and that the relative amounts of the radioactive thyroxine bound to the antibody and the unbound radioactive thyroxine are determined. EP 0026103A1 also describes a method for determining the concentration of the free fraction of a ligand present in a biological fluid. The fluid may also contain the ligand bound to one or more natural binding agents, wherein the bound and free fractions of the ligand are in equilibrium with each other. The method comprises (a) mixing a sample of the fluid with a labeled derivative of the ligand and with a specific binding agent for the ligand; (b) causing a reaction between the free ligand,its labeled derivative and the specific binding agent; (c) if necessary, separating that portion of the ligand and its labeled derivative which has been bound to the specific binding agent from the portion not so bound; (d) measuring the amount of labeled derivative of the ligand which is bound or not bound to the specific binding agent, and (e) using this measurement to determine the concentration of free ligand in the biological fluid, wherein the labeled derivative of the ligand is selected such that it binds to the specific binding agent, but does not bind to the natural binding agents at all or binds much weaker than the ligand itself, and the specific binding agent is used in an amount which is insufficient,to significantly disrupt the equilibrium of bound to free ligand. Such solutions known from the prior art may offer further potential for improvement. This relates in particular to the reliability and efficiency of the synthesis as well as the chemical stability of the radiolabel in different physiological and non-physiological environments. It is therefore the object of the present invention to at least partially overcome the disadvantages known from the prior art. In particular, it is the object of the present invention to provide a process for the synthesis of a thyroxine radiolabel, which is simple and can be carried out in high yields. Furthermore, it is the object of the present invention to provide a novel radiolabel and its use,wherein the radiomarker is characterized by improved in vivo or in vitro properties. The object is achieved by the features of the independent claims, directed to the process according to the invention, the intermediates and radiomarkers according to the invention, and the use according to the invention. Preferred embodiments of the invention are specified in the subclaims, in the description, or in the figures, whereby further features described or shown in the subclaims, in the description, or in the figures may, individually or in any combination, constitute an object of the invention, as long as the context does not clearly indicate the opposite. According to the invention, there is a process for producing L-thyroxine radioiodine-labeled in the 3-position on the inner ring, which comprises at least the steps: a) reacting 3,5-diiodo-L-thyronine (compound I) with one or more protecting group reagents Z, Z',wherein the protecting group reagent(s) react with the amine group and the carboxylic acid group of thyronine to obtain an amino acid-protected thyronine compound (compound II), wherein the individual protecting groups Z, Z' can be covalently bonded to one another and used as a single compound:, b) Exchange of the two iodine atoms in the 3,5-position of the inner thyronine ring of compound II by stannylation with an organotin compound to obtain a di-3,5-stannyl compound (compound III), wherein R3, R3' are independently selected from the group of C1-C4 alkyl or mixtures thereof: c) Deprotection of the amino acid protected compound III to obtain the free amino acid compound (compound IV): d) Selective iodination of compound IV in the 5-position of the inner ring with elimination of a stannyl group and obtaining the 5-mono-iodo compound V: IV V e) Exchange of the further stannyl group with radioiodine to obtain a thyroxine compound radioiodine-labelled in the 3-position of the inner ring (compound VI): V VI f) Iodination of the outer ring of compound VI to obtain a compound VII iodinated in the 3'- and 5'-positions: . VI VII It was found that advantageous radioiodine compounds, which are particularly suitable as markers in imaging procedures, can be obtained very reproducibly using the defined synthesis route with high yields and high specific activity. Due to their high activity, the markers can be used in physiological concentrations even under in vivo conditions. The radioactive label on the inner ring of thyronine is more stable than alternative labeling sites on the inner and outer rings, which can lead to significantly fewer measurement artifacts, for example in imaging procedures. The radiotracer (VII) is produced in a 6-step synthesis starting from 3,5-diiodo-L-thyronine (I). First, the 4-step organic preparative synthesis of a monostannylated radiolabel precursor (V) takes place.Subsequently, a 2-step one-pot radiosynthesis via radioiodination of V to VI and subsequent non-radioactive diiodination of the outer phenolic ring leads to the target compound L- [. *I]Thyroxine (VII), in which an iodine atom of the inner ring is labeled. This synthesis route can be carried out much more efficiently than previously known syntheses, which show an overall lower yield and a lower specific activity of the product. The labeling on the inner ring of the thyronine also has the advantage that, in combination with a label on the outer ring, all enzyme cascades with different DIOs can be studied. Tracers labeled on the outer ring are rapidly metabolized under in vivo conditions and are chemically significantly more labile. A further advantage of the markers labeled on the inner ring is that, due to their high activity and stability, they can be used with little carrier. The process according to the invention is a process for the production of L-thyroxine that is radioiodine-labeled in the 3-position on the inner ring.L-thyroxine is a non-proteinogenic α-amino acid and has two aromatic rings connected by an oxygen bridge. The inner ring is the ring carrying the side chain with the amino acid function. The outer ring is the aromatic ring carrying the OH group. The labeling position in the 3-position is named according to IUPAC nomenclature based on the target compound. Accordingly, a radioactive iodine atom is covalently bonded to at least this position of the inner ring. The compound can also be present in the form of a salt or generally charged. The radioactive iodine isotopes in general, and in particular the radioactive iodine isotopes used in medicine, are known to those skilled in the art.The process comprises process step a), in which 3,5-diiodo-L-thyronine (compound I) is reacted with one or more protecting group reagents Z, Z', wherein the protecting group reagent(s) react with the amine group and the carboxylic acid group of the thyronine to obtain an amino acid-protected thyronine compound (compound II), wherein the individual protecting groups Z, Z' can be covalently bonded to one another and used as a single compound. I II In the first process step, the amino acid group on the side chain of the inner ring is protected. For this purpose, compound I is reacted with one or more protecting groups simultaneously or consecutively. Two different protecting groups can be used, one for the amine function and one for the carboxylic acid function. However, it is also possible to use only one protecting group, which has two functionalities, one for reaction with the amine function and one for reaction with the carboxylic acid function. After the reaction, both the amine function and the carboxylic acid function are protected. The process comprises process step b), in which the two iodine atoms in the 3,5-position of the inner thyronine ring of compound II are exchanged by stannylation with an organotin compound.A di-3,5-stannyl compound (compound III) is obtained, wherein R3, R3' are independently selected from the group of C1-C4 alkyl or mixtures thereof: In the second process step, the two iodine groups of the inner ring are replaced by organotin compounds in the form of stannyl groups. The stannyl groups each carry 3 alkyl chains, where the alkyl chains can have the same or different numbers of carbon atoms. The alkyl chains can preferably have the same number of carbon atoms, where the alkyl chains can range from methyl, ethyl, propyl to butyl. As a result of the reaction, the inner ring carries a stannyl group in each of the 3 and 5 positions. The process comprises process step c), in which the amino acid-protected compound III is deprotected to obtain the free amino acid compound (compound IV). After stannylation of the inner ring, the protecting group functions on the amine group and the carboxylic acid group can be removed again. The reactions required for this depend on the selected protecting groups and are known to the person skilled in the art. Depending on the selected protecting groups, this can be carried out in one or two steps, for example, whereby the intermediate can be isolated in a two-step process, but this does not have to be the case. The only important thing is that the stannyl groups are not removed or converted by removing the protecting group. The process comprises process step d), in which the 5-monoiodo compound V is obtained by selective iodination of compound IV in the 5-position of the inner ring with elimination of a stannyl group: IV V In this process step, one of the stannyl groups is replaced by reaction with an iodine compound, so that an iodine group takes up this position instead of the stannyl group. The reaction of just one stannyl group can, for example, take place in an alcoholic solution by adding iodine which is also dissolved in an alcoholic solvent. The reaction of just one organotin group can, for example, be controlled stoichiometrically. The process comprises process step e), with replacement of the further stannyl group with radioiodine to obtain a thyroxine compound (compound VI) which is radioiodine-labeled in the 3-position on the inner ring: V VI In this step, the remaining stannyl group on the inner ring is replaced by a radioactive iodine atom. This can, for example, be carried out by reaction with an iodine salt from the group of alkali or alkaline earth elements in aqueous solution.The reaction can preferably be carried out in the presence of an acid at a pH of less than or equal to 4.0. The process comprises process step f), in which the outer ring of compound VI is iodinated to obtain a compound VII iodinated in the 3'- and 5'-positions. . VI VII As a final synthesis step, the outer ring is cleaved to obtain an (S)-2-amino-3-[4-(4-hydroxy-3',5'-diiodophenoxy)-3,5-[3- *[I]diiodophenyl]propanoic acid is doubly iodinated. This step can be carried out, for example, in aqueous solution using an alkali or alkaline earth iodide. The reaction can be initiated, for example, using chloramine-T. A phosphate buffer, for example, can be used to control the pH of this step. Suitable pH ranges for the selective diiodination of the outer ring can be between pH 5.5 and pH 9.5. In a preferred embodiment of the process, 9-borabicyclo[3.3.1]nonane can be used as a protecting group reagent in process step a). For the simple, rapid, and efficient conversion of the two amino acid functions, the use of only a single protecting group reagent has proven particularly suitable. This reagent reacts with both the amine and the carboxylic acid group to form the complex compound 4'-(4-(4-hydroxyphenoxy)-3,5-diiodobenzyl)-9 ^ 4-boraspiro[bicyclo[3.3.1]- nonan-9,2'-[1,3,2]oxazaborolidin]-5'-one according to the following structural formula: The reaction can be carried out with high yields in an organic, preferably alcoholic solvent under a protective gas. In a further preferred embodiment of the process, the stannylation in process step b) can be carried out with organotin compounds in a pressure range of greater than or equal to 100 MPa and less than or equal to 800 MPa. To achieve the fastest and most complete stannylation of the amino acid-protected thyroxine, it has proven very advantageous to carry out the reaction under elevated pressure. Complete reactions are achieved within short reaction times. The pressure range in the reaction can preferably be greater than or equal to 110 MPa and less than or equal to 700 MPa, furthermore preferably greater than or equal to 110 MPa and less than or equal to 600 MPa. The reaction can preferably be carried out under a protective gas in an organic solvent, for example dioxane.Within a further preferred aspect of the process, the radioactive iodination of the inner thyronine ring in process step e) can be carried out at a pH of greater than or equal to 1 and less than or equal to 2. The radioactive iodination can, for example, be carried out in aqueous solution under acidic conditions. This step can preferably be carried out in hydrochloric acid solution in the pH range specified above. Alkali or alkaline earth iodides, for example, can be used as the radioactive iodine source. Under these conditions, very rapid and complete reactions with a high specific activity of the products are achieved. The chemical purity can thus be greater than or equal to 85%, preferably greater than or equal to 90%, and further preferably greater than or equal to 95%.Within a further preferred aspect of the process, the non-radioactive iodination of the outer thyronine ring in process step f) can take place at a pH greater than or equal to pH 8.0 and less than or equal to pH 12.0. The final step of the non-radioactive iodination of the outer ring can preferably take place in the pH range specified above. In particular, this pH range can lead to rapid and selective iodination in the 3' and 5' positions of the outer ring. The reaction can be carried out, for example, in a buffered ammonium hydroxide solution using an alkali or alkaline earth iodide. The reaction can be initiated, for example, by the addition of chloramine-T. The pH can preferably be, for example, greater than or equal to pH 8.5 and less than or equal to pH 11.0, further preferably greater than or equal to pH 9.5 and less than or equal to pH 10.5.Within these ranges, radioactive markers with very high specific activity and very high chemical purity can be obtained. Furthermore, the invention relates to an intermediate in the production of radioactive iodine compounds of thyronine, wherein the intermediate is selected from the group consisting of compounds VIII or their amino acid-protected derivatives, wherein the X is selected from the group consisting of I,. *I or SnR3 or combinations thereof, where X and X' are not simultaneously I: . VIII These compounds are extremely well suited to being labeled with radioiodine atoms at the 3-position in a simple synthetic step. The reactions can be controlled to a high degree and show very high selectivity for the desired target compounds with high yields within short reaction times. The X and X' groups can independently of one another be I, stannyl or radioiodine groups, whereby the intermediates according to the invention do not carry two iodine atoms on the inner ring. Possible examples are X = I and X' = SnR3 or X = *I and X' = SnR3 or X = SnR3 and X' = SnR3. Furthermore, the invention relates to a radioiodine marker, wherein the radioiodine marker comprises radioactive (S)-2-amino-3-[4-(4-hydroxy-3',5'-diiodophenoxy)-3,5-[3- * I]diiodophenyl]propanoic acid (compound VII) or a salt thereof comprises: . VII This radioiodine marker is characterized by high specific activity and improved stability of the compound in a wide variety of media. Compared to known markers with a radioiodine label on the outer ring, the bond of the radioactive iodine to the inner ring is more stable, resulting in fewer artifacts caused by the radioiodine detaching from the inner ring. This increases the reliability of in vitro and in vivo studies using the markers according to the invention. In a further preferred embodiment of the radioiodine marker, the radioactive iodine compound VII can comprise the iodine isotopes iodine-120, iodine-122, iodine-123, iodine-124, iodine-125, iodine-131 or mixtures of these isotopes. The radioiodine markers according to the invention can be labeled with a variety of different radioactive iodine isotopes.Very stable radioiodine markers are obtained, which can be used flexibly under a wide variety of different environmental conditions. In a further embodiment of the radioiodine marker, the radioiodine marker can have a molar activity of greater than or equal to 3.5 GBq / µmol. Compared to known radioiodine markers, the radioiodine markers according to the invention can have a particularly high specific initial activity. These high activities can, in particular, contribute to the markers according to the invention being able to deliver statistically very significant signals even in very small concentrations, for example, under in vivo conditions and concentrations. This allows for better determination of further or different distributions of the hormone in the human body. The activity is measured using known methods. Depending on the time of the examination and the isotope used, the initial activity after synthesis must be calculated back.Furthermore, the invention provides for the use of a radiomarker according to the invention as a marker in imaging methods in nuclear medicine or as a radiomarker in in vitro applications. Due to the improved chemical and radiochemical stability and the high specific activity of the radiomarkers according to the invention, these are significantly more suitable for examination in physiological and non-physiological media than known radiomarkers labeled on the outer ring. Improved images of the distribution of the markers can be obtained, which are characterized by reduced measurement artifacts, particularly due to the chemical stability in the 3-marking position of the inner ring. Within the scope of a further preferred embodiment of the use, the imaging methods in nuclear medicine can be selected from the group of positron emission tomography (PET) or single photon emission computed tomography (SPECT).Due to the improved chemical and radiochemical stability and the high specific activity of the radiomarkers according to the invention, these are significantly more suitable for imaging diagnostics than known radiomarkers labeled on the outer ring. Even with physiological amounts, very specific in vivo and in vitro experiments can be carried out with improved imaging, which, due to the chemical stability of the radioiodine bond, leads to significantly fewer measurement artifacts. Examples: Synthesis Figure 1 shows the general 6-step synthesis scheme starting from 3,5-diiodo-L-thyronine to obtain the radioiodine marker (S)-2-amino-3-[4-(4-hydroxy-3',5'-diiodophenoxy)-3,5-[3-. *[I]diiodophenyl]propanoic acid. In the first four steps, the intermediates according to the invention are prepared, and the last two steps (box) show the radioiodine labeling of the inner ring and the iodination of the outer ring. In this example, the protection of the amino acid group is carried out in one step using a reagent that simultaneously encompasses the amine and carboxylic acid functions. A trimethylstannyl group is chosen for the stannylation. 1st step: 4'-(4-(4-Hydroxyphenoxy)-3,5-diiodobenzyl)-9 ^4-boraspiro[bicyclo[3.3.1]nonan-9,2'-[1,3,2]oxazaborolidin]-5'-one 8.4 mL of 9-borabicyclo[3.3.1]nonane (9-BBN) dimer in THF (0.5 M, 4.19 mmol) was added to 25 mL of methanol under argon. The mixture was heated at reflux for approximately 30 min until the 9-BBN was completely dissolved. 3,5-Diiodo-L-thyronine (I) (2.0 g, 3.81 mmol) was added, and the resulting suspension was heated at reflux overnight. Methanol was removed under reduced pressure, and the residue was triturated with hot hexane. The crude product was purified by flash column chromatography (ethyl acetate / n-hexane, 50 / 50, v / v) to afford compound II as colorless crystals. Yield: 1.97 g, 3.05 mmol, 80%. 1 H-NMR: (400 MHz, DMSO-d6) δ 9.10 (s, 1H), 7.93 (s, 2H), 6.69 (d, 2H), 6.54–6.47 (d, 2H), 6.49 (dd, 1H), 5.82 (dd, 1H), 3.99–3.89 (m, 1H), 3.14 (dd, 1H), 2.91 (dd, 1H), 1.83–1.33 (m, 12H), 0.50 (s, 1H). 2nd step 4'-(4-(4-Hydroxyphenoxy)-3,5-bis(trimethylstannyl)benzyl)-9^ 4 -boraspiro[bicyclo[3.3.1] nonan-oxazaborolidin]-5'-one (3,5-Bis(trimethylstannyl)-L-thyronine 9-BBN complex (III)) This step is shown using an exemplary reaction with a trimethylstannyl compound. 3,5-Diiodo-L-thyronine-9-BBN complex (II) (1.50 g, 2.33 mmol) and Pd(PPh3)4 (270 mg, 0.23 mmol) were placed in a pressure vessel and purged with argon before the addition of 1,4-dioxane (20 mL) and hexamethyldistannane (1.207 mL, 1.91 g, 5.80 mmol). The pressure vessel was sealed, the suspension was stirred for 1.5 h at 150°C (p=160,000 Pa), and cooled to room temperature overnight. The resulting reaction mixture was filtered through Celite and diluted with ethyl acetate, then washed with 10% aqueous potassium fluoride, water, and brine. The solvents were evaporated, and the crude product was purified by flash column chromatography (ethyl acetate / n-hexane, 50 / 50, v / v) to obtain compound III as colorless crystals. Yield: 0.746 g, 1.035 mmol, 45%. 1H NMR: (400 MHz, DMSO-d6) δ 8.93 (s, 1H), 7.45 (s, 2H), 6.62 (d, 2H), 6.59 (dd, 1H), 6.42 (d, 2H), 5.35 (dd, 1H), 3.97–3.86 (m, 1H), 3.08 (dd, 2H), 1.80–1.23 (m, 12H), 0.47 (s, 1H), 0.03 (s, 18H), -0.38 (s, 1H). 3rd stage (S)-2-amino-3-(4-(4- (3,5-Bis(trimethylstannyl)-L-thyronine (IV)) Bis(trimethylstannyl)-L-thyronine 9-BBN complex (III) (490 mg, 0.68 mmol) was dissolved in 2.35 mL of methanol, diluted with 117.6 mL of chloroform, and stirred at room temperature for 48 h. The solvents were evaporated under reduced pressure, and the residue was purified by column chromatography (dichloromethane / methanol, 80 / 20, v / v) to obtain IV as light yellow crystals. Further purification was carried out by preparative HPLC (Knauer Eurospher II 100-5 C18H, 250 x 20 mm, 55% methanol / 45% aqueous formic acid (0.2%), v / v, 20 mL / min, t r= 6.0 – 7.5 min) followed by lyophilization to obtain compound IV as voluminous, colorless crystals. Yield: 163 mg, 0.272 mmol, 40%. 1 H-NMR: (400 MHz, MeOD) δ 7.48 (s, 2H), 6.68 (d, 2H), 6.52 (d, 2H), 3.80 (s , 1H), 3.35 (s , 1H), 3.03 (s, 1H), 0.09 (s, 18H). MS: m / z: [M + H] + Calculated: 600; observed: 600. 4th step (S)-2-Amino-3-(4-(4-hydroxyphenoxy)-3-iodo-5-(trimethylstannyl)phenyl)propanoic acid (3-iodo-5-(trimethylstannyl)-L-thyronine (V)) A well-stirred solution of 3,5-bis(trimethylstannyl)-L-thyronine (IV) (60 mg, 0.1 mmol) in methanol (5 mL) is treated dropwise at room temperature with 0.1 M methanolic iodine solution (1 mL, 0.1 mmol). The brown solution is stirred for 6 h. Removal of solvent and trimethyltin iodide under vacuum at <50°C yields a residue which is purified by semi-preparative HPLC (Phenomenex Gemini 5µ C18110 Å, 250 x 10, 35% methanol / 55% aqueous formic acid (0.2%), v / v, 4.7 mL / min, tr = 6.5 – 8.0 min) and then lyophilized. Compound V is obtained as voluminous, colorless crystals. Yield: 37 mg, 0.065 mmol, 65%. 1 H NMR: (400 MHz, MeOD) δ 7.85 (d, 1H), 7.47 (d, 1H), 6.69 (d, 2H), 6.53 (d, 2H), 3.89 (dd, 1H), 3.25 (dd, 1H), 3.04 (dd, 1H), 0.13 (s, 9H). MS: m / z: [M + H] + Calculated: 564; observed: 564. 5th Step A synthesis using iodine-131 is described as an example. This synthesis step is general and can be carried out in this way for all iodine isotopes. (S)-2-Amino-3-[4-(4- ([ 131 I]Diiodo-L-thyronine, VI) V VI An aliquot of a radioiodide solution ([ 131]NaI solution with a radioactivity concentration > 0.4 GBq / mL from POLATOM, Poland), which contains the desired radioiodide activity, is placed in a reaction vessel. The activity is measured in a suitable activity meter (100%, starting value). The solution is adjusted to pH 1–2 with hydrochloric acid, typically 0.1 M. The ethanolic precursor solution of V (10 µL, 8 nmol) is then pipetted in. The reaction is started by adding aqueous chloramine-T solution (20 µL, 8 nmol). After a reaction time of 1 min, the resulting [ 131 I]VI was further reacted in situ. The chemical purity of [ 131 I]VI is > 95%, the radiochemical purity is > 99% (HPLC), and the molar activity is 13 GBq / µmol. 6. Step (S)-2-Amino-3-[4-(4-hydroxy-3',5'-diiodophenoxy)-3,5-[3- 131 I]diiodophenyl]propanoic acid (L-[ 131 I]Thyroxine, VII) . VI VII For the implementation of the resulting [ 131 I]VI to [131I]VII with non-radioactive sodium iodide, the reaction solution is adjusted to a pH of 10 by adding 10 mM ammonium hydroxide solution. Subsequently, non-radioactive aqueous sodium iodide solution is added (20 µL, 16.5 nmol sodium iodide). The reaction is started by pipetting in a chloramine-T solution in phosphate buffer (0.1 M, pH 7.5). Care must be taken to adjust the volume of buffer used so that the final pH of the reaction solution is approximately 7.5. After a reaction time of 1 min, the reaction solution is separated by HPLC. If the reaction solution is analyzed or purified in an acidic eluent, the reaction is first quenched with 1 µL of concentrated formic acid.An HPLC system consisting of a Kromasil column 5RP18250X4.6 mm, the eluent consisting of methanol, water, and acetic acid in a ratio of 60:40:0.1 at a flow rate of 1 ml / min, and UV detection at 254 nm is suitable for separating and detecting the relevant compounds. Typical capacity factors (k' values) are 1.1 for VI and 7 for VII. The peak cutoff of the radioiodinated L-[ 131 I]Thyroxine ([ 131 I]VII) is collected and measured in an activity meter. The radiochemical yield is expressed as the ratio of the product activity to the applied activity. This value is multiplied by 100 to obtain the radiochemical yield in percent. If short-lived radioiodine isotopes are used, the product activities must be calculated back to the time of measurement of the initial activity (decay correction). The radiochemical yield of [ 131I]VII is 60 + / - 5% (n=3) using the method described here, the chemical purity is > 95%, the radiochemical purity > 99% (HPLC) and the molar activity is 5 x 10 -4 GBq / µmol. The labeling product [ 131 [I]VII in the eluent listed above has been found to be stable over a period of one week. No more than 1% of the radioactivity, determined using the HPLC conditions mentioned above, is present as product. The product-containing eluate is further processed for further use. It can be evaporated to dryness, formulated in suitable aqueous solutions, and sterile filtered. After appropriate quality control tests, the radioiodinated product can then be administered as a radiopharmaceutical.

Claims

Patent claims 1. A process for the preparation of an L-thyroxine radioiodine-labelled in the 3-position on the inner ring, comprising at least the steps: a. reacting 3,5-diiodo-L-thyronine (compound I) with one or more protecting group reagents Z, Z', wherein the protecting group reagent(s) react with the amine group and the carboxylic acid group of the thyronine to obtain an amino acid-protected thyronine compound (compound II), wherein the individual protecting groups Z, Z' can be covalently bonded to one another and used as a single compound: I II b. Exchange of the two iodine atoms in the 3,5-position of the inner thyronine ring of compound II by stannylation with an organotin compound, to obtain a di-3,5-stannyl compound (compound III), wherein R3, R3' are independently selected from the group of C1-C4 alkyl or mixtures thereof: c. Deprotection of the amino acid protected compound III to obtain the free amino acid compound (compound IV): d. Selective iodination of compound IV in the 5-position of the inner ring with elimination of a stannyl group and obtaining the 5-mono-iodo compound V: IV V e. Exchange of the further stannyl group with radioiodine to obtain a thyroxine compound radioiodine-labelled in the 3-position of the inner ring (compound VI): V VI f. Iodination of the outer ring of compound VI to obtain a compound VII iodinated in the 3'- and 5'-positions: . VI VII 2. The process according to claim 1, wherein in process step a) 9-borabicyclo[3.3.1]nonane is used as a protecting group reagent.

3. The process according to any one of the preceding claims, wherein the stannylation in process step b) is carried out with organotin compounds in a pressure range of greater than or equal to 100 MPa and less than or equal to 800 MPa.

4. The process according to any one of the preceding claims, wherein the radioactive iodination of the inner thyronine ring in process step e) is carried out at a pH of greater than or equal to 1 and less than or equal to 2.

5. A process according to any one of the preceding claims, wherein the non-radioactive iodination of the outer thyronine ring in process step f) takes place at a pH of greater than or equal to pH 8.0 and less than or equal to pH 12.

0.

6. An intermediate in the preparation of radioactive iodine compounds of thyronine, characterized in that the intermediate is selected from the group consisting of compounds VIII or their amino acid-protected derivatives, wherein X is selected from the group consisting of I, * I or SnR3 or combinations thereof, where X and X' are not simultaneously I: . VIII 7. Radioiodine marker, characterized in that the radioiodine marker contains radioactive (S)-2-amino-3-[4-(4-hydroxy-3',5'-diiodophenoxy)-3,5-[3- * I]diiodophenyl]propanoic acid (Compound VII) or a salt thereof comprises: .

8. The radioiodine marker according to claim 7, wherein the radioactive iodine compound VII comprises the iodine isotopes iodine-120, iodine-122, iodine-123, iodine-124, iodine-125, iodine-131, or mixtures of these isotopes.

9. The radioiodine marker according to claim 7 or 8, wherein the radioiodine marker has a molar activity of greater than or equal to 3.5 GBq / µmol.

10. Use of a radiomarker according to any one of claims 7-9 as a marker in nuclear medicine imaging methods or as a radiomarker in in vitro or ex vivo applications.

11. Use according to claim 10, wherein the nuclear medicine imaging methods are selected from the group of positron emission tomography (PET) or single photon emission computed tomography (SPECT).

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