JP7714224B2 - Boronophenylalanine amide derivatives - Google Patents

Description

The present invention relates to boronophenylalanine amide derivatives.

Boron neutron capture therapy (BNCT) is a cancer treatment method. Boron neutron capture therapy involves incorporating a boron compound containing the boron-10 isotope ( ¹⁰ B) into cancer cells, irradiating them with low-energy neutron rays (e.g., thermal neutrons), and locally destroying the cancer cells through a nuclear reaction that occurs within the cells. In this treatment method, it is important to selectively accumulate the boron compound containing ¹⁰ B in the cells of cancer tissue in order to enhance the therapeutic effect, so it is necessary to develop a boron compound that can be selectively incorporated into cancer cells.

Derivatives of 4-borono-phenylalanine, in which a boron atom or boron atom group has been introduced into the basic skeleton, have been synthesized as drugs for use in BNCT. Drugs currently in clinical use include 4-borono-phenylalanine derivatives (L-BPA) and mercaptoundecahydrododecaborate (BSH). 4-borono-phenylalanine mimics phenylalanine and is taken up by LAT1 (L-type Amino Acid Transporter 1), a type of amino acid transporter. Because LAT1 expression is elevated in cancer cells, L-BPA tends to accumulate, and this property is exploited for its use in cancer treatment (see, for example, Non-Patent Document 1).

Japanese Patent Application Laid-Open No. 2008-214319

However, depending on the type and malignancy of tumor cells, LAT1 may not be overexpressed. 4-Borono-phenylalanine is taken up via LAT1, so it does not accumulate in areas where LAT1 is not overexpressed, making BNCT in such cases unsuitable.

Therefore, there is a need to create new groups of compounds that have the potential to be taken up by tumor cells even if they are not taken up via LAT1.

The present invention aims to provide boronophenylalanine amide derivatives.

As a result of extensive research aimed at solving the above-mentioned problems, the inventors discovered a new boronophenylalanine amide derivative and completed the present invention.

That is, the present invention provides the following compounds:
[1]
A compound represented by the following formula (I) or a pharmaceutically acceptable salt thereof:
Here, in formula (I),
R ¹ and R ² together with the B atom represent a substituent of boronic acid (—B(OH) ₂ ), boronic acid ester, or boronic acid amide;
R ³ represents a group independently selected from the group consisting of H, halogen, hydroxy, cyano, amino, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, benzyloxy, C1-C6 alkoxyC1-C6 alkyl, nitro, C1-C6 haloalkyl, carbamoyl, C1-C6 alkylaminocarbonyl, C1-C6 alkoxycarbonyl, C1-C6 alkylcarbonyl, COOR ¹⁰ (R ¹⁰ is H, C1-C6 alkyl, amino, C1-C6 alkylamino), C1-C6 haloalkylsulfanyl, C1-C6 haloalkylsulfinyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylthio, C1-C6 alkylsulfinyl, C1-C6 alkylsulfonyl, aminosulfonyl, sulfo, and sulfamoyl;
s represents an integer of 1 to 4;
^R4 represents H, C1-C6 alkyl, benzyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl;
R ⁵ represents H, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-6 alkenyl, substituted or unsubstituted C2-6 alkynyl, hydroxy, cyano, substituted or unsubstituted amino, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 alkoxyC1-C6 alkyl, substituted or unsubstituted acyl, substituted or unsubstituted sulfonyl, substituted or unsubstituted carbamoyl, C1-C6 alkoxycarbonyl, substituted or unsubstituted C3-C7 cycloalkyl, substituted or unsubstituted C3-C7 cycloalkenyl, substituted or unsubstituted non-aromatic heterocyclic group, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl, or R ⁴ R ⁵ together with N form a C3-C7 heterocycloalkyl;
^R6 represents H or optionally substituted C1-C6 alkyl, or may form a ring structure with the adjacent methylene moiety fused to a benzene ring, wherein the ring structure represents unsubstituted C5-7 cycloalkyl or unsubstituted C5-7 cycloalkenyl.
[2]
The compound according to [1], or a pharmaceutically acceptable salt thereof, wherein R ³ independently represents H, Cl, F, C1-C3 alkyl, C1-C3 alkoxy, C1-C6 alkylthio, CH ₂ X, CHX ₂ , or CX ₃ (X represents F).
[3]
^R4 represents H or C1-C6 alkyl;
The compound according to [1] or [2], or a pharmaceutically acceptable salt thereof, wherein R ⁵ represents a substituted or unsubstituted aryl, or a substituted or unsubstituted heteroaryl.
[4]
^R4 represents H or C1-C6 alkyl;
The compound or pharmaceutically acceptable salt thereof according to [1] or [2], wherein R ⁵ represents an aryl-substituted C1-C6 alkyl.
[5]
The compound or pharmaceutically acceptable salt thereof according to [1] or [2], wherein R ⁴ R ⁵ together with N forms a C3-C7 heterocycloalkyl.
[6]
A drug for BNCT, comprising the compound according to any one of [1] to [5] or a pharmaceutically acceptable salt thereof.
[7]
A diagnostic agent comprising a radioisotope as a substituent at any one of R ³ , R ⁴ or R ⁵ of the compound according to any one of [1] to [5] or a pharmaceutically acceptable salt thereof.

The novel compounds of the present invention, used alone or in combination with other compounds, may be useful in further expanding the applications of BNCT.

In this specification, when a compound having an asymmetric carbon is referred to, unless otherwise specified, the compound may be in either the racemic, R- or S-form.

[Boronophenylalanine amide derivatives]
The boronophenylalaninamide derivative of the present invention is a compound represented by the following formula (I) or a pharmaceutically acceptable salt thereof:
(I)
Here, in formula (I),
R ¹ and R ² together with the B atom represent a substituent of boronic acid (—B(OH) ₂ ), boronic acid ester, or boronic acid amide;
R ³ represents a group independently selected from the group consisting of H, halogen, hydroxy, cyano, amino, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, benzyloxy, C1-C6 alkoxyC1-C6 alkyl, nitro, C1-C6 haloalkyl, carbamoyl, C1-C6 alkylaminocarbonyl, C1-C6 alkoxycarbonyl, C1-C6 alkylcarbonyl, COOR ¹⁰ (R ¹⁰ is H, C1-C6 alkyl, amino, C1-C6 alkylamino), C1-C6 haloalkylsulfanyl, C1-C6 haloalkylsulfinyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylthio, C1-C6 alkylsulfinyl, C1-C6 alkylsulfonyl, aminosulfonyl, sulfo, and sulfamoyl;
s represents an integer of 1 to 4;
^R4 represents H, C1-C6 alkyl, benzyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl;
R ⁵ represents H, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-6 alkenyl, substituted or unsubstituted C2-6 alkynyl, hydroxy, cyano, substituted or unsubstituted amino, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 alkoxyC1-C6 alkyl, substituted or unsubstituted acyl, substituted or unsubstituted sulfonyl, substituted or unsubstituted carbamoyl, C1-C6 alkoxycarbonyl, substituted or unsubstituted C3-C7 cycloalkyl, substituted or unsubstituted C3-C7 cycloalkenyl, substituted or unsubstituted non-aromatic heterocyclic group, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl, or R ⁴ R ⁵ together with N form a C3-C7 heterocycloalkyl;
^R6 represents H or optionally substituted C1-C6 alkyl, or may form a ring structure with the adjacent methylene moiety fused to a benzene ring, wherein the ring structure represents unsubstituted C5-C7 cycloalkyl or unsubstituted C5-7 cycloalkenyl.

In this specification, halogen may be any of F, Cl, Br, and I, but F, Cl, and Br are particularly preferred.

As used herein, C1-C6 alkyl refers to a linear or branched C1-C6 saturated hydrocarbon group. Examples of C1-C6 alkyl groups include methyl, ethyl, propyl (e.g., n-propyl and isopropyl), butyl (e.g., n-butyl, isobutyl, t-butyl), pentyl (e.g., n-pentyl, isopentyl, neopentyl), etc. Preferably, it is a linear or branched C1-C4 alkyl group, and examples include, but are not limited to, a methyl group, an ethyl group, an isopropyl group, and a butyl group.

In this specification, C2-C6 alkenyl refers to a linear or branched C2-C6 unsaturated hydrocarbon group containing a double bond. Examples of C2-C6 alkenyl groups include ethenyl, propenyl, and butenyl.

As used herein, C2-C6 alkynyl refers to a linear or branched C2-C6 unsaturated hydrocarbon group containing a triple bond. Examples of C2-C6 alkynyl groups include acetylene, methylacetylene, butyne, and pentyne.

As used herein, C1-C6 haloalkyl refers to a C1-C6 alkyl group having one or more halogen substituents. The _C1 -C6 haloalkyl group is preferably represented by _C2X5 , _CH2X , _CHX2 , or _CX3 (X represents Cl, F, Br, or I), and includes, but is not limited to, for example, _CF3 , _C2F5 , _CHF2 , _CCl3 , _CHCl2 , _C2Cl5 , and _{the like} .

As used herein, C1-C6 alkoxy refers to a group having a linear or branched C1-C6 alkyl group and an oxygen molecule. C1-C6 alkoxy preferably has a linear or branched C1-C4 alkyl group, and examples include, but are not limited to, methoxy, ethoxy, isopropoxy, and butoxy.

As used herein, C1-C6 alkoxyC1-C6 alkyl includes, but is not limited to, methoxyethyl, ethoxyethyl, etc.

As used herein, C1-C6 alkylamino refers to a group represented by NR ¹¹ R ¹² , where R ¹¹ R ¹² each independently represent H or C1-C6 alkyl (except when R ¹¹ and R ¹² are both H). Examples include, but are not limited to, methylamino, dimethylamino, ethylamino, i-propylamino, and the like.

As used herein, C1-C6 alkylaminocarbonyl is represented by CONR ¹³ R ¹⁴ , and R ¹³ and R ¹⁴ each independently represent H or C1-C6 alkyl (excluding the case where R ¹³ and R ¹⁴ are both H). Examples include, but are not limited to, methylaminocarbonyl, dimethylaminocarbonyl, ethylaminocarbonyl, i-propylaminocarbonyl, and the like.

As used herein, C1-C6 alkylcarbonyl includes, but is not limited to, methylcarbonyl, ethylcarbonyl, etc.

As used herein, C1-C6 alkoxycarbonyl includes, but is not limited to, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, sec-butoxycarbonyl, tert-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, etc.

In this specification, examples of COOR ¹⁰ (R ¹⁰ is H or C1-C6 alkyl, amino, alkylamino (NR ¹¹ R ¹² (R ¹¹ R ¹² each independently represents H or C1-C6 alkyl)) include, but are not limited to, methyloxycarbonyl, aminooxycarbonyl, and the like.

In this specification, C1-C6 haloalkylsulfanyl, C1-C6 haloalkylsulfinyl, and C1-C6 haloalkylsulfonyl include, but are not limited to, trifluoromethylsulfanyl, trifluoromethylsulfinyl, and trifluoromethylsulfonyl.

As used herein, C1-C6 alkylthio includes, but is not limited to, methylthio, ethylthio, propylthio, isopropylthio, butylthio, sec-butylthio, tert-butylthio, pentylthio, and hexylthio.

As used herein, C1-C6 alkylsulfinyl includes, but is not limited to, methylsulfinyl, ethylsulfinyl, etc.

As used herein, C1-C6 alkylsulfonyl includes, but is not limited to, methylsulfonyl, ethylsulfonyl, etc.

As used herein, substituted C1-C6 alkyl includes, but is not limited to, straight-chain or branched C1-C6 alkyl in which 1 to 3 hydrogen atoms have been replaced with other groups.

As used herein, substituted C2-6 alkenyl includes, but is not limited to, straight-chain or branched C2-6 alkenyl in which one or two hydrogen atoms have been replaced with other groups.

As used herein, substituted C2-6 alkynyl includes, but is not limited to, straight-chain or branched C2-6 alkynyl in which one or two hydrogen atoms have been replaced with other groups.

As used herein, substituted C1-C6 alkoxy includes, but is not limited to, straight-chain or branched C1-C6 alkoxy in which one or two hydrogen atoms have been replaced with other groups.

As used herein, substituted C1-C6 alkoxyC1-C6 alkyl includes, but is not limited to, straight-chain or branched C1-C6 alkoxyC1-C6 alkyl in which one or two hydrogen atoms have been replaced with other groups.

Here, in the above-mentioned substituted C1-C6 alkyl, substituted C2-6 alkenyl, substituted C2-6 alkynyl, substituted C1-C6 alkoxy, substituted C1-C6 alkoxyC1-C6 alkyl, etc., the group substituted in place of the hydrogen atom is, for example, a halogen, a substituted or unsubstituted non-aromatic heterocyclic group, a substituted or unsubstituted arylthio (e.g., phenylthio), a substituted or unsubstituted arylamino (e.g., phenylamino), a substituted or unsubstituted aryl, or a substituted or unsubstituted heteroaryl.

As used herein, substituted or unsubstituted amino includes, for example, amino optionally substituted with C1-C6 alkyl. Non-limiting examples of substituted or unsubstituted amino include amino, methylamino, dimethylamino, ethylamino, diethylamino, ethylmethylamino, cyclopropylamino, and cyclohexylamino. Other optionally substituted amino groups include hydrazine, C1-C6 alkyl-substituted hydrazine, benzylamino, acetylamino, benzoylamino, methylsulfonylamino, tetrahydropyranylamino, tetrahydrofuranylamino, morpholinoamino, morpholinylamino, piperidinylamino, and piperazinylamino.

Examples of the substituted or unsubstituted acyl include aliphatic acyl and aroyl having 1 to 7 carbon atoms. Specific examples include, but are not limited to, formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl, hexanoyl, acryloyl, propioloyl, methacryloyl, crotonoyl, and benzoyl.

Examples of substituted or unsubstituted sulfonyl groups include methylsulfonyl, ethylsulfonyl, propylsulfonyl, isopropylsulfonyl, tert-butylsulfonyl, isobutylsulfonyl, sec-butylsulfonyl, phenylsulfonyl, naphthylsulfonyl, cyclopropylsulfonyl, cyclohexylsulfonyl, cyclohexenylsulfonyl, piperidinylsulfonyl, and tetrahydrofurylsulfonyl.

Substituted or unsubstituted carbamoyl groups include carbamoyl, N-methylcarbamoyl, N,N-dimethylcarbamoyl, N-ethyl-N-methylcarbamoyl, N,N-diethylcarbamoyl, N-n-propylaminocarbamoyl, N-isopropylcarbamoyl, N-morpholinocarbamoyl, N-tetrahydrofuranylcarbamoyl, N-piperidylcarbamoyl, N-tetrahydropyranylcarbamoyl, N-benzylcarbamoyl, N-acetylcarbamoyl, N-methylsulfonylcarbamoyl, N-(2,2,2-trifluoroethyl)carbamoyl, and N-(2-hydroxy-1-methylethyl)carbamoyl. In different embodiments, examples include carbamoyl, N-methylcarbamoyl, N,N-dimethylcarbamoyl, N-n-propylaminocarbamoyl, N-isopropylcarbamoyl, N-morpholinocarbamoyl, N-tetrahydrofuranylcarbamoyl, N-piperidylcarbamoyl, N-tetrahydropyranylcarbamoyl, N-methylsulfonylcarbamoyl, N-(2,2,2-trifluoroethyl)carbamoyl, and N-(2-hydroxy-1-methylethyl)carbamoyl.

Examples of substituted or unsubstituted C3-C7 cycloalkyl include cyclopropyl, cyclobutyl, cyclohexyl, etc.

Examples of substituted or unsubstituted C3-C7 cycloalkenyl include cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclohexadienyl, etc.

Substituted or unsubstituted non-aromatic heterocyclic groups include aziridinyl, oxiranyl, thiiranyl, azetidinyl, oxetanyl, thietanyl, tetrahydrothienyl, tetrahydrofuranyl, pyrrolinyl, benzodioxane, pyrrolidinyl, imidazolinyl, imidazolidinyl, oxazolinyl, oxazolidinyl, pyrazolinyl, pyrazolidinyl, thiazolinyl, and thiazolinyl, which may be optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen. Examples include thiazolidinyl, tetrahydroisothiazolyl, tetrahydrooxazolyl, tetrahydroisoxazolyl, piperidinyl, piperazinyl, tetrahydropyridinyl, dihydropyridinyl, dihydrothiopyranyl, tetrahydropyrimidinyl, tetrahydropyridazinyl, dihydropyranyl, tetrahydropyranyl, tetrahydrothiopyranyl, morpholinyl, thiomorpholinyl, azepanyl, diazepanyl, azepinyl, oxepanyl, azocanyl, and diazocanyl.

Substituted or unsubstituted aryl includes C6-C14 aryl optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen, and more specific examples include phenyl, naphthyl, azulenyl, anthryl, etc. The aryl is preferably phenyl.

Substituted or unsubstituted heteroaryls include thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, 1,2,4-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,4-thiadiazolyl, 1,3,4-thiadiazolyl, triazolyl, tetrazolyl, triazinyl, benzothiophenyl, benzofuranyl, benzimidazolyl, benzoxazolyl, benzodioxolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl, and benzotriazolyl, which may be optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen. Examples include imidazopyridinyl, imidazopyridinyl, thienopyridinyl, furopyridinyl, pyrrolopyridinyl, pyrazolopyridinyl, oxazolopyridinyl, thiazolopyridinyl, imidazopyrazinyl, imidazopyrimidinyl, thienopyrimidinyl, furopyrimidinyl, pyrrolopyrimidinyl, pyrazolopyrimidinyl, oxazolopyrimidinyl, thiazolopyrimidinyl, pyrazolotriazinyl, naphtho[2,3-b]thienyl, phenoxathiinyl, indolyl, isoindolyl, 1H-indazolyl, purinyl, isoquinolyl, quinolyl, phthalazinyl, naphthyridinyl, quinoxalinyl, quinazolinyl, cinnolinyl, carbazolyl, β-carbolinyl, phenanthridinyl, acridinyl, phenazinyl, phenothiazinyl, and phenoxazinyl.

In the derivatives of the present invention, R ¹ and R ² represent any of substituents of boronic acid (—B(OH) ₂ ), boronic acid ester, or boronic acid amide. Examples of the boronic acid ester or boronic acid amide group in this definition include groups having a chain structure such as —B(NR ⁷¹ ) ₂ or —B(OR ⁷¹ ) ₂ at the R ¹ and R ² positions, or groups having a cyclic structure together with atom B. Here, R ⁷¹ represents a linear or branched C1-C10 alkyl group. Here, the term “linear or branched C1-C10 alkyl group” may refer to any alkyl group having 1 to 10 carbon atoms. A linear or branched C1-C8 alkyl group is preferred, and a linear or branched C1-C6 alkyl group is more preferred. Examples of these groups include, but are not limited to, a methyl group, an ethyl group, an isopropyl group, and a butyl group.

Furthermore, in groups having a cyclic structure with atom B, the atoms do not necessarily have to be separated only by oxygen atoms, and may also have nitrogen atoms interposed therebetween. Examples include, but are not limited to, groups formed from esters or ester analogs formed from atom B and a member selected from the group consisting of pinacol, 2,2-dimethyl-1,3-propanediol, N-methyldiethanolamine, 1-6-diaminonaphthalene, N-methyliminodiacetic acid, 1,1,1-trishydroxymethylethane, and catechol. Examples include, but are not limited to, pinacol boronate ester, MIDA boronate ester, 1,3-propanediol boronate ester, neopentyl glycol boronate ester, catechol boronate ester, pinanediol boronate ester, biscyclohexyldiol boronate ester, MPM boronate ester, trifluoroborate salts, cyclic triol borate salts, and cyclic compounds of diaminonaphthalene amide and boron.

Here, the proportion of boron atoms is not limited, but may be preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

Natural boron (boron) contains the isotopes boron-10 and boron-11, with the ratio being 20% boron-10 and 80% boron-11. Therefore, prior to producing the boronophenylalanine amide derivative of the present invention, it is also preferable to enrich boron with a mass number of 10 (boron-10). In the present invention, for example, commercially available products may be used as the boron atom source. For example, 10B enriched boric acid (manufactured by Stella Chemifa Corporation) can be used as a commercially available product.

The boron-10 measurement method here can be performed using an Agilent 710 (manufactured by Agilent) with multi-type inductively coupled plasma (ICP) optical emission spectroscopy (ICP-OES). The ICP-OES used for the measurement is adjusted in accordance with JIS K0116.

In the above compounds, although not limited thereto, R ¹ R ² together with the B atom are preferably boronic acid (B(OH) ₂ ) or a boronic acid ester having a chain or cyclic structure, more preferably boronic acid (B(OH) ₂ ) or a pinacol ester of boronic acid.

In the above compounds, although not limited thereto, it is particularly preferred that any 1 to 4 of the R ^3s are independently H, Cl, F, C1-C3 alkyl, C1-C3 alkoxy, C1-C6 alkylthio, CH ₂ F, CHF ₂ , or CF ₃ .

In the above compounds, although not limited thereto, it is preferable that R ⁴ is H or C1-C6 alkyl.

In the above compounds, ^R5 is H, C1-C6 alkyl, C3-C7 cycloalkyl, C1-C6 alkoxy, halogen-substituted C1-C3 alkyl, substituted or unsubstituted phenyl (in the case of substitution, it is not limited, but it is preferable that it is phenyl substituted with halogen, C1-C3 alkyl, C1-C3 alkoxy, nitro, etc.), naphthyl, C1-C6 alkyl substituted with substituted or unsubstituted phenyl (here, substituted phenyl is not limited, but it is preferable that it is phenyl substituted with halogen, C1-C3 alkyl, C1-C3 alkoxy, nitro, etc.), and C1-C6 alkoxy substituted with substituted or unsubstituted phenyl (wherein substituted phenyl is preferably substituted with, but not limited to, halogen, C1-C3 alkyl, C1-C3 alkoxy, nitro, etc.), thienyl, furyl, pyrimidine, thienyl-substituted C1-C6 alkyl, furyl-substituted C1-C6 alkyl, pyrimidine-substituted C1-C6 alkyl, phenylthio-substituted C1-C6 alkyl, phenylamino-substituted C1-C6 alkyl, benzodioxolyl, dihydrobenzodioxine, or a C3-C7 heterocycloalkyl formed by ^R4 and ^R5 together with the N atom. When ^R4 and ^R5 together with the N atom form a C3-C7 heterocycloalkyl, examples of the C3-C7 heterocycloalkyl include, but are not limited to, morpholino, pyrrolidine, etc.

In the above compounds, although not limited thereto, ^R6 is preferably H or C1-C6 alkyl, or ^R6 and the adjacent methylene are fused to a benzene ring to form a ring structure, where the ring structure is preferably unsubstituted C5-C7 cycloalkyl, and more preferably ^R6 represents H, methyl, or ethyl.

Among the boronophenylalaninamide derivatives of the present invention, one selected from the group consisting of the following compounds or a salt thereof is particularly preferred:
(S)-(4-(2-amino-3-(ethylamino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((2,2,2-trifluoroethyl)amino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(p-tolylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(m-tolylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3,4-dimethylphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3,5-dimethoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-(benzo[d][1,3]dioxol-5-ylamino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((2,3-dihydroxybenzo[b][1,4]dioxin-6-yl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(phenethylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-fluorophenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((2-phenoxyethyl)amino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((3-phenoxypropyl)amino)propyl)phenyl)boronic acid; and (S)-(4-(2-amino-3-oxo-3-(pyridin-2-ylamino)propyl)phenyl)boronic acid.

In the present invention, "pharmaceutically acceptable salts" include salts with inorganic bases, salts with organic bases, salts with inorganic acids, salts with organic acids, salts with basic or acidic amino acids, and the like. Suitable examples of salts with inorganic bases include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; as well as aluminum salts and ammonium salts. Suitable examples of salts with organic bases include salts with trimethylamine, triethylamine, pyridine, picoline, ethanolamine, diethanolamine, triethanolamine, dicyclohexylamine, N,N'-dibenzylethylenediamine, and the like. Suitable examples of salts with inorganic acids include salts with hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, and the like. Suitable examples of salts with organic acids include salts with formic acid, acetic acid, trifluoroacetic acid, fumaric acid, oxalic acid, tartaric acid, maleic acid, citric acid, succinic acid, malic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and the like. Suitable examples of salts with basic amino acids include salts with arginine, lysine, ornithine, etc., and suitable examples of salts with acidic amino acids include salts with aspartic acid, glutamic acid, etc.

[Method for producing boronophenylalanine amide derivatives]
In the present invention, the method for producing the novel boronophenylalanine amide derivative is not limited, and a conventional amino acid synthesis method can be used. Although not limited, a particularly preferred method may be, for example, the following method.
First, an organic halide represented by the following general formula (II) is reacted with a protected amino acid in the presence of an organic solvent, a basic aqueous solution, and a phase transfer catalyst.

Here, in formula (II),
X ¹ and X ² independently represent a halogen (F, Cl, Br, I).
Furthermore, in formula (II), the benzene ring may be optionally substituted with 1 to 4 substituents ^R3 at positions other than where ^X1 is present.

Here, as the organic halide represented by formula (II), a compound prepared by a known method can be used as is, or a commercially available product can be used.

Of these, for example, 4-iodobenzyl bromide and 4-bromo-2-fluorobenzyl bromide are available from Tokyo Chemical Industry Co., Ltd. and Combi-Blocks. 4-bromo-3-fluorobenzyl bromide, 1-bromo-4-(bromomethyl)-2,3-difluorobenzene, 4-bromo-1-(bromomethyl)-2-methoxybenzene, 4-bromo-1-(bromomethyl)-2-nitrobenzene, 4-bromo-1-(bromomethyl)-2-chlorobenzene, 4-bromo-1-(bromomethyl)-2-(trifluoromethyl)benzene, 4-bromo-1-(bromomethyl)-2-(trifluoromethyl)benzene, and 1-bromo-4-(bromomethyl)-2-methylbenzene are available from Combi-Blocks. 4-Bromo-1-(bromomethyl)-2-methylbenzene and 4-bromo-2,6-difluorobenzyl bromide are available from Fluorochem Ltd.

5-Bromo-2-(bromomethyl)benzonitrile can be prepared, for example, from 5-bromo-2-methylbenzonitrile, available from Tokyo Chemical Industry Co., Ltd., while 1-bromo-4-(bromomethyl)-2-chloro-5-fluorobenzene and 5-bromo-2-methylthioanisole can be prepared from 4-bromo-5-chloro-2-fluorotoluene, available from Combi-Blocks. These compounds can be prepared, for example, by reacting commercially available compounds with N-bromosuccinimide in the presence of 2,2'-azobis(isobutyronitrile).

4-(Bromomethyl)-1-iodo-2-nitrobenzene can be prepared, for example, by brominating (4-iodo-3-nitrophenyl)-methanol, available from Combi-Blocks, with hydrobromic acid.

Other benzyl bromides are commercially available; those that are not available can be prepared, for example, by reacting a correspondingly substituted toluene with N-bromosuccinimide in the presence of 2,2'-azobis(isobutyronitrile), or by reducing a correspondingly substituted benzaldehyde or methyl benzoate with sodium borohydride or lithium aluminum hydride to obtain benzyl alcohol, which can then be brominated with hydrobromic acid or phosphorus tribromide.

The reaction of the organic halide represented by formula (II) with the protected amino acid can be carried out in the presence of an organic solvent, a basic aqueous solution, and a phase transfer catalyst. Examples of the protected amino acid include p-chlorobenzaldehyde imine and benzophenone imine. Preferably, the protected amino acid is p-chlorobenzaldehyde imine having the following structure:

Here, R ⁶ represents H or an optionally substituted C1-C6 alkyl.

The organic solvent used here is not limited, but preferred examples include toluene, benzene, xylene, mesitylene, ethyl ether, isopropyl ether, tetrahydrofuran, dioxane, ethyl acetate, isopropyl acetate, cyclopentyl methyl ether, and methyl t-butyl ether.

The basic aqueous solution is preferably an aqueous solution of calcium hydroxide, cesium hydroxide, potassium hydroxide, etc.

The phase transfer catalyst may be, for example, a Maruoka reagent. Maruoka reagents are not limited to, but are preferably, (R)-4,4-dibutyl-2,6-bis(3,4,5-trifluorophenyl)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]azepinium bromide, (R)-4,4-dibutyl-2,6-bis(3,4,5-trifluorophenyl)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]azepinium bromide, Examples of compounds that can be used include (S)-4,4-dibutyl-2,6-bis(3,4,5-trifluorophenyl)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]azepinium bromide, (S)-4,4-dibutyl-2,6-bis(3,4,5-trifluorophenyl)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]azepinium bromide, and the like.

The reaction temperature is preferably between -20°C and 10°C, and the reaction time can be approximately 1 hour to 60 hours.

After the reaction is complete, the product can be extracted with an organic solvent such as toluene and then washed, dried, and filtered as appropriate.

Next, a solvent is added to this reaction product and reacted with the acid. Preferably, an ether-based solvent is used. Examples of ether-based solvents include, but are not limited to, diethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, cyclopentyl methyl ether, glyme, and diglyme. In the present invention, tetrahydrofuran is particularly preferred.

Acids include organic acids such as citric acid, acetic acid, trichloroacetic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, toluenesulfonic acid, and methanesulfonic acid, and inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

The reaction is preferably carried out at a temperature ranging from 0°C to 50°C.

The reaction time is approximately 1 to 10 hours, more preferably 2 to 8 hours, and even more preferably 3 to 6 hours.

The amino group of the resulting compound is protected using standard methods. Protecting groups are not limited, but carbamate protecting groups, amide protecting groups, and alkyl protecting groups are preferred. Examples of carbamate protecting groups include tert-butoxycarbonyl (Boc), benzyloxycarbonyl (Cbz), 9-fluorenylmethyloxycarbonyl (Fmoc), and 2,2,2-trichloroethoxycarbonyl (Troc). Examples of amide protecting groups include acetyl and benzoyl groups. Examples of alkyl protecting groups include benzyl groups.

Next, the compound obtained as described above or an amine having a boronic acid or borono group is reacted with an amine compound in a solvent together with a condensing agent to condense.

Condensing agents include, but are not limited to, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HATU), diphenylphosphoryl azide, and the like.

The above reaction can also be carried out in the presence of a base. Examples of bases include organic bases such as TEA, DIPEA, and pyridine.

Additives can also be used in the above reaction to suppress racemization. Examples of additives include 1-hydroxybenzotriazole, 1-hydroxybenzotriazole monohydrate, 1-hydroxy-7-azabenzotriazole, N-hydroxy-5-norbornene-2,3-dicarboximide, 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine, and N-hydroxysuccinimide.

Solvents that can be used include, but are not limited to, halogenated solvents, ether solvents, amides, nitriles, or mixtures thereof.

Examples of halogen-based solvents include, but are not limited to, dichloromethane, chloroform, and carbon tetrachloride.

Examples of ether solvents include, but are not limited to, diethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, cyclopentyl methyl ether, glyme, and diglyme.

Examples of amide solvents include, but are not limited to, dimethylformamide (DMF), dimethylacetamide (DMA), and N-methylpyrrolidone (NMP).

Examples of nitrile solvents include acetonitrile and propionitrile.

The reaction temperature is not limited, but is preferably between -78°C and 200°C, and more preferably between -20°C and 50°C.

The reaction time is not limited, but is usually about 1 to 24 hours.

Next, the resulting compound is reacted with a boron compound, if necessary, in a solvent in the presence of a palladium catalyst, an organophosphorus compound, and a base. If the compound already contains a boronic acid or borono group, this step can be omitted.

Here, examples of palladium catalysts include, but are not limited to, palladium(II) acetate, palladium(II) chloride, tris(dibenzylideneacetone)dipalladium(0), [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride dichloromethane adduct, and tetrakis(triphenylphosphine)palladium(0).

Organophosphorus compounds include, but are not limited to, triphenylphosphine, tricyclohexylphosphine, 1,1'-bis(diphenylphosphino)ferrocene, 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl, 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl, and 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl.

Examples of bases include, but are not limited to, potassium acetate, sodium acetate, sodium carbonate, cesium carbonate, potassium carbonate, and sodium bicarbonate.

Examples of boron compounds include boric acid esters and boric acid amides, and preferably refer to compounds represented by B(OR) ₃ , B(NR) ₃ , B(OR) ₂ (NR), (RO) ₂ B-B(OR) ₂ , or B(OR)(NR) ₂ (R is a linear or branched C1-C10 alkyl group, a phenyl group, or a benzyl group). Of these, compounds represented by (RO) ₂ B-B(OR) ₂ are particularly preferred. Here, the term "linear or branched C1-C10 alkyl group" refers to any alkyl group having 1 to 10 carbon atoms, but is preferably a linear or branched C1-C8 alkyl group, and more preferably a linear or branched C1-C6 alkyl group. Examples of these groups include, but are not limited to, a methyl group, an ethyl group, an isopropyl group, and a butyl group. A representative example of the boron compound is, but is not limited to, bis(pinacolato)diboron.

Solvents include, but are not limited to, ether solvents such as 1,4-dioxane, tetrahydrofuran, and 1,2-dimethoxyethane; hydrocarbon solvents such as toluene; and polar solvents such as N,N-dimethylformamide and dimethyl sulfoxide. A preferred solvent is dimethyl sulfoxide. The reaction temperature is, for example, 20°C to 160°C, and preferably 60°C to 120°C.

The resulting compound is then sequentially deprotected or directly subjected to the next step. Deprotection can be carried out according to conventional methods, such as hydrolysis, catalytic hydrogenation, decarboxylation, or oxidation.

In each step of the production process, purification is carried out according to standard methods, and may be modified as appropriate.

In particular, when the compound is a racemate, it can be used as is, or the optical purity of the R or S isomer can be increased to obtain a compound suitable for use in, for example, boron neutron capture therapy.

Optical resolution may be performed using known techniques as appropriate. For example, a method that involves a hydrolysis step, an esterification step, and then optical resolution (using α-chymotrypsin, for example) can be used, as well as a simplified method that involves a hydrolysis step followed by a simplified step using acylase.

[BNCT (boron neutron capture therapy) drugs]
The boronophenylalanine amide derivatives of the present invention can be conveniently used for BNCT in the form of the above-mentioned compound or a pharmaceutically acceptable salt thereof, as is, or in the form of a formulation known to those skilled in the art after mixing with a pharmaceutically acceptable carrier, or in the form of being encapsulated in micro/nanoparticles, etc.

Treatment with the boronophenylalaninamide derivative formulations of the present invention is carried out by administering them via any suitable route in a manner that allows the boronophenylalaninamide derivative to accumulate in the target tumor. The boronophenylalaninamide derivative is preferably concentrated in the tumor prior to radiation exposure, with a tumor:blood ratio of at least 1.5:1, preferably 2:1 or greater, prior to radiation exposure. The boronophenylalaninamide derivative can be administered all at once or over a continuous period. In some cases, it can be administered in divided doses. After the desired accumulation of the compound in the tumor has been achieved, the site is irradiated with an effective amount of low-energy neutron radiation (e.g., epithermal neutron radiation). The site can be irradiated through the skin, or the site can be fully or partially exposed prior to irradiation. Administration of the boronophenylalaninamide derivative followed by subsequent radiation exposure can be repeated as necessary. If desired, treatment with the boronophenylalaninamide derivative can be followed by surgery to shrink the tumor to a surgically feasible size. Alternatively, surgery can be performed, followed by destruction of the remaining tumor using the boronophenylalaninamide derivative of the present invention. In another embodiment, a patient is administered an appropriate amount of a boronophenylalanine amide derivative and irradiated with an effective amount of the naturally occurring neutron emitter, californium-252, which is preferably inserted into the tumor and removed at an appropriate time.

Here, the type of tumor is not particularly limited, but particularly suitable tumors include brain tumors, including glioblastoma and malignant glioma, as well as other head and neck cancers, malignant melanoma, breast cancer, and prostate cancer. Other tumors that may be targeted include epithelial cell cancers such as lung cancer, uterine cancer, kidney cancer, and liver cancer, as well as various sarcomas.

The boronophenylalanine amide derivatives of the present invention can be administered orally or parenterally. Parenteral administration can be intra-arterial (e.g., via the carotid artery), intramuscular, subcutaneous, intramedullary, intrathecal, intraventricular, intravenous, intraperitoneal, or intranasal.

The formulation may be in any form, such as powder, granules, fine granules, dry syrup, tablets, capsules, injections, or liquids. Depending on the dosage form, the formulation may be mixed with appropriate additives and/or pharmaceutically acceptable carriers using methods known in pharmaceutical science, and administered to patients alone or in combination with other drugs. Examples of additives include excipients; disintegrants; binders; lubricants; diluents; buffers such as phosphate, citric acid, succinic acid, acetic acid, and other organic acids or their salts; isotonicity agents; preservatives; wetting agents; emulsifiers; dispersing agents; stabilizers; solubilizers; antioxidants such as ascorbic acid; low molecular weight (fewer than about 10 residues) polypeptides (e.g., polyarginine or tripeptides); proteins (e.g., serum albumin, gelatin, or immunoglobulins); hydrophilic polymers (e.g., polyvinylpyrrolidone); amino acids (e.g., glycine, glutamic acid, aspartic acid, or arginine); monosaccharides, disaccharides, and other carbohydrates (including cellulose or derivatives thereof, glucose, mannose, or dextrin); chelating agents (e.g., EDTA); sugar alcohols (e.g., mannitol or sorbitol); counterions (e.g., sodium); and/or non-ionic surfactants (e.g., polysorbates, poloxamers). These pharmaceutical additives can be mixed or diluted/dissolved as needed to prepare a formulation. Preferred carriers include, but are not limited to, pharmaceutically inert aqueous carriers. Examples of such carriers include saline, buffered saline, dextrose, and water. In one embodiment of the present invention, the pharmaceutically acceptable carrier is pharmaceutically inert. Suitable additives and/or pharmaceutically acceptable carriers are non-toxic to recipients at the dosages and concentrations used. A particularly preferred formulation is an injectable solution prepared with an aqueous carrier.

Techniques for formulation and administration are described, for example, in the latest edition of the Japanese Pharmacopoeia and its latest supplement, "REMINGTON'S PHARMACEUTICAL SCIENCES" (Maack Publishing Co., Easton, PA).

The formulations of the boronophenylalaninamide derivatives of the present invention contain a target drug in an amount effective to achieve its intended purpose, and the terms "therapeutically effective amount" or "pharmacologically effective amount" are well-recognized by those skilled in the art and refer to an amount of drug effective to produce a pharmacological result. Determination of a therapeutically effective dose is well known to those skilled in the art.

A therapeutically effective amount, as used herein, refers to the amount of a drug that alleviates a disease state following administration by irradiation. The therapeutic efficacy and toxicity of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals. The dosage is preferably within a range of circulating concentrations that includes the _ED50 with little or no toxicity. This dosage will vary within this range depending on the dosage form used, the sensitivity of the patient, and the route of administration. For example, the dosage is selected appropriately depending on the age and other conditions of the patient, the type of disease, the type of conjugate used, and the like. A preferred dosage is, but is not limited to, 5 to 1,000 mg/kg of derivative administered in a single treatment. In particular, the dosage may be 5 to 500 mg, more preferably 6 to 480 mg, of the derivative per kg of body weight of the subject to be treated.

[Radioisotope-containing diagnostic agents]
The boronophenylalanine amide derivatives of the present invention can also be prepared as pharmaceuticals containing radioisotopes. When preparing pharmaceuticals containing radioisotopes, typically, but not limited to, ^18F can be used as the F atom contained in the compound, ^131I or ^123I can be used as the I atom contained in the compound, or ^11C can be used as the C atom contained in the compound. The position of these radioisotopes can be any position in ^R3 , or, when ^R4 or ^R5 contains an aryl or heteroaryl, they can be introduced as a substituent thereon. The compounds obtained in this manner can be used, for example, for RI tests or nuclear medicine tests. These include, but are not limited to, agents for scintigraphy tomography, SPECT (Single Photon Emission Computed Tomography), and PET (Positron Emission Tomography). That is, the radioactive boronophenylalanine amide derivative of the present invention is administered to a subject as an agent for PET or SPECT, and images are obtained before treatment, allowing information such as the distribution of accumulation of the derivative in the body and the tumor tissue/normal tissue abundance ratio (T/N ratio) to be obtained. Based on this information, it is possible to predict the therapeutic effect of BNCT in advance and formulate research or treatment plans. The mode of administration and other details are in accordance with the contents described in the section [Agent for BNCT (Boron Neutron Capture Therapy)].

The present invention will be further described in detail by the following examples, but the invention is not limited thereto.

In the examples below, the analysis, separation, and purification of compounds were performed using the following equipment and reagents.

NMR spectrum:
(JEOL RESONANCE/JNM-ECZ500R/500MHz

Example 1
Preparation of (S)-(4-(2-amino-3-(benzo[d][1,3]dioxol-5-ylamino)-3-oxopropyl)phenyl)boronic acid

Step 1
Preparation of tert-butyl (S)-(1-(benzo[d][1,3]dioxol-5-ylamino)-3-(4-iodophenyl)-1-oxopropan-2-yl)carbamate Boc-4-iodo-L-phenylalanine (4.00 g, 10.2 mmol), 1,2,3-benzotriazol-1-ol monohydrate (1.87 g, 12.2 mmol), and 3,4-methylenedioxyaniline (1.67 g, 12.2 mmol) were dissolved in DMF (80 mL). 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (2.74 g, 14.3 mmol), which had been dissolved in DMF (27 mL), was added to the solution in an ice bath. The mixture was then allowed to cool to room temperature and stirred overnight. After completion of the reaction, ethyl acetate (27 mL) and distilled water (27 mL) were added. After stirring for approximately 5 minutes, the mixture was transferred to a separatory funnel. The aqueous layer was further extracted with ethyl acetate (29 mL). The resulting ethyl acetate layers were combined and washed with saturated brine (27 mL). After drying over anhydrous magnesium sulfate, the residue obtained by filtration was roughly purified by silica gel column chromatography to obtain 4.2 g of the target product (yield 81%).
¹ H NMR (DMSO-d ₆ ); 1.26 (s, 9H, t-Bu), 2.75 (dd, J = 10.5, 14.0 Hz, 1H, β-H), 2.92 (dd, J = 4.0, 13.5 Hz, 1H, β-H), 3.71 (s, OC H ₂ O), 4.23-4.28 (m, 1H, α-H), 6.63 (d, J = 8.0 Hz, 1H, NH), 7.11-7.13 (m, 3H, ArH), 7.20 (t, J = 8.0 Hz, 2H, ArH), 7.24 (s, 1H, ArH), 7.63 (d, J = 8.0 Hz, 2H, ArH), 10.05 (s, 1H, NH).

Step 2
Preparation of (S)-(4-(3-(benzo[d][1,3]dioxol-5-ylamino)-2-((tert-butoxycarbonyl)amino)-3-oxopropyl)phenyl)boronic acid The Boc compound obtained in Step 1 (4.20 g, 8.23 mmol), Pd(dppf) _2.CH2Cl2 (336 mg, 0.412 mmol), and _potassium acetate (1.60 _g , 16.5 mmol) were added to DMSO (42 mL), and the mixture was reacted at 100°C for 2 hours. After completion of the reaction, the reaction solution was cooled in an ice bath, and ethyl acetate (42 mL) and distilled water (42 mL) were added. After stirring for approximately 5 minutes, the mixture was filtered through Celite, and the obtained filtrate was transferred to a separatory funnel. The aqueous layer was further extracted with ethyl acetate (42 mL), and the obtained ethyl acetate layers were combined and washed with saturated brine (42 mL). After drying over anhydrous magnesium sulfate, the residue obtained by filtration was roughly purified by silica gel column chromatography.
The obtained crude product was dissolved in acetone (200 mL). A separate aqueous solution of sodium periodate (4.40 g, 20.6 mmol) and ammonium acetate (2.00 g, 20.6 mmol) dissolved in distilled water (200 mL) was added to this acetone solution. The mixture was then allowed to react at room temperature for two days. After the reaction was completed, the acetone was evaporated under reduced pressure, and the resulting aqueous solution was extracted twice with ethyl acetate (84 mL). The extract was then dried over anhydrous magnesium sulfate, filtered, and the ethyl acetate solution was evaporated under reduced pressure. This was purified by silica gel column chromatography to obtain 1.9 g of the target product (yield: 55%).
¹ H NMR (DMSO-d ₆ ); 1.30 (s, 9H, t-Bu), 2.81 (dd, J = 10.0, 13.5 Hz, 1H, β-H), 2.96 (dd, J = 5.0, 14.0 Hz, 1H, β-H), 3.71 (s, OC H ₂ O), 4.27-4.32 (m, 1H, α-H), 6.62 (d, J = 7.5 Hz, 1H, NH), 7.08-7.13 (m, 2H, ArH), 7.20 (t, J = 8.0 Hz, 1H, ArH), 7.25-7.27 (m, 3H, ArH), 7.69 (d, J = 8.0 Hz, 2H, ArH), 7.98 (s, 2H, B(OH) ₂ ), 10.04 (s, 1H, NH).

Step 3
Preparation of (S)-(4-(2-amino-3-(benzo[d][1,3]dioxol-5-ylamino)-3-oxopropyl)phenyl)boronic acid The pinacol-removed product (1.00 g, 2.34 mmol) obtained in Step 2 was dissolved in trifluoroacetic acid (10 mL). After standing for about 3 hours, the solution was concentrated under reduced pressure. The solution was dissolved in a small amount of distilled water and neutralized with sodium carbonate to precipitate the target product. This was collected by filtration and washed with cold water to obtain 0.35 g of the target product (yield 46%).
¹ H NMR (3.5% DCl in D ₂ O); 3.22 (dd, J = 8.5, 13.0 Hz, 1H, β-H), 3.37 (dd, J = 6.5, 13.0 Hz, 1H, β-H), 4.27 (dd, J = 6.5, 9.0 Hz, 1H, α-H), 5.96 (s, 1H, OCH ₂ O), 6.60 (dd, J = 2.5, 8.5 Hz, 1H, ArH), 6.76 (d, J = 2.5 Hz, 1H, ArH). 6.81 (d, J = 8.0 Hz, 1H, ArH), 7.34 (d, J = 7.5 Hz, 1H, ArH), 7.75 (d, J = 7.5 Hz, 1H, ArH).

Example 2
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2,3-diamino-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.54 (d, J = 7.5 Hz, 0.8H, ArH (minor)), 7.53 (d, J = 7.5 Hz, 1.2H, ArH (major)), 7.19 (d, J = 7.5 Hz, 0.8H, ArH), 7.17 (d, J = 7.5 Hz, 1.2H, ArH (major)), 4.24 (dd, J = 6.0, 8.5 Hz, 0.4H, CH (minor)), 3.66 (t, J = 6.5 Hz, 0.6H, CH (major)), 3.04 (dd, J = 6.0, 14.0 Hz, 0.4H, CH ₂ ), 2.97-2.91 (m, 1H, CH ₂ ), 2.86 (dd, J = 6.5, 14.0 Hz, 0.6H, CH ₂ (major)).

Example 3
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(methylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.53-7.51 (m, 2H, ArH), 7.15-7.10 (m, 2H, ArH), 4.21 (t, J = 7.0 Hz, 0.4H, CH (minor)), 3.59 (t, J = 6.5 Hz, 0.6H, CH (major)), 3.02-2.84 (m, 2H, CH ₂ ), 2.69 (s, 1.2H, CH ₃ (minor)), 2.65 (s, 1.8H, CH ₃ (major)).

Example 4
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(dimethylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.63-7.60 (m, 2H, ArH), 7.23 (d. J = 8.0 Hz, 0.4H, ArH (minor)), 7.19 (d, J = 6.5 Hz, 1.6H, ArH (major)), 4.77 (t, J = 8.0 Hz, 0.2H, CH (minor)), 4.21 (t, J = 7.0 Hz, 0.8H, CH (major)), 2.99-2.72 (m, 8H, CH ₂ , CH ₃ ).

Example 5
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(ethylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 0.93 (t, J = 7.5 Hz, 3H, OCH ₂ CH ₃ ), 3.08 (dd, J = 8.0, 13.5 Hz, 1H, β-H), 3.17 (q, J = 7.5 Hz, 2H, O CH ₂ CH ₃ ), 3.29 (dd, J = 6.5, 13.5 Hz, 1H, β-H), 4.22 (dd, J = 6.5, 8.0 Hz, 1H, α-H), 7.34 (d, J = 8.0 Hz, 2H, ArH), 7.76 (d, J = 8.0 Hz, 2H, ArH).

Example 6
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(diethylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.52 (d, J = 5.0 Hz, 2H, ArH), 7.15 (dd, J = 5.0, 10.0 Hz, 2H, ArH), 4.71 (t, J = 10.0 Hz, 0.5H, CH), 4.03 (t, J = 10.0 Hz, 0.5H, CH), 3.46 (m, 1H, ArH), 3.26-2.99 (m, 3H, CH ₂ ), 2.91-2.82 (m, 2H, CH ₂ ), 1.07-0.99 (m, 6H, CH ₃ ).

Example 7
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(tert-butylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.52 (d, J = 7.5 Hz, 0.6H, ArH (minor)), 7.52 (d, J = 8.0 Hz, 1.4H, ArH (major)), 7.16 (d, J = 7.5 Hz, 0.6H, ArH (minor)), 7.13 (d, J = 8.0 Hz, 1.4H, ArH (major)), 4.13 (t, J = 6.5 Hz, 0.3H, CH (minor)), 3.49 (t, J = 7.0 Hz, 0.7H, CH (major)), 2.93-2.80 (m, 2H, CH ₂ ), 1.24 (s, 2.7H, CH ₃ (minor)), 1.21 (s, 6.3H, CH ₃ ).

(Example 8)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(cyclohexylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.75 (d, J = 8.0 Hz, 2H, ArH), 7.30 (d, J = 8.0 Hz, 2H, ArH), 4.07 (dd, J = 6.0, 9.5 Hz, 1H, CH), 3.47 (m, 1H, CH), 3.27 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.09 (dd, J = 9.5, 13.5 Hz, 1H, CH ₂ ), 1.72 (m, 1H, CH ₂ ), 1.62 (m, 1H, CH ₂ ), 1.53-1.49 (m, 2H, CH ₂ ), 1.41 (m, 1H, CH ₂ ), 1.29-1.02 (m, 4H, CH ₂ ), 0.81 (m, 1H, CH ₂ ).

Example 9
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(pyrrolidin-1-yl)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.51-7.49 (m, 2H, ArH), 7.16-7.12 (m, 2H, ArH), 4.53 (dd, J = 6.5, 8.25 Hz, 0.5H, CH (A-isomer)), 3.91 (dd, J = 6.0, 8.5 Hz, 0.5H, CH (B-isomer)), 3.53-3.23 (m, 3H, CH2), 2.95-2.80 (m, 3H, CH ₂ ), 1.81-1.59 (m, 4H, CH ₂ ).

Example 10
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-morpholino-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.78 (d, J = 8.0 Hz, 2H, ArH), 7.33 (d, J = 8.0 Hz, 2H, ArH), 4.76 (dd, J = 6.0, 9.5 Hz, 1H, CH), 3.71-3.62 (m, 2H, CH ₂ ), 3.50-3.39 (m, 3H, CH ₂ ), 3.34-3.27 (m, 2H, CH ₂ ), 3.12 (dd, J = 9.5, 13.5 Hz, 1H, CH ₂ ), 3.01 (m, 1H, CH ₂ ), 2.69 (m, 1H, CH ₂ ).

Example 11
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(phenylamino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.74 (dd, J = 5.0, 10.0 Hz, 2H, ArH), 7.41-7.34 (m, 4H, ArH), 7.28-7.24 (m, 3H, ArH), 4.39 (t, J = 15.0 Hz, 1H, CH), 3.38 (dd, J = 5.0, 15.0 Hz, 1H, CH ₂ ), 3.26 (dd, J = 5.0, 15.0 Hz, 1H, CH ₂ ).

Example 12
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(naphthalen-1-ylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 10.27 (brd, J = 9.5 Hz, 1H), 8.47 (brs, 3H), 8.12 (s, 1H), 7.93 (d, J = 8.0 Hz, 1H, ArH), 7.82-7.3 (m, 10H, ArH), 4.40 (t, J = 8.0 Hz, 1H, CH), 3.27-3.16 (m, 2H, CH ₂ ).

Example 13
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(methyl(phenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O containing K ₂ CO ₃ ): δ 7.63-6.86 (m, 9H, ArH), 4.34 (t, J = 10.0 Hz, 0.6H, CH (major)), 3.62 (t, J = 10.0 Hz, 0.4H, CH (minor)), 3.20 (s, 1.8H CH ₃ (major)), 3.18 (s, 1.4H, CH ₃ (minor)), 2.84 (m, 1H, CH ₂ ), 2.65 (m, 1H, CH ₂ ).

Example 14
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(benzylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.36-7.32 (m, 3H, ArH), 7.06-7.02 (m, 4H, ArH), 6.78-6.75 (m, 2H, ArH), 4.44 (d, J = 15.0 Hz, 1H, CH ₂ ), 4.18 (dd, J = 6.0, 10.0 Hz, 1H, CH), 4.13 (d, J = 15.0 Hz, 1H, CH ₂ ), 3.19 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.01 (dd, J = 10.0, 13.5 Hz, 1H, CH ₂ ).

Example 15
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(benzyl(methyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 8.34 (brs, 1H), 7.71-7.68 (m, 2H, ArH), 7.27-6.97 (m, 7H, ArH), 4.53-4.24 (m, 3H, CH ₂ , CH), 2.91-2.89 (m, 2H, CH ₂ ), 2.70 (s, 3H, CH ₃ (minor)), 2.67 (s, 3H, CH ₃ (major)).

Example 16
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(dibenzylamino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 7.99 (brs, 2H), 7.68 (d, J = 8.0 Hz, 2H, ArH), 7.28-7.01 (m, 12H, ArH), 4.53-4.29 (m, 4H, CH ₂ ), 3.90 (t, J = 7.0 Hz, 1H, CH), 2.90 (dd, J = 7.0, 13.0 Hz, 1H, CH ₂ ), 2.72 (dd, J = 7.0, 13.0 Hz, 1H, CH ₂ ).

(Example 17)
The following compounds were prepared in the same manner as in Example 1.
(4-((S)-2-amino-3-oxo-3-(((S)-1-phenylethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.54 (d, J = 7.5 Hz, 2H, ArH), 7.31-7.25 (m, 3H, ArH), 7.12 (d, J = 7.5 Hz, 2H, ArH), 6.92-6.90 (m, 2H, ArH), 4.82 (m, 1H, CH), 4.15 (dd, J = 6.0, 10.0 Hz, 1H, CH), 3.25 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.01 (dd, J = 10.0, 13.5 Hz, 1H, CH ₂ ), 1.35 (d, J = 7.5 Hz, 3H, _CH3 ).

(Example 18)
The following compounds were prepared in the same manner as in Example 1.
(4-((S)-2-amino-3-oxo-3-(((R)-1-phenylethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.79 (d, J = 8.0 Hz, 2H, ArH), 7.40-7.26 (m, 7H, ArH), 4.72 (m, 1H, CH), 4.19 (m, 1H, CH), 3.32 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.14 (dd, J = 9.0, 13.5 Hz, 1H, CH ₂ ), 1.12 (d, J = 7.0 Hz, 3H, CH ₃ ).

Example 19
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((2-phenylpropan-2-yl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.82 (d, J = 7.5 Hz, 2H, ArH), 7.36-7.26 (m, 5H, ArH), 7.12 (d, J = 7.5 Hz, 2H, ArH), 4.31 (dd, J = 6.0, 9.0 Hz, 1H, CH), 3.27 (dd, J = 6.0, 14.0 Hz, 1H, CH ₂ ), 3.12 (dd, J = 9.0, 14.0 Hz, 1H, CH ₂ ), 1.51 (s, 3H, CH ₃ ), 1.43 (s, 3H, CH ₃ ).

(Example 20)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(p-tolylamino)propyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 2.23 (s, 3H, CH ₃ ), 3.28 (dd, J = 8.5, 13.5 Hz, 1H, β-H), 3.40 (dd, J = 6.0, 13.5 Hz, 1H, β-H), 4.44 (dd, J = 6.5, 8.0 Hz, 1H, α-H), 7.11 (d, J = 8.0 Hz, 2H, ArH), 7.20 (d, J = 8.5 Hz, 2H, ArH), 7.37 (d, J = 8.0 Hz, 2H, ArH), 7.73 (d, J = 8.0 Hz, 2H, ArH).

(Example 21)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(m-tolylamino)propyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 10.37 (brs, 1H), 8.35 (brs, 3H), 8.13 (brs, 1H), 7.73 (d, J = 8.0 Hz, 1.3H, ArH (major)), 7.62 (d, J = 7.5 Hz, 0.7H, ArH (minor)), 7.34-7.20 (m, 5H, ArH), 6.93 (d, J = 7.5 Hz, 1H, ArH), 4.16 (t, J = 7.0 Hz, 1H, CH), 3.17 (m, 1H, CH ₂ ), 3.08 (m, 1H, CH ₂ ), 2.28 (s, 3H, _CH3 ).

Example 22
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3,4-dimethylphenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 2.18 (s, 6H, CH ₃ ×2), 3.22 (dd, J = 9.0, 13.5 Hz, 1H, β-H), 3.39 (dd, J = 6.5, 13.5 Hz, 1H, β-H), 4.32 (dd, J = 7.0, 9.0 Hz, 1H, α-H), 6.86 (d, J = 2.0 Hz, 1H, ArH), 6.96 (dd, J = 2.5, 8.5 Hz, 1H, ArH), 7.12 (d, J = 8.0 Hz, 1H, ArH), 7.33 (d, J = 8.0 Hz, 2H, ArH), 7.74 (d, J = 8.0 Hz, 2H, ArH).

(Example 23)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((4-(tert-butyl)phenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 10.45 (brs, 0.25H (minor)), 10.42 (brs, 0.75H (major)), 8.38 (brs, 2H), 7.74 (d, J = 7.5 Hz, 1.5H, ArH (major)), 7.62 (d, J = 7.5 Hz, 0.5H, ArH (minor)), 7.43 (d, J = 6.5 Hz, 2H, ArH), 7.35 (d, J = 6.5 Hz, 2H, ArH), 7.29 (d, J = 7.5 Hz, 0.5H, ArH (minor)), 7.23 (d, J = 7.5 Hz, 1.5H, ArH (major), 4.17 (m, 1H, CH), 3.21-3.07 (m, 2H, CH ₂ ), 1.27 (s, 2.25H, CH ₃ (minor)), 1.25 (s, 6.75H, CH ₃ (major)).

(Example 24)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((2-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 9.68 (s, 1H), 8.37 (s, 3H), 8.14 (s, 2H), 7.82 (dd, J = 1.5, 8.0 Hz, 1H, ArH), 7.75 (d, J = 7.5 Hz, 2H, ArH), 7.26 (d, J = 7.5 Hz, 2H, ArH), 7.13 (dt, J = 1.5, 8.0 Hz, 1H, ArH), 7.05 (dd, J = 1.5, 8.0 Hz, 1H, ArH), 6.93 (dt, J = 1.5, 8.0 Hz, 1H, ArH), 4.44 (t, J = 7.0 Hz, 1H, CH), 3.78 (s, 3H, CH ₃ ), 3.14 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ), 3.08 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ).

Example 25
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 3.27 (dd, J = 8.5, 14.0 Hz, 1H, β-H), 3.40 (dd, J = 7.0, 14.0 Hz, 1H, β-H), 3.77 (s, 3H, OCH ₃ ), 4.46 (dd, J = 7.0, 8.5 Hz, 1H, α-H), 6.78-81 (m, 2H, ArH), 6.89-6.90 (m, 1H, ArH), 7.37 (d, J = 8.0 Hz, 2H, ArH), 7.73 (d, J = 8.0 Hz, 2H, ArH).

(Example 26)
The following compounds were prepared in the same manner as in Example 1.
(R)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 3.27 (dd, J = 8.5, 14.0 Hz, 1H, β-H), 3.40 (dd, J = 7.0, 14.0 Hz, 1H, β-H), 3.77 (s, 3H, OCH ₃ ), 4.46 (dd, J = 7.0, 8.5 Hz, 1H, α-H), 6.78-81 (m, 2H, ArH), 6.89-6.90 (m, 1H, ArH), 7.37 (d, J = 8.0 Hz, 2H, ArH), 7.73 (d, J = 8.0 Hz, 2H, ArH).

(Example 27)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3,4-dimethoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 3.23 (dd, J = 8.5, 13.0 Hz, 1H, β-H), 3.41 (dd, J = 6.0, 13.5 Hz, 1H, β-H), 3.75 (s, 3H, OCH ₃ ), 3.78 (s, 3H, OCH ₃ ), 4.42 (dd, J = 6.0, 8.5 Hz, 1H, α-H), 6.63 (d, J = 2.5 Hz, 1H, ArH), 6.79 (dd, J = 2.5, 8.5 Hz, 1H, ArH), 6.87 (d, J = 8.5 Hz, 1H, ArH), 7.36 (d, J = 8.0 Hz, 2H, ArH), 7.75 (d, J = 8.0 Hz, 2H, ArH).

(Example 28)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((3,4,5-trimethoxyphenyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.76 (d, J = 8.0 Hz, 2H, ArH), 7.33 (d, J = 8.0 Hz, 2H, ArH), 6.42 (s, 2H, ArH), 4.31 (dd, J = 6.5, 9.5 Hz, 1H, CH), 3.80 (s, 6H, CH ₃ ), 3.74 (s, 3H, CH ₃ ), 3.44 (dd, J = 6.5, 13.5 Hz, 1H, CH ₂ ), 3.18 (dd, J = 9.5, 13.5 Hz, 1H, CH ₂ ).

(Example 29)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((2,3-dihydroxybenzo[b][1,4]dioxin-6-yl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 3.27 (dd, J = 8.5, 14.0 Hz, 1H, β-H), 3.38 (dd, J = 7.0, 14.0 Hz, 1H, β-H), 4.24 (s, 4H, OCH ₂ CH ₂ O), 4.44 (dd, J = 7.0, 8.5 Hz, 1H, α-H), 6.69 (dd, J = 2.0 Hz, 8.5, 1H, Ar), 6.78 (d, J = 2.0 Hz, 1H, ArH), 6.81 (d, J = 8.5 Hz, 1H, ArH), 7.36 (d, J = 8.0 Hz, 2H, ArH), 7.73 (d, J = 8.0 Hz, 2H, ArH).

(Example 30)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((4-nitrophenyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 3.12 (dd, J = 7.5, 13.5 Hz, 1H, β-H), 3.19 (dd, J = 6.5, 13.5 Hz, 1H, β-H), 4.26 (dd, J = 6.5, 8.0 Hz, 1H, α-H), 7.15 (d, J = 8.0 Hz, 2H, ArH), 7.32 (d, J = 9.0 Hz, 2H, ArH), 7.54 (d, J = 8.0 Hz, 2H, ArH), 7.92 (d, J = 9.5 Hz, 2H, ArH).

(Example 31)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(phenethylamino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.73 (d, J = 7.5 Hz, 2H, ArH), 7.34 (t, J = 7.5 Hz, 2H, ArH), 7.28 (dd, J = 6.0, 7.5 Hz, 1H, ArH), 7.21 (d, J = 7.5 Hz, 2H, ArH), 7.14 (d, J = 7.5 Hz, 2H, ArH), 4.13 (t, J = 8.0 Hz, 1H, CH), 3.55 (ddd, J = 7.0, 8.0, 13.5 Hz, 1H, CH ₂ ), 3.31 (ddd, J = 7.0, 8.0, 13.5 Hz, 1H, CH ₂ ), 3.15 (dd, J = 8.0, 13.5 Hz, 1H, CH ₂ ), 3.08 (dd, J = 8.0, 13.5 Hz, 1H, CH ₂ ), 2.71-2.61 (m, 2H, ArH).

(Example 32)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((4-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.70 (dd, J = 2.5, 8.5 Hz, 2H, ArH), 7.16 (dd, J = 2.5, 8.0 Hz, 2H, ArH), 7.04 (dd, J = 2.5, 8.5 Hz, 2H, ArH), 6.89 (dd, J = 2.5, 8.0 Hz, 2H, ArH), 4.12 (dd, J = 6.5, 8.0 Hz, 1H, CH), 3.79 (s, 3H, CH ₃ ), 3.53 (ddd, J = 6.5, 7.0, 13.5 Hz, 1H, CH ₂ ), 3.25 (ddd, J = 6.5, 7.0, 13.5 Hz, 1H, CH ₂ ), 3.13 (dd, J = 6.5, 14.0 Hz, 1H, CH ₂ ), 3.06 (dd, J = 8.0, 14.0 Hz, 1H, CH ₂ ), 2.60 (m, 2H, CH ₂ ).

(Example 33)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.68 (d, J = 8.0 Hz, 2H, ArH), 7.26 (t, J = 8.0 Hz, 1H, ArH), 7.15 (d, J = 8.0 Hz, 2H, ArH), 6.85 (m, 1H, ArH), 6.76-6.74 (m, 2H, ArH), 4.12 (dd, J = 6.5, 8.5 Hz, 1H, CH), 3.79 (s, 3H, CH ₃ ), 3.56 (m, 1H, CH ₂ ), 3.29 (m, 1H, CH ₂ ), 3.12 (dd, J = 6.5, 13.5 Hz, 1H, CH ₂ ), 3.05 (dd, J = 8.5, 13.5 Hz, 1H, CH ₂ ), 2.66-2.63 (m, 2H, CH ₂ ).

(Example 34)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((4-fluorophenethyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 8.48 (t, J = 5.5 Hz, 1H), 8.22 (brs, 3H), 7.75 (d, J = 8.0 Hz, 2H, ArH), 7.16-7.06 (m, 6H, ArH), 3.93 (m, 1H, CH), 3.39 (m, 1H, CH ₂ ), 3.18 (m, 1H, CH ₂ ), 2.99 (dd, J = 6.5, 13.5 Hz, 1H, CH ₂ ), 2.92 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ), 2.60 (m, 2H, CH ₂ ).

(Example 35)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((3-phenylpropyl)amino)propyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 8.05-8.03 (m, 2H), 7.72 (d, J = 7.5 Hz, 2H, ArH), 7.28-7.11 (m, 9H, ArH, NH ₂ ), 3.58 (t, J = 7.0 Hz, 1H, CH), 3.10-2.97 (m, 2H, CH ₂ ), 2.94 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ), 2.76 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ), 2.49-2.46 (m, 2H, CH ₂ ), 1.65-1.59 (m, 2H, CH ₂ ).

(Example 36)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((2-phenoxyethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.51 (d, J = 8.0 Hz, 2H, ArH), 7.35 (dd, J = 7.5, 9.0 Hz, 2H, ArH), 7.24 (d, J = 7.5 Hz, 2H, ArH), 7.04 (t, J = 7.5 Hz, 1H, ArH), 6.81 (d, J = 8.0 Hz, 2H, ArH), 4.19 (dd, J = 6.0, 10.0 Hz, 1H, CH), 3.83 (m, 1H, CH ₂ ), 3.75 (m, 1H, CH ₂ ), 3.55 (m, 1H, CH ₂ ), 3.28 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.22 (m, 1H, CH ₂ ), 3.05 (dd, J = 10.0, 13.5 Hz, 1H, CH ₂ ).

(Example 37)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((4-phenoxybutyl)amino)propyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 8.42 (brs, 2H), 8.21 (t, J = 6.0 Hz, 1H), 7.70 (d, J = 8.0 Hz, 2H, ArH), 7.27-7.24 (m, 2H, ArH), 7.16-7.13 (m, 5H, ArH), 3.71 (t, J = 7.0 Hz, 1H, CH), 3.09 (m, 1H, CH ₂ ), 3.00-2.92 (m, 2H, CH ₂ ), 2.84 (dd, J = 7.0, 13.5 Hz, 1H, CH ₂ ), 1.47-1.41 (m, 2H, CH ₂ ), 1.34-1.26 (m, 2H, CH ₂ ), 1.05 (t, J = 7.0 Hz, 2H, CH ₂ ).

(Example 38)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((3-phenoxypropyl)amino)propyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 1.66-1.71 (m, 2H, CH ₂ CH ₂ CH ₂ ), 3.04-3.11 (m, 2H, CH ₂ CH ₂ CH ₂ ), 3.31 (dd, J = 5.5, 13.0 Hz, 1H, β-H), 3.44-3.53 (m, 3H, β-H+CH ₂ CH ₂ CH ₂ ), 4.25 (dd, J = 6.0, 10.0 Hz, 1H, α-H), 6.85 (d, J = 8.0 Hz, 2H, ArH), 7.05 (t, J = 7.5 Hz, 1H, ArH), 7.30 (d, J = 8.0 Hz, 2H, ArH), 7.36 (t, J = 7.0 Hz, 2H, ArH), 7.66 (d, J = 7.5 Hz, 2H, ArH).

(Example 39)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((3-(phenylamino)propyl)amino)propyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 1.66-1.72 (m, 2H, CH ₂ CH ₂ CH ₂ ), 2.99-3.10 (m, 4H, CH ₂ CH ₂ CH ₂ ), 3.27 (dd, J = 6.5 Hz, 14.0, 1H, β-H), 3.35 (d, J = 10.5, 14.0 Hz, 1H, β-H), 4.17 (dd, J = 6.0, 10.5 Hz, 1H, α-H), 7.26 (d, J = 8.0 Hz, 2H, Ar), 7.38-7.40 (m, 2H, ArH), 7.58-7.62 (m, 5H, ArH).

(Example 40)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((3-(phenylthio)propyl)amino)propyl)phenyl)boronic acid
¹ H NMR (3.5% DCl in D ₂ O); 1.42-1.50 (m, 2H, CH ₂ CH ₂ CH ₂ ), 2.39-2.47 (m, 2H, CH ₂ CH ₂ CH ₂ ), 2.96 (dd, J = 6.0, 13.5 Hz, 1H, β-H), 3.06 (dd, J = 10.0, 13.5 Hz, 1H, β-H), 3.31-3.39 (m, 2H, CH ₂ CH ₂ CH ₂ ), 4.24 (dd, J = 6.0, 10.0 Hz, 1H, α-H), 7.26-7.31 (m, 5H, ArH), 7.35-7.38 (m, 2H, ArH), 7.68 (d, J = 8.0 Hz, 2H, ArH).

(Example 41)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3-(benzyloxy)propyl)amino)-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.75 (d, J = 8.0 Hz, 2H, ArH), 7.45-7.34 (m, 5H, ArH), 7.28 (d, J = 8.0 Hz, 2H, ArH), 4.42-4.37 (m, 2H, CH ₂ ), 4.11 (dd, J = 6.0, 10.0 Hz, 1H, CH 2 ), 3.31 (m, 1H, CH ₂ ), 3.25 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.17 (m, 1H, CH ₂ ), 3.07-2.94 (m, 3H, CH ₂ ), 1.58-1.46 (m, 2H, CH ₂ ).

(Example 42)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(pyridin-2-ylamino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 8.47-8.43 (m, 2H, ArH), 7.75 (dd, J = 3.0, 8.5 Hz, 2H, ArH), 7.70 (dt, J = 2.5, 8.0 Hz, 1H, ArH), 7.50 (d, J = 9.0 Hz, 1H, ArH), 7.38 (dd, J = 3.0, 8.5 Hz, 2H, ArH), 4.60 (dd, J = 7.0, 8.0 Hz, 1H, CH), 3.45 (dd, J = 7.0, 14.0 Hz, 1H, CH ₂ ), 3.36 (dd, J = 8.0, 14.0 Hz, 1H, CH ₂ ).

(Example 43)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((pyridin-2-ylmethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 8.65 (dd, J = 2.0, 5.5 Hz, 1H, ArH), 8.45 (dt, J = 2.0, 8.5 Hz, 1H, ArH), 7.97 (dt, J = 2.0, 7.5 Hz, 1H, ArH), 7.63 (d, J = 8.0 Hz, 2H, ArH), 7.41 (d, J = 8.5 Hz, 1H, ArH), 7.22 (d, J = 8.0 Hz, 2H, ArH), 4.80 (d, J = 16.5 Hz, 1H, CH ₂ ), 4.49 (d, J = 16.5 Hz, 1H, CH ₂ ), 4.34 (dd, J = 6.5, 9.5 Hz, 1H, CH), 3.33 (dd, J = 6.5, 13.5 Hz, 1H, CH ₂ ), 3.12 (dd, J = 9.5, 13.5 Hz, 1H, CH ₂ ).

(Example 44)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(pyridin-3-ylamino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 9.19 (s, 1H, ArH), 8.59 (d, J = 3.0 Hz, 1H, ArH), 8.36 (d, J = 9.0 Hz, 1H, ArH), 8.04 (dd, J = 3.0, 9.0 Hz, 1H, ArH), 7.73 (d, J = 8.0 Hz, 2H, ArH), 7.36 (d, J = 8.0 Hz, 2H, ArH), 4.50 (t, J = 7.5 Hz, 1H, CH), 3.37 (d, J = 7.5 Hz, 2H, CH ₂ ).

(Example 45)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((pyridin-3-ylmethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 8.71 (d, J = 8.0 Hz, 1H, ArH), 8.52 (s, 1H, ArH), 8.07 (d, J = 8.0 Hz, 1H, ArH), 7.95 (t, J = 8.0 Hz, 1H, ArH), 7.58 (dd, J = 3.0, 8.5 Hz, 2H, ArH), 7.20 (dd, J = 3.0, 8.5 Hz, 2H, ArH), 4.67 (m, 1H, CH), 4.28-4.23 (m, 2H, CH ₂ ), 3.33 (dd, J = 6.0, 13.5 Hz, 1H, CH ₂ ), 3.06 (t, J = 10.0 Hz, 1H, _CH2 ).

(Example 46)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-(pyridin-4-ylamino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 8.59 (m, 2H, ArH), 8.01 (m, 2H, ArH), 7.71 (m, 2H, ArH), 7.34 (m, 2H, ArH), 4.51 (t, J = 7.5 Hz, 1H, CH), 3.37 (d, J = 7.5 Hz, 2H, CH ₂ ).

(Example 47)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((pyridin-4-ylmethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 8.43 (d, J = 5.5 Hz, 2H, ArH), 7.56 (d, J = 7.5 Hz, 2H, ArH), 7.19-7.16 (m, 4H, ArH), 4.43-4.33 (m, 3H, CH ₂ , CH), 3.04-2.95 (m, 2H, _CH2 ).

(Example 48)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-oxo-3-((thiophen-2-ylmethyl)amino)propyl)phenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 8.96 (t, J = 6.0 Hz, 1H), 8.41 (brs, 2H), 7.69 (d, J = 8.0 Hz, 2H, ArH), 7.38 (dd, J = 1.0, 5.0 Hz, 1H, ArH), 7.15 (d, J = 8.0 Hz, 2H, ArH), 6.92 (dd, J = 3.5, 5.0 Hz, 1H, ArH), 6.83 (d, J = 1.5 Hz, 1H, ArH), 4.47 (dd, J = 6.0, 15.0 Hz, 1H, CH ₂ ), 4.39 (dd, J = 6.0, 15.0Hz, 1H, _CH2 ), 3.86 (t, J = 6.5 Hz, 1H, CH), 3.02 (dd, J = 6.5, 14.0 Hz, 1H, CH ₂ ), 2.90 (dd, J = 6.5, 14.0 Hz, 1H, CH ₂ ).

(Example 49)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-2-methyl-3-oxopropyl)phenyl)boronic acid
¹ H NMR (D ₂ O): δ 7.71 (d, J = 8.0 Hz, 2H, ArH), 7.33 (t, J = 8.5 Hz, 1H, ArH), 7.26 (d, J = 8.0 Hz, 2H, ArH), 6.92-6.84 (m, 3H, ArH), 3.78 (s, 3H, CH ₃ ), 3.39 (d, J = 14.0 Hz, 1H, CH ₂ ), 3.25 (d, J = 14.0 Hz, 1H, CH ₂ ), 1.79 (s, 3H, CH ₃ ).

(Example 50)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)-3-chlorophenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 10.29 (s, 1H), 8.67 (brs, 4H), 7.79 (s, 1H, ArH), 7.63 (d, J = 8.0 Hz, 1H, ArH), 7.30 (d, J = 7.5 Hz, 1H, ArH), 7.22 (t, J = 8.0 Hz, 1H, ArH), 7.10 (t, J = 4.5 Hz, 1H, ArH), 7.00 (dd, J = 2.0, 8.0 Hz, 1H, ArH), 6.69 (dd, J = 3.0, 8.5 Hz, 1H, ArH), 4.14 (brs, 1H, CH), 3.71 (s, 3H, CH ₃ ), 3.29 (dd, J = 5.5, 14.0 Hz, 1H, CH ₂ ), 3.22 (d, J = 9.0, 14.0 Hz, 1H, CH ₂ ).

(Example 51)
The following compounds were prepared in the same manner as in Example 1.
(S)-(4-(2-amino-3-(benzo[d][1,3]dioxol-5-ylamino)-3-oxopropyl)-3-chlorophenyl)boronic acid
¹ H NMR (DMSO-d ₆ ): δ 10.18 (s, 1H), 8.52 (brs, 4H), 7.80 (d, J = 1.0 Hz, 1H, ArH), 7.64 (dd, J = 0.5, 7.5 Hz, 1H, ArH), 7.29 (d, J = 7.5 Hz, 1H, ArH), 7.12 (d, J = 2.0 Hz, 1H, ArH), 6.86 (d, J = 8.0 Hz, 1H, ArH), 6.78 (dd, J = 2.0, 8.0 Hz, 1H, ArH), 6.00 (s, 2H, CH ₂ ), 4.07 (brs, 1H, CH), 3.27 (dd, J = 8.0, 13.5 Hz, 1H, CH ₂ ), 3.20 (dd, J = 7.5, 13.5 Hz, 1H, CH ₂ ).

(Example 52)
Preparation of (S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)-3-fluorophenyl)boronic acid N,N-Dimethylformamide (3.1 mL) was added to (S)-3-(4-borono-2-fluorophenyl)-2-((tert-butoxycarbonyl)amino)propanoic acid (1.00 g, 3.06 mmol). To this solution were added triethylamine (341 mg, 3.37 mmol), m-anisidine (415 mg, 3.37 mmol), 1-hydroxybenzotriazole (454 mg, 3.37 mmol), and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (646 mg, 3.37 mmol) in an ice bath, and the mixture was warmed to room temperature. After stirring for 20 hours, water (10 mL) was added to quench the reaction, and the mixture was extracted with ethyl acetate (50 mL). The organic phase was washed successively with saturated aqueous sodium bicarbonate (10 mL), 1% hydrochloric acid (10 mL), and saturated brine (10 mL), dried over anhydrous sodium sulfate, and then filtered. The filtrate was concentrated under reduced pressure. Diisopropyl ether (30 mL) was added to the resulting crude product to cause crystallization, followed by suction filtration and washing with diisopropyl ether (30 mL) to give (S)-(4-(2-((tert-butoxycarbonyl)amino)-3-((3-methoxyphenyl)amino)-3-oxopropyl)-3-fluorophenyl)boronic acid (700 mg) as a white solid.
Trifluoroacetic acid (3.69 g, 32.4 mmol) was added to the obtained condensate (700 mg). After 16 hours, the mixture was concentrated under reduced pressure, and toluene (20 mL × 3) was added and azeotroped under reduced pressure to distill off the trifluoroacetic acid. The obtained solid was filtered and washed using chloroform (50 mL) as a washing solvent to obtain (S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)-3-fluorophenyl)boronic acid (754 mg, 1.68 mmol, 55% for 2 steps) as a pale yellow solid.
¹ H NMR (D ₂ O): δ 7.43-7.37 (m, 2H, ArH), 7.25-7.19 (m, 2H, ArH), 6.77-6.75 (m, 2H, ArH), 6.69 (m, 1H, ArH), 4.26 (m, 1H, CH), 3.71 (s, 3H, CH ₃ ), 3.36 (m, 1H, CH ₂ ), 3.20 (m, 1H, CH ₂ ).

[Uptake Test 1]
(1) Preparation of HEK293 cell lines highly expressing human LAT1 and LAT2 HEK293 cells stably expressing high levels of human LAT1 and LAT2 were prepared according to the method described in the paper by Khunweeraphong, N et al. (Journal of Pharmacology Science, 2012, vol. 119, pp. 368-380).
Shuttle vector DNA (LAT1: EX-H4509-M02, LAT2: EX-U0514-M02, GeneCopoeia) was constructed containing ampicillin and neomycin resistance markers and the full-length cDNA of human LAT1 or LAT2 inserted under the CMV (cytomegalovirus) promoter. This vector was transfected into HEK293 cells using Lipofectamine® 2000 (Invitrogen) according to the manufacturer's instructions. Cell clones stably expressing the transgene were then selected by limiting dilution in the presence of 0.9 mg/mL Geneticin®, and cell clones showing approximately 2- to 5-fold increased L-boronophenylalanine (L-BPA) uptake compared to HEK293 cells prior to transfection were isolated. These cells were then passaged and used to evaluate the selective uptake of LAT1 and LAT2.

(2) Evaluation of LAT1 and LAT2 Selective Uptake The method for evaluating cellular uptake is the same as that described in the paper by Khunweeraphong, N et al. (Journal of Pharmacology Science, 2012, vol. 119, pp. 368-380). The evaluation is performed using the cells obtained in (1). However, no radioisotopes are used, and a substrate concentration of 0.1 mM and 2 mM BCH (2-amino-2-norbornanecarboxylic acid) are used as an LAT1 and LAT2 inhibitor. After the reaction, the cells are recovered with 0.05% Tween 20, and the concentration of the boronophenylalanine amide derivative in the resulting cell solution is determined.
Quantification of intracellular boronophenylalanine amide derivatives is carried out according to the method described in Hattori, Y et al. (Sensors 2017, 17, 2436) using 2-(2-hydroxyphenyl)pyridine (boron sensor 5) as a boron sensor.
When evaluating cellular uptake, taking into consideration inter-experimental variations, the uptake is evaluated as a relative value (LAT1 selectivity) to the uptake of L-BPA, which is a control, performed on the same day.
LAT1 selectivity = (quantitative uptake of compound in LAT1 cells/quantitative uptake of control LBPA in LAT1 cells)/(quantitative uptake of compound in LAT2 cells/quantitative uptake of control LBPA in LAT2 cells)

[Uptake Test 2]
(1) Evaluation test of uptake into tumor cells (biological evaluation 2)
1.5 x ¹⁰⁶ human tongue cancer cells (SAS cells), human glioma cells (A172 cells), or human breast cancer cells (MCF-7) were seeded onto a 100 mm dish and pre-cultured at 37°C in a 5% _CO2 atmosphere for 24 hours. The culture medium was removed by aspiration, and a culture medium containing 1 mM of each Example or Reference Example drug was added. Exposure culture was then performed for 3 hours at 37°C in a 5% _CO2 atmosphere. After removing the culture medium by aspiration, the cells were washed once with PBS and then trypsinized to recover the cells. The recovered cells were counted and packed by centrifugation. Then, _HClO4 (60%, 0.3 mL) and _{H2O2 (} 31%, 0.6 mL) were added and heated overnight at 75°C to prepare an ashing solution. The ashing solution was filled up to 5 mL with pure water and then filtered through a 5C filter paper. The boron concentration in the solution was measured using an Agilent ⁷¹⁰ ICP-OES to determine the amount of boron (μg) per 10 cells. Cellular uptake was evaluated as a relative value to the uptake of L-BPA from the reference example, which was performed on the same day, taking into account variations between experiments.

The results of the uptake test are shown in the table. The control used was 4-borono-L-phenylalanine (L-BPA), which has been used in clinical studies of BNCT.

As a result, it was found that many of the compounds of the present invention were taken up into cells at levels equal to or greater than those of BPA when treated at the same concentration.

The results for the uptake of other major compounds are shown in the table below. In the table, uptake A: more than three times higher than BPA, B: equal to or less than three times that of BPA, C: taken up but lower than BPA.
(In the following tables, unless otherwise specified, the L-form is represented.)

In addition, in Tables 1 to 8, each substituent of the compounds shown below is shown by substituent.

As is clear from the table, the compounds of the examples were shown to have excellent uptake ability into tumor cells. The compounds shown in Table 9 have particularly high uptake ability into PC3 cells and LNCap cells. It is known that PC3 cells highly express LAT1, while LNCap cells do not express LAT1 (Reference: The Prostate 77:222-233 (2017)). These results suggest that these compounds may be taken up by other mechanisms without passing through LAT1.

Claims (8)

A compound represented by the following formula (I) or a pharmaceutically acceptable salt thereof:
Here, in formula (I),
R ¹ and R ² together with the B atom represent a substituent of boronic acid (—B(OH) ₂ ), boronic acid ester, or boronic acid amide;
R ³ represents a group independently selected from the group consisting of H, halogen, hydroxy, cyano, amino, C1-C6 alkylamino, C1-C6 alkyl, C1-C6 alkoxy, benzyloxy, C1-C6 alkoxyC1-C6 alkyl, nitro, C1-C6 haloalkyl, carbamoyl, C1-C6 alkylaminocarbonyl, C1-C6 alkoxycarbonyl, C1-C6 alkylcarbonyl, COOR ¹⁰ (R ¹⁰ is H, C1-C6 alkyl, amino, or C1-C6 alkylamino), C1-C6 haloalkylsulfanyl, C1-C6 haloalkylsulfinyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylthio, C1-C6 alkylsulfinyl, C1-C6 alkylsulfonyl, aminosulfonyl, sulfo, and sulfamoyl; s represents an integer of 1 to 4;
^R4 represents H, C1-C6 alkyl, or benzyl;
R ⁵ represents H, substituted or unsubstituted C1-C6 alkyl , substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 alkoxyC1-C6 alkyl , C3 -C7 cycloalkyl , C3 -C7 cycloalkenyl , substituted or unsubstituted non-aromatic heterocyclic group, substituted or unsubstituted C6 to C14 aryl, or substituted or unsubstituted heteroaryl, or R ⁴ R ⁵ together with N form a C3 -C7 heterocycloalkyl ( wherein in the substituted C1-C6 alkyl, substituted C1-C6 alkoxy, or substituted C1-C6 alkoxyC1-C6 alkyl, the group substituted for the hydrogen atom is a substituted or unsubstituted non-aromatic heterocyclic group, substituted or unsubstituted arylthio, substituted or unsubstituted arylamino, substituted or unsubstituted C6 to C14 aryl, or substituted or unsubstituted heteroaryl;
wherein the substituents of the non-aromatic heterocyclic group, arylthio, arylamino, aryl, or heteroaryl are optionally selected from 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen;
^R6 represents H or C1 -C6 alkyl . The compound according to claim 1, or a pharmaceutically acceptable salt thereof, wherein R ³ independently represents H, Cl, F, C1-C3 alkyl, C1-C3 alkoxy, C1-C6 alkylthio, CH ₂ X, CHX ₂ , or CX ₃ (X represents F). R ⁴ represents H or C1-C6 alkyl;
The compound according to claim 1 or 2, or a pharmaceutically acceptable salt thereof, wherein ^R5 represents aryl optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen , or heteroaryl optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or halogen . R ⁴ represents H or C1-C6 alkyl;
The compound according to claim 1 or 2, or a pharmaceutically acceptable salt thereof, wherein R5 represents C1-C6 alkyl optionally substituted with 1 to 3 C1-C6 alkyl, C1-C6 alkoxy, amino, nitro, cyano, or aryl ^optionally substituted with 1 to 3 halogen atoms. The compound or pharmaceutically acceptable salt thereof according to claim 1 or 2, wherein R ⁴ R ⁵ together with N form a C3-C7 heterocycloalkyl. 2. The compound of claim 1, which is one selected from the group consisting of the following compounds or a pharmaceutically acceptable salt thereof:
(S)-(4-(2-amino-3-(ethylamino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((2,2,2-trifluoroethyl)amino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(p-tolylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(m-tolylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3,4-dimethylphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3,5-dimethoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3-methoxyphenyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-(benzo[d][1,3]dioxol-5-ylamino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((2,3-dihydroxybenzo[b][1,4]dioxin-6-yl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-(phenethylamino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((3-methoxyphenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-((4-fluorophenethyl)amino)-3-oxopropyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((2-phenoxyethyl)amino)propyl)phenyl)boronic acid;
(S)-(4-(2-amino-3-oxo-3-((3-phenoxypropyl)amino)propyl)phenyl)boronic acid; and
(S)-(4-(2-amino-3-oxo-3-(pyridin-2-ylamino)propyl)phenyl)boronic acid. A drug for BNCT, comprising the compound according to any one of claims 1 to 6 or a pharmaceutically acceptable salt thereof. A diagnostic agent comprising a radioisotope as a substituent at any one of ^R3 , ^R4 , or ^R5 of the compound according to any one of claims 1 to 6 or a pharmaceutically acceptable salt thereof.