WO2024098530A1 - Intermediate and method for preparing pyrroloquinoline quinone - Google Patents

Abstract

The present application provides an intermediate and method for preparing pyrroloquinoline quinone. The method comprises: using a compound of formula (II) as a starting raw material to prepare a compound of formula (III) by means of a Fischer indole synthesis method, hydrolyzing the compound of formula (III) to prepare a compound of formula (IV), and oxidizing the compound of formula (IV) to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, wherein R1 is C1-C3 linear or branched alkyl, and R3 is selected from hydrogen and C1-C3 linear or branched alkyl. The method is simple, the yield is high, the reaction conditions are mild, the operation is simple, the production period is obviously shortened, the method of the present application is easy to scale up, the production scale can reach a hundred-gram level, and large-scale production can be realized.

Description

Intermediates and methods for preparing pyrroloquinoline quinone

The present invention claims the priority of the Chinese patent application filed with the Chinese Patent Office on November 11, 2022, with application number 202211415318.7 and invention name “Intermediates and methods for preparing pyrroloquinoline quinone”, the entire contents of which are incorporated by reference into the present invention.

Technical Field

The present application relates to the field of preparation of organic compounds, and in particular to an intermediate and method for preparing pyrroloquinoline quinone.

Background technique

The information disclosed in the background technology of this application is intended to increase the understanding of the overall background of this application, and this disclosure should not necessarily be regarded as an admission or any form of suggestion that this information has become the prior art known to ordinary technicians in this field.

4,5-Dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, also known as pyrroloquinoline quinone (PQQ, methoxatin), CAS No. 72909-34-3, is a natural product. PQQ is widely present in various common foods such as fruits, vegetables, grains and beverages, including plant-derived foods and animal-derived foods. However, the concentration of PQQ available in food sources is very low, only at the level of nanograms to micrograms per kilogram. Therefore, it is impossible to obtain sufficient PQQ through dietary supplementation alone, and chemical synthesis of PQQ becomes inevitable.

Corey et al. first achieved the total synthesis of PQQ, referred to as the Corey method, see Corey E J, Tramontano A. Total synthesis of the quinonoid alcohol dehydrogenase coenzyme (1) of methylotrophic bacteria [J]. Journal of the American Chemical Society, 1981, 103 (18): 5599-5600. According to Corey's report, PQQ can be prepared by total synthesis from commercial raw materials through a 10-step chemical process. Subsequently, Martin et al. improved the route of the Corey method and reduced the total synthesis steps to 9 steps, referred to as the Martin method, see Martin P, Steiner E, Auer K, et al. Zur Herstellung von PQQ in kg-Mengen [J]. Helvetica chimica acta, 1993, 76 (4): 1667-1673. In 2006, Kempf et al. synthesized PQQ on a large scale by combining the Corey method and the Martin method, referred to as the Kempf method, see WO2006/102642A1. Both the Corey method and the Martin method are difficult to achieve the preparation of PQQ on a gram scale. The Corey method can only obtain PQQ on a 50 mg scale. This method is suitable for laboratory preparation and difficult to apply industrially. Although the Martin method has fewer synthesis steps than the Corey method, the overall process route is very similar and the synthesis scale has not been significantly improved, especially in the last step of the synthesis, it still requires a cumbersome two-stage separation process. Although the Kempf method can achieve the production of gram-scale PQQ, it further requires the purification of the final compound with sulfuric acid, and multiple steps involve the separation of intermediates, which is a cumbersome process. In 2014, ANTHEM BIOSCIENCES PVT provided a PQQ synthesis method, see patent WO2014/195896. The difference of this method is that methyl halobenzene is used as a raw material to synthesize PQQ on a large scale. However, the above method and the existing route involving the total chemical synthesis of PQQ must be used in the latter stage of the reaction to mildly oxidize the methoxy-pyrroloquinoline intermediate to the pyrroloquinoline quinone intermediate by ammonium cerium nitrate (CAN). Although the product selectivity of this process is high, the consumption of ammonium cerium nitrate is extremely large (generally more than 8 times the mass of the raw material), and the final separation and purification are difficult, resulting in the optimized yield of this step being only about 60%. In addition, the high price of ammonium cerium nitrate leads to the high overall synthesis cost of PQQ, and the cerium salt can only be treated as waste, which has a high sewage discharge pressure. In addition, due to the low efficiency of the process, it is difficult to achieve high efficiency and industrialization in the production of PQQ.

Summary of the invention

The present application provides an intermediate and method for preparing pyrroloquinoline quinone. The reaction route for preparing pyrroloquinoline quinone with the intermediate of the present application is simple, the reaction yield is high, the purity is good, the reaction conditions are mild, and the reaction raw materials of the present application are cheap and easy to obtain, which can greatly reduce the reaction cost, and the reaction route can be controlled within 6 steps or less, which greatly simplifies the reaction route and improves the reaction efficiency, significantly shortens the production cycle, and the method of the present application is easy to scale up, and the production scale can reach the hundred-gram level, which can realize large-scale production.

Specifically, this application provides the following technical solutions:

In the first aspect of the present application, the present application provides compounds as shown in Formula I and Formula II, whose structural formula is:

Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group, _R2 is a nitro group or an amino group; and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.

Furthermore, the compound described in the present application has the structure shown below:

wherein R ₁ , R ₂ and R ₃ are as defined above.

In some embodiments of the present application, R ₁ is preferably methyl or ethyl.

In some embodiments of the present application, R ₃ is preferably hydrogen, methyl, ethyl or propyl.

In the second aspect of the present application, the present application provides the use of a compound of formula I, a compound of formula II or a compound of formula X as an intermediate in the preparation of 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (also known as pyrroloquinoline quinone, PQQ or methoxatin);

wherein R ₁ , R ₂ and R ₃ are as defined above.

As an example, the intermediate compound that can be used to prepare pyrroloquinoline quinone in the first aspect above is selected from the following structures:

3,4-Dimethoxy-5-nitroaniline;

3,4-diethoxy-5-nitroaniline;

(Z)-2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazine)propanoic acid ethyl ester (compound I-1-1, R ₁ is methyl, R ₂ is nitro);

(Z)-2-(2-(3,4-diethoxy-5-nitrophenyl)hydrazine)propanoic acid ethyl ester (compound I-1-2, R ₁ is ethyl, R ₂ is nitro);

(Z)-2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazine)propanoic acid ethyl ester (compound I-2-1, R ₁ is methyl, R ₂ is amino);

(Z)-2-(2-(3-amino-4,5-diethoxyphenyl)hydrazine)propanoic acid ethyl ester (compound I-2-2, R ₁ is methyl, R ₂ is amino);

(Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid (compound II-1-1, R ₁ is methyl, R ₃ is hydrogen);

(Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dimethyl ester (compound II-1-2, R ₁ is methyl, R ₃ is methyl);

(Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid diethyl ester (Compound II-1-3, R ₁ is methyl, R ₃ is ethyl);

(Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dipropyl ester (Compound II-1-4, R ₁ is methyl, R ₃ is propyl);

(Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid (compound II-2-1, R ₁ is ethyl, R ₃ is hydrogen);

(Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid dimethyl ester (compound II-2-2, R ₁ is ethyl, R ₃ is methyl);

(Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid diethyl ester (compound II-2-3, R ₁ is ethyl, R ₃ is ethyl);

(Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid dipropyl ester (Compound II-2-4, R ₁ is ethyl, R ₃ is propyl).

In particular, when the above-mentioned compounds are used to prepare pyrroloquinoline quinone, the reaction yield is high and the purity is good. The reaction is simple and the conditions are mild. The reaction route can be achieved in only 6 steps, which greatly simplifies the reaction method and improves the reaction efficiency. In addition, the reaction raw materials are cheap and easily available, which greatly reduces the cost of the reaction. The above-mentioned intermediate compounds are used to prepare pyrroloquinoline quinone, which is easy to scale up and can be produced on a large scale.

In the third aspect of the present application, the present application provides a method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: preparing a compound of formula III from a compound of formula II by Fischer indole synthesis, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and finally oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

Wherein, R ₁ and R ₃ are as defined above;

Preferably, _R1 is methyl or ethyl, and _R3 is selected from hydrogen, methyl, ethyl and propyl.

In one embodiment of the present application, the compound of formula II can be prepared by reacting a compound of formula I-2 with a compound of formula V under the catalysis of Lewis acid.

Wherein, R ₁ and R ₃ are as defined above.

Preferably, _R1 is methyl or ethyl, and _R3 is selected from hydrogen, methyl, ethyl and propyl.

In the fourth aspect of the present application, the present application provides a method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: preparing a compound of formula II from a compound of formula I-2 and a compound of formula V under Lewis acid catalysis, then preparing a compound of formula III from the compound of formula II by Fischer indole synthesis, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and finally oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

Wherein, R ₁ and R ₃ are as defined above.

Preferably, _R1 is methyl or ethyl, and _R3 is selected from hydrogen, methyl, ethyl and propyl.

In one embodiment of the present application, the compound of formula I-2 can be prepared by reducing the compound of formula I-1.

In the fifth aspect of the present application, the present application provides a method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: reducing a compound of formula I-1 to prepare a compound of formula I-2, then reacting the compound of formula I-2 with a compound of formula V under Lewis acid catalysis to prepare a compound of formula II, then reacting the compound of formula II to prepare a compound of formula III by Fischer indole synthesis, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and finally oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

Wherein, R ₁ and R ₃ are as defined above.

Preferably, _R1 is methyl or ethyl, and _R3 is selected from hydrogen, methyl, ethyl and propyl.

In one embodiment of the present application, the compound of formula I-1 can be prepared by diazotizing 3,4-dialkoxy-5-nitroaniline (such as the compound of formula X) and condensing it with ethyl 2-methylacetoacetate, wherein R ₁ is as defined above.

In the sixth aspect of the present application, the present application provides a method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: 3,4-dialkoxy-5-nitroaniline (compound of formula X) is diazotized and then condensed with ethyl 2-methylacetoacetate to prepare a compound of formula I-1, the compound of formula I-1 is reduced to prepare a compound of formula I-2, and then the compound of formula I-2 and the compound of formula V are catalyzed by Lewis acid to prepare a compound of formula II, and then the compound of formula II is prepared by Fischer indole synthesis to prepare a compound of formula III, and then the compound of formula III is hydrolyzed to prepare a compound of formula IV, and finally the compound of formula IV is oxidized to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

Wherein, R ₁ and R ₃ are as defined above.

Preferably, _R1 is methyl or ethyl, and _R3 is selected from hydrogen, methyl, ethyl and propyl.

In one embodiment of the present application, the 3,4-dialkoxy-5-nitroaniline (compound of formula X) can be prepared using 3,4-dialkoxy-5-nitrobenzoic acid or 3,4-dialkoxy-5-nitrobenzamide as a raw material, wherein R ₁ is as defined above.

In one embodiment of the present application, the last oxidation step in the above preparation method, i.e., the step of oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, can be directly oxidized or include: reacting the compound of formula IV with a protonic acid to prepare 2-(ethoxycarbonyl)-4,5-dihydroxy-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid, and then oxidizing 2-(ethoxycarbonyl)-4,5-dihydroxy-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid under the action of an oxidant to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid.

In an embodiment of the present application, the protonic acid may be hydrobromic acid, hydroiodic acid or hydrochloric acid. The oxidant may be hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid or ozone.

Compared with the prior art, the advantages of the present application are: when the intermediate described in the present application is used to prepare pyrroloquinoline quinone, the reaction route is simple, the reaction yield is high (the single-step yield is above 75%, and the total yield is significantly improved), the purity is good, the reaction conditions are mild, and the reaction raw materials of the present application are cheap and easy to obtain, which can greatly reduce the reaction cost. The reaction route can be controlled within 6 steps or less, which greatly simplifies the reaction route and improves the reaction efficiency, shortens the reaction cycle, and the method of the present application is easy to scale up, and the production scale can reach the hundred-gram level, which can be mass-produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constituting part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. The implementation scheme of the present application is described in detail below in conjunction with the drawings, wherein:

FIG1 is a hydrogen spectrum of an exemplary compound of formula I-1.

FIG2 is a carbon spectrum of an exemplary compound of formula I-1.

FIG3 is a hydrogen spectrum of an exemplary compound of formula I-2.

FIG4 is a carbon spectrum of an exemplary compound of formula I-2.

Detailed ways

The present application is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. The reagents or raw materials used in this application can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in this application are used in a conventional manner in the art or in accordance with the product instructions. In addition, any method and material similar to or equivalent to the content described herein can be applied to the method of this application. The preferred implementation methods and materials described in the text are for demonstration purposes only.

The present application provides compounds of formula I and formula II and methods for preparing the same, as well as a method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid using compounds of formula I, formula II and/or formula X as intermediates.

In some embodiments of the present application, the method for preparing pyrroloquinoline quinone using formula II as an intermediate can be carried out according to the following reaction scheme:

Wherein, _R1 is a _C1 - _C3 straight chain or branched chain alkyl group, and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched chain alkyl group.

In a more preferred embodiment of the present application, _R1 is a methyl group or an ethyl group, and _R3 is a methyl group, an ethyl group or a propyl group.

In the reaction route of the present application, when the Fischer indole synthesis is carried out using the compound of formula II as an intermediate, the quinoline in the structure can play a placeholder role to improve the selectivity of indole synthesis, avoid the generation of unnecessary side reaction substances, greatly improve the synthesis efficiency and yield, and reduce the subsequent complicated purification work.

In some embodiments of the present application, the method for preparing pyrroloquinoline quinone using Formula I as an intermediate (Formula I-2) can be carried out according to the following reaction route:

Wherein, _R1 is a _C1 - _C3 straight chain or branched chain alkyl group, _R2 is an amino group, and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched chain alkyl group.

In a more preferred embodiment of the present application, _R1 is a methyl group or an ethyl group, and _R3 is a methyl group, an ethyl group or a propyl group.

Wherein, further, the reaction route can be:

Wherein, _R1 is a _C1 - _C3 straight chain or branched chain alkyl group, and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched chain alkyl group.

In a more preferred embodiment of the present application, _R1 is a methyl group or an ethyl group, and _R3 is a methyl group, an ethyl group or a propyl group.

In the reaction route of the present application, when preparing pyrroloquinoline quinone using the compound of formula I as an intermediate, the quinoline structure is first synthesized, and then the Fischer indole synthesis is performed. The selectivity of the indole synthesis is improved by the quinoline occupancy, the generation of unnecessary side reaction substances is avoided, the synthesis efficiency and yield are greatly improved, and the subsequent complicated purification work is reduced.

In some embodiments of the present application, the method for preparing pyrroloquinoline quinone using a 3,4-dialkoxy-5-nitroaniline compound (compound of formula X) can be carried out according to the following reaction route:

Wherein, _R1 is a _C1 - _C3 straight chain or branched chain alkyl group, and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched chain alkyl group.

In a more preferred embodiment of the present application, _R1 is a methyl group or an ethyl group, and _R3 is a methyl group, an ethyl group or a propyl group.

In the reaction route of the present application, 3,4-dialkoxy-5-nitroaniline compound (compound of formula X) is used as an intermediate to prepare pyrroloquinoline quinone by first synthesizing the quinoline structure and then performing the Fischer indole synthesis. The selectivity of the indole synthesis is improved by quinoline occupation, the generation of unnecessary side reaction substances is avoided, the synthesis efficiency and yield are greatly improved, and the subsequent complicated purification work is reduced.

In some embodiments of the present application, the last step of the above-mentioned multiple reactions is an oxidation reaction, which can be carried out in one step or according to the following reaction route:

For example, in a more specific embodiment, the preparation method of pyrroloquinoline quinone includes:

(1) diazotizing the compound 3,4-dialkoxy-5-nitroaniline (compound of formula X) with sodium nitrite solution under acidic conditions, and then condensing with ethyl 2-methylacetoacetate under alkaline conditions to form a compound of formula I-1;

In some embodiments of the present application, the molar ratio of the compound of formula X to ethyl 2-methylacetoacetate is 1:1-5.

In some embodiments of the present application, the temperature of the reaction stage of step (1) is controlled at -10°C to 0°C.

For example, in some embodiments of the present application, step (1) comprises: stirring and mixing anhydrous ethanol as a solvent and a compound of formula X, cooling the reaction system to -10°C-0°C, adding an acid (such as concentrated hydrochloric acid or concentrated sulfuric acid), maintaining the reaction system temperature at -10°C-0°C, adding sodium nitrite, stirring at -10°C-0°C, adding ethyl 2-methylacetoacetate, and adding sodium acetate, and stirring and reacting at -10°C-0°C.

(2) the compound of formula I-1 undergoes a reduction reaction under the action of a reducing agent to obtain a compound of formula I-2;

In some embodiments of the present application, the compound of formula I-1 is subjected to a reduction reaction with a reducing agent such as iron powder in an acetic acid solution, and the reaction temperature is controlled at 60-80°C.

(3) The compound of formula I-2 reacts with the compound of formula V under the catalysis of Lewis acid in an oxygen atmosphere to obtain a compound of formula II;

In some embodiments of the present application, the molar ratio of the compound of formula I-2 to the compound of formula V is 1:1-5.

For example, in some embodiments of the present application, step (3) comprises: after the compound of formula I-2 and a solvent (such as dichloromethane) are stirred evenly, a compound of formula V and a Lewis acid (such as zinc chloride) are added, and the reaction is stirred at room temperature.

(4) The compound of formula II is prepared by Fischer indole synthesis to obtain the compound of formula III;

In some embodiments of the present application, the reaction temperature is controlled at 30-55°C.

For example, in some embodiments of the present application, step (4) comprises: uniformly stirring excess sulfuric acid and compound II, heating the reaction system to 30-55° C. and stirring the reaction.

(5) the compound of formula III undergoes ester hydrolysis reaction to obtain the compound of formula IV;

In some embodiments of the present application, the ester hydrolysis reaction occurs in an alkaline environment and the temperature is controlled at 80-90°C.

(6) oxidizing the compound of formula IV to obtain PQQ, or, preparing intermediate F from the compound of formula IV and then oxidizing it to obtain PQQ;

For example, intermediate E can be prepared by reacting with a protonic acid to obtain intermediate F, and the protonic acid can be hydrobromic acid, hydrochloric acid or hydroiodic acid, preferably hydroiodic acid; for example, the oxidation can use an oxidant, and the oxidant can be selected from one or more of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid and ozone, preferably hydrogen peroxide.

It should be affirmed that the most important part of this application is the design of the intermediates and the design of the experimental route for obtaining the target product PQQ using the intermediates. Based on the intermediates disclosed in this application and the routes designed based on the intermediates, the operations of debugging or changing the reaction environment and reaction parameters to further optimize the reaction are all basic operating skills of those skilled in the art, and cannot substantially constitute an improvement on the technical solution described in this application, and should all be part of the protection scope of this application.

Specifically, in combination with the above reaction route, the present application provides the following preparation examples.

Unless otherwise specified, the room temperature in the experiments of this application refers to 20-25°C.

Among them, the starting reactant 3,4-dimethoxy-5-nitroaniline can be prepared using 3,4-dimethoxy-5-nitrobenzoic acid or 3,4-dimethoxy-5-nitrobenzamide as raw materials. For example, 3,4-dimethoxy-5-nitroaniline can be prepared according to the method in U.S. Pat. No. 5,236,952, and the relevant contents of the patent are incorporated into this application by reference. Alternatively, as an example, 3,4-dimethoxy-5-nitroaniline can be prepared according to the following method:

908g of toluene, 180g of thionyl chloride and 227g of 3,4-dimethoxy-5-nitrobenzoic acid were put into a 2000mL reaction bottle, heated to 80°C, and kept at 70-80°C for 8h. After the reaction was completed, toluene was distilled under reduced pressure to 85°C, the residue was slightly cooled to 50°C, diluted with 100g of acetone, and the residue was slowly added back to 1000g of 25% ammonia water pre-cooled to below 5°C. After the addition was completed, the solid material precipitated was 3,4-dimethoxy-5-nitrobenzamide. Filtered to obtain 490g of 3,4-dimethoxy-5-nitrobenzamide wet product.

Add 950g of 10% sodium hypochlorite and 1060g of 10% sodium carbonate to another 3000mL reaction bottle and cool to below 20°C. Add 490g of wet 3,4-dimethoxy-5-nitrobenzamide to the reaction bottle and stir at 15-20°C for 3h. After the reaction is complete, heat to 70°C within 1h and stir at 70-75°C for 3h. After the reaction is complete, cool to below 5°C, stir and crystallize for 3h, filter to obtain 390g of wet 3,4-dimethoxy-5-nitroaniline, and dry in an oven at 90°C to obtain 168.3g of dry 3,4-dimethoxy-5-nitroaniline. Molar yield: 85%, HPLC purity 99%.

According to the above method, 3,4-diethoxy-5-nitrobenzoic acid is used as a raw material to replace 3,4-dimethoxy-5-nitrobenzoic acid to prepare 3,4-diethoxy-5-nitroaniline.

The above-mentioned charging reaction is carried out multiple times to accumulate 3,4-dimethoxy-5-nitroaniline material and 3,4-diethoxy-5-nitroaniline material for the preparation of the target product.

The following examples illustrate the preparation process of the intermediates described in the present application and the specific process of preparing PQQ using the intermediates described in the present application under certain conditions. The following examples are examples of preparing products at the 100-gram level. In order to accumulate sufficient materials for each step of the reaction, the following examples will perform multiple feeding reactions in actual operations, and each feeding process is the same. The following preparation examples only illustrate a single feeding preparation process.

Example 1 Preparation of Compounds of Formula I

Preparation Example 1: Preparation of (Z)-2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazine)propionic acid ethyl ester (Compound I-1-1)

Add 500g of anhydrous ethanol and 198g of 3,4-dimethoxy-5-nitroaniline to the reaction bottle and stir to mix evenly. Cool the reaction system to -10°C, drip 365g of concentrated hydrochloric acid into the reaction bottle, cool the reaction system to -10°C after dripping, and start to quickly drip 233g of 40% sodium nitrite. After the dripping is completed, stir at -5°C for 1h. After the reaction is completed, add 200g of ethyl 2-methylacetoacetate to the reaction bottle at -5°C, and after the addition, drip 1366.7g of 30% sodium acetate at -5°C. After the dripping is completed, keep warm and stir at -5°C-0°C for 4h. After the reaction is completed, warm the reaction system to room temperature and stir for 16h. After the reaction is completed, filter, wash the solid material with water once, dry and dry to obtain compound I-1-1, with a yield of 280g, a yield of 89.9%, and an HPLC purity of 97%. The hydrogen spectrum and carbon spectrum of compound formula I-1-1 are shown in Figures 1 and 2, respectively.

Preparation Example 2: Preparation of (Z)-2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazine)propanoic acid ethyl ester (Compound I-1-1)

Add 500g of anhydrous ethanol and 198g of 3,4-dimethoxy-5-nitroaniline to the reaction bottle and stir to mix evenly. Cool the reaction system to -10℃, drip 365g of concentrated hydrochloric acid into the reaction bottle, cool the reaction system to -10℃ after dripping, and start to quickly drip 233g of 40% sodium nitrite, and control the dripping temperature at -5-0℃. After the dripping is completed, stir at -5-0℃ for 1h. After the reaction is completed, add 200g of ethyl 2-methylacetoacetate to the reaction bottle at 0℃, and after the addition, drip 1366.7g of 30% sodium acetate at -5-0℃. After the dripping is completed, keep warm and stir at -5℃-0℃ for 4h. After the reaction is completed, heat the reaction system to 20-25℃ and stir for 16h. After the reaction is completed, filter, wash the solid material with water once, and dry to obtain compound I-1-1, with a yield of 268g, and its NMR data is basically consistent with the compound prepared in Preparation Example 1. Yield: 86.2%, HPLC purity 98%.

Preparation Example 3: Preparation of (Z)-ethyl 2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazine)propanoate (Compound I-1-1)

Add 500g of anhydrous ethanol and 198g of 3,4-dimethoxy-5-nitroaniline to the reaction bottle and stir to mix evenly. Cool the reaction system to -10°C, drip 900g of 40% sulfuric acid into the reaction bottle, cool the reaction system to -10°C after dripping, and start to quickly drip 233g of 40% sodium nitrite, and control the dripping temperature at -10°C. After the dripping is completed, stir at -5-0°C for 1h. After the reaction is completed, add 200g of ethyl 2-methylacetoacetate to the reaction bottle at -5-0°C, and after the addition, drip 2263g of 30% sodium bicarbonate at -5-0°C. After the dripping is completed, keep warm and stir at -5-0°C for 4h. After the reaction is completed, heat the reaction system to room temperature and stir for 16h. After the reaction is completed, filter, wash the solid material with water once, and dry to obtain compound I-1-1, with a yield of 251.9g, and its nuclear magnetic resonance data is basically consistent with the compound prepared in Preparation Example 1. Yield: 81%, HPLC purity 97.2%.

By replacing the raw material 3,4-dimethoxy-5-nitroaniline with 3,4-diethoxy-5-nitroaniline, (Z)-2-(2-(3,4-diethoxy-5-nitrophenyl)hydrazine)ethyl propionate (compound formula I-1-2) can be prepared according to the method described in Preparation Example 1-3, with a molar yield of more than 85% and an HPLC purity of more than 95%.

Preparation Example 4: Preparation of (Z)-ethyl 2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazine)propanoate (Compound I-2-1)

Add 168g of iron powder and 1000g of 10% acetic acid to the reaction bottle, stir evenly, heat to 80°C and stir to react for 1h. Slightly cool and slowly add 311g of compound I-1-1 (Preparation Example 1). After mixing evenly, heat to 75-80°C and stir to react for 6h, and the reaction is completed. Cool the reaction solution to room temperature, adjust the pH to 8-9 with saturated sodium carbonate solution, and filter with suction. After the solid is washed repeatedly with hot alcohol twice, collect the ethanol filtrate, decompress and spin-dry the ethanol, precipitate a large amount of crystals, cool to 20°C, filter with suction, collect the solid and dry it to obtain 267g of granular crystals, namely compound I-2-1. Molar yield: 95%, HPLC purity: 98.9%, the hydrogen spectrum and carbon spectrum of compound formula I-2-1 are shown in Figures 3 and 4, respectively.

Preparation Example 5: Preparation of (Z)-ethyl 2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazine)propanoate (Compound Formula I-2-1)

Add 168g of iron powder and 1000g of 10% acetic acid to the reaction bottle, stir evenly, heat to 80°C and stir to react for 1h. Cool slightly, slowly add 311g of compound I-1-1 (Preparation Example 1) to the reaction bottle at 50-65°C. After mixing evenly, heat to 60-70°C and stir to react for 6h, and the reaction is completed. Cool the reaction solution to 20-25°C, adjust the pH to 8-9 with saturated sodium carbonate solution, and filter. After the solid is washed repeatedly with hot ethanol twice, collect the ethanol filtrate, decompress and spin-dry the ethanol, precipitate a large amount of crystals, cool to 20°C, filter, collect the solid and dry it to obtain 250g of granular crystals, namely compound I-2-1, whose nuclear magnetic resonance data is basically consistent with the compound prepared in Preparation Example 4. Molar yield: 89%, HPLC purity: 98%.

Preparation Example 6: Preparation of (Z)-ethyl 2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazine)propanoate (Compound I-2-1)

Add 168g iron powder, 500g ethanol and 500g of 20% acetic acid into the reaction bottle, stir evenly, heat to 80℃ and stir for 1h. Slightly cool and slowly add 311g of compound I-1-1 (Preparation Example 1). After mixing evenly, heat to 75-80℃ and stir for 6h, and the reaction is completed. Cool the reaction solution to room temperature, adjust the pH to 8-9 with saturated sodium carbonate solution, and filter. After the solid is washed repeatedly with hot alcohol twice, collect the ethanol filtrate, decompress and spin-dry the ethanol, precipitate a large amount of crystals, cool to 20℃, filter, collect the solid and dry it to obtain 258.5g of granular crystals, namely compound formula I-2-1, whose nuclear magnetic resonance data is basically consistent with the compound prepared in Preparation Example 4. Molar yield: 92%, HPLC purity: 99%.

The raw material (Z)-2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazine)propionic acid ethyl ester (compound formula I-1-1) is replaced with (Z)-2-(2-(3,4-diethoxy-5-nitrophenyl)hydrazine)propionic acid ethyl ester (compound I-1-2), and (Z)-2-(2-(3-amino-4,5-diethoxyphenyl)hydrazine)propionic acid ethyl ester (compound I-2-2) is prepared according to the method described in Preparation Example 4-6, with a molar yield of more than 90% and a purity of more than 98%.

Example 2 Preparation of Compound Formula II

Preparation Example 7: Preparation of (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dimethyl ester (Compound II-1-2)

Add 562g of compound I-2-1 (Preparation Example 4) and 3000g of dichloromethane to the reaction bottle, stir evenly, then add 980g of (E)-4-oxopentan-2-enedioic acid dimethyl ester and 544g of zinc chloride, and stir at room temperature for 24h. After the reaction is completed, evaporate the solvent at normal pressure and then at reduced pressure. Add 2000g of 70% ethanol to the residue, heat to 70℃ and stir for 30min, after stirring, cool to 15℃, and precipitate a light yellow solid. Filter and dry to obtain 703g of compound II-1-2. Molar yield: 81.2%, HPLC purity 99.1%.

Preparation Example 8: Preparation of (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid diethyl ester (Compound II-1-3)

Add 562g of compound I-2-1 (Preparation Example 4) and 3000g of dichloromethane into the reaction bottle, stir evenly, then add 980g of (E)-4-oxopentan-2-enedioic acid diethyl ester and 544g of zinc chloride, and stir at 20-25°C for 24h. After the reaction is completed, evaporate the solvent at normal pressure and then at reduced pressure. Add 2000g of 70% ethanol to the residue, heat to 70°C and stir for 30min. After stirring, cool to 15°C to precipitate a light yellow solid. Filter and dry to obtain 733g of compound II-1-3. Molar yield: 79.5%, HPLC purity 99.1%

Preparation Example 9: Preparation of (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dipropyl ester (Compound II-1-4)

Add 562g of compound I-2-1 (Preparation Example 4) and 3000g of acetonitrile to the reaction bottle, stir evenly, then add 980g of (E)-4-oxopentan-2-enedioic acid dipropyl ester and 544g of zinc chloride, and stir the reaction at room temperature for 24h. After the reaction is completed, evaporate the solvent at normal pressure and then at reduced pressure. Add 2000g of 50% ethanol to the residue, heat to 70°C and stir for 30min. After stirring, cool to 15°C to precipitate a light yellow solid. Filter and dry to obtain 743.3g of compound formula II-1-4. Molar yield: 76%, HPLC purity 99.1%

The raw material (Z)-2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazine)propionic acid ethyl ester (Compound I-2-1) in Preparation Example 7-9 was replaced with (Z)-2-(2-(3-amino-4,5-diethoxyphenyl)hydrazine)propionic acid ethyl ester (Compound I-2-2), and (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazine)quinoline-2,4-dimethoxybenzene was prepared according to the method described in Preparation Example 7-9. The molar yields of the following compounds were all above 75% and the HPLC purity was above 99%.

Example 3 Preparation of Compound III

Preparation Example 10: Preparation of ethyl 4,5-dimethoxy-7,9-bis(methoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylate (Compound III-1-2)

2200g sulfuric acid and 433g compound II-1-2 (Preparation Example 7) were added to the reaction flask, stirred evenly, and the reaction system was heated to 40°C and stirred for 16h. After the reaction was completed, the reaction solution was added back to 8800g of ice-water mixture to precipitate solid material, which was filtered, washed with water until neutral, filtered, and dried to obtain 382.7g compound III-1-2. Molar yield: 92%, HPLC purity 99%.

Preparation Example 11: Preparation of ethyl 4,5-dimethoxy-7,9-bis(ethoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylate (Compound III-1-3)

2200g sulfuric acid and 461g compound II-1-3 (Preparation Example 8) were added to the reaction flask, stirred evenly, and the reaction system was heated to 45-55°C and stirred for 16h. After the reaction was completed, the reaction solution was added back to 8800g of ice-water mixture to precipitate solid material, filtered, washed with water until neutral, filtered, and dried to obtain 390.7g compound III-1-3. Molar yield: 88%, HPLC purity 99%.

Preparation Example 12: Preparation of ethyl 4,5-dimethoxy-7,9-bis[(propyloxy)carbonyl]-1H-pyrrolo[2,3-f]quinoline-2-carboxylate (Compound III-1-4)

2200g sulfuric acid and 489g compound II-1-4 (Preparation Example 9) were added to the reaction bottle, stirred evenly, and the reaction system was heated to 30-40°C and stirred for 16h. After the reaction was completed, the reaction solution was added back to 8800g of ice-water mixture to precipitate solid material, filtered, washed with water until neutral, filtered, and dried to obtain 424.8g compound III-1-4. Molar yield: 90%, HPLC purity 98.6%.

The raw materials (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dimethyl ester (Compound II-1-2), (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid diethyl ester (Compound II-1-3) and (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid diethyl ester (Compound II-1-3) were prepared as follows: The dimethyl (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylate (compound II-1-4) was replaced by dimethyl (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylate (compound II-2-2), (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylate (compound II-3-2), respectively. 4,5-diethoxy-7,9-bis(methoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound II-2-3) and (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxoprop-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid dipropyl ester (compound II-2-4) were prepared according to the method described in Preparation Example 7-9 to obtain 4,5-diethoxy-7,9-bis(methoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester ( Compound III-2-2), 4,5-diethoxy-7,9-bis(ethoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound III-2-3) and 4,5-diethoxy-7,9-bis[(propyloxy)carbonyl]-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound III-2-4), their molar yields are all above 85%, and their HPLC purities are all above 98%.

Example 4 Preparation of Compound IV

Preparation Example 13: Preparation of 4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (Compound IV-1)

160 g of sodium hydroxide and 1680 g of purified water were added to the reaction flask, stirred until the solid material was completely dissolved, and then 433 g of compound III-1-2 (Preparation Example 10) was added. After the addition, the temperature was raised to 90 ° C and stirred for 8 h. After the reaction was completed, the mixture was cooled to 30 ° C, the acid was adjusted to pH 2-3, and the mixture was filtered. The solid material was washed with water once, filtered, and the solid material was dried at 90 ° C to obtain compound IV-1, with a yield of 335 g. The molar yield was 93%, and the HPLC purity was 98.5%.

Preparation Example 14: Preparation of 4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (Compound IV-1)

160 g of sodium hydroxide and 1680 g of purified water were added to the reaction flask, stirred until the solid material was completely dissolved, and then 461 g of compound III-1-3 (Preparation Example 11) was added. After the addition, the temperature was raised to 80-90 ° C and stirred for 8 hours. After the reaction was completed, it was cooled to 30 ° C, the acid was adjusted to pH 2-3, and the solid material was filtered. The solid material was washed with water once, filtered, and the solid material was dried at 90 ° C to obtain compound IV-1, with a yield of 320 g. The molar yield was 88.9%, and the HPLC purity was 98.7%.

Preparation Example 15: Preparation of 4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (Compound IV-1)

Add 224g of potassium hydroxide and 1680g of purified water to the reaction flask, stir until the solid material is completely dissolved, then add 489g of compound III-1-4 (Preparation Example 12), after adding, heat to 80-90℃ and stir to react for 8h. After the reaction is completed, cool to 30℃, adjust the pH to 2-3 with acid, filter, wash the solid material with water once, filter, dry the solid material at 90℃ to obtain compound IV-1, with a yield of 327.6g. Molar yield 91%, HPLC purity 99.05%.

The raw materials 4,5-dimethoxy-7,9-bis(methoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound formula III-1-2), 4,5-dimethoxy-7,9-bis(ethoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound formula III-1-3) and 4,5-dimethoxy-7,9-bis[(propyloxy)carbonyl]-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (compound formula III-1-4) in Preparation Example 13-15 were replaced by 4,5-diethoxy-7,9-bis(methoxycarbonyl)-1H-pyrrolo[2,3- f] quinoline-2-carboxylic acid ethyl ester (Compound III-2-2), 4,5-diethoxy-7,9-bis(ethoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (Compound III-2-3) and 4,5-diethoxy-7,9-bis[(propyloxy)carbonyl]-1H-pyrrolo[2,3-f]quinoline-2-carboxylic acid ethyl ester (Compound III-2-4) were prepared according to the methods in Preparation Examples 13-15 to obtain 4,5-diethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (Compound IV-2) with a molar yield of more than 88% and an HPLC purity of more than 98%.

Example 5 Preparation of 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (PQQ)

Preparation Example 16:

360g of compound IV-1 (Preparation Example 13) and 1800g of acetic acid were added to the reaction flask. After the materials were stirred evenly, 1080g of 40% HI solution was slowly added to the reaction flask at 20-30°C. After the addition was completed, the temperature was raised to 60-70°C and stirred for 12h. After the reaction was completed, the materials were cooled to 20°C and slowly added to 3000g of ice water to precipitate solid materials, filtered, and washed with purified water until the pH reached 4-5. The solid materials were filtered and recrystallized with methanol to obtain 587.6g of intermediate compound VI wet product. 587.6g of intermediate compound VI wet product and 1800g of 30% hydrogen peroxide solution were added to the reaction flask and stirred to make the materials in the reaction flask evenly stirred. The temperature was raised to 35°C and stirred at 30-35°C for 24h. After the reaction was completed, the temperature was lowered to 20°C, filtered, and the solid materials were dried at 90°C to obtain 297g of PQQ. The molar yield was 90%, and the HPLC purity was 99.5%.

Preparation Example 17:

360g of compound IV-1 (Preparation Example 13) and 1800g of acetic acid were added to the reaction flask. After the materials were stirred evenly, 1080g of 40% HI solution was slowly added to the reaction flask at 30-40°C. After the addition was completed, the temperature was raised to 70-80°C and stirred for 12h. After the reaction was completed, the materials were cooled to 20°C and slowly added to 3000g of ice water to precipitate solid materials, filtered, and the solid materials were washed with purified water until the pH reached 4-5, filtered, and the solid materials were recrystallized with methanol. The solid materials obtained 544.4g of intermediate compound VI wet product. 544.4g of intermediate compound VI wet product and 1800g of 30% hydrogen peroxide solution were added to the reaction flask and stirred to stir the materials in the reaction flask evenly. The temperature was raised to 35°C and stirred at 30-35°C for 24h. After the reaction was completed, the temperature was lowered to 20°C, filtered, and the solid materials were dried at 90°C to obtain 292.7g of PQQ. The molar yield was 88.7%, and the HPLC purity was 99.5%.

Preparation Example 18:

360g of compound IV-1 (Preparation Example 13) and 1800g of acetic acid were added to the reaction flask. After the materials were stirred evenly, 1080g of 30% HI solution was slowly added to the reaction flask at 20-30°C. After the addition was completed, the temperature was raised to 60-70°C and stirred for 12h. After the reaction was completed, the materials were cooled to 20°C and slowly added to 3000g of ice water to precipitate solid materials, filtered, and the solid materials were washed with purified water until the pH reached 4-5, filtered, and the solid materials were recrystallized with methanol to obtain 568g of intermediate compound VI wet product. 568g of intermediate compound VI wet product and 1800g of 30% hydrogen peroxide solution were added to the reaction flask and stirred to stir the materials in the reaction flask evenly. The temperature was raised to 35°C and stirred at 30-35°C for 24h. After the reaction was completed, the temperature was lowered to 20°C, filtered, and the solid materials were dried at 90°C to obtain 290g of PQQ. The molar yield was 87.9%, and the HPLC purity was 99.5%.

The raw material 2-(ethoxycarbonyl)-4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid (compound IV-1) was replaced with 4,5-diethoxy-2-(ethoxycarbonyl)-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid (compound IV-2), and PQQ was prepared according to the method described in Preparation Examples 16-18, with a molar yield of more than 86% and an HPLC purity of more than 99%.

Comparative Example

In this comparative example, N-(5-amino-3-bromo-2-methoxyphenyl)acetamide was used as an intermediate to prepare PQQ. During the reaction, the quinoline ring was first synthesized, and then the indole ring was synthesized. The reaction was carried out according to the following reaction route:

Among them, in the third step reaction, compound C will close to form an indole ring while closing to form a quinoline ring, so there is a side reaction in this step, which seriously affects the yield and productivity. The molar yield of this step is only 52%, and the HPLC purity is only about 98%. In the above embodiments of the present application, the molar yield can be maintained at more than 75% when synthesizing the quinoline ring, and the HPLC purity is more than 99%; at the same time, the bromine atom on the benzene ring of the starting material needs to be converted from -Br to _-OCH3 through the Ullmann reaction in the sixth step, and the reaction route becomes longer, resulting in a further decrease in the final yield and purity, and the total yield of the reaction route is less than 20%. At present, the existing intermediates for preparing PQQ often have this problem, so the intermediates in the prior art will choose to close the indole ring first and then close the quinoline ring.

Specifically, the specific operation process is as follows:

(1) Add 1200 g of 30% hydrochloric acid, 500 g of anhydrous ethanol and 147.5 g of compound A to a clean and dry reaction bottle, cool the reaction solution to -5°C and stir for 1 hour. When the internal temperature reaches -5°C, begin to add 197 g of 40% sodium acetate dropwise with rapid stirring, and control the dropping speed so that the internal temperature does not exceed 5°C. After the addition is completed, stir at 0-5°C for 120-180 min, and detect the disappearance of compound A.

Cool to -15°C with a cold trap, then add 144g of ethyl 2-methylacetoacetate. After the addition, cool the reaction solution to -10 to -15°C. Start to add 462g of 30% sodium acetate, control the flow acceleration so that the internal temperature is not higher than -5°C. After the addition is complete, slowly heat up to 20 to 25°C with rapid stirring and stir for 12h. After the reaction is complete, cool the reaction solution to below 0°C, filter, wash the solid material with water twice, centrifuge, and dry the solid material to obtain 150g of compound B. The molar yield is 80%, and the HPLC purity is 98.6%.

(2) Install a reflux condenser on the clean and dried reaction bottle. After installation, add 1300 g of ethanol, 200 g of methanesulfonic acid and 372 g of compound B into the reaction bottle. After addition, heat to 80-85 °C and reflux for 6 h (liquid phase detection shows that the substrate reaction is complete). After the reaction is completed, cool to 20 °C and start adding 1000 g of 10% sodium carbonate. After addition, heat and reflux for 1 h. Detect the pH of the reaction solution to be 7-8 (based on pH), cool, crystallize, filter, store the solid material temporarily, recover ethanol from the ethanol filtrate, cool the residue and crystallize, filter, combine the solid materials, wash the residual salt with water, and dry to obtain 247.5 g of compound C. The molar yield is 75%, and the HPLC purity is 99.3%.

(3) Add 165g of compound C and 1500g of dichloromethane to the reaction flask, stir evenly, then add 490g of (E)-4-oxopentan-2-enedioic acid dipropyl ester and 25g of zinc chloride, and stir at room temperature for 24h. After the reaction is completed, evaporate the solvent at normal pressure and then at reduced pressure. Add 1000g of 70% ethanol to the residue, heat to 70°C and stir for 30min. After stirring, cool to below 15°C to precipitate a light yellow solid. Filter and dry to obtain 145g of compound D. The molar yield is 52%, and the HPLC purity is 98%.

(4) Add 2000 g of methanesulfonic acid and 538 g of compound D to a clean and dry reaction bottle. After addition, heat to 70 °C and stir for 24 h (liquid phase detection shows that the substrate reaction is complete). After the reaction is completed, add the reaction solution to 15,000 °C of ice water and control the temperature to no higher than 40 °C and stir for 1 h to precipitate crystals. Adjust the pH to 6-7 with 10% sodium carbonate while stirring, filter with suction, wash the residual salt with 1000 g of solid material, and cool the reaction solution to 20 °C for 1 h to crystallize. Filter with suction, dry the solid material (water content less than 0.5%), and obtain 468.9 g of compound E. The molar yield is 90%, and the HPLC purity is 98.8%.

(5) Install a reflux condenser on the clean and dried reaction bottle. After installation, add 1800g of 30% methanol/sodium methoxide, 1500g of pyridine, 48g of CuI and 260.5g of compound E into the reaction bottle. After addition, heat and reflux for 8h. After the reaction is completed, remove methanol and pyridine under reduced pressure until the maximum internal temperature is 110°C. Add 2000g of water to the residue, heat it to 80-85°C, and keep it warm for 2h when the temperature reaches 90-95°C. After the reaction is completed, cool the reaction liquid to 30°C and filter it. Adjust the pH value of the filtrate to 2-3 with dilute sulfuric acid to precipitate a large number of crystals. Filter it, add water to the solid material, boil the residual acid and copper sulfate with 1000-2000g of water, cool and filter it, and dry it to obtain 153g of compound F with a molar yield of 85% and a HPLC purity of 98.5%.

(6) Install a reflux condenser on the clean and dried reaction bottle. After installation, add 3600g of 30% methanol/sodium methoxide, 3000g of pyridine, 96g of CuI and 521g of compound F into the reaction bottle. After addition, heat and reflux for 8h. After the reaction is completed, remove methanol and pyridine under reduced pressure to a maximum internal temperature of 90°C. Add 4000g of water to the residue, heat it to 80-85°C, and keep it warm for 2h when the temperature reaches 90-95°C. After the reaction is completed, cool the reaction solution to 30°C, adjust the pH value of the filtrate to 2-3 with dilute sulfuric acid, precipitate a large amount of crystals, cool, filter, and dry to obtain 325.8g of compound G, with a molar yield of 90.5% and HPLC purity of 99.2%.

(7) Add 360 g of compound G and 1800 g of acetic acid to the reaction flask. After the materials are stirred evenly, slowly add 1080 g of 30% HI solution to the reaction flask at 20-30°C. After the addition is complete, heat to 60-70°C and stir for 12 h. After the reaction is complete, cool the materials to below 20°C and slowly add them back to 3000 g of ice water to precipitate solid materials. Filter and wash the solid materials with purified water until the pH reaches 4-5. Filter and recrystallize the solid materials with methanol to obtain 568 g of wet intermediate of compound PQQ. Add 568 g of wet intermediate of compound G and 1800 g of 30% hydrogen peroxide solution to the reaction flask and stir to make the materials in the reaction flask evenly stirred. Heat to 35°C and stir at 30-35°C for 24 h. After the reaction is complete, cool to below 20°C, centrifuge, and dry the solid materials at 90°C to obtain 290 g of compound PQQ. The molar yield was 87.9%, and the HPLC purity was 99.5%.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims (10)

1. A method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: using a compound of formula II as a starting material to prepare a compound of formula III by a Fischer indole synthesis method, hydrolyzing the compound of formula III to prepare a compound of formula IV, and oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group; _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.
2. A method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: using a compound of formula I-2 as a starting material and a compound of formula V to prepare a compound of formula II under the catalysis of Lewis acid, preparing a compound of formula III from the compound of formula II by Fischer indole synthesis, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group; _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.
3. A method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: using a compound of formula I-1 as a starting material, reducing formula I-1 to prepare formula I-2, then preparing a compound of formula II with a compound of formula V under the catalysis of Lewis acid, then preparing a compound of formula III from the compound of formula II by Fischer indole synthesis, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group; _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.
4. A method for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the method comprising: using a compound of formula X as a starting material, diazotizing the compound of formula X and condensing it with ethyl 2-methylacetoacetate to prepare a compound of formula I-1, reducing the compound of formula I-1 to prepare a compound of formula I-2, then reacting the compound of formula I-2 with a compound of formula V under Lewis acid catalysis to prepare a compound of formula II, then using the compound of formula II to prepare a compound of formula III through a Fischer indole synthesis method, then hydrolyzing the compound of formula III to prepare a compound of formula IV, and oxidizing the compound of formula IV to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group; _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.
5. The method according to any one of claims 1 to 4, characterized in that the oxidation of 4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid comprises: reacting 4,5-dimethoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid with a protonic acid to prepare 2-(ethoxycarbonyl)-4,5-dihydroxy-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid, and then oxidizing 2-(ethoxycarbonyl)-4,5-dihydroxy-1H-pyrrolo[2,3-f]quinoline-7,9-dicarboxylic acid to prepare 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid.
6. The method according to any one of claims 1 to 4, characterized in that R ₁ is methyl or ethyl, and R ₃ is methyl, ethyl or propyl;

   Preferably, the compound of formula X is diazotized with sodium nitrite solution under acidic conditions, and then condensed with ethyl 2-methylacetoacetate under alkaline conditions to form the compound of formula I-1; preferably, the molar ratio of the compound of formula X to ethyl 2-methylacetoacetate is 1:1-5; preferably, the temperature of the reaction stage of this step is controlled at -10°C-0°C;

   Preferably, the compound of formula I-1 undergoes a reduction reaction under the action of a reducing agent to obtain a compound of formula I-2, and the reaction temperature of this step is preferably 60-80°C;

   Preferably, when preparing the compound of formula II, the molar ratio of the compound of formula I-2 to the compound of formula V is 1:1-5;

   Preferably, when preparing the compound of formula III, the reaction temperature is controlled at 30-55°C;

   Preferably, the hydrolysis of the compound of formula III to prepare the compound of formula IV occurs in an alkaline environment, preferably at a temperature of 80-90° C.;

   Preferably, the compound of formula IV is oxidized with an oxidant, wherein the oxidant is selected from one or more of hydrogen peroxide, concentrated sulfuric acid, concentrated nitric acid and ozone.
7. A compound for preparing 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, the structure of which is as shown in Formula I or Formula II:

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched chain alkyl group, _R2 is a nitro group or an amino group, and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched chain alkyl group.
8. The compound according to claim 7, characterized in that the compound has the structure shown below:

   

   Wherein, _R1 is methyl or ethyl, and _R3 is hydrogen, methyl, ethyl or propyl;

   Preferably, the compound is selected from the following structures:

   (Z)-ethyl 2-(2-(3,4-dimethoxy-5-nitrophenyl)hydrazino)propanoate;

   (Z)-ethyl 2-(2-(3,4-diethoxy-5-nitrophenyl)hydrazinyl)propanoate;

   (Z)-ethyl 2-(2-(3-amino-4,5-dimethoxyphenyl)hydrazino)propanoate;

   (Z)-ethyl 2-(2-(3-amino-4,5-diethoxyphenyl)hydrazinyl)propanoate;

   (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid;

   (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid dimethyl ester;

   (Z)-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylic acid diethyl ester;

   (Z)-dipropyl 5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)-7,8-dimethoxyquinoline-2,4-dicarboxylate;

   (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid;

   (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid dimethyl ester;

   (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid diethyl ester;

   (Z)-7,8-diethoxy-5-(2-(1-ethoxy-1-oxopropan-2-ylidene)hydrazino)quinoline-2,4-dicarboxylic acid dipropyl ester.
9. Use of the compound described in claim 7 or 8 and/or the compound of formula X as an intermediate in the preparation of 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid;

   

   Wherein, _R1 is a _C1 - _C3 straight chain or branched alkyl group, _R2 is a nitro group or an amino group; and _R3 is selected from hydrogen and a _C1 - _C3 straight chain or branched alkyl group.
10. The use according to claim 9, characterized in that _R1 is methyl or ethyl, _R2 is nitro or amino, and _R3 is hydrogen, methyl, ethyl or propyl.

Images