JP4559531B1 - Method for producing nobiletin - Google Patents

Abstract

A method for producing nobiletin and its derivatives is provided.
A method for synthesizing nobiletin and its derivatives by β-diketone synthesis and subsequent flavone cyclization reaction:
A method of labeling by reacting with labeled methyl iodide.
[Selection figure] None

Description

  The present invention relates to a novel synthesis method and labeling method of nobiletin.

  It has been reported that nobiletin contained in certain citrus fruits exhibits various physiological activities such as antihypertensive and anticancer effects (for example, WO2006 / 049234). In addition, attention has been focused on Alzheimer's memory impairment improving action and antidementia activity. Nobiletin is a food ingredient and is considered to be highly safe in taking. Therefore, if the mechanism of physiological action is elucidated, application as a safe pharmaceutical product can be expected.

  However, nobiletin currently available as a reagent is extracted from natural products and is expensive because of the cost of purification. In addition, various derivatives of nobiletin have not been obtained. For this reason, there has been little research on structure-activity relationships or effects on animals.

WO2006 / 049234

  An object of the present invention is to provide a novel method for synthesizing nobiletin and its derivatives, and a method for selective labeling of nobiletin and its derivatives.

The present invention is directed to formula (I):
[Wherein R ₁ is H or methyl]
A compound represented by the formula (nobiletin or a 5-OH derivative thereof) is synthesized. This method
(A) Formula (II):
And a compound represented by formula (III):
(Wherein, R represents base Nzotoriazoriru)
Is reacted with a compound represented by formula (IV):
A compound represented by:
(B) cyclizing the compound of formula (IV) to form formula (V):
A compound represented by:
(C) Optionally reacting the compound of formula (V) with AlCl ₃ and ethanethiol to give formula (VI):
A compound represented by the formula:
Including each step.

In another aspect, the present invention provides a compound of formula (VII):
[Wherein * Me represents a methyl group labeled with ¹¹ C or ¹⁴ C]
The method of manufacturing the compound represented by this is provided. This method uses the formula (V):
Is reacted with AlCl ₃ and ethanethiol to give the formula (VI):
A compound represented by:
Reacting a compound of formula (VI) with methyl iodide labeled with ¹¹ C or ¹⁴ C in the presence of a base to give a compound of formula (VII),
Including each step.

  According to the method of the present invention, nobiletin and its various derivatives can be synthesized easily and conveniently and can be selectively labeled.

The present invention provides nobiletin (1) by efficient β-diketone synthesis followed by flavone cyclization reaction:
And methods for synthesizing derivatives thereof.

Throughout this specification, the positions of the flavones rings and substituents are represented by the following formula:
Notation according to

In the first step of the method of the present invention, the acetophenone derivative (8) corresponding to the flavone A ring portion is changed to the dimethoxybenzoic acid derivative (9) corresponding to the flavone B ring portion (R is Cl or benzotriazolyl). ) Is treated by treatment with LHMDS (lithium hexamethyldisilazide) in THF to obtain β-diketone (10) which is a flavone precursor.

Acetophenone derivative (8) which is the starting material corresponding to the A ring part of flavone:
Can be produced as follows. First, a hydroxyl group is introduced into the 4-position of 1,2,3,5-tetramethoxybenzene (2) by the following four steps to produce 2,3,4,6-tetramethoxyphenol (6).

The starting material 1,2,3,5-tetramethoxybenzene is commercially available. First, (3) is produced by Friedel-Crafts reaction with 1,2,3,5-tetramethoxybenzene. The Friedel-Crafts reaction can be carried out by reacting with acetyl chloride in the presence of a Lewis acid such as aluminum chloride in an aprotic solvent. Methylation of (3) by reaction with methyl iodide under basic conditions produces 1- (2,3,4,6-tetramethoxyphenyl) ethanone (4). Next, hydrogen peroxide is allowed to act in the presence of a SeO ₂ catalyst, and the ketone of (4) is esterified by the Bayer-Billiger reaction to produce (5), and 2,3,4,6 by persolvolysis. -Tetramethoxyphenol (6) can be obtained.

Next, a methyl group is introduced into the hydroxyl group at the 4-position of 2,3,4,6-tetramethoxyphenol (6) to form pentamethoxyphenol (7). Methylation is performed by reacting with methyl iodide under basic conditions.

Next, the compound (7) is acylated to obtain an acetophenone derivative (8) corresponding to the A-ring part of the flavone. The acylation can be carried out in the same manner as in the first step by Friedel-Crafts reaction.

In addition, a dimethoxybenzoic acid derivative (9 ′), which is a starting material corresponding to the flavone B ring in the method of the present invention:
Is obtained by reacting commercially available 3,4-dimethoxybenzoic acid with thionyl chloride, acyl benzotriazole (9 "):
Can be obtained by reacting the acid chloride obtained above with benzotriazole in the presence of a base.

In the second step of the method of the present invention, the target nobiletin (1) is obtained by cyclizing the β-diketone obtained in the first step. Cyclization is performed by acid treatment with TFA in methanol.

In the third step, which is an optional step of the method of the present invention, a derivative in which the 5-position of the A ring is demethylated is produced by reacting nobiletin (1) with AlCl ₃ and ethanethiol.

Through the above steps, the following nobiletin and its derivatives can be synthesized.

In another aspect of the invention, a method for selective labeling of nobiletin is provided.

In this method, similar to the third step described above, nobiletin is selectively demethylated by treating it with AlCl ₃ and ethanethiol, then ¹¹ C or D ^{11 in} DMF in the presence of a base. ^By heating with methyl iodide labeled with ¹⁴ C, nobiletin (1 *) labeled with the methyl group at the 5-position can be easily obtained. Nobiletin labeled in this way is useful for PET measurements and trace experiments.

  Since the method of the present invention does not require column chromatography for purification, it can be easily scaled up. Furthermore, various combinations of nobiletin and regioselective labeling are possible by appropriately combining the method of the present invention and known organic synthesis methods and changing the A ring methoxy group and the B ring triazole unit. is there. In the future, it is considered that further derivatization of nobiletin, for example, biotin tagging, introduction of a fluorescent probe, etc. can greatly contribute to elucidation of the physiological action mechanism.

  EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1: Synthesis of 1- (2-hydroxy-3,4,6-trimethoxyphenyl) ethanone (3)
Dissolve aluminum chloride (1.5 g, 10.6 mL) in dry diethyl ether solution (7.5 mL) under ice-free conditions, expand the sales for 10 minutes, and then, at the same temperature, 1,2,3,5-tetramethoxybenzene (2) 1.5 g, 7.57 mmol of diethyl The mixture was stirred for 10 minutes at room temperature with the ether solution added. Subsequently, 714 μL of acetyl chloride, 9.8 mmol was added at room temperature, and the solution was stirred as it was for 4 hours. After confirming the completion of the reaction by TLC, the reaction solution was cooled to 0 ° C. and quenched with 6N hydrochloric acid. Toluene was added to the reaction solution and extracted. The organic layer was extracted with 1N aqueous sodium hydroxide solution, and 6N hydrochloric acid was slowly added until the aqueous layer reached pH 2. The precipitated solid was collected by filtration to give 1- (2-hydroxy-3,4,6-trimethoxyphenyl) ethanone (3) (1.3 g, yield 76%) as pale yellow crystals.
1H NMR (500 MHz, CDCl3): d 13.8 (s, 1H, OH), 5.97 (s 1H, Ar), 3.94 (s, 3H, OCH3), 3.90 (s, 3H, OCH3), 3.82 (s, 3H , OCH3), 2.62 (s, 3H, CH3).

Example 2: Synthesis of 1- (2,3,4,6-tetramethoxyphenyl) ethanone (4)
1- (2-Hydroxy-3,4,6-trimethoxyphenyl) ethanone (3) 16 g, 71 mmol is dissolved in dimethylformamide 80 mL, and at room temperature, potassium carbonate 20 g, 145 mmol and methyl iodide 6.6 mL, 106 mmol were sequentially added, and the reaction solution was heated to 60 ° C. and stirred for 1.5 hours. After confirming completion of the reaction by TLC, the reaction solution was cooled to room temperature, 200 mL of diethyl ether was added, and insoluble salts were removed by Celite filtration. The filtrate was washed with water and saturated brine, and the organic layer was taken and dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure to give 1- (2,3,4,6-tetramethoxyphenyl) ethanone (4) (17 g, yield 94%) as a pale yellow oil.
1H NMR (500 MHz, CDCl3): d 6.26 (s, 1H, Ar), 3.89 (s, 6H, OCH3), 3.81 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 2.48 (s, 3H, CH3).

Example 3: Synthesis of 2,3,4,6-tetramethoxyphenol (6)
Selenium dioxide is added to a tert-butanol solution of 1- (2,3,4,6-tetramethoxyphenyl) ethanone (4) at room temperature, and the reaction mixture is heated to 50 ° C. Under the same temperature, 30% aqueous hydrogen peroxide was added dropwise over 10 minutes, and the mixture was stirred for 10 hours. After confirming the completion of the reaction by NMR, the reaction solution was cooled to room temperature, and then 200 mL of benzene was added. The organic layer was washed four times with a saturated aqueous ammonium chloride solution, then the organic layer was taken, dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure to obtain 2,3,4,6-tetramethoxyphenyl acetate (5) as an orange solid.
To a methanol solution of 2,3,4,6-tetramethoxyphenyl acetate (5), potassium carbonate was added and stirred at room temperature under an argon atmosphere. After confirming the completion of the reaction by TLC, the reaction solution was cooled to 0 ° C. with ice, and the reaction solution was added with 6N hydrochloric acid until the reaction solution reached pH 1 to stop the reaction. Subsequently, 200 mL of diethyl ether was added and extraction was performed 5 times, followed by drying over anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure to obtain 2,3,4,6-tetramethoxyphenol (6) as white needle crystals.
1H NMR (500 MHz, CDCl3): d 6.33 (s, 1H, Ar), 5.23 (s, 1H, OH), 3.96 (s, 3H, OCH3), 3.87 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 3.83 (s, 3H, OCH3).

Example 4: Synthesis of pentamethoxybenzene (7)
To an acetone solution of 2,3,4,6-tetramethoxypheninol (6) and methyl iodide was added potassium carbonate under an argon atmosphere, and the mixture was stirred as it was. After confirming the completion of the reaction by TLC, the reaction solution was cooled to room temperature, 200 mL of diethyl ether was added, and insoluble salts were removed by Celite filtration. The filtrate was concentrated under reduced pressure and purified by silica gel column chromatography (developing solvent hexane: ethyl acetate = 6: 1) to obtain pentamethoxybenzene (7) as a white solid.
1H NMR (270 MHz, CDCl3): d 6.30 (s, 1H, Ar), 3.95 (s, 3H, OCH3), 3.85 (s, 6H, OCH3), 3.83 (s, 6H, OCH3); 13C NMR (67.8 (MHz, CDCl3): d 149.1, 147.8, 136.8, 93.8, 61.4, 61.3, 56.4; MS (FAB) m / z calcd for C11H17O5 + (M + H) + 228, measured 228.

Example 5: Synthesis of 1- (2-hydroxy-3,4,5,6-tetramethoxyphenyl) ethanone (8)
To 16 mL of a dry methylene chloride solution of 1.5 g, 6.6 mmol of pentamethoxybenzene (7), 728 μL of acetyl chloride, 9.8 mmol was added under zero ice, followed by 900 mg of aluminum chloride, 10.6 mmol, and the solution was added at room temperature. Stir for hours. After zero ice, diethyl ether was added to the reaction solution, and then 2N aqueous sodium hydroxide solution was added until pH 11 was reached. The organic layer was taken and dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure to recover the raw material pentamethoxybenzene (1.0 g, recovery 66%). Further, the aqueous layer was taken, washed with diethyl ether, and 6N hydrochloric acid was added until the pH reached 1 under zero ice. The aqueous solution was extracted 3 times with diethyl ether, the organic layer was taken, dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was purified by flash silica gel column chromatography (developing solvent hexane: ethyl acetate = 4: 1 → 2: 1) to give 1- (2-hydroxy-3,4,5 , 6-Tetramethoxyphenyl) ethanone (500 mg, 30% yield) was obtained as a yellow oil.
The recovered raw material was dissolved again in 10 mL of dry methylene chloride, and acetyl chloride (485 μL, 6.2 mmol) was added under ice zero, followed by the addition of aluminum chloride (560 mg, 6.6 mmol), and the solution was stirred at room temperature for 4 hours. After zero ice, diethyl ether was added to the reaction solution, and then 2N aqueous sodium hydroxide solution was added until pH 11 was reached. The organic layer was taken and dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure to recover the raw material pentamethoxybenzene (513 mg, 51% recovery). The aqueous layer was taken, washed with diethyl ether, and 6N hydrochloric acid was added until the pH reached 1 under zero ice. The aqueous solution was extracted 3 times with diethyl ether, the organic layer was taken, dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was purified by flash silica gel column chromatography (developing solvent hexane: ethyl acetate = 4: 1 → 2: 1) to give 1- (2-hydroxy-3,4,5 , 6-Tetramethoxyphenyl) ethanone (508 mg, 45% yield) was obtained as a yellow oil. Combining them, 1- (2-hydroxy-3,4,5,6-tetramethoxyphenyl) ethanone (8) (1.0 g, 60% yield) and the raw material pentamethoxybenzene (513 mg, yield 34) %).
1H NMR (500 MHz, CDCl3): d 13.2 (s, 1H, OH), 4.08 (s, 3H, OCH3), 3.95 (s, 3H, OCH3), 3.90 (s, 3H, OCH3), 3.95 (s, 3H, OCH3) (s, 3H, OCH3).

Example 6: Synthesis of (1H-benzo [d] [1,2,3] triazo-1-yl) (3,4-dimethoxyphenyl) methanone (9 ")
Thionyl chloride 9.0 mL, 123 mL and dimethylformamide 2.5 mL, 33 mmol were added to 200 mL of a methylene chloride solution of 2,3-dimethoxybenzoic acid 15 g, 82 mmol in an argon atmosphere at 0 ° C., followed by stirring for 1 hour and a half. After concentration under reduced pressure, the residue was redissolved in 170 mL of dry methylene chloride. Triethylamine 11.4 mL, 82 mmol, and then benzotriazole 9.8 g, 82 mmol were sequentially added at 0 ° C. under an argon atmosphere, and the mixture was stirred as it was for 30 minutes. . Then, 1N sodium hydroxide aqueous solution was added, the organic layer was taken, and anhydrous magnesium sulfate was added and dried. After filtration, the filtrate was concentrated under reduced pressure, and (1H-benzo [d] [1,2,3] triazo-1-yl) (3,4-dimethoxyphenyl) was recrystallized from the residue (solvent hexane-methylene chloride). ) Methanone (9 ") (19 g, 82% yield) was obtained as a white solid.
1H NMR (500 MHz, CDCl3): d 8.37 (d, J = 8.5 Hz, 1H, Ar), 8.05 (d, J = 8.5, 1H, Ar), 7.82 (s, 1H, Ar), 7.70 (t, J = 7.5 Hz, 1H, Ar), 7.55 (t, J = 7.5 Hz, 1H, Ar), 7.04 (d, J = 7.5 Hz, 1H, Ar), 4.01 (s, 3H, OCH3), 4.00 (s , 3H, OCH3); 13C NMR (125 MHz, CDCl3): d 165.5, 153.9, 148.7, 145.5, 132.5, 130.2, 127.2, 126.1, 123.3, 120.0, 114.8, 113.9, 110.2, 56.1, 56.0; MS (FAB) m / z calcd for C15H14N3O3 + (M + H) + 283, measured value 283.

Example 7: Synthesis of nobiletin (1)
1- (2-hydroxy-3,4,5,6-tetramethoxyphenyl) ethanone (8) and (1H-benzo [d] [1,2,3] triazo-1-yl) (3,4-dimethoxy To an anhydrous tetrahydrofuran solution of phenyl) methanone (9 ") was added 1M lithium hexamethyldisilazane in tetrahydrofuran at -30 ° C under an argon atmosphere, and the mixture was warmed to 0 ° C and stirred for 2.5 hours. An aqueous ammonium solution was added, and the organic layer extracted with diethyl ether was washed with saturated brine, dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated under reduced pressure to give a residue. Hexane-ethyl acetate) gave nobiletin precursor (10) (7.8 g, 91%) as a yellow solid.3.1 g, 7.4 mmol of nobiletin precursor was dissolved in methanol, and trifluoroacetic acid was added. The mixture was heated to 0 ° C. and stirred for 24 hours, and then concentrated under reduced pressure, It was obtained by nobiletin (1) (2.9 g, 98% yield) as pale yellow crystals - Recrystallization (hexane solvent methanol).
1H NMR (500 MHz, CDCl3): d 7.57 (d, J1 = 8.6 Hz, J2 = 2.1 Hz, 1H, Ar), 7.42 (d, J = 2.1, 1H, Ar), 7.00 (d, J = 8.6 Hz , 1H, Ar), 6.62 (d, 1H, CH), 4.11 (s, 3H, OCH3), 4.03 (s, 3H, OCH3), 4.00-3.95 (m, 12H, OCH3).

Example 8: Position specific labeling of nobiletin
Nobiletin (1) 11 mg, 27 μmol of methylene chloride solution 1.0 mL was added at 0 ° C. with aluminum chloride 3.5 mg, 27 μmol of ethanethiol 20 μL solution, and stirred at room temperature for 1.5 hours. Thereafter, a solution of aluminum chloride (16 mg, 135 μmol) in ethanethiol (100 μL) was further added and stirred for 5 hours. After confirming disappearance of the raw materials by TLC, the reaction solution was cooled to 0 ° C., 6N hydrochloric acid was added, and the mixture was stirred for 1 hour. Next, the mixture was extracted with methylene chloride, dried using sodium sulfate, and the solvent was distilled off. The residue was purified by silica gel column chromatography (developing solvent hexane: ethyl acetate = 4: 1 → 1: 1), and 5-demethylnobiletin (11) (9.5 mg, yield 91%) was obtained as yellow needle-like crystals. Obtained. ¹ H NMR (500 MHz, CDCl ₃ ): d 12..5 (s, 1H), 7.69 (d, J ₁ = 8.6 Hz, J ₂ = 2.6 Hz, 1H, Ar), 7.43 (d, J = 2.7 , 1H, Ar), 7.01 (d, J = 8.6 Hz, 1H, Ar), 6.61 (s, 1H, CH), 4.12 (s, 3H, OCH ₃ ), 4.00-3.95 (m, 9H, OCH ₃ )
Next, using an automatic synthesizer, 5-demethylnobiletin was dissolved in DMF, and 10% tetrabutylammonium hydroxide aqueous solution was added. [11C] -labeled MeI was added, sealed, heated for 1 minute and then cooled. The color of the solution changed from dark yellow to light yellow. The reaction solution was purified by HPLC to obtain [11C] -labeled nobiletin (RT: 11 min) having radioactivity.

Claims (1)

Formula (I):
[Wherein R ₁ is H or methyl]
A method for synthesizing a compound represented by:
(A) Formula (II):
And a compound represented by formula (III):
(Wherein, R represents base Nzotoriazoriru)
Is reacted with a compound represented by formula (IV):
A compound represented by:
(B) cyclizing the compound of formula (IV) to form formula (V):
A compound represented by:
(C) Optionally reacting the compound of formula (V) with AlCl ₃ and ethanethiol to give formula (VI):
A compound represented by the formula:
The method including each process of these.