A process for the preparation of a key intermediate for the synthesis of a tubulin inhibitor

Abstract

The present application relates to a kind of preparation method for the key intermediate of tubulin synthesis inhibitor, overcome the shortcomings such as long step, low yield, low ee value in prior art, the target product can be prepared by only reducing amination, upper protection, split, free, not only high reaction yield, and ee value is also improved, with unexpected technical effect.Moreover, the synthesis method provided by the present application has mild reaction conditions, simple and convenient operation method, not only suitable for laboratory small amount preparation, also suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to a method for preparing a key intermediate for synthesizing microtubule inhibitors, and belongs to the field of organic synthesis technology. Background Technology

[0002] Microtubules are heterodimers formed from α-tubulin and β-tubulin, and are long, filamentous protein polymers. Microtubules participate in many cellular processes crucial for cell function, including organelle and vesicle transport, cell migration, and mitosis. Microtubule inhibitors work by disrupting microtubules, thereby inhibiting chromosome segregation during cell division. Taltobulin (CAS: 228266-40-8), a synthetic tripeptide-cysteine ​​analog, is a potent antimicrotubule agent that can circumvent P-glycoprotein-mediated resistance in vitro and in vivo. It inhibits the polymerization of purified tubulin, disrupts microtubule organization in cells, and induces mitotic arrest and apoptosis.

[0003] The preparation of Taltobulin also commonly uses the key intermediate (S)-2-((tert-butoxycarbonyl)(methyl)amino)-3-methyl-3-phenylbutyric acid (CAS: 228266-38-4). Patent WO2003082268A2 (family CN1633289A) discloses the following synthesis method for this key intermediate (11 steps in total), without giving specific operations. From the disclosed route, it can be seen that vii is an optically pure product obtained after chiral resolution. However, after the next step of methyl ester hydrolysis, the ee value of the product drops to only 80%, and the total yield is only 22%. It can be seen that the product obtained by this method has poor quality indicators and cannot meet the requirements of drug indicators.

[0004]

[0005] Patent WO2004026814A2 (family CN1705639A) discloses the following method for synthesizing this key intermediate, which involves 9 steps and has a total yield of only 14.6% and an ee value of only 97.4%. It can be seen that this method has a long procedure, extremely low yield, poor atom economy, and is not conducive to industrial scale-up.

[0006]

[0007] The literature Molecular Diversity (2014), 18(2), 357-373 discloses the following synthesis method for this key intermediate, which has an overall yield of only 45% in 8 steps and an ee value of only 97.1%, indicating poor quality. In addition, the reaction conditions also use NaH, which poses a significant safety hazard and is not suitable for industrial scale-up.

[0008]

[0009] Therefore, designing and implementing a synthesis method that is suitable for industrial production, easy to operate, safe, and has high yield and ee value has become the focus of research and development for those skilled in the art. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing a key intermediate for synthesizing microtubule inhibitors, in order to solve the problems mentioned in the background art.

[0011] To address the aforementioned technical problems, a first aspect of the present invention provides a method for preparing compound 5, comprising the following steps:

[0012] Step 1: Compound 1 undergoes a reductive amination reaction in the presence of a base and a reducing agent, as shown in the following formula, to obtain compound 2;

[0013] Step 2: In a solvent, compound 2 reacts with an organic carbonate in the presence of a base to undergo an amino protection reaction as shown in the following formula, to give compound 3;

[0014] Step 3: In a solvent, compound 3 reacts with an NH2- resolving base in the following resolving reaction to yield compound 4;

[0015] Step 4: Compound 4 is subjected to a free reaction in the presence of acid as shown in the following formula to obtain compound 5;

[0016]

[0017] The R is selected from H, straight-chain alkyl groups with 1 to 4 carbon atoms, and alkoxy groups with 1 to 4 carbon atoms.

[0018] In a preferred embodiment, the base mentioned in step 1 is methylamine; preferably, the molar ratio of compound 1 to methylamine is 1:(1-7), for example 1:(2-6), or even 1:6; preferably, the methylamine is added in the form of a methylamine alcohol solution; preferably, the methylamine alcohol solution can be a methylamine methanol solution or a methylamine ethanol solution.

[0019] In a preferred embodiment, the reducing agent in step 1 is 2-methylpyridineborane; preferably, the molar ratio of compound 1 to the reducing agent is 1:(1-2), for example 1:(1-1.5), or even 1:1.1.

[0020] In a preferred embodiment, the reaction temperature of the reductive amination reaction in step 1 is room temperature.

[0021] In a preferred embodiment, the reaction time of the reductive amination reaction in step 1 is 16-65 h, preferably 40-65 h; for example, 60 h.

[0022] In a preferred embodiment, the solvent for the reaction in step 1 is an ether solvent, which may be selected from one or more of ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, and methyltetrahydrofuran, for example, tetrahydrofuran.

[0023] In a preferred embodiment, the preparation method of step 1 includes the following steps: adding compound 1 to a reaction flask, adding an organic solvent under inert gas protection, adding a methylamine alcohol solution under an ice-water bath, heating the reaction solution to room temperature and reacting for 1 to 3 hours, adding a reducing agent, stirring the reaction at room temperature for 40 to 65 hours, and then performing post-processing to obtain the final product.

[0024] In a preferred embodiment, the post-processing step described in step 1 is selected from one or more of concentration, pulping, filtration, washing, and drying; the solvent for pulping is preferably tetrahydrofuran; the solvent for washing is preferably tetrahydrofuran or methyl tert-butyl ether.

[0025] In a preferred embodiment, the solvent in step 2 is a combination of an organic solvent and water; preferably, the organic solvent is selected from one or more of tert-butanol, tetrahydrofuran, and 1,4-dioxane; preferably, the solvent is a combination of tert-butanol and water; preferably, the volume ratio of tert-butanol to water is 1:(0.5 to 1.5), for example, 1:1.

[0026] In a preferred embodiment, the alkali mentioned in step 2 is selected from potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, sodium hydroxide, and potassium hydroxide; preferably, the alkali is potassium carbonate; preferably, the molar ratio of compound 2 to the alkali is 1:(1-5); for example, 1:3.

[0027] In a preferred embodiment, the organic carbonate in step 2 is di-tert-butyl dicarbonate; preferably, the molar ratio of compound 2 to di-tert-butyl dicarbonate is 1:(1-3), for example 1:2.

[0028] In a preferred embodiment, the reaction temperature of the reaction in step 2 is room temperature.

[0029] In a preferred embodiment, the reaction time of the reaction described in step 2 is 24 to 45 hours, for example 35 to 45 hours, or even 40 hours.

[0030] In a preferred embodiment, the preparation method of step 2 includes the following steps: adding compound 2 into a reaction flask, adding solvent and alkali, stirring to dissolve, cooling the reaction solution to 0-10°C in an ice-water bath, adding organic carbonate, heating to room temperature, reacting for 24-45 hours, and then performing post-processing after the reaction is completed.

[0031] In a preferred embodiment, the post-processing step described in step 2 is selected from one or more of pH adjustment, extraction, washing, and drying; preferably, the solvent for pH adjustment is citric acid; preferably, the solvent for extraction is methyl tert-butyl ether; preferably, the solvent for washing is brine.

[0032] In a preferred embodiment, the solvent in step 3 is petroleum ether.

[0033] In a preferred embodiment, the NH2-resolving base in step 3 is (S)-(-)-α-methylbenzylamine, (S)-(-)-α-methyl-4-nitro-benzylamine, (1R,2S)-(-)-norephedrine, or (1S,2R)-(+)-norephedrine; preferably, the NH2-resolving base is (S)-(-)-α-methylbenzylamine; preferably, the molar ratio of compound 3 to the resolving base is 1:(1-2), for example, 1:1.2.

[0034] In a preferred embodiment, the reaction temperature of the reaction in step 3 is room temperature.

[0035] In a preferred embodiment, the reaction time of the reaction in step 3 is 10 to 20 hours, for example, 16 hours.

[0036] In a preferred embodiment, the preparation method of step 3 includes the following steps: adding compound 3 into a reaction flask, adding solvent under inert gas protection, stirring to dissolve, adding NH2- dissolving base, reacting at room temperature for 10-20 hours, and after the reaction is completed, filtering, washing, and drying to obtain the product.

[0037] In a preferred embodiment, the washing solvent in step 3 is petroleum ether.

[0038] In a preferred embodiment, the acid mentioned in step 4 is selected from hydrochloric acid, sulfuric acid, and citric acid; for example, citric acid.

[0039] In a preferred embodiment, the preparation method of step 4 includes the following steps: after adding a solvent to compound 4, adjusting the pH with acid, separating the layers, extracting the aqueous phase, combining the organic phases, washing, drying, and concentrating to obtain the product; preferably, the solvent in step 4 is a combination of water and methyl tert-butyl ether; preferably, the pH value is adjusted to 4-6, for example 4; preferably, the solvent for extraction can be methyl tert-butyl ether.

[0040] A second aspect of the present invention provides a method for preparing compound 2, the method comprising the following steps: compound 1 undergoes a reductive amination reaction in the presence of a base and a reducing agent, as shown in the following formula, to obtain compound 2;

[0041]

[0042] The definition of R is as described in any embodiment of the present invention;

[0043] The conditions and operations for preparing compound 2 can be as described in any embodiment of the present invention.

[0044] A third aspect of the present invention provides a method for preparing compound 3, the method comprising the following steps: in a solvent, compound 2 reacts with an organic carbonate in the presence of a base to undergo an amino protection reaction as follows, to obtain compound 3;

[0045]

[0046] The definition of R is as described in any embodiment of the present invention;

[0047] The conditions and operations for preparing compound 3 can be as described in any embodiment of the present invention.

[0048] A fourth aspect of the present invention provides a method for preparing compound 4, the method comprising the following steps: in a solvent, compound 3 is reacted with an NH2-resolving base in a resolution reaction as follows to obtain compound 4;

[0049]

[0050] The definition of R is as described in any embodiment of the present invention;

[0051] The conditions and procedures for preparing compound 4 can be as described in any embodiment of the present invention.

[0052] Beneficial effects

[0053] Compared with the prior art, the beneficial effects of the present invention include:

[0054] 1) This invention provides a method for preparing a key intermediate for the synthesis of tubulin inhibitors, overcoming the shortcomings of existing technologies such as long steps (8-11 steps), low yield (14.6%-45%), and low ee value (80%-97.4%). This invention can obtain the target product by only reducing amination, protecting, resolving, and freeing the product. Not only is the reaction yield high, but the ee values ​​of compounds 3 and 4 obtained are not less than 99%, which has unexpected technical effects. It meets the quality requirements of tubulin inhibitors for intermediates and is more conducive to further drug research and production.

[0055] 2) This invention is designed for special substrate structures and preferably uses specific reducing agents to effectively avoid the side reaction of reducing the substrate ketone of compound 1, thereby further improving the reaction yield.

[0056] 3) By changing the reaction route and optimizing the reaction conditions, this invention can effectively reduce the difficulty of post-reaction processing. In particular, by optimizing the combination of alkali and solvent in the upper protection step, the post-processing method can be simplified and the conversion rate can be improved, with a yield of 95%. Compared with the prior art, the pure target product can be obtained in high yield by direct extraction and washing, which greatly improves the experimental efficiency.

[0057] 4) The synthesis method has mild reaction conditions and is simple and convenient to operate, making it suitable not only for small-scale preparation in the laboratory but also for large-scale industrial production. Detailed Implementation

[0058] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0059] Unless otherwise specified, all raw materials or reagents used in the examples are commercially available.

[0060] The room temperature range mentioned in the examples refers to 15–30°C. Unless otherwise specified, the reagents are used directly without purification. All solvents were purchased from commercial suppliers, such as Leyen and Aldrich, and are ready for use without treatment.

[0061] The reaction was analyzed by TLC and / or LCMS, with termination determined by the consumption of starting materials. Analytical thin-layer chromatography (TLC) was performed on glass plates (EMD Chemicals) pre-coated with silica gel 60F254 0.25 mm plates, using UV light (254 nm) and / or iodine development on the silica gel, and / or heating with TLC staining agents such as alcohol-modified phosphomolybdic acid, ninhydrin hydrate solution, potassium permanganate solution, or cerium persulfate solution.

[0062] The abbreviations used in this invention have their conventional meanings in the art, such as: Boc2O represents ditert-butyl dicarbonate; NaBH4 represents sodium borohydride; NaBH3CN represents sodium cyanoborohydride; NaBH(AcO)3 represents sodium triacetoxyborohydride; THF represents tetrahydrofuran; 1,4-Dioxane represents 1,4-dioxane; t-BuOH represents tert-butanol; DIEA represents N,N-diisopropylethylamine; DMAP represents 4-dimethylaminopyridine; the palladium on carbon in this invention is 10 wt%;

[0063] The preparation method of compound 1-1 of the present invention can be obtained with high yield by referring to JACS (2004), 126(32), 9898-9899.

[0064] Unless otherwise stated, the units used in the following specific experimental descriptions represent the following definitions: V: ml / g.

[0065] Example 1

[0066]

[0067] Compound 1-1 (510 g, 2.65 mol) was added to a reaction flask, and tetrahydrofuran (4.30 L) was added under nitrogen protection. The reaction solution was heated to 0–10 °C in an ice-water bath, and methylamine methanol solution (1646 g; of which methylamine was 30 wt%, 15.90 mol) was slowly added dropwise. After the addition was complete, the reaction solution was heated to room temperature and reacted for 2 h. Then, 2-methylpyridine-borane (312.3 g, 2.92 mol) was added, and the reaction was stirred at room temperature for 60 h. After the reaction was completed, no byproduct of the reduction of compound 1-1 ketone was detected. The reaction solution was concentrated, tetrahydrofuran was added and stirred, filtered, and the filter cake was washed with tetrahydrofuran and methyl tert-butyl ether in sequence, filtered, and dried to obtain pure compound 2-1 (505.74 g, yield 92%).

[0068] The operation methods of Comparative Examples 1 to 5 were the same as those in Example 1, except that the type of reducing agent was changed to prepare Compound 2-1. Except for palladium on carbon, which was added at a mass percentage of 10 wt%, the amount of reducing agent added in the other comparative examples was the same as that in Example 1. After the reaction was completed, the proportions of the product (Compound 2-1) and the byproduct (Compound 1-1 ketone was reduced) in the reaction solution were tested by LCMS. The specific reaction conditions are shown in Table 1 below.

[0069] Table 1

[0070] Comparative Example reducing agent Reaction status Comparative Example 1 Pyridineborane Product 55%, by-product 25% Comparative Example 2 Pd / C Product 12%, with a large amount of unknown byproducts. Comparative Example 3 <![CDATA[NaBH4]]> Product 10%, large amount of unknown byproducts Comparative Example 4 <![CDATA[NaBH3CN]]> Product 26%, with a large amount of unknown byproducts. Comparative Example 5 <![CDATA[NaBH(AcO)3]]> Product 35%, by-product 40%

[0071] Example 2

[0072]

[0073] Compound 2-1 (672 g, 3.24 mol) was added to a reaction flask, along with tert-butanol (3.36 L, 5 V) and water (3.36 L, 5 V). Potassium carbonate (1.34 kg, 9.72 mol) was added with stirring. After dissolving, the reaction solution was cooled to 0–10 °C in an ice-water bath. Boc₂O (1.41 kg, 6.48 mol) was added dropwise. After the addition was complete, the reaction solution was heated to room temperature and reacted for approximately 40 h. After the reaction was complete, the pH of the reaction solution was adjusted to 4 with a 10% citric acid aqueous solution. The solution was extracted with methyl tert-butyl ether, and the combined organic phases were washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated to obtain pure compound 3-1 (947.76 g, 95% yield).

[0074] The operation methods of Comparative Examples 6 to 10 were the same as in Example 2, with the types of base and reaction solvent changed to prepare compound 3-1. After the reaction was completed, the proportion of product (compound 3-1) in the reaction solution was tested by LCMS. The specific reaction conditions are shown in Table 2 below.

[0075] Table 2

[0076] Comparative Example alkali reaction solvent Reaction status Comparative Example 6 Potassium carbonate <![CDATA[THF / H2O]]> 71% of the product Comparative Example 7 Potassium carbonate <![CDATA[1,4-Dioxane / H2O]]> Product 63% Comparative Example 8 DIEA / DMAP = 5:1 <![CDATA[t-BuOH / H2O]]> 20% of the product Comparative Example 9 NaOH <![CDATA[t-BuOH / H2O]]> Product 52% Comparative Example 10 NaOH <![CDATA[THF / H2O]]> 40% of the product

[0077] Example 3

[0078]

[0079] Compound 3-1 (700 g, 2.28 mol) was added to a reaction flask. Under nitrogen protection, petroleum ether was added and stirred until dissolved. Then, (S)-(-)-α-methylbenzylamine (331.55 g, 2.74 mol) was added dropwise at room temperature. After the addition was complete, the reaction was allowed to proceed at room temperature for 16 h. After the reaction was completed, the reaction solution was filtered directly. The filter cake was washed with petroleum ether and dried under vacuum to obtain compound 4-1 (441.43 g, yield 45%, ee value 99.04%).

[0080] Comparative Example 11

[0081] The operation method of Comparative Example 11 is the same as that of Example 3. The difference between Comparative Example 11 and Example 3 is that the solvent used in this comparative example is methyl tert-butyl ether, and compound 4-1 is obtained (yield 25%, ee value 97%).

[0082] Example 4

[0083]

[0084] 500 g, 1.17 mol of compound 4-1 was added to water (2 L) and methyl tert-butyl ether (2 L), and the pH was adjusted to 4 with 10% citric acid aqueous solution. After separation, the aqueous phase was extracted with methyl tert-butyl ether (1 L × 2), the organic phases were combined and washed with saturated brine, filtered, dried over anhydrous sodium sulfate, and concentrated to obtain pure compound 5-1 (341.2 g, yield 95%, ee value 99.04%).

[0085] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing compound 5, characterized in that, It includes the following steps: Step 1: Compound 1 undergoes a reductive amination reaction in the presence of a base and a reducing agent, as shown in the following formula, to obtain compound 2, wherein the reducing agent is 2-methylpyridineborane; Step 2: In a solvent, compound 2 reacts with an organic carbonate in the presence of a base to undergo an amino protection reaction as shown in the following formula, to give compound 3; Step 3: In a solvent, compound 3 reacts with an NH2- resolving base in the following resolving reaction to yield compound 4; Step 4: Compound 4 is subjected to a free reaction in the presence of acid as shown in the following formula to obtain compound 5; in, The R is H; The alkali mentioned in step 1 is methylamine; The solvent mentioned in step 2 is a combination of an organic solvent and water; the organic solvent is selected from one or more of tert-butanol, tetrahydrofuran, and 1,4-dioxane. The alkali mentioned in step 2 is selected from one of potassium carbonate, sodium carbonate, sodium bicarbonate, and potassium bicarbonate; In step 3, the solvent is petroleum ether, the NH2-resolving base is (S)-(-)-α-methylbenzylamine, and the molar ratio of compound 3 to the NH2-resolving base is 1:(1~2).

2. The preparation method according to claim 1, characterized in that, The reaction in step 1 satisfies one or more of the following conditions: (1) The molar ratio of compound 1 to methylamine is 1:(1~7); (2) The reaction temperature for the reductive amination reaction in step 1 is room temperature; (3) The reaction time for the reductive amination reaction in step 1 is 40-65 h; and (4) The solvent for the reaction in step 1 is an ether solvent, which is selected from one or more of ethylene glycol dimethyl ether, 1,4-dioxane and tetrahydrofuran.

3. The preparation method according to claim 1, characterized in that, The molar ratio of compound 1 to methylamine is 1:(2~6).

4. The preparation method according to claim 1, characterized in that, The molar ratio of compound 1 to methylamine is 1:

6.

5. The preparation method according to claim 1, characterized in that, The methylamine was added in the form of a methylamine alcohol solution.

6. The preparation method according to claim 5, characterized in that, The methylamine alcohol solution is either a methylamine methanol solution or a methylamine ethanol solution.

7. The preparation method according to claim 1, characterized in that, The molar ratio of compound 1 to the reducing agent is 1:(1~2).

8. The preparation method according to claim 1, characterized in that, The molar ratio of compound 1 to the reducing agent is 1:(1~1.5).

9. The preparation method according to claim 1, characterized in that, The molar ratio of compound 1 to the reducing agent is 1:1.

1.

10. The preparation method according to claim 1, characterized in that, The reaction time for the reductive amination reaction in step 1 is 60 hours.

11. The preparation method according to claim 1, characterized in that, The solvent for the reaction in step 1 is tetrahydrofuran.

12. The preparation method according to claim 1, characterized in that, The reaction in step 2 satisfies one or more of the following conditions: (1) The solvent is a combination of tert-butanol and water; the volume ratio of tert-butanol to water is 1:(0.5~1.5); (2) The alkali mentioned is potassium carbonate; (3) The organic carbonate mentioned in step 2 is ditert-butyl dicarbonate; (4) The reaction temperature in step 2 is room temperature; and (5) The reaction time for step 2 is 24~45h.

13. The preparation method according to claim 1, characterized in that, The solvent is a combination of tert-butanol and water; the volume ratio of tert-butanol to water is 1:(0.5~1.5).

14. The preparation method according to claim 1, characterized in that, The solvent is a combination of tert-butanol and water; the volume ratio of tert-butanol to water is 1:

1.

15. The preparation method according to claim 1, characterized in that, The molar ratio of compound 2 to the base is 1:(1~5).

16. The preparation method according to claim 1, characterized in that, The molar ratio of compound 2 to the base is 1:

3.

17. The preparation method according to claim 12, characterized in that, The molar ratio of compound 2 to ditert-butyl dicarbonate is 1:(1~3).

18. The preparation method according to claim 12, characterized in that, The molar ratio of compound 2 to ditert-butyl dicarbonate is 1:

2.

19. The preparation method according to claim 1, characterized in that, The reaction time for step 2 is 35-45 hours.

20. The preparation method according to claim 1, characterized in that, The reaction time for step 2 is 40 hours.

21. The preparation method according to claim 1, characterized in that, The reaction temperature for step 3 is room temperature.

22. The preparation method according to claim 1, characterized in that, The reaction time for step 3 is 10-20 hours.

23. The preparation method according to claim 1, characterized in that, The molar ratio of compound 3 to the NH2-resolving base is 1:1.

2.

24. The preparation method according to claim 1, characterized in that, The reaction time for step 3 is 16 hours.

25. The preparation method according to claim 1, characterized in that, The acid mentioned in step 4 is selected from hydrochloric acid, sulfuric acid, and citric acid.

26. The preparation method according to claim 1, characterized in that, The acid mentioned in step 4 is citric acid.

27. A method for preparing compound 4, characterized in that, The preparation method of compound 4 includes the following steps: in a solvent, compound 3 is reacted with an NH2-resolving base in a resolution reaction as shown in the following formula to obtain compound 4; in, The R is defined as a substituent in claim 1; In step 3, the solvent is petroleum ether, the NH2-resolving base is (S)-(-)-α-methylbenzylamine, and the molar ratio of compound 3 to the NH2-resolving base is 1:(1~2).

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