11C-labeled catechol derivative, pet probe of phosphorylated tau aggregation inhibitor using the same, and production method of the same

Abstract

An object of the invention is to provide an .sup.11C-labeled catechol derivative having sufficient radioactivity to obtain an imaging image by a PET apparatus, a PET probe of a phosphorylated tau aggregation inhibitor using the same, and a method for producing them. The .sup.11C-labeled catechol derivative of the present invention is represented by the following general formula (a) (wherein R is a substituent having an isopropylamino group, and the carbon at the 2-position of the isopropylamino group is labeled with .sup.11C). ##STR00001##

Claims

1. A PET probe comprising .sup.11C-labeled catechol derivative represented by the following general formula (a) (wherein R is a substituent having an isopropylamino group, and the carbon at the 2-position of the isopropylamino group is labeled with .sup.11C) ##STR00007##

2. The .sup.11C-labeled catechol derivative according to claim 1, wherein the .sup.11C-labeled catechol derivative is represented by the following structural formula (b) (wherein carbon of * is labeled with 11C) ##STR00008##

3. A PET probe comprising the .sup.11C-labeled catechol derivative according to claim 2.

4. An imaging method of .sup.11C-labeled catechol, comprising administering the PET probe of claim 3 to a living body, and photographing a PET image.

5. A method for producing the .sup.11C-labeled catechol derivative according to either claim 1 or claim 2, comprising performing reductive alkylation reaction of catechol derivative represented by the following general formula (c) (wherein R1 represents a substituent having a primary or secondary amine) and [2-.sup.11C] acetone in the presence of reducing agent ##STR00009##

6. The method for producing the .sup.11C-labeled catechol derivative according to claim 5, wherein the catechol derivative represented by the general formula (c) is norepinephrine.

7. The method for producing the .sup.11C-labeled catechol derivative according to claim 6, characterized by using an acid catalyst having a pKa value of 3.7 to 4.8.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the results of HPLC analysis of DMF and DMSO solution containing commercially available norepinephrine and isoproterenol (non-activated), p-trifluoromethylbenzoic acid (4-TFMBA), and NaBH(OAc).sub.3 by using various columns.

(2) FIG. 2 are (A1) a radio HPLC analysis chart of the labeled compound captured in the second reaction vessel by heating and nitrogen bubbling after preparation of [2-.sup.11C] acetone, and (A2) a radio HPLC analysis chart of the residue of the first reaction vessel when diphenylamine THF solution/hydrogen chloride diethyl ether solvent was used as a quenching agent. Also, FIG. 2 are (B1) a radio HPLC analysis chart of the labeled compound captured in the second reaction vessel by heating and nitrogen bubbling after preparation of [2-.sup.11C] acetone, and (B2) a radio HPLC analysis chart of the residue of the first reaction vessel when a diphenylamine THF solution/phenol THF solution is used as a quenching agent.

(3) FIG. 3 is a chart showing the results of HPLC analysis of the synthesized [.sup.11C] isoproterenol solution (without addition of tartaric acid) immediately after isolation (A) and 60 minutes after isolation (B).

(4) FIG. 4 is a chart showing the results of HPLC analysis of the synthesized [.sup.11C] isoproterenol solution (with tartaric acid addition) immediately after isolation (A) and after 60 minutes from isolation (B).

MODE FOR CARRYING OUT THE INVENTION

(5) <Reductive Alkylation Reaction of Norepinephrine and Acetone>

(6) Prior to the synthesis of [.sup.11C] isoproterenol, unlabeled isoprotenol was synthesized. 4-(trifluoromethyl) benzoic acid (pKa: 3.69, 1.16 mg 6 μmol) and (R, S)-norepinephrine hydrochloride (6.30 mg 30 μmol) were added to a dried 5 mL eggplant flask, sealed and then replaced with argon. After adding NaBH (OAc).sub.3 (32.8 mg 30 μmol), acetone (0.22 μL 6 μmol) and DMSO/DMF (3:2) (0.4 ml) to make a solution, the solution was heated at 100° C. for 10 minutes. The reaction solution was added with 0.6 mL of 1 N hydrochloric acid to stop the reaction, the solution was diluted with 8.1 mL of CH.sub.3CN/ammonium acetate buffer (pH 5.3), added carbazole (82.8 μM DMSO solution, 900 μL, 12.5 μg, 74.5 nmol) as an internal standard substance, and was subjected to (pretreatment) HPLC analysis.

(7) (HPLC Column, Conditions, Etc.)

(8) In ODS column and HILIC column, which are generally used in general, it was difficult to isolate the target compound from the reaction mixture (see the upper part of FIG. 1). In contrast, when a cation exchange resin column (sulfonic acid resin column) was used, (R, S)-isoproterenol could be separated with high purity (see the lower part of FIG. 1)

(9) Analysis Conditions when ODS Column was Used:

(10) Column: CAPCELL PAK C 18, 4.6 (i.d.)×150 mm; eluent: CH.sub.3CN/20 mM NaH.sub.2PO.sub.4=1:99 (v/v); flow rate: 1 mL/min; detection: detector: UV, 254 nm

(11) Analysis Conditions when HILIC is Used:

(12) Column: Inertsil Amide, 4.6 (i.d.)×150 mm; eluent: CH.sub.3CN/20 mM NaH.sub.2PO.sub.4=80:20 (v/v); flow rate: 2 mL/min; detector: UV, 254 nm

(13) Conditions when cation exchange resin column is used: see paragraph 0021

(14) <Synthesis of [2-.sup.11C] Acetone>

(15) The [.sup.11C] CO.sub.2 produced by the .sup.14N (p, α) .sup.11C reaction of the cyclotron was mixed with introduced into a first reactor containing a mixed solution of methyllithium (0.7 mL, about 1 mol/L diethylether solution, 700 μmol) and cyclopentylmethylether (hereinafter referred to as CPME, 0.5 mL) cooled to keep it below −10° C. After heating for 2 minutes at 85° C., it was cooled to −10° C., then diphenylamine (CPME solution, 0.7 mL, 0.95 mmol) was added. It was kept at that temperature for about 2 minutes and heated at 85° C. for about 1 minute to neutralize excess methyllithium. Subsequently, phenol (0.7 mL CPME solution 1 mmol) was added. By bubbling with nitrogen gas while heating the first reaction vessel at 100° C., [2-.sup.11C] acetone was captured (1.62 GBq) in the second reaction solution containing a mixed solvent (0.4 mL) of DMSO/DMF (3:2) cooled to below −10° C. The time required from the introduction of [.sup.11C] CO.sub.2 into the first reaction vessel to the capture of [2-.sup.11C] acetone in the second reaction solution was 14 minutes. The decay corrected yield of [2-.sup.11C] acetone obtained calculated based on [.sup.11C] CO.sub.2 was 54%.

(16) Even when DMF was used as a trapping solvent for [2-.sup.11C] acetone, the same operation was carried out. [2-.sup.11C] acetone was prepared in the same manner using tetrahydrofuran solvent of methyllithium, and [2-.sup.11C] acetone was captured (4.32 GBq) in a second reaction vessel containing DMF (Required time 17 minutes, decay corrected yield 63%).

(17) [2-.sup.11C] acetone was confirmed by co-injection with unlabeled acetone on HPLC (mobile phase, CH.sub.3CN and 20 mM sodium dihydrogen phosphate (pH 4.8)=1:99, CAPCELL PAK C 18, 4.6 (id)×150 mm; flow rate, 1 mL/min; UV detection, 254 nm; retention time, 4.5 min).

(18) ##STR00005##

(19) The production efficiency of [2-.sup.11C] acetone was investigated when using a combination of a THF solution of diphenylamine and a diethyl ether solution of hydrogen chloride as a quenching agent after preparation of acetone. After the reaction in the first reaction solution, the labeled compound captured in the second reaction solution containing a mixed solution of DMSO and DMF cooled to 0° C. or less was analyzed, and it was found that acetone and [2-.sup.11C] tert-butyl alcohol (See A1 in FIG. 2). In addition, a large amount of diethylether solvent, which interferes with the reductive alkylation reaction, was transferred to the second reaction vessel together with [2-.sup.11C] acetone. Neutralization of excess methyllithium with diphenylamine is insufficient, and [2-.sup.11C] tert-butyl alcohol is by-produced from [2-11C] acetone produced in the process of neutralization with strong acid. From the results of actual HPLC analysis, no iminium ion or aldol condensate between [2-.sup.11C] acetone and diphenylamine has been confirmed (see A2 in FIG. 2). In this way, only the target [2-.sup.11C] acetone could be obtained (see B2 in FIG. 2), and the transfer of the solvent to the second reaction vessel was suppressed.

Reductive Alkylation Reaction of Norepinephrine and [2-.SUP.11.C] Acetone

Example 1

(20) A reductive alkylation reaction of [2-.sup.11C] acetone synthesized as described above with norepinephrine was carried out to synthesize [.sup.11C] isoproterenol.

(21) ##STR00006##

(22) The mixture with sodium triacetoxyborohydride (NaBH (OAc)) (32.6 mg, 149 μmol), 4-(trifluoromethyl) benzoic acid (pKa: 3.69, 1.20 mg, 6 μmol) mg 30 μmol), DL-norepinephrine hydrochloride (6.36 (6.36 mmol)), and 0.4 ml of DMSO/DMF (3:2) was cooled and kept below −10° C. until the introduction of [2-.sup.11C] acetone was complete. [2-.sup.11C] acetone was gasified by heating at 100° C. and transferred to a reaction vessel containing the above mixture by a nitrogen gas stream. After heating at 100° C. for 10 minutes in a closed system, it was diluted with ammonium acetate buffer solution (pH 5.3, 1.6 mL) and purified by preparative HPLC (mobile phase, CH.sub.3CN/acetic acid-ammonium acetate buffer (pH 5.2) 10:90; column, CAPCELL PAK SCX UG 80, 20 (id)×250 mm; flow rate, 10 mL/min; UV detection, 278 nm; retention time, 25 min).

(23) Radiochemical purity and chemical purity of [2-.sup.11C] isoproterenol in the solution after HPLC fractionation were analyzed by HPLC (CH.sub.3CN/acetic acid-ammonium acetate (pH 5.3), 10:90; column, CAPCELL PAK SCX UG 80, 4.6 (id)×150 mm; flow rate, 1 mL/min; UV detection, 278 nm; retention time, 6.5 min). [.sup.11C] isoproterenol was confirmed by co-injection of unlabeled isoproterenol in HPLC. In the absence of addition of tartaric acid, the radiochemical purity immediately after isolation was 96%, whereas the radiochemical purity after 60 minutes dropped to 84% (see FIG. 3). In contrast, when tartaric acid was added, no drop in radiochemical purity was observed even after 60 minutes (see FIG. 4). This is presumed to be due to inhibition of deprotonation of two adjacent phenolic hydroxyl groups present in the catechol nucleus under acidic conditions and suppression of subsequent oxidative decomposition by oxygen molecules or superoxide. Also, the chemical purity measured at the above wavelength was >93%

EXAMPLES 2 TO 10

(24) In Examples 2 to 10, [.sup.11C] isoproterenol was synthesized by performing a reductive alkylation reaction of norepinephrine with [2-.sup.11C]acetone under various conditions shown in Table 1.

(25) TABLE-US-00001 TABLE 1 Reducing agent Acid (equivalent (equivalent for for Yield.sup.b Entry.sup.a norepinephrine) norepinephrine) Solvent (%) Example 2 NaBH.sub.3CN — ethylene  68.sup.c (1.3) glycol Example 3 NaBH.sub.3CN CH.sub.3COOH (1) ethylene 75 (1.4) glycol Example 4 NaBH.sub.3CN CH.sub.3COOH (2) ethylene 79 (1.1) glycol Example 5 NaBH.sub.3CN Benzoic acid (1) ethylene 72 (1.2) glycol Example 6 NaBH(OAc).sub.3 CH.sub.3COOH (1) DMSO/DMF 65 (0.12) (60:40 v/v) Example 7 NaBH(OAc).sub.3 CH.sub.3COOH (1) DMSO/DMF 75 (1.3) (60:40 v/v) Example 8 NaBH(OAc).sub.3 Benzoic acid (1) DMSO/DMF 86 (1.1) (60:40 v/v) Example 9 NaBH(OAc).sub.3 Benzoic acid (2) DMSO/DMF 87 (1.1) (60:40 v/v) Example 10 NaBH(OAc).sub.3 p-TFMBA (1) DMSO/DMF 79 (1.0) (60:40 v/v) .sup.aReaction of [2-.sup.11C]acetone and (R,S)-norepinephrine (30 μmol) was carried out in the presence of NaBH.sub.3CN or NaBH(OAc).sub.3 in solvent (400 μL) under the heating by setting at 100° C. for 10 min. .sup.bHPLC analytical yield of [.sup.11C]isoproterenol was calculated by peak area ratio of the [.sup.11C]compounds distributions. The identification of [.sup.11C]isoproterenol was conducted by co-injecting with the corresponding non-radioactive isoproterenol. .sup.cWhen (R,S)-norepinephrine hydrochloride salt was used as a substrate without neutralization, the yield was decreased to 57%.

(26) That is, in Example 2, [.sup.11C] isoproterenol was synthesized by reacting sodium cyanoborohydride (NaBH.sub.3CN) and DL-norepinephrine hydrochloride with ethylene glycol as a solvent without adding acid. In addition, in Example 3 and Example 4, [.sup.11C] isoproterenol was synthesized in the same manner except that acetic acid was added as an acid. Furthermore, in Example 5, benzoic acid was used as an acid, and [.sup.11C] isoproterenol was similarly synthesized. Further, in Examples 6 and 7, [.sup.11C] isoproterenol was synthesized by reacting sodium triacetoxyborohydride (NaBH (OAc)) with DL-norepinephrine hydrochloride by using DMSO/DMF (3:2) as a solvent and acetic acid as an acid. Further, in Examples 8 and 9, [.sup.11C] isoproterenol was synthesized by reacting sodium triacetoxyborohydride (NaBH (OAc)) and DL-norepinephrine hydrochloride by using DMSO/DMF (3:2) as a solvent and benzoic acid as an acid. Further, in Example 10, [C]isoproterenol was synthesized by reacting sodium triacetoxyborohydride (NaBH (OAc)) and DL-norepinephrine hydrochloride by using DMSO/DMF (3:2) as a solvent and 4-(Trifluoromethyl) benzoic acid as an acid.

(27) Details of the synthesis procedure and analysis method in Example 3 will be described below as an example. The other examples can be carried out in accordance with the procedure of the Example 3.

(28) DL-norepinephrine hydrochloride (6.36 mg, 30 μmol) was weighed in a dry flask purged with argon and a 25 wt. % methanol solution of tetramethylammonium hydroxide (12.6 μL, 30 μmol) was added under ice cooling, and the solution was concentrated under reduced pressure and dried. A mixed solution was prepared by adding sodium cyanoborohydride (2.1 mg, 33 μmol), acetic acid (3.43 μL, 60 μmol), and ethylene glycol (0.4 mL), and the mixture was cooled to −10° C. until introduction of [2-.sup.11C] acetone was completed. [2-.sup.11C] acetone was gasified by heating at 100° C. and transferred to a reactor containing the above mixture under a nitrogen gas flow. After heating at 100° C. for 10 minutes in a closed system, hydrochloric acid (1 mol/L, 0.1 mL) was added and diluted with ammonium acetate buffer (pH 5.3, 1.5 mL) and analyzed by HPLC (mobile phase, CH.sub.3CN/Analysis by acetic acid-ammonium acetate buffer, (pH 5.2) 10:90; column, CAPCELL PAK SCX UG 80, 4.6 (id)×250 mm; flow rate 1 mL/min; UV detection, 254 nm; retention time, 13 min).

(29) <Result>

(30) As shown in Table 1, in Examples 2 to 10, the objective [.sup.11C]isoproterenol was obtained in a high yield (by radio HPLC analysis) of 65% or more. Also, in the case of using sodium cyanoborohydride (NaBH.sub.3CN) as the reducing agent, Example 3 and Example 4 using acetic acid (pKa=4.76) as the acid was higher yield than Example 5 using benzoic acid (pKa=4.21) as the acid. Further, in the case of using sodium triacetoxyborohydride (NaBH (OAc).sub.3 as a reducing agent, Examples 8 and 9 using benzoic acid (pKa=4.21) as the acid was higher yield than Example 6, 7 using acetic acid (pKa=4.76) and Example 10 using 4-(Trifluoromethyl) benzoic acid.

(31) In addition to the scope of claims, the above embodiments have the following technical features (1) to (4).

(32) (1) A method for producing [2-.sup.11C] acetone by reacting [.sup.11C] CO.sub.2 with methyllithium, wherein an acid (phenol) having a pKa value of 9 or more and 12 or less is used as a reaction terminator.

(33) (2) The method for producing [2-.sup.11C] acetone according to (1), wherein the reaction terminator is phenol or a phenol derivative.

(34) (3) The method for producing [2-.sup.11C] acetone according to (1), wherein an ether compound having a boiling point of 80° C. or higher is used as a reaction solvent.

(35) (4) The method for producing a compound having a partial structure of .sup.11C-labeled isopropylamine including a reductive alkylation reaction of a primary amine compound or a secondary amine compound and [2-.sup.11C]acetone in the presence of a reducing agent.

(36) In the method for producing [2-.sup.11C] acetone of the above (3), since an ether compound having a boiling point of 80° C. or higher is used as a reaction solvent, hygroscopicity is lowered and it is possible to reduce the contamination of moisture which inhibits the reaction. In addition, when it is used for a reductive alkylation reaction, contamination of an ether solvent inhibiting a reductive alkylation reaction can be suppressed to a low level. More preferred is an ether solvent (for example, cyclopentyl methyl ether or the like) at 100° C. or higher.

(37) PET probes of various physiologically active compounds having a partial structure of isopropylamine can be synthesized by using the production method of the above (4). For example, it is bisoprolol (ß receptor blocker) which is a secondary amine compound, Disopyramide (sodium channel inhibitor) which is a tertiary amine compound, Roscovitine (cyclin dependent kinase inhibitor), LY-53,857 (5-HT2 antagonist) and the like.

(38) The present invention is not limited to the embodiments and examples of the invention. Various modifications are also included in the present invention as long as those skilled in the art can easily devise without departing from the scope of the claims.

INDUSTRIAL APPLICABILITY

(39) By utilizing the present invention, development of [2-.sup.11C] isoproterenol into animal and human clinical research becomes possible, and it is expected to obtain useful pharmacokinetic images (especially brain images). In addition, by conducting the PET microdose test using [11C]isoproterenol, relationships between plasma concentration of isoproterenol and brain concentration are clarified, and the lowest effective concentration in the brain that can be achieved without side effects in humans is determined. It also serves as a basis for dose setting in Phase 2 trials as a tau aggregation inhibitor. Furthermore, isoproterenol itself becomes a promising candidate compound for the treatment of dementia drugs, and the use of isoproterenol as a biomarker can also be useful for narrowing down the optimal compounds by early diagnosis of Alzheimer's disease and evaluation of pharmacological efficacy of various drug candidate compounds.