RU2776178C1 - Method for producing 18f-bpa and an intermediate compound - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for producing ¹⁸F-BPA (2-fluoro-4-boron-L-phenylalanine) with the following structure:

The method includes the interaction of an intermediate compound I-2 with an ¹⁸F ion, resulting in an ¹⁸F-substituted compound

I-2

removal of protection from the ¹⁸F-substituted compound, resulting in ¹⁸F-BPA

wherein R₁₀ and R₂₀ constitute OH or, taken together with the boron atom whereto they are attached, constitute a substituent hydrolysable to a boric acid group, R₃ or R₄ independently constitute hydrogen, an amino-protective group, or -NR₃R₄ constitutes

and R₅ constitutes a carboxyl-protective group. Also proposed are an intermediate compound I and an application thereof for producing ¹⁸F-BPA.

EFFECT: proposed method is a simple and effective way for producing ¹⁸F-BPA, with mild reaction conditions and high output, and it satisfies the clinical needs.

12 cl, 3 dwg, 7 ex

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the field of pharmaceutical and chemical synthesis, and more specifically to a method for producing ¹⁸ F-BPA (2-fluoro-4-boron-L-phenylalanine) and an intermediate.

PRIOR ART

[0002] Malignant tumors are major diseases that seriously threaten human health and life. Currently, the treatment of malignant tumors is carried out mainly with the help of radiation therapy or chemotherapy. Boron neutron capture therapy (BNCT) uses nuclear reactions that occur in tumor cells to kill cancer cells. By exploiting the high capture cross section characteristics of boron( ¹⁰ V)-containing thermal neutron drugs, two heavy charged particles ⁴ He and ⁷ Li are formed in the ¹⁰ B(n, α) ⁷ Li neutron capture reactions and nuclear fission. The two charged particles have an average energy of approximately 2.33 MeV, as well as a high linear energy loss (LET) and a short range. The LET and the range of α-particles are 150 keV/µm and 8 µm, respectively, while the LET and the range of heavy charged particles ⁷ Li are 175 keV/µm and 5 µm, respectively. The total range of these two particles is approximately equal to the size of a cell, and thus radiation damage to organisms can be limited to the cellular level. When boron-containing drugs are selectively aggregated in tumor cells, tumor cells can be killed locally by selecting an appropriate neutron source without causing too much damage to normal tissues. Since the effect of BNCT depends on the concentration of boron-containing drugs and the number of thermal neutrons at tumor cell sites, BNCT is also called binary cancer therapy. Obviously, in addition to creating a neutron source, the development of boron-containing drugs plays an important role in BNCT research. 4-( ¹⁰ B)boron-L-phenylalanine (L- ¹⁰ BPA) is a boron-containing drug for the treatment of cancer with BNCT, showing good therapeutic effects in the treatment of various malignancies such as glioblastoma multiforme and melanoma. BNCT treatment planning is based on the results of using 2-fluoro-4-boron-L-phenylalanine ( ¹⁸ F-BPA) for targeted delivery to the tumor site using BPA labeled with ¹⁸ F positron radionuclide in combination with positron emission tomography (PET) for the diagnosis of brain tumors and other types of solid tumors.

[0003] CN105916836A discloses a process for the preparation of 2-fluoro-4-boron-L-phenylalanine and the precursor 2-fluoro-4-boron-L-phenylalanine. Said patent application discloses the preparation of ¹⁸ F-BPA by replacing the leaving group with the ¹⁸ F ion on the benzene ring to give the ¹⁸ F-labeled halogen-substituted phenylalanine compound, followed by a coupling reaction. In ^CN105348309B , after the benzene ring is labeled ^18F , 18F-BPA is produced by reacting the aldehyde group with phenylazolinone in the benzene ring. In CN102887913B, ¹⁸ F-BPA is prepared by replacing the nitro group with the ¹⁸ F ion on the benzene ring to give the ¹⁸ F-labeled iodosubstituted phenylalanine compound, followed by a coupling reaction. In the above methods, all boric acid ester substitution reactions are carried out after ¹⁸ F labeling involving many reaction steps and long preparation times.

[0004] Since the half-life ^{of 18} F is approximately 110 minutes, after labeling with g, the question of how to simplify the preparation steps and reduce the preparation time is an important and difficult study associated with radiochemical yield and limitations of the synthesis. Thus, for the application of ¹⁸ F-BPA, it is extremely important to develop a simple and efficient production method having mild reaction conditions and high yield, as well as meeting clinical needs.

BRIEF DESCRIPTION OF THE INVENTION

[0005] The present invention relates to a process and an intermediate for the preparation of 2-fluoro-4-boron-L-phenylalanine ( ¹⁸ F-BPA, F-BPA). The method for obtaining ¹⁸ F-BPA simplifies the steps for obtaining after labeling ¹⁸ F. The method is simple and efficient, has a high yield and high purity of the product, and also improves the radiochemical yield of the synthesis.

[0006] According to a first aspect, the present invention relates to a method for producing ¹⁸ F-BPA having the structure

comprising the use of an intermediate compound I having the structure

where R ₁ or R ₂ represents halogens, boric acid groups or substituents hydrolysable to boric acid groups, R ₃ or R ₄ independently represents hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ represents hydrogen or a carboxyl protecting group.

[0007] In another preferred embodiment, Intermediate I comprises Intermediate I-1 and Intermediate I-2, wherein Intermediate 1-1 has the structure

and intermediate I-2 has the structure

where X ₁ and X ₂ are both halogens, and preferably X ₁ and X ₂ are Cl, Br or I, where R ₁₀ and R ₂₀ are OH or, taken together with the boron atom to which they are attached, are a substituent hydrolysable to a boric acid group, R ₃ or R ₄ is independently hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ is hydrogen or a carboxyl protecting group.

[0008] In another preferred embodiment, R ₃ or R ₄ as an amino protecting group includes an alkoxycarbonyl protecting group, an acyl protecting group, and an alkyl protecting group. Preferably, R ₃ or R ₄ as an amino protecting group further comprises substituents selected from the group consisting of benzyloxycarbonyl, t-butyloxycarbonyl, fluorenylmethoxycarbonyl, allyloxycarbonyl, trimethylsilylethoxycarbonyl, methoxy (or ethoxy) carbonyl, phthalolyl, tosyl, trifluoroacetyl, o- (or p-) nitrobenzenesulfonyl, pivaloyl, benzoyl, trityl, 2,4-dimethoxybenzyl, p-methoxybenzyl and benzyl.

[0009] In another preferred embodiment, R ₃ or R ₄ as an amino protecting group, taken together with N, form a C=N bond, preferably -NR ₃ R ₄ is

[0010] In another preferred embodiment, the substituent hydrolysable to a boric acid group is a boric acid ester group. More preferably -BR ₁₀ R ₂₀ is a boric acid pinacol ester group, B is preferably ¹⁰ V.

[0011] In another preferred embodiment, the carboxyl protecting group comprises a substituted or unsubstituted C1-20 alkyl group. The substituent includes phenyl, halogen, nitro, hydroxy and methoxy. Preferably the carboxyl protecting group is C1-10 alkyl, phenyl and benzyl. Preferably the carboxyl protecting group comprises a substituted or unsubstituted C1-C20 alkyl group and the substituent includes phenyl, halogen, nitro, hydroxy and methoxy, preferably C1-C10 alkyl, phenyl and benzyl. Preferably, the carboxyl protecting group further comprises methyl, ethyl, isopropyl, t-butyl, benzhydryl, benzyl, p-nitrobenzyl, p-methoxybenzyl, 4-pyridylbenzyl, trichloroethyl, methylthioethyl, p-toluenesulfonylethyl, p-nitrophenylthioethyl, phenyl, and benzyl.

[0012] In another preferred embodiment, Intermediate I is selected from the following compounds:

[0013] In another preferred embodiment, the method comprises reacting intermediate I-2 with an ¹⁸ F ion to produce a ¹⁸ F-substituted compound

where R ₁₀ and R ₂₀ represent OH or, taken together with the boron atom to which they are attached, represent a substituent hydrolysable to a boric acid group, R ₃ or R ₄ independently represents hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ is hydrogen or a carboxyl protecting group.

[0014] In another preferred embodiment, the method comprises deprotecting the ¹⁸ F-substituted compound to provide ¹⁸ F-BPA

[0015] In another preferred embodiment, reacting Intermediate I-2 with the ¹⁸ F ion further comprises the use of a copper catalyst, preferably comprising Cu(OTf) ₂ Py ₄ or Cu(OTf) ₂ .

[0016] In another preferred embodiment, the interaction of intermediate I-2 with ion ¹⁸ F is carried out at a temperature of from 20 to 150°C, preferably from 100 to 130°C.

[0017] In another preferred embodiment, reaction of intermediate I-2 with ¹⁸ F ion is carried out in a solvent including water, methanol, DMF, DMA, DMSO, acetonitrile, n-butanol, ethanol, dichloromethane, or any mixture thereof.

[0018] In another preferred embodiment, intermediate I-1 is reacted with boric acid or a boric acid ester to form intermediate I-2

where X ₁ and X ₂ are both halogens, and preferably X ₁ and X ₂ are Cl, Br or I, R ₁₀ and R ₂₀ are OH or, taken together with the boron atom to which they are attached, represent a substituent hydrolysable to a boric acid group, R ₃ or R ₄ independently represents hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ represents hydrogen or a carboxyl protecting group.

[0019] In another preferred embodiment, the reaction of intermediate 1-1 with boric acid or a boric acid ester is carried out under a nitrogen atmosphere.

[0020] In another preferred embodiment, the reaction of intermediate I-1 with boric acid or a boric acid ester is carried out at a temperature of from 20 to 100°C, preferably from 50 to 100°C.

[0021] The palladium catalyst is not particularly limited. Preferably the palladium catalyst is selected from the group consisting of tris(dibenzylideneacetone)dipalladium (Pd ₂ (dba) ₃ ), tetrakis(triphenylphosphine)palladium (Pd(PPh ₃ ) ₄ ), palladium acetate, palladium chloride, dichlorobis(triphenylphosphine), palladium trifluoroacetate , triphenylphosphine palladium, [1,1'-bis(diphenylphosphino)ferrocene]palladium dichloride, bis(tri-o-tolylphosphine)palladium dichloride, [1,2-bis(diphenylphosphino)ethane]palladium dichloride, or combinations thereof.

[0022] The boric acid ester is not particularly limited. Preferably the boric acid ester is selected from the group consisting of bis(pinacolato)diborone, bis(catecholato)diborone, bis(3,3-dimethyl-2,4-pentanediol)borate, triethanolamineborate, trimethylborate, triisopropylborate, triethylborate, tributylborate, bis (neopentylglycolate)diborone; or combinations thereof.

[0023] In another preferred embodiment, the method further comprises chirally separating intermediate I-1 to give compound I-1a in the L configuration and compound I-1b in the D configuration, and then reacting compound I-1a and compound I-1b with boric acid or boric acid ester, respectively

[0024] In another preferred embodiment, the method further comprises i) reacting intermediate II with intermediate III to obtain intermediate I-1

where each X ₁ , X ₂ and X ₃ independently represents halogens, preferably X ₁ , X ₂ and X ₃ represent Cl, Br or I, R ₃ or R ₄ independently represents hydrogen or an amino protecting group, or an imino group combined with an amino group to protect the amino group, and R ₅ is hydrogen or a carboxyl protecting group.

и промежуточное соединение I-1 представляет собой

где X₁ и Х₂ представляют собой галогены, предпочтительно X₁ и Х₂ представляют собой Cl, Br или I, и R₅ представляет собой водород или карбоксилзащитную группу.[0025] In another preferred embodiment, intermediate III is

and intermediate I-1 is

where X ₁ and X ₂ are halogens, preferably X ₁ and X ₂ are Cl, Br or I, and R ₅ is hydrogen or a carboxyl protecting group.

а затем взаимодействие с борной кислотой или сложным эфиром борной кислоты, где взаимодействие предпочтительно проводят при комнатной температуре, и R₅ представляет собой предпочтительно С1-10 алкильную группу.[0026] In another preferred embodiment, the method further comprises deprotecting the amino group in Intermediate I-1 by hydrolysis under acidic conditions, reacting with Boc ₂ O under basic conditions, protecting the amino group in Intermediate I-1 with Boc to obtain the compound

and then reaction with boric acid or ester of boric acid, where the reaction is preferably carried out at room temperature, and R ₅ is preferably a C 1-10 alkyl group.

[0027] According to the second aspect, the present invention relates to an intermediate compound I having the structure

where R ₁ or R ₂ represents halogens, boric acid groups or substituents hydrolysable to boric acid groups, R ₃ or R ₄ independently represents hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ represents hydrogen or a carboxyl protecting group.

[0028] In another preferred embodiment, Intermediate I comprises Intermediate I-1 and Intermediate I-2, wherein Intermediate I-1 has the structure

and intermediate I-2 has the structure

where X ₁ and X ₂ are both halogens, B is boron, preferably ¹⁰ B, R ₁₀ and R ₂₀ are OH or, taken together with the boron atom to which they are attached, are a substituent hydrolysable to a boric acid group , R ₃ or R ₄ independently represents hydrogen, an amino protecting group or an imino group combined with an amino group to protect the amino group, and R ₅ represents hydrogen or a carboxyl protecting group.

[0029] In another preferred embodiment, the substituent hydrolysable to a boric acid group is a boric acid ester group, preferably a boric acid pinacol ester group, R ₃ or R ₄ includes an alkoxycarbonyl protecting group, an acyl protecting group and an alkyl protecting group, and R ₅ includes substituted or unsubstituted C1-20 alkyl, preferably t-butyl.

[0030] In another preferred embodiment, Intermediate I is selected from the following compounds:

[0031] According to a third aspect, the present invention relates to the use of intermediate I, corresponding to the second aspect, to obtain ¹⁸ F-BPA, where ¹⁸ F-BPA has the structure

[0032] It should be understood that, within the scope of the present invention, the aforementioned technical features of the present invention and the technical features specifically described below (such as embodiments) may be combined with each other to form a new or preferred technical solution. For the sake of brevity, the details will not be described again.

BRIEF DESCRIPTION OF GRAPHICS

[0033] Figure 1 shows the ¹ H-NMR spectrum of N,N-bis(tert-butoxycarbonyl)-2,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2- yl)-phenylalanine tert-butyl ester prepared in Example 6,

[0034] in FIG. 2 is a ¹⁸ F-BPA radio-HPLC chromatogram of the present invention, and

[0035] in FIG. 3 is a radio-HPLC chromatogram of ¹⁸ F-BPA of the present invention mixed with standard ¹⁹ F-BPA.

DETAILED DESCRIPTION OF THE INVENTION

[0036] After extensive and in-depth research, the inventors have obtained an intermediate compound for obtaining ¹⁸ F-BPA. The intermediate includes the bis(pinacolato)diborone-substituted phenylalanine intermediate. ¹⁸ F-BPA can be obtained by replacing the pinacol boric acid ester group with ¹⁸ F at the ortho position of the alanine group. This method shortens the steps for obtaining ¹⁸ F-BPA after ¹⁸ F labeling, which is simple and efficient, has a high yield and high purity of the product, and improves the radiochemical yield of the synthesis. The present invention is based on this study.

Definitions

[0037] Unless otherwise indicated, all scientific and technological terms in this application have the meanings generally accepted by those skilled in the art to which the claims belong. Unless otherwise indicated, all patents, patent applications and publications mentioned in this specification are hereby incorporated by reference in their entirety.

[0038] It should be understood that the above summary of the invention and the following detailed description of the invention are illustrative and are used for explanation only and are not intended to limit the scope of the present invention. In this application, unless otherwise indicated, the plural forms of words include their corresponding singular forms. It should be noted that in this description, unless expressly stated otherwise, the singular forms, in the context of the present description and the claims, include their respective plural forms. It should also be noted that, unless otherwise indicated, the terms "or", "alternatively" mean "and/or". In addition, the terms "comprise", "include" and other grammatical forms such as "comprising", "including" and "having", are not limiting.

[0039] When a substituent is described by a conventional left-to-right chemical formula, it also includes chemically equivalent substituents whose structural formula is written from right to left. For example, -CH ₂ O- is equivalent to -OCH ₂ -.

[0040] The section headings, in the context of this application, are intended only to organize the application and should not be construed as limiting the scope of the present invention. All documents or parts of documents referred to in this application, including but not limited to patents, patent applications, articles, books, instruction manuals and documents, are hereby incorporated by reference in their entirety.

[0041] In addition to the foregoing, in the context of the description and claims of the present invention, unless otherwise indicated, the following terms have the following meanings.

[0042] As used herein, the term "halogen" refers to F, Cl, Br, and I. "F" refers to fluorine, including radioactive and non-radioactive fluorine such as ¹⁸ F and ¹⁹ F, preferably ¹⁸ F. "B" refers to to boron, including radioactive and non-radioactive boron, preferably ¹⁰ V. "N" refers to nitrogen. "Nitro" refers to the -NO ₂ group. "Amino" refers to the group -NH ₂ . A "boric acid group" refers to a -B(OH) ₂ group.

[0043] In the context of this document, the term "alkyl" as a group or part of other groups (for example, in a halogenated alkyl group, etc.) refers to a group with a straight or branched hydrocarbon chain, consisting only of carbon and hydrogen atoms without unsaturated bonds having, for example, from 1 to 10 carbon atoms, and associated with the rest of the molecule by a single bond. Examples of an alkyl group include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, and the like. The term "C1-10 alkyl group" refers to an alkyl group having 1 to 10 carbon atoms such as methyl, ethyl, propyl, isopropyl, pentyl, and the like.

[0044] Preferably, the inert solvent is selected from the group consisting of toluene, benzene, water, methanol, ethanol, isopropanol, ethylene glycol, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, dichloromethane, chloroform, 1,2-dichloroethane, acetonitrile, N,N -dimethylformamide, N,N-dimethylacetamide, dioxane, or combinations thereof. More preferably, the inert solvent is a mixed solvent of benzene and water.

[0045] The term "substituent hydrolyzable to a boric acid group" is a substituent that can form a boric acid group (-B(OH) ₂ ) after hydrolysis, for example, a boric acid ester group.

или

предпочтительно группу сложного пинаколового эфира борной кислоты.The substituent includes, but is not limited to, the following substituents

or

preferably a pinacolic boric acid ester group.

Две вышеуказанные формы защитных групп включены в объем термина "аминозащитная группа" в настоящем описании. Среди указанных защитных групп алкоксикарбонильная защитная группа включает, но не ограничивается ими, бензилоксикарбонил (Cbz), трет-бутилоксикарбонил (Boc), флуоренилметоксикарбонил (Fmoc), аллилоксикарбонил (Alloc), триметилсилилэтоксикарбонил (Теос) и метоксикарбонил (Теос) или этоксикарбонил. Ацилзащитная группа включает, но не ограничивается ими, фталоил (Pht), тозил (Tos), трифторацетил (Tfa), о-(п-) нитробензолсульфонил (Ns), пивалоил и бензоил. Алкилзащитная группа включает, но не ограничивается ими, тритил (Trt), 2,4-диметоксибензил (Dmb), п-метоксибензил (РМВ) и бензил (Bn).[0046] As used herein, R ₃ or R ₄ as an amino protecting group may independently be a protecting group including, but not limited to, an alkoxycarbonyl protecting group, an acyl protecting group, and an alkyl protecting group, or R ₃ or R ₄ may also be combined with N to form imino (C=N) to protect the amino group, for example

The above two forms of protecting groups are included within the scope of the term "amino protecting group" in this specification. Among these protecting groups, an alkoxycarbonyl protecting group includes, but is not limited to, benzyloxycarbonyl (Cbz), tert-butyloxycarbonyl (Boc), fluorenylmethoxycarbonyl (Fmoc), allyloxycarbonyl (Alloc), trimethylsilylethoxycarbonyl (Teos), and methoxycarbonyl (Teos) or ethoxycarbonyl. The acyl protecting group includes, but is not limited to, phthaloyl (Pht), tosyl (Tos), trifluoroacetyl (Tfa), o-(p-)nitrobenzenesulfonyl (Ns), pivaloyl, and benzoyl. The alkyl protecting group includes, but is not limited to, trityl (Trt), 2,4-dimethoxybenzyl (Dmb), p-methoxybenzyl (PMB), and benzyl (Bn).

[0047] The term "carboxyl protecting group" refers to a protecting group that can combine with a carboxyl to form an ester, amide, or hydrazide group, including, but not limited to, alkyl, phenyl, and alkyl-substituted amino. "Alkyl" is preferably straight or branched and substituted or unsubstituted substituted alkyl having from 1 to 20 carbon atoms, such as methyl, ethyl, isopropyl, t-butyl, benzhydryl, benzyl, p-nitrobenzyl, p-methoxybenzyl, 4 -pyridylbenzyl, trichloroethyl, methylthioethyl, p-toluenesulfonylethyl, p-nitrophenylthioethyl, and the like.

[0048] As used herein, "optional" or "optional" means that the event or condition described below may or may not occur, and the description includes both the occurrence and absence of the event or condition. For example, "optionally substituted aryl group" means that the aryl group is substituted or unsubstituted, and the description includes both a substituted aryl group and an unsubstituted aryl group.

[0049] The present invention includes various stereoisomers and mixtures thereof. "Stereoisomers" refers to compounds consisting of the same atoms linked by the same bonds, but having different three-dimensional structures. All tautomeric forms of the compounds of the present invention are also included within the scope of the present invention. "Tautomer" refers to an isomer formed by the transfer of a proton from one atom of a molecule to another atom of the same molecule.

[0050] the Intermediates of the present invention contain chiral carbon atoms and, therefore, can form enantiomers, diastereomers and other stereoisomeric forms. Each chiral carbon atom can be defined as (R)- or (S)- based on stereochemistry. The present invention includes all possible isomers, as well as their racemates and optically pure forms. For the preparation of the compounds of the present invention, racemates, diastereomers or enantiomers may be selected as starting materials or intermediates. Optically active isomers can be obtained using chiral synthons or chiral reagents, or can be separated using conventional methods such as crystallization and chiral chromatography. The "intermediate" of the present invention has both the L-configuration phenylalanine structure and the D-configuration phenylalanine structure, which are within the scope of the present invention.

Method for obtaining ¹⁸ F-BPA

[0051] the Present invention relates to a new method for obtaining ¹⁸ F-BPA, for example, using the methods shown in the following examples, but not limited to illustrative methods. The amino and carboxyl protecting groups and the boric acid ester group used in the following reaction scheme may be appropriately modified and are not limited to the example method.

[0052] The method comprises reacting intermediate I-2 with an ¹⁸ F ion to produce a ¹⁸ F-substituted compound

deprotection of the ¹⁸ F-substituted compound, for example, by hydrolysis of the amino and carboxyl protecting group and boric acid ester group to give ¹⁸ F-BPA

[0053] For each step, the reaction temperature can be appropriately selected depending on the solvents, raw materials and reagents, and the reaction time can also be appropriately selected depending on the reaction temperatures, solvents, raw materials and reagents. After completion of the interaction in each step, the target compound can be isolated and purified from the reaction system by conventional methods such as filtration, extraction, recrystallization, washing, silica gel column chromatography, and the like. Without affecting the following reactions, the target compound can also be used directly in the next steps without separation and purification.

[0054] In the step of obtaining ¹⁸ F-BPA with intermediate I, the ¹⁸ F ion ([ ¹⁸ F]F ^- ) used can be obtained by bombarding H ₂ ¹⁸ O with a proton beam through the reaction ¹⁸ O(p, n) or using methods known in the art. The ¹⁸ F ion was captured by an ion exchange column, eluted with a mixed solution of K2.2.2/K ₂ CO ₃ , dried to remove water, and then used for the labeling reaction. Intermediate I-2 is reacted with the ¹⁸ F ion, and the resulting mixed solution is purified on a cationic column, dried and hydrolyzed to remove the amino and carboxyl protecting groups, thus obtaining ¹⁸ F-BPA. The reagent used includes hydrogen fluoride and potassium fluoride. The solvent used includes water, methanol, DMF (dimethylformamide), DMA (N,N,-dimethylacetamide), DMSO (dimethyl sulfoxide), acetonitrile, n-butanol, ethanol, dichloromethane, or any mixed solvents thereof. The reaction temperature is preferably 20 to 150°C, more preferably 100 to 130°C. The reaction time is preferably 5 to 60 minutes, and more preferably 10 to 30 minutes. Drying by adding a dry organic solvent can azeotrope to remove water. The organic solvent that can be used includes, but is not limited to, acetonitrile, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), or any combination thereof. In a preferred embodiment, a copper catalyst may be added to the reaction of intermediate I and the ¹⁸ F ion. Copper catalyst that can be used includes, but is not limited to, Cu(OTf) ₂ Py ₄ , Cu(OTf) ₂ or a combination thereof.

[0055] It should be noted that the intermediate I and ¹⁸ F-BPA of the present invention includes all their optical isomers, including the L-configuration phenylalanine isomer and the D-configuration phenylalanine isomer. For example, ¹⁸ F-BPA includes ¹⁸ FL-BPA having an L-configuration phenylalanine structure, or ¹⁸ FD-BPA having a D-configuration phenylalanine structure. In the preparation method of the present invention, intermediate I can be subjected to a chiral resolution to obtain a compound with one configuration for use in the reaction, or directly used in the reaction without separation to obtain ¹⁸ F-BPA.

[0056] The present invention is further illustrated below with reference to specific examples. It should be understood that the following description is only the most preferred implementation of the present invention, and should not be construed as limiting the scope of legal protection of the present invention. It should be understood that in the present description, the experimental methods without special conditions in the following examples generally correspond to the usual conditions or conditions recommended by the manufacturer. A person skilled in the art may make minor changes to the technical solutions of the present invention, and such changes should be included in the scope of legal protection of the present invention. Unless otherwise indicated, percentages and fractions are mass percent and mass fractions, respectively.

Example 1 Preparation of N-diphenylmethylene-2,4-dibromophenylalanine tert-butyl ester

[0057] N-diphenylmethyleneglycine tert-butyl ester (40 g, 135.42 mmol, 1 eq.), 1,4-dibromobenzyl bromide (44.53 g, 135.42 mmol, 1 eq.) and tetra-n -butylammonium bromide (TBAB, 436.55 mg, 1.35 mmol, 0.01 eq.) was dissolved in 300 ml of toluene and 80 ml of potassium hydroxide solution (100.00 g, 1.78 mol, 13.16 eq.) was added. ) in water. The mixture was stirred at 25°C for 12 hours to complete the reaction. The reaction mixture was diluted with 100 ml of ethyl acetate, and then was extracted with 400 ml (200 ml × 2) of ethyl acetate. The organic phases were mixed, washed with 600 ml (300 ml×2) brine, dried over Na ₂ SO ₄ and filtered to give a solid. The crude product was separated by column chromatography (petroleum ether/ethyl acetate=100:1-20:1) to obtain 15 g of product.

[0058] LCMS: MS(M+H ⁺ )=544.0.

[0059] ¹ H NMR: 400 MHz, CDCl ₃

[0060] δ 7.56 - 7.46 (m, 3H), 7.35 - 7.16 (m, 7H), 7.01 (d, J=8.2 Hz, 1H), 6.59 ( br d, J=6.8 Hz, 2H), 4.23 (dd, 3=4.2, 9.5 Hz, 1H), 3.31 (dd, J=4.0, 13.4 Hz, 1H), 3.11 (dd, J=9.6, 13.5 Hz, 1H), 1.41-1.28 (m, 9H).

Example 2 Preparation of N-tert-butyloxycarbonyl-2,4-dibromophenylalanine tert-butyl ester

[0061] N-diphenylmethylene-2,4-dibromophenylalanine tert-butyl ester (30 g, 55.22 mmol, 1 eq) was dissolved in THF (70 ml) and 20 ml of aqueous citric acid (31.83 g, 165.66 mmol, 31.86 ml, 3 eq.), and stirred at 25°C for 12 hours, 50 ml of Na ₂ CO ₃ solution (29.26 g, 276.10 mmol, 5 eq.) in water and Boc ₂ O (13.26 g, 60.74 mmol, 13.95 ml, 1.1 eq.) and stirred an additional 4 hours. After completion of the reaction, the reaction mixture was extracted with 400 ml (200 ml×2) of ethyl acetate. The organic phases were mixed, washed with 400 ml (200 ml × 2) brine, dried over Na ₂ SO ₄ and filtered to obtain a solid. The crude product was separated by column chromatography (petroleum ether/ethyl acetate=100:1-10:1) to give 19.6 g of product (73.48% yield, 99.2% purity).

[0062] LCMS: MS (M-155 ⁺ )=323.9.

[0063] ¹ H NMR: 400 MHz, CDCl ₃

[0064] δ7.72 (d, J=1.5 Hz, 1H, 7.37 (dd, J=1.8, 8.1 Hz, 1H), 7.13 (br d, J=8.1 Hz, 1H), 5.06 (br d, J=8.3 Hz, 1H), 4.59 - 4.38 (m, 1H), 3.23 (dd, J=5.9, 13.9 Hz, 1H), 3.00 (br dd, J=8.6,13.8 Hz, 1H), 1.40 (br d, J=16.6 Hz, 17H).

Example 3 Chiral Resolution of N-tert-butyloxycarbonyl-2,4-dibromophenylalanine tert-butyl ester.

[0065] 19.6 g of N-tert-butyl oxycarbonyl-2,4-dibromophenylalanine tert-butyl ester were separated by ultra high temperature liquid chromatography (SFC) (column: DAICEL CHIRALPAK AY (250 mm*50 mm, 10 μm ), mobile phase: [0.1% NH ₃ H ₂ O MEOH]) to give 9.1 g of product (yield 46.84%, purity 97.8%) and 9.2 g of product (yield 48.18% , purity 99.5%).

Example 4 Preparation of N-tert-butoxycarbonyl-2,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenylalanine tert-butyl ester.

[0066] N-tert-butyloxycarbonyl-2,4-dibromophenylalanine tert-butyl ester (7.50 g, 15.6 mmol, 1.00 eq.), bis(pinacolato)diborone (19.8 g, 78 2 mmol, 5.00 eq.), KOAc (6.14 g, 62.6 mmol, 4.00 eq.), Pd(dppf)Cl ₂ (1.15 g, 1.57 mmol, 0.10 eq. .) and dioxane (75.0 ml) were stirred under nitrogen at 90° C. for 1 hour. After completion of the reaction, the resulting reaction mixture was filtered and 200 ml of water was added. The reaction mixture was extracted with 300 ml (100 ml x 3) ethyl acetate. The organic phases were mixed, washed with 200 ml (100 ml × 2) brine, dried over Na ₂ SO ₄ and filtered to obtain a solid. The crude product was purified by HPLC to give 6.5 g of product (purity 96.3%).

[0067] LCMS: MS (M+H ⁺ -156)=418.0.

[0068] ¹ H NMR: 400 MHz, CDCl ₃

[0069] 8.24 (s, 1H), 7.84 (d, J=7.6, 1H), 7.30 (d, J=7.6, 1H), 5.90 (d, J= 8.4, 1H), 4.24 - 4.19 (m, 1H), 3.24 - 3.19 (m, 2H), 1.47 (s, 9H), 1.39 (s, 12H) , 1.34 (s, 12H), 1.32 (s, 9H).

Example 5 Preparation of N-tert-butoxycarbonyl-2,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenylalanine tert-butyl ester.

[0070] O-tert-butyloxycarbonyl-2,4-dibromophenylalanine tert-butyl ester (7.00 g, 14.6 mmol, 1.00 eq.), bis(pinacolato)diborone (18.5 g, 73, 0 mmol, 5.00 eq.), KOAc (5.73 g, 58.4 mmol, 4.00 eq.), Pd(dppf)Cl ₂ (5.73 g, 58.4 mmol, 4.00 eq. .) and dioxane (70.0 ml) were stirred under nitrogen at 90° C. for 3 hours. After completion of the reaction, the resulting reaction mixture was filtered and 200 ml of water was added. The reaction mixture was extracted with 300 ml (100 ml x 3) ethyl acetate. The organic phases were mixed, washed with 200 ml (100 ml × 2) brine, dried over Na ₂ SO ₄ and filtered to obtain a solid. The crude product was purified by HPLC to give 5.37 g of product (97.35% purity).

[0071] LCMS: MS (M-100-55+H ⁺ ): 418.3

[0072] ¹ H NMR: 400 MHz, CDCl ₃

[0073] δ 1.31 - 1.35 (m, 21H), 1.39 (s, 12H), 1.47 (s, 9H), 3.16 - 3.29 (m, 2H), 4, 19 - 4.26 (m, 1H), 5.89 (br d, J=8.40 Hz, 1H), 7.30 (d, J=8.00 Hz, 1H), 7.84 (dd , J=7.60, 1.47 Hz, 1H), 8.24 (s, 1H).

Example 6 Preparation of N,N-bis(tert-butoxycarbonyl)-2,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenylalanine tert-butyl ester

[0074] N-tert-butyloxycarbonyl-2,4-dibromophenylalanine tert-butyl ester (7.00 g, 14.6 mmol, 1.00 eq.), bis(pinacolato)diborone (18.5 g, 73, 0 mmol, 5.00 eq.), KOAc (5.73 g, 58.4 mmol, 4.00 eq.), Pd(dppf)Cl ₂ (5.73 g, 58.4 mmol, 4.00 eq. .) and dioxane (70.0 ml) were stirred under nitrogen at 90° C. for 3 hours. After completion of the reaction, the resulting reaction mixture was filtered and 200 ml of water was added. The reaction mixture was extracted with 300 ml (100 ml x 3) ethyl acetate. The organic phases were mixed, washed with 200 ml (100 ml × 2) brine, dried over Na ₂ SO ₄ and filtered to obtain a solid. The crude product was purified by HPLC to give 5.37 g of product (97.35% purity). The ¹ H NMR spectrum is shown in FIG. one.

Example 7 Preparation ^{of 18} F-BPA

[0075] H ₂ ¹⁸ O was irradiated with accelerated protons to produce ¹⁸ F ions via the ¹⁸ O(p, n) reaction. The ions were captured on an ion exchange column, eluted with a mixed solution of K2.2.2/K ₂ CO ₃ , dried to remove water, and then used for the labeling reaction. The compound obtained in Example 5 was reacted with ¹⁸ F ions in a DMA solution in the presence of Cu(OTf) ₂ Py ₄ for 15 min. After completion of the reaction, the mixed solution was purified by a cation column and dried. The reaction was carried out in HCl solution at 110°C for 10 min and NaOH solution was added to neutralize. The amino and carboxyl protecting groups were removed by hydrolysis to give the crude product. The crude product was purified by HPLC to give ¹⁸ F-BPA with a purity greater than 99%.

[0076] The radio-HPLC chromatogram is shown in FIG. 2. The product was mixed with a small amount of standard ¹⁹ B-BPA and co-injected into the HPLC column. Under the same conditions, a peak appeared at the time of retention (retention time 11 min ± 1 min), indicating that the labeled product was ¹⁸ F-BPA. See fig. 3.

[0077] Using the same production method described above, ¹⁸ F-BPA was obtained from the compound obtained in Example 6, and ¹⁸ F-BPA with a purity greater than 99% can also be obtained.

[0078] All documents mentioned in this application are incorporated into this application by reference, to the same extent as if each document were separately indicated as included by reference. In addition, it should be understood that after reading the above description of the present invention, various changes or modifications may be made to the present invention by those skilled in the art, and such equivalent forms also fall within the scope of the appended claims of the present invention.

Claims (38)

1. Method for producing ¹⁸ F-BPA (2-fluoro-4-boron-L-phenylalanine) having the structure

, including interaction of intermediate I-2 with ¹⁸ F ion to give ¹⁸ F-substituted compound

, I-2 deprotection of ¹⁸ F-substituted compound to give ¹⁸ F-BPA

, where R ₁₀ and R ₂₀ are OH or taken together with the boron atom to which they are attached, represent a substituent hydrolysable to a boric acid group, R ₃ or R ₄ is independently hydrogen, an amino protecting group, or —NR ₃ R ₄ is

and R ₅ is a carboxyl protecting group. 2. The method of claim 1 wherein intermediate I-2 is selected from

3. The method of claim 1 wherein reacting intermediate I-2 with the ¹⁸ F ion further comprises the use of a copper catalyst, preferably comprising Cu(OTf) ₂ Py ₄ or Cu(OTf) ₂ . 4. The method according to p. 1, where the interaction of intermediate compound I-2 with ion ¹⁸ F is carried out at a temperature of from 20 to 150°C, preferably from 100 to 130°C. 5. The method according to p. 1, where the interaction of intermediate I-2 with ion ¹⁸ F is carried out in a solvent including water, methanol, DMF (dimethylformamide), DMA (dimethylacetamide), DMSO (dimethyl sulfoxide), acetonitrile, n-butanol, ethanol , dichloromethane or any solvents mixed therefrom. 6. The method of claim 1 wherein intermediate I-1 is reacted with boric acid or a boric acid ester to form intermediate I-2

where X ₁ and X ₂ are the same halogens and preferably X ₁ and X ₂ are Cl, Br or I, R ₁₀ and R ₂₀ are OH or, taken together with the boron atom to which they are attached, represent a substituent hydrolysable to a boric acid group, R ₃ or R ₄ is independently hydrogen, an amino protecting group, or —NR ₃ R ₄ is

and R ₅ is a carboxyl protecting group. 7. The method of claim 6, further comprising chiral separation of intermediate I-1 and then reacting with boric acid or a boric acid ester, respectively. 8. Intermediate I having the structure

I each R ₁ and R ₂ independently represents boric acid groups or substituents hydrolysable to boric acid groups, R ₃ or R ₄ is independently hydrogen, an amino protecting group, or —NR ₃ R ₄ is

and R ₅ is a carboxyl protecting group. 9. Intermediate I according to claim 8, which includes intermediate I-2 having the structure

I-2, where B is boron, preferably ¹⁰ B, R ₁₀ and R ₂₀ are OH or, taken together with the boron atom to which they are attached, represent a substituent hydrolysable to a boric acid group, R ₃ or R ₄ is independently hydrogen, an amino protecting group, or —NR ₃ R ₄ is

and R ₅ is a carboxyl protecting group. 10. Intermediate I according to claim 8, wherein the substituent hydrolysable to a boric acid group is a boric acid ester group, preferably a boric acid pinacol ester group, R ₃ and R ₄ include an alkoxycarbonyl protecting group, an acyl protecting group and an alkyl protecting group and R ₅ includes a substituted or unsubstituted C _1-20 alkyl group, preferably t-butyl. 11. Intermediate I according to claim 8, where intermediate I is selected from the following compounds:

12. Use of intermediate I according to claim 8 or 9 to obtain ¹⁸ F-BPA, where ¹⁸ F-BPA has the structure

.

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