A guanine and a method for preparing the same

Abstract

The application provides guanine and a preparation method thereof. The method comprises the following steps: firstly, using alkyl cyanoacetate and guanidine salt as raw materials, performing cyclization reaction in a first alkaline substance and a first solvent system, and adding water to prepare 2,4-diamino-6-hydroxy pyrimidine reaction solution; secondly, mixing nitrite salt, dropping the mixed solution into a first inorganic acid to complete nitrosation, and obtaining a nitroso-substituted pyrimidine intermediate; then, using a hydrogenation catalyst to catalyze hydrogen reduction of the nitroso group, and obtaining 2,5,6-triamino-4-hydroxy pyrimidine; after adding a second inorganic acid to form a salt, condensation and ring closure are performed with a carbonyl compound to obtain guanine. The application realizes continuous preparation of guanine by using hydrogen reduction, simplifies the process flow, reduces energy consumption and three-waste emissions, in-situ salt formation effectively inhibits the generation of xanthine impurities, improves the product yield and purity, and adapts to the stable production demand of large-scale industrialization.

Description

Technical Field

[0001] This application relates to the field of organic chemical synthesis, and in particular to a guanine and a method for its preparation. Background Technology

[0002] Guanine is an important heterocyclic purine compound widely used in pharmaceuticals, biochemicals, and feed additives. It is a core intermediate in the preparation of broad-spectrum antiviral drugs such as acyclovir, ganciclovir, and valacyclovir, and also a fundamental raw material for nucleic acid synthesis, genetic engineering research, and food fortification. With the rapid development of the biopharmaceutical industry, the market demand for guanine continues to grow, placing increasingly higher demands on the efficiency, cost, purity, and environmental friendliness of its industrial production.

[0003] Currently, the mainstream industrial preparation route for guanine uses alkyl cyanoacetate and guanidine salt as starting materials, and synthesizes it through steps such as cyclization, reduction, salt formation, and condensation. However, existing processes generally have many insurmountable drawbacks: First, the reduction step often uses chemical reducing agents such as hydrazine hydrate, sodium hydrosulfite, and iron powder, resulting in numerous and complex byproducts in the reaction system. Multiple separation and purification operations, such as filtration, washing, and drying, are necessary to separate and purify the intermediate obtained from cyclization before proceeding to the next step of the reaction. This results in a lengthy process flow, long production cycle, and significant material transfer losses. Second, the free triaminopyrimidine generated during reduction is chemically... The guanine is extremely unstable and prone to oxidation and degradation during separation and storage, leading not only to low overall yields but also to the introduction of large quantities of difficult-to-remove byproducts. Thirdly, the condensation reaction is carried out at high temperatures, where the reactive free triaminopyrimidine is susceptible to amino hydrolysis, generating xanthine impurities with structures highly similar to guanine. These impurities are difficult to remove using conventional purification methods, severely hindering product quality improvement. Fourthly, the multi-step separation process is energy-intensive, consumes large amounts of organic solvents and water, generates significant amounts of waste, and incurs high environmental treatment costs, which is inconsistent with the trend of green chemistry. Therefore, simplifying the process, reducing production costs, minimizing impurity generation, and improving product quality in the industrial preparation of guanine are critical technical challenges that urgently need to be overcome in this field. Summary of the Invention

[0004] This application provides guanine and its preparation method. This application utilizes hydrogen reduction to achieve continuous guanine preparation, simplifying the process flow and reducing energy consumption and waste emissions; in-situ salt formation effectively inhibits the formation of xanthine impurities, improving product yield and purity, and meeting the needs of large-scale industrial stable production.

[0005] This application provides a method for preparing guanine, comprising the following steps:

[0006] S1. A cyclization reaction is carried out by mixing alkyl cyanoacetate, guanidine salt, the first basic substance and the first solvent. After the cyclization reaction is completed, water is added to dissolve the system material to obtain a reaction solution containing 2,4-diamino-6-hydroxypyrimidine.

[0007] S2. The reaction solution obtained in step S1 is mixed with nitrite, and the resulting mixture is added dropwise to the first inorganic acid to react, thereby obtaining a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine.

[0008] S3. In the presence of a hydrogenation catalyst, the reaction solution obtained in step S2 is contacted with hydrogen gas to reduce the 2,4-diamino-5-nitroso-6-hydroxypyrimidine to obtain a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine.

[0009] S4. Add a second inorganic acid to the reaction solution obtained in step S3 to carry out a salt formation reaction, and obtain a reaction solution containing a 2,5,6-triamino-4-hydroxypyrimidine salt intermediate; then carry out a condensation reaction between the reaction solution containing the 2,5,6-triamino-4-hydroxypyrimidine salt intermediate and a carbonyl compound to obtain the guanine.

[0010] According to one embodiment of this application, the alkyl cyanoacetate includes methyl cyanoacetate;

[0011] And / or, the guanidine salt includes guanidine hydrochloride and / or guanidine nitrate;

[0012] And / or, the first alkaline substance includes sodium methoxide;

[0013] And / or, the first solvent includes methanol.

[0014] According to one embodiment of this application, the molar ratio of the alkyl cyanoacetate to the guanidine salt is 1:(1~1.1).

[0015] And / or, the molar ratio of the alkyl cyanoacetate to the first basic substance is 1:(1~2.1).

[0016] And / or, the molar ratio of the alkyl cyanoacetate to the first solvent is 1:(8~8.3).

[0017] According to one embodiment of this application, the nitrite includes sodium nitrite;

[0018] And / or, the first inorganic acid includes sulfuric acid with a mass concentration of 20-60%;

[0019] And / or, the second inorganic acid includes sulfuric acid with a mass concentration of 65-98%;

[0020] And / or, the hydrogenation catalyst comprises Raney nickel.

[0021] According to one embodiment of this application, the molar ratio of the 2,4-diamino-6-hydroxypyrimidine to the nitrite is 1:(1~1.2).

[0022] And / or, the molar ratio of the 2,4-diamino-6-hydroxypyrimidine to the first inorganic acid is 1:(0.5~0.7).

[0023] According to one embodiment of this application, the molar ratio of 2,4-diamino-5-nitroso-6-hydroxypyrimidine to the hydrogenation catalyst is 1:(0.24~0.27).

[0024] And / or, the molar ratio of the 2,5,6-triamino-4-hydroxypyrimidine to the second inorganic acid is 1:(1.9~2.1).

[0025] And / or, the carbonyl compound includes formamide and / or formic acid;

[0026] And / or, the molar ratio of the 2,5,6-triamino-4-hydroxypyrimidine salt intermediate to the carbonyl compound is 1:(14~18).

[0027] According to one embodiment of this application, the cyclization reaction is carried out at a temperature of 50°C to 60°C for 2 hours to 4 hours.

[0028] And / or, the reduction reaction is carried out at a temperature of 40°C to 60°C for a time of 2 hours to 10 hours;

[0029] And / or, the salt formation reaction is carried out at a temperature of 20°C to 30°C for 1 to 2 hours.

[0030] According to one embodiment of this application, the condensation reaction temperature is 130°C to 160°C, and the reaction time is 16h to 24h.

[0031] According to one embodiment of this application, after the condensation reaction is completed, the crude guanine hydrochloride obtained by the condensation reaction is subjected to alkaline precipitation in the presence of a second alkaline substance to obtain the guanine.

[0032] According to one embodiment of this application, the second alkaline substance includes ammonia.

[0033] The implementation of this application has at least the following beneficial effects: This application uses hydrogen reduction to achieve continuous preparation of guanine, which simplifies the process flow and reduces energy consumption and emissions of waste gas, wastewater, and solid waste; in-situ salt formation effectively inhibits the generation of xanthine impurities, improves product yield and purity, and meets the needs of large-scale industrial stable production. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. The specific embodiments listed below are only for describing the principles and features of this application, and the examples are only used to explain this application and are not intended to limit the scope of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] This application provides a method for preparing guanine, comprising the following steps: S1, mixing alkyl cyanoacetate, guanidine salt, a first basic substance, and a first solvent to carry out a cyclization reaction; after the cyclization reaction is completed, water is added to dissolve the system materials to obtain a reaction solution containing 2,4-diamino-6-hydroxypyrimidine; S2, mixing the reaction solution obtained in step S1 with a nitrite; adding the resulting mixture dropwise to a first inorganic acid to carry out a reaction to obtain a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine; S3, adding a hydrogenation catalyst... In the presence of hydrogen gas, the reaction solution obtained in step S2 is contacted with hydrogen gas to reduce 2,4-diamino-5-nitroso-6-hydroxypyrimidine, yielding a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine; S4, a second inorganic acid is added to the reaction solution obtained in step S3 to carry out a salt formation reaction, yielding a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine salt intermediates; the reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine salt intermediates is then subjected to a condensation reaction with a carbonyl compound to obtain guanine.

[0036] According to the inventors' research, this application uses alkyl cyanoacetate and guanidine salt as starting materials to sequentially complete cyclization, nitrosation, hydrogenation reduction, salt formation, and condensation in a continuous liquid-phase transformation. No filtration, washing, drying, or separation of any intermediates is required throughout the process: after the cyclization reaction, only water is added to dissolve the material, which then directly enters the nitrosation process; after the nitrosation reaction, the nitrosopyrimidine intermediate is not separated, and hydrogen is directly introduced for catalytic hydrogenation reduction. The core innovation is the use of high-pressure hydrogen to replace traditional chemical reducing agents such as hydrazine hydrate and sodium metabisulfite to complete the nitroso reduction, reducing reduction byproducts. After reduction, the system does not require discharge; a second inorganic acid is added in situ to complete the salt formation, converting the easily oxidized and hydrolyzed free 2,5,6-triamino-4-hydroxypyrimidine into a stable salt intermediate, significantly suppressing the generation of xanthine impurities through amino hydrolysis during the condensation stage; the salt intermediate directly undergoes high-temperature cyclization with a carbonyl compound to obtain guanine. The entire process eliminates multiple solid-liquid separation steps, simplifies the process, shortens the production cycle, and avoids intermediate transport and oxidation losses. It reduces water, organic solvent, and energy consumption throughout the process, significantly reduces the discharge of waste, and lowers the pressure of product purification, enabling continuous, green, low-cost, and large-scale industrial production of guanine.

[0037] Specifically, the structural formula of guanine is shown below:

[0038] .

[0039] Specifically, the structural formula of the above-mentioned 2,4-diamino-6-hydroxypyrimidine is shown below:

[0040] .

[0041] In some embodiments, the alkyl cyanoacetate described above includes methyl cyanoacetate. The alkyl cyanoacetate provides a reaction site between the active methylene group and the ester group; the methyl ester group in the methyl cyanoacetate molecule has low steric hindrance, high reactivity, and a fast cyclization reaction rate with guanidine salts, resulting in high conversion rates; its high reactivity can shorten the cyclization reaction time and improve production efficiency.

[0042] Specifically, the structural formula of the above-mentioned methyl cyanoacetate is shown below:

[0043] .

[0044] In some embodiments, the guanidine salts described above include guanidine hydrochloride and / or guanidine nitrate. The guanidine salts provide a guanidine nitrogen source; guanidine hydrochloride and guanidine nitrate exhibit good stability and can release free guanidine under alkaline conditions to participate in the cyclization reaction, simplifying the process flow. Guanidine hydrochloride exhibits good solubility in an alcohol-water system, facilitating the construction of a homogeneous reaction system. Furthermore, guanidine hydrochloride has high purity and few impurities, helping to reduce the formation of cyclization reaction byproducts. Guanidine nitrate is highly hydrophilic, and the reaction byproduct nitrate has excellent solubility, facilitating the removal of inorganic salt impurities through water clarification, further reducing the formation of cyclization reaction byproducts. Both can be used alone or in combination to minimize the formation of byproducts in the cyclization reaction.

[0045] In some embodiments, the first basic substance comprises sodium methoxide. The first basic substance is used to promote the release of the guanidine salt and drive the cyclization reaction; sodium methoxide is a strongly basic alkoxide that can effectively abstract the active hydrogen from the alkyl cyanoacetate to generate a carbanion, promoting the nucleophilic addition reaction with the guanidine salt; simultaneously, sodium methoxide has good solubility in alcohol solvents, high catalytic activity, and can significantly accelerate the cyclization reaction rate; its moderate basicity makes it less likely to trigger excessive side reactions, which helps to improve the selectivity of the cyclization product.

[0046] In some embodiments, the first solvent includes methanol. The first solvent serves as a reaction medium, dissolving the reactants and promoting full contact between the materials; as a polar protic solvent, methanol can stabilize cyclization reaction intermediates, promote the cyclization process, buffer the alkalinity of the system, and inhibit the formation of by-products; at the same time, methanol is miscible with water in any proportion, which facilitates the construction of a homogeneous reaction system, makes it easy to separate water-soluble impurities such as inorganic salts, and helps to reduce the formation of cyclization reaction by-products.

[0047] In some embodiments, the molar ratio of the alkyl cyanoacetate to the guanidine salt can be 1:(1~1.1), for example, 1:1, 1:1.03, 1:1.06, 1:1.08, 1:1.1, or any combination thereof. A molar ratio of alkyl cyanoacetate to guanidine salt of not less than 1:1 ensures sufficient reaction of the guanidine salt, improves the conversion rate of the guanidine salt, and reduces raw material waste; a molar ratio of not more than 1:1.1 helps avoid excessive alkyl cyanoacetate residue, reducing the difficulty of subsequent purification; controlling the molar ratio within the above range is beneficial for ensuring reaction conversion while balancing production costs and product purity.

[0048] In some embodiments, the molar ratio of the alkyl cyanoacetate to the first basic substance can be 1:(1~2.1), for example, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2.1, or any combination thereof. A molar ratio not lower than 1:1 helps maintain an alkaline environment in the reaction system, promoting the cyclization reaction; a molar ratio not higher than 1:2.1 helps avoid an excess of basic substance leading to an increase in side reactions, thereby improving the purity of the cyclization product; controlling the molar ratio within the above range is beneficial for obtaining higher reaction conversion and product selectivity.

[0049] In some embodiments, the molar ratio of the alkyl cyanoacetate to the first solvent is 1:(8~8.3), for example, 1:8, 1:8.1, 1:8.2, 1:8.3, or any combination thereof. A molar ratio of alkyl cyanoacetate to the first solvent of not less than 1:8 helps avoid excessively high concentrations and viscosity in the reaction system due to insufficient solvent usage, improves the heat and mass transfer effect of the system, reduces side reactions caused by local overheating, and facilitates stirring and material transport in industrial production. A molar ratio of not more than 1:8.3 helps ensure the complete dissolution of the alkyl cyanoacetate, guanidine salt, and the first basic substance, allowing the reaction to proceed smoothly in a homogeneous system, improving the stability and reproducibility of the reaction, while avoiding excessive solvent usage leading to a slow reaction rate and prolonged production cycle. Controlling the molar ratio of alkyl cyanoacetate to the first solvent within the above range is beneficial for ensuring the conversion rate and product selectivity of the cyclization reaction while also considering production efficiency, operational convenience, and solvent recovery costs, thus meeting the needs of continuous industrial production.

[0050] In some embodiments, the molar ratio of 2,4-diamino-6-hydroxypyrimidine to nitrite is 1:(1~1.2). For example, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.1, 1:1.2, or any combination thereof. A molar ratio not lower than 1:1 facilitates the full conversion of the substrate in the nitrosation reaction, avoids 2,4-diamino-6-hydroxypyrimidine residue, and reduces the introduction of unreacted raw materials into subsequent hydrogenation and condensation processes, thus generating impurities. A molar ratio not higher than 1:1.2 can prevent excessive decomposition of nitrite and the generation of acidic byproducts, prevent drastic pH fluctuations in the system from interfering with the subsequent hydrogenation buffer environment, and is suitable for the continuous liquid-phase process without intermediate separation in this application. Controlling the molar ratio within the above range can achieve high conversion rates in the nitrosation step while reducing nitrite waste.

[0051] In some embodiments, the molar ratio of the 2,4-diamino-6-hydroxypyrimidine to the first inorganic acid is 1:(0.5~0.7). For example, 1:0.5, 1:0.52, 1:0.54, 1:0.56, 1:0.58, 1:0.62, 1:0.7, or any combination thereof. A molar ratio not less than 1:0.5 provides a sufficient acidic environment to stabilize the nitrosation reaction process, ensuring efficient grafting of nitroso groups onto the pyrimidine ring; a molar ratio not greater than 1:0.7 avoids excessive acidity that corrodes high-pressure hydrogenation equipment, while also preventing excessive acid neutralization of the subsequent hydrogenation system's alkalinity, eliminating the need for additional alkali adjustment; controlling the molar ratio within the above range ensures a complete nitrosation reaction and that the system's acid-base conditions are compatible with downstream hydrogenation processes, simplifying intermediate control steps.

[0052] In some embodiments, the first inorganic acid comprises sulfuric acid with a mass concentration of 20-60%. Sulfuric acid with a mass concentration of 20-60% is sufficiently ionized, providing ample hydrogen ions to promote complete conversion in the nitrosation reaction. Simultaneously, the corrosiveness of sulfuric acid within this concentration range is moderate, reducing corrosion of high-pressure reaction equipment and improving the safety of industrial production. Furthermore, the system has sufficient water content, allowing for complete homogeneous dissolution of the nitrosopyrimidine intermediate and preventing solid salt precipitation that could cause pipeline blockage. In some embodiments, the molar ratio of 2,5,6-triamino-4-hydroxypyrimidine to the second inorganic acid is 1:(1.9-2.1). For example, 1:1.9, 1:1.95, 1:2.0, 1:2.05, 1:2.1, or any combination thereof. A molar ratio of not less than 1:1.9 can completely convert easily oxidized and hydrolyzed free triaminopyrimidine into stable salt intermediates, inhibiting the generation of xanthine impurities in the condensation stage from the source; a molar ratio of not more than 1:2.1 can avoid excessive strong acid from being introduced into the condensation system and damaging carbonyl compounds, reducing the consumption of subsequent alkaline precipitation ammonia water, and lowering material costs and saline wastewater production; controlling the molar ratio within the above range is beneficial to further improve the stability of intermediates and the purity of guanine product.

[0053] In some embodiments, the second inorganic acid comprises sulfuric acid with a mass concentration of 65-98%. It can rapidly and completely convert easily oxidized and hydrolyzed free 2,5,6-triamino-4-hydroxypyrimidine into a stable sulfate intermediate, reducing the generation of oxidative and hydrolytic impurities, increasing reaction yield, and simultaneously removing free water from the system through strong dehydration, creating a low-water reaction environment conducive to ring closure. It can also act as an acidic catalyst to accelerate the condensation rate of pyrimidine and carbonyl compounds into rings. In the embodiments of this invention, the molar ratio of 2,4-diamino-6-hydroxypyrimidine to the first inorganic acid, and the molar ratio of 2,5,6-triamino-4-hydroxypyrimidine to the second inorganic acid, are calculated based on the amount of pure sulfuric acid solute in the first and second inorganic acids.

[0054] In some embodiments, the reaction temperature of the cyclization reaction can be 50°C to 60°C, for example, a range of 50°C, 52°C, 55°C, 58°C, 60°C, or any combination thereof. A cyclization reaction temperature not lower than 50°C helps to accelerate the reaction rate, shorten the reaction time, and improve production efficiency; a reaction temperature not higher than 60°C helps to reduce the formation of by-products and improve the purity of the cyclization product; controlling the reaction temperature within the above range is beneficial for obtaining high product selectivity while ensuring the reaction rate.

[0055] The reaction time for the above-mentioned cyclization reaction can be 2 hours to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any combination thereof. A cyclization reaction time of not less than 2 hours helps ensure the reaction proceeds fully and improves the raw material conversion rate; a reaction time of not more than 4 hours helps shorten the production cycle and improve production efficiency; controlling the reaction time within the above range is beneficial for ensuring both reaction conversion rate and production efficiency and product quality.

[0056] In some embodiments, the molar ratio of 2,4-diamino-5-nitroso-6-hydroxypyrimidine to the hydrogenation catalyst can be 1:(0.24~0.27). For example, 1:0.24, 1:0.25, 1:0.26, 1:0.27, or any combination thereof. A molar ratio not lower than 1:0.24 provides sufficient catalytic active sites to promote complete hydrogenation reduction of nitrosamines, reducing the amount of unreduced intermediates carried into the condensation process and generating impurities, which is suitable for the all-liquid-phase continuous process of this application without intermediate separation. A molar ratio not higher than 1:0.27 can reduce the amount of hydrogenation catalyst required, lower raw material costs, and avoid excessive hydrogenation catalyst causing system viscosity and affecting material transport and solid-liquid filtration and recovery efficiency. Controlling the molar ratio within the above range can achieve efficient and complete reduction of nitrosamines, ensure the purity of subsequent intermediates, reduce catalyst consumption, facilitate multiple recycling of the catalyst after filtration, and further reduce material and energy costs in industrial production. After the hydrogenation catalyst reaction is completed, it can be separated and recovered from the reaction liquid with only simple filtration. The recovered hydrogenation catalyst does not need to be scrapped, but can be directly put into the next batch of reduction reaction for recycling. It can be continuously reused for at least 10 batches of production without significant decay of catalytic activity, and can still ensure complete reduction reaction and stable product purity.

[0057] Specifically, the structural formula of 2,5,6-triamino-4-hydroxypyrimidine is shown below:

[0058] .

[0059] In some embodiments, the reaction temperature of the reduction reaction is 40°C to 60°C, for example, a range of 40°C, 45°C, 50°C, 55°C, 60°C, or any combination thereof. A reduction reaction temperature not lower than 40°C helps to improve the solubility of hydrogen and the activity of the catalyst, thus accelerating the reduction reaction rate; a reaction temperature not higher than 60°C helps to protect the catalyst activity, extend the catalyst lifespan, and reduce the occurrence of side reactions; controlling the reaction temperature within the above range is beneficial for obtaining a higher reduction reaction rate and conversion rate.

[0060] The reaction time for the above reduction reaction is 2 to 10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or any combination thereof. A reduction reaction time of no less than 2 hours helps ensure the reduction reaction proceeds fully and improves product conversion rate; a reaction time of no more than 10 hours helps shorten the production cycle and improve production efficiency. Controlling the reaction time within the above range helps to ensure complete reduction while balancing production efficiency and product quality.

[0061] In some embodiments, the second inorganic acid includes sulfuric acid. The second inorganic acid is used to salt the reaction solution after the reduction of 2,4-diamino-6-hydroxypyrimidine, in order to convert the basic free intermediate in the reaction system into the corresponding salt, thereby improving the stability of the intermediate and reducing its activity fluctuations in subsequent condensation processes. When sulfuric acid is used as the second inorganic acid, it can react with the protonable amino group in the intermediate with strong acidity to rapidly form 2,5,6-triamino-4-hydroxypyrimidine salt intermediates, making the reaction solution state more suitable for direct connection to subsequent formylation condensation. Simultaneously, because sulfuric acid has stable sources, low cost, and well-defined acid strength, it can ensure sufficient salt formation while reducing system fluctuations caused by changes in acid type, and is beneficial for controlling the acidification endpoint in scale-up production.

[0062] Specifically, the 2,5,6-triamino-4-hydroxypyrimidine salt intermediates include 2,5,6-triamino-4-hydroxypyrimidine sulfate. The structural formula of the above-mentioned 2,5,6-triamino-4-hydroxypyrimidine sulfate is shown below:

[0063] .

[0064] In some embodiments, the reaction temperature of the above-mentioned salt-forming reaction is 20°C to 30°C, for example, a range of 20°C, 22°C, 25°C, 27°C, 30°C, or any combination thereof. A salt-forming reaction temperature not lower than 20°C helps to accelerate the salt-forming reaction rate and rapidly generate salt intermediates; a reaction temperature not higher than 30°C helps to ensure the complete precipitation of salt intermediates and improve the salt yield; controlling the reaction temperature within the above range is beneficial for obtaining a higher salt yield and a suitable crystal morphology.

[0065] The reaction time for the above-mentioned salt-forming reaction is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.7 hours, 2 hours, or any combination thereof. A reaction time of not less than 1 hour helps ensure the salt-forming reaction proceeds fully and improves the salt conversion rate; a reaction time of not more than 2 hours helps shorten the production cycle and improve production efficiency; controlling the reaction time within the above range is beneficial for improving production efficiency while ensuring complete salt formation.

[0066] In some embodiments, the carbonyl compound comprises formamide and / or formic acid. The carbonyl compound can undergo a condensation reaction with a 2,5,6-triamino-4-hydroxypyrimidine salt intermediate to form a purine bicyclic structure. Formamide and formic acid are both commonly used industrial raw materials, inexpensive and readily available, which helps reduce production costs. They can be used alone or in combination, facilitating adjustment of the reaction rate and selectivity according to production needs, thus solving the problems of expensive raw materials and harsh reaction conditions in existing technologies.

[0067] In some embodiments, the molar ratio of the above-mentioned 2,5,6-triamino-4-hydroxypyrimidine salt intermediate to the carbonyl compound can be 1:(14~18), for example, 1:14, 1:15, 1:16, 1:17, 1:18, or any combination thereof. A molar ratio not lower than 1:14 helps ensure the condensation reaction proceeds fully and improves the product yield; a molar ratio not higher than 1:18 helps avoid excessive carbonyl compound residue and reduces the difficulty of subsequent purification; controlling the molar ratio within the above range is beneficial to ensure reaction conversion while balancing production costs and product purity.

[0068] In some embodiments, the reaction temperature of the condensation reaction is 130°C to 160°C, for example, a range of 130°C, 140°C, 145°C, 150°C, 160°C, or any combination thereof. A condensation reaction temperature not lower than 130°C helps to accelerate the condensation reaction rate and shorten the reaction time; a reaction temperature not higher than 160°C helps to suppress the occurrence of amino hydrolysis side reactions and reduce the formation of xanthine impurities; controlling the reaction temperature within the above range is beneficial for significantly reducing the content of xanthine impurities in the product while ensuring the reaction rate.

[0069] In some embodiments, the reaction time of the condensation reaction is 16h to 24h, for example, a range of 16h, 18h, 20h, 22h, 24h, or any combination thereof. A condensation reaction time of not less than 16h helps to ensure that the condensation reaction proceeds fully and improves the product yield; a reaction time of not more than 24h helps to shorten the production cycle and reduce the occurrence of side reactions; controlling the reaction time within the above range is beneficial to obtaining higher product purity while ensuring the reaction conversion rate.

[0070] In some embodiments, after the condensation reaction step, the crude guanine hydrochloride obtained from the condensation reaction is further subjected to alkaline precipitation in the presence of a second alkaline substance to obtain guanine. The condensation reaction is carried out in an acidic system, and the generated guanine is dissolved in the reaction solution in the form of a salt. The alkaline precipitation process can separate guanine from the acidic reaction solution, efficiently converting the crude salt product into free guanine, solving the problem that guanine cannot be directly separated in acidic systems. The alkaline precipitation process is simple to operate, does not require the use of large amounts of organic solvents, and helps to reduce production costs and waste emissions. At the same time, the alkaline precipitation process can remove some soluble impurities, initially improving the purity of the product.

[0071] In some embodiments, the second alkaline substance includes ammonia. The second alkaline substance is used as an alkaline medium for alkaline precipitation of crude guanine hydrochloride. Its function is to adjust the acid-base environment of the system, causing the target product to be converted from its salt form to a free alkaline form and precipitate. "Ammonia" is an aqueous solution of ammonia. When added as the second alkaline substance, it can rapidly increase the pH value of the system under relatively mild alkalization conditions, while avoiding side reactions or crystal form degradation caused by strong alkali, thus facilitating the separation and purification of guanine.

[0072] Specifically, the concentration of the ammonia water can be 10% to 25%, for example, 10%, 15%, 20%, 22%, 25%, or any combination thereof.

[0073] Specifically, after the above-mentioned alkaline precipitation treatment is completed, the precipitate obtained from the alkaline precipitation treatment is successively washed and dried to obtain guanine.

[0074] Specifically, the washing solution used in the above washing process can be water.

[0075] Specifically, the temperature of the above drying process is 120℃~150℃, for example, 120℃, 125℃, 130℃, 140℃, 150℃ or any combination thereof; the drying time is 5min~10min (continuous drying, about 5-10min from feeding to discharging), for example, 5min, 7min, 8min, 9min, 10min or any combination thereof.

[0076] In specific implementation, alkyl cyanoacetate, guanidine salt, and a first alkaline substance are added to the first solvent and stirred to obtain a first material, with the pH of the first material controlled at 14; the first material undergoes a cyclization reaction to obtain a reaction solution containing 2,4-diamino-6-hydroxypyrimidine; the reaction solution is mixed with nitrite and added dropwise to an inorganic acid to react, obtaining a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine; under a hydrogen atmosphere, a nickel-based catalyst (Raney-Ni) is added to the reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine to carry out a reduction reaction, obtaining a product containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine. A reaction solution containing 5,6-triamino-4-hydroxypyrimidine was prepared. A second inorganic acid was added to the reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine to induce a salt formation reaction, yielding a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine salt intermediates. A carbonyl compound was added to the reaction solution containing the 2,5,6-triamino-4-hydroxypyrimidine salt intermediates to induce a condensation reaction, yielding crude guanine hydrochloride. A second basic substance was added to the crude guanine hydrochloride, and the pH of the reaction system was controlled at 7.5–8.5 for alkaline precipitation. The mixture was then washed and dried sequentially to obtain guanine.

[0077] In summary, this application utilizes hydrogen reduction to achieve continuous preparation of guanine, simplifying the process flow and reducing energy consumption and emissions; in-situ salt formation effectively inhibits the formation of xanthine impurities, improves product yield and purity, and meets the needs of large-scale industrial stable production.

[0078] The present application will be further described below through specific embodiments.

[0079] The raw materials used in the following examples and comparative examples can all be obtained by conventional means in the art, such as commercial purchases.

[0080] In the following examples and comparative examples, the dropping rate of methyl cyanoacetate is not limited; the dropping time of methyl cyanoacetate should be controlled to be 2-3 hours, and the system should be kept stable throughout the process to obtain the first material. The dropping rate of the obtained mixture added to 50wt% sulfuric acid is not limited; the dropping time should be controlled to be 1-2 hours.

[0081] Example 1

[0082] The method for preparing guanine in this embodiment includes the following steps:

[0083] As shown in the reaction formula below, 400 mL of methanol, 121.32 g (1.27 mol) of guanidine hydrochloride, and 134.1 g (2.48 mol) of sodium methoxide were added to a 2 L four-necked flask and stirred. Then, 120.0 g (1.21 mol) of methyl cyanoacetate was added dropwise (over 2-3 hours) to obtain the first material. The pH of the first material was controlled at 14. The cyclization reaction was carried out at 60 °C for 2 hours. After the cyclization reaction was completed, deionized water was added to the system and stirred until the solid was completely dissolved, yielding a reaction solution containing 2,4-diamino-6-hydroxypyrimidine.

[0084] Add 88 g (1.28 mol) of sodium nitrite to the above reaction solution of 2,4-diamino-6-hydroxypyrimidine, and stir until the solid is completely dissolved to obtain a mixture. Under stirring conditions, add the obtained mixture dropwise (dropwise time is 1 h) to 132.8 g (1.33 mol) of 50 wt% sulfuric acid to carry out the nitrosation reaction. After the reaction is completed, the reaction solution of 2,4-diamino-5-nitroso-6-hydroxypyrimidine is obtained.

[0085] The reaction solution of 2,4-diamino-5-nitroso-6-hydroxypyrimidine was transferred into a closed high-pressure reactor. The air inside the reactor was first replaced with nitrogen three times, and then hydrogen was introduced to maintain the pressure at 0.3 MPa. 18 g of Raney nickel was added for reduction reaction. The reaction was carried out at 60 °C for 2 h to obtain a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine. 240 g of 98 wt% sulfuric acid was added to the reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine, and the salt formation reaction was carried out at 30 °C for 1 h to obtain a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine sulfate.

[0086] 860 g (19 mol) of formamide was added to the reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine sulfate, and the condensation reaction was carried out at 130 °C for 20 h. After the condensation reaction was completed, the formamide was recovered by vacuum distillation at 150 °C and -0.08 MPa. The vacuum distillation was stopped when no obvious fraction flowed out. Then 180 mL of hydrochloric acid was added, and the mixture was stirred and acidified before filtration to obtain crude guanine salt.

[0087] Ammonia was added to crude guanine hydrochloride, and the mixture was stirred. The pH of the reaction system was controlled at 7.5 for alkaline precipitation for 0.5 h. Then, the mixture was washed with water and dried (drying temperature was 120℃, time was 5 min) to obtain guanine.

[0088] Among them, methyl cyanoacetate has a molecular weight of 99.09, 2,4-diamino-6-hydroxypyrimidine has a molecular weight of 126.1, 2,5,6-triamino-4-hydroxypyrimidine has a molecular weight of 141.13, 2,5,6-triamino-4-hydroxypyrimidine sulfate has a molecular weight of 239.2, crude guanine salt has a molecular weight of 187.59, and guanine has a molecular weight of 151.13.

[0089]

[0090] Example 2

[0091] The preparation method of guanine in this embodiment includes the following steps:

[0092] As shown in the reaction formula below, 312 mL of anhydrous methanol, 127.3 g (1.33 mol) of guanidine hydrochloride, and 126.0 g (2.33 mol) of sodium methoxide were added to a 2 L four-necked flask and stirred. Then, 120.0 g (1.21 mol) of methyl cyanoacetate was added dropwise (over 2-3 hours) to obtain the first material. The mixture was heated to 60 °C and maintained at this temperature for 2 hours to induce a cyclization reaction. After the cyclization reaction was complete, deionized water was added to the system and stirred until the solid was completely dissolved, yielding a reaction solution containing 2,4-diamino-6-hydroxypyrimidine.

[0093] Add 96 g (1.39 mol) of sodium nitrite to the above reaction solution containing 2,4-diamino-6-hydroxypyrimidine, and stir until the solid is completely dissolved to obtain a mixture; control the temperature at 0~30℃, and slowly add the mixture dropwise (dropwise time is 1 hour) to 145 g (1.46 mol) of 50wt% sulfuric acid to carry out the nitrosation reaction. After the reaction is completed, a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine is obtained.

[0094] The above nitrosation reaction solution and 22 g of Raney nickel were transferred into a sealed high-pressure reactor. The air in the reactor was replaced with nitrogen three times, and hydrogen was introduced to maintain the pressure at 0.3 MPa. The temperature was raised to 40°C and the reduction reaction was maintained for 10 h. A reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine was obtained. 252 g of 98 wt% sulfuric acid was added to the filtrate, and the mixture was stirred at 20°C for 2 h to complete the salt formation reaction, resulting in a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine sulfate.

[0095] Add 360 g of 94% formic acid and 20 mL of concentrated hydrochloric acid to the above sulfate reaction solution, heat to 160 ℃ and maintain the temperature for condensation reaction for 20 h; after the condensation reaction is completed, control the vacuum degree to -0.08 MPa and the kettle temperature to 75 ℃ and distill under reduced pressure to recover formic acid. Stop the reduced pressure distillation when no obvious fraction flows out; add 180 mL of concentrated hydrochloric acid to the remaining material in the kettle, stir to acidify and precipitate solid, and filter to obtain crude guanine hydrochloride.

[0096] The crude guanine hydrochloride was mixed with water and slurryed. Ammonia was slowly added dropwise while stirring, and the pH of the system was controlled at 8.5. The mixture was kept warm and stirred for 1 hour to complete the alkaline precipitation treatment. The mixture was filtered, and the filter cake was washed with deionized water. Then it was placed in an oven and vacuum dried at 120 °C for 5 minutes to obtain the guanine product.

[0097] Among them, methyl cyanoacetate has a molecular weight of 99.09, 2,4-diamino-6-hydroxypyrimidine has a molecular weight of 126.1, 2,5,6-triamino-4-hydroxypyrimidine has a molecular weight of 141.13, 2,5,6-triamino-4-hydroxypyrimidine sulfate has a molecular weight of 239.2, crude guanine salt has a molecular weight of 187.59, and guanine has a molecular weight of 151.13.

[0098]

[0099] Comparative Example 1

[0100] The process for preparing guanine according to Example 1 of patent document CN100491377C is as follows:

[0101] Add 400 mL of anhydrous ethanol to a 2 L four-necked flask, then add 18.0 g (0.783 mol) of metallic sodium and stir continuously until the sodium is completely dissolved. Next, add 110.0 g (0.898 mol) of guanidine nitrate and heat to 70 °C with stirring for 0.8 h. Slowly add 56.0 g (0.486 mol) of ethyl cyanoacetate to the system dropwise. After the addition is complete, maintain the system temperature at 70 °C and continue the reaction for 2 h. After the reaction is complete, remove all ethanol solvent by vacuum distillation.

[0102] Add 600 mL of formamide to the material in the reactor after evaporation and stir to dissolve. Place the system in an ice-water bath to cool to 4°C. Add 40.0 g (0.580 mol) of sodium nitrite in batches and stir until the solid is evenly dispersed. Slowly add a mixed acid solution prepared by 100 mL of formamide and 100 mL of 98 wt% formic acid, keeping the temperature below 5°C throughout the process. After the addition is complete, maintain the temperature at 4°C for 2.5 h.

[0103] After the low-temperature reaction was completed, the system was heated to 100 °C, and 20.0 g (0.192 mol) of sodium bisulfite was added. The reduction reaction was maintained at 100 °C for 1.5 h. The temperature was then further increased to 180 °C for a ring-closure condensation reaction for 2 h. After the reaction solution was naturally cooled to room temperature, it was filtered. The filter cake was washed multiple times with deionized water and dried to obtain 147 g of brown crude solid.

[0104] The obtained brown crude solid was added to 2000 mL of 2.75 mol / L hydrochloric acid, 12 g of activated carbon was added, and the mixture was heated under reflux for 3 h to remove the color. The activated carbon was removed by hot filtration, and the filtrate was allowed to stand and cool to crystallize. After being placed at low temperature overnight, it was filtered to obtain a yellow solid.

[0105] The above-mentioned yellow solid was recrystallized again using 500 mL of 2.75 mol / L hydrochloric acid. 8 g of activated carbon was added and the mixture was heated under reflux for 1 h to remove the color. The activated carbon was removed by hot filtration. After the filtrate was cooled slightly, 30 wt% sodium hydroxide aqueous solution was slowly added dropwise to neutralize the system to pH 7. The mixture was cooled to 4 °C in an ice-water bath, allowed to stand overnight to allow crystals to form, and then filtered and dried to obtain 50.1 g of light yellow guanine solid, with a total yield of 68.2%.

[0106] Comparative Example 2

[0107] As shown in the reaction formula below, 400 mL of anhydrous methanol, 120.0 g (1.21 mol) of methyl cyanoacetate, 121.32 g (1.27 mol) of guanidine hydrochloride and 134.1 g (2.48 mol) of sodium methoxide were added to a 2L four-necked flask and stirred to obtain the first material; the temperature was raised to 55 ℃ for cyclization reaction for 3 h to obtain a reaction solution containing 2,4-diamino-6-hydroxypyrimidine.

[0108] 88 g (1.28 mol) of sodium nitrite was added to the reaction solution containing 2,4-diamino-6-hydroxypyrimidine and stirred until dissolved. The temperature was controlled at 30℃, and 132.8 g (1.33 mol) of 50 wt% sulfuric acid was slowly added dropwise to carry out the nitrosation reaction. After the reaction was completed, a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine was obtained.

[0109] 122 g (0.64 mol) of sodium metabisulfite (Na2S2O5) was added in portions to a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine. 500 mL of 50 wt% formic acid was added, and the temperature was raised to 100 °C and maintained for 6 h for reduction. After reduction, a reaction solution containing 5-formamido-2,4-diamino-6-hydroxypyrimidine was obtained.

[0110] After the above-mentioned reduced reaction solution was subjected to vacuum distillation to remove low-content formic acid (mainly to remove water), 860 g (19 mol) of formamide was added, and the temperature was raised to 140 °C for condensation reaction for 18 h. After the condensation reaction was completed, the solvent was recovered by vacuum distillation, acidified with concentrated hydrochloric acid, filtered, and the crude product was subjected to alkaline precipitation with ammonia water, washed with water, and dried to obtain guanine.

[0111] Among them, methyl cyanoacetate has a molecular weight of 99.1, 2,4-diamino-6-hydroxypyrimidine has a molecular weight of 126.1, 2,4-diamino-5-nitroso-6-hydroxypyrimidine has a molecular weight of 155.1, and guanine has a molecular weight of 151.13.

[0112]

[0113] The purity and yield of guanine prepared in the examples and comparative examples of this application were determined by the following methods, and the results are shown in Table 2.

[0114] (1) Determination of purity:

[0115] The instrument used was an Agilent high-performance liquid chromatograph. Before the determination, 0.01 g of guanine sample was weighed, dissolved and diluted with distilled water, and filtered through a 0.22 μm organic phase filter membrane to obtain the sample solution to be tested.

[0116] Chromatographic conditions: The column was an Agela Promosil C18 reversed-phase column (100). The column was set to 4.6 mm × 250 mm (5 μm); the flow rate was 0.8 mL / min; the detection wavelength was 265 nm; the column temperature was 30℃; the injection volume was 10 μL; the total run time was 20 min; mobile phase A was 0.1% trifluoroacetic acid (TFA) aqueous solution, and mobile phase B was methanol. Both mobile phases were filtered through a 0.45 μm microporous membrane before use. The gradient elution program is shown in Table 1 below:

[0117] Table 1

[0118]

[0119] After the instrument baseline stabilizes, blank methanol, guanine standard solution and the sample solution to be tested are injected sequentially, the chromatogram is recorded, and the content of guanine in the sample is calculated by peak area using the external standard method.

[0120] (2) Determination of yield:

[0121] Total yield (%) = (finished product quality × finished product purity / total theoretical mass of guanine) × 100%, where total theoretical mass of guanine = mass of alkyl cyanoacetate added × (molar mass of guanine / molar mass of alkyl cyanoacetate).

[0122] Table 2

[0123]

[0124] Analysis of Table 2 shows that, compared with Comparative Examples 1-2, the guanine prepared in Examples 1-2 has both higher yield and purity.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing guanine, characterized in that, Includes the following steps: S1. A cyclization reaction is carried out by mixing alkyl cyanoacetate, guanidine salt, the first basic substance and the first solvent. After the cyclization reaction is completed, water is added to dissolve the system material to obtain a reaction solution containing 2,4-diamino-6-hydroxypyrimidine. S2. The reaction solution obtained in step S1 is mixed with nitrite, and the resulting mixture is added dropwise to the first inorganic acid to react, thereby obtaining a reaction solution containing 2,4-diamino-5-nitroso-6-hydroxypyrimidine. S3. In the presence of a hydrogenation catalyst, the reaction solution obtained in step S2 is contacted with hydrogen gas to reduce the 2,4-diamino-5-nitroso-6-hydroxypyrimidine to obtain a reaction solution containing 2,5,6-triamino-4-hydroxypyrimidine. S4. Add a second inorganic acid to the reaction solution obtained in step S3 to carry out a salt formation reaction, and obtain a reaction solution containing a 2,5,6-triamino-4-hydroxypyrimidine salt intermediate; then carry out a condensation reaction between the reaction solution containing the 2,5,6-triamino-4-hydroxypyrimidine salt intermediate and a carbonyl compound to obtain the guanine.

2. The method for preparing guanine according to claim 1, characterized in that, The alkyl cyanoacetate includes methyl cyanoacetate; And / or, the guanidine salt includes guanidine hydrochloride and / or guanidine nitrate; And / or, the first alkaline substance includes sodium methoxide; And / or, the first solvent includes methanol.

3. The method for preparing guanine according to claim 1 or 2, characterized in that, The molar ratio of the alkyl cyanoacetate to the guanidine salt is 1:(1~1.1). And / or, the molar ratio of the alkyl cyanoacetate to the first alkaline substance is 1:(1~2.1). And / or, the molar ratio of the alkyl cyanoacetate to the first solvent is 1:(8~8.3).

4. The method for preparing guanine according to claim 1 or 2, characterized in that, The nitrite includes sodium nitrite; And / or, the first inorganic acid includes sulfuric acid with a mass concentration of 20-60%; And / or, the second inorganic acid includes sulfuric acid with a mass concentration of 65-98%; And / or, the hydrogenation catalyst includes a nickel-based catalyst.

5. The method for preparing guanine according to claim 1 or 2, characterized in that, The molar ratio of the 2,4-diamino-6-hydroxypyrimidine to the nitrite is 1:(1~1.2). And / or, the molar ratio of the 2,4-diamino-6-hydroxypyrimidine to the first inorganic acid is 1:(0.5~0.7).

6. The method for preparing guanine according to claim 1 or 2, characterized in that, The molar ratio of the 2,4-diamino-5-nitroso-6-hydroxypyrimidine to the hydrogenation catalyst is 1:(0.24~0.27). And / or, the molar ratio of the 2,5,6-triamino-4-hydroxypyrimidine to the second inorganic acid is 1:(1.9~2.1). And / or, the carbonyl compound includes formamide and / or formic acid; And / or, the molar ratio of the 2,5,6-triamino-4-hydroxypyrimidine salt intermediate to the carbonyl compound is 1:(14~18).

7. The method for preparing guanine according to claim 1 or 2, characterized in that, The cyclization reaction is carried out at a temperature of 50℃~60℃ for 2h~4h. And / or, the reduction reaction is carried out at a temperature of 40°C to 60°C for a time of 2 hours to 10 hours; And / or, the salt formation reaction is carried out at a temperature of 20°C to 30°C for 1 to 2 hours.

8. The method for preparing guanine according to claim 1 or 2, characterized in that, The condensation reaction is carried out at a temperature of 130℃ to 160℃ for a duration of 16h to 24h.

9. The method for preparing guanine according to claim 1 or 2, characterized in that, After the condensation reaction is completed, the crude guanine hydrochloride obtained from the condensation reaction is subjected to alkaline precipitation in the presence of a second alkaline substance to obtain the guanine.

10. The method for preparing guanine according to claim 9, characterized in that, The second alkaline substance includes ammonia.

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