Description:FORM 2

THE PATENTS ACT,
(39 OF 1970)
THE PATENT RULES, 2003.

COMPLETE SPECIFICATION
(SECTION 10 AND RULE 13)

AN IMPROVED PROCESS FOR PREPARATION OF “2-AMINOHYPOXANTHINE” AND ITS PURIFICATION THEREOF

Suraj Laboratories Pvt Ltd
Raja Praasadamu, Plot No.6/A 6/B,
Masjid Banda, Kondapur,
Hyderabad, Telangana, INDIA-500084.

The following specification particularly describes the invention and the manner in which it is to be performed
AN IMPROVED PROCESS FOR PREPARATION OF “2-AMINOHYPOXANTHINE AND ITS PURIFICATION THEREOF”

FIELD OF THE INVENTION
The present invention relates to an improved process for preparation of 2-aminohypoxanthine of Formula-I. The invention further relates to purification of 2-aminohypoxanthine of Formula-I.

Formula I

BACKGROUND OF THE INVENTION:
2-aminohypoxanthine is a 2-aminopurine carrying a 6-oxo substituent. It has a role as a human metabolite, an algal metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite. It is a purine nucleobase, an oxopurine and a member of 2-aminopurines. 2-aminohypoxanthine is an important intermediate for synthesis of many pharmacologically active compounds, in particular of antiviral active compounds.
EP415028 discloses a process in which the sulfate of 2,4,5-triamino-6-hydroxypyrimidine (TAHP sulfate) was used as raw material and is reacted with formic acid with a content of more than 99% at higher temperatures to prepare 2-aminohypoxanthine. Also, it requires a multi-step reaction to prepare TAHP sulfate, which can be used after separation and purification. In addition, due to the instability of TAHP, TAHP sulfate must be made first, which brings in a large amount of inorganic salts, which brings inconvenience to the purification of crude 2-aminohypoxanthine and makes the purification cost relatively expensive.
The synthetic process disclosed in CN106478630 involves use of a large excess of sulfuric acid to nitrosate with sodium nitrite, producing a large amount of high-salt, high-acid wastewater. Since, the concentration of sulfuric acid in the mother liquor is too low and the concentration of sodium sulfate is too high, the mother liquor cannot be reused, so that the waste of excessive sodium nitrite and sulfuric acid is caused, and the treatment cost of wastewater is increased, which is not suitable for environment and large scale synthesis.
CN1966504 discloses a process for preparation of 2-aminohypoxanthine using ethyl cyanoacetate and guanidine nitrate as starting materials. This technology uses a mixed solution and reducing agent to perform nitrosation and reduction reactions, and then further performs a cyclization reaction to produce 2-aminohypoxanthine. Since this process involves usage of excess equivalents of guanidine nitrate (in between 1.4 to 2.0 equivalents) with respect to ethyl cyanoacetate, the impurities formed in the product are more complicated and affects purification procedures of the final product. Our impugned invention avoids the usage of excess amount of guanidine nitrate and formamide and achieves high purity and yields by a simple and improved process.
The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art and provide a one-pot synthesis of 2-aminohypoxanthine starting from guanidine nitrate without the need for separation and purification of intermediates and with a short synthesis route method.
SUMMARY OF THE INVENTION:
An embodiment of the present invention provides an improved process for the preparation of 2-aminohypoxanthine of Formula (I),

Formula I
Which comprises,
Step-a) reaction of guanidinium nitrate with alkyl cyanoacetate to obtain 2,6-diaminopyrimidin-4-ol, which further undergoes nitrosation, reduction and cyclization reactions in presence of sodium nitrite, sodium bisulfite and formamide- formic acid mixture respectively to obtain crude 2-aminohypoxanthine,
Step-b) purification of crude 2-aminohypoxanthine obtained in step a) using a polar protic solvent.
DETAILED DESCRIPTION OF THE INVENTION:

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description. The present invention described below in conjunction with specific embodiments. The examples are only preferred embodiments of the present invention and are not intended to limit the present invention.
In one embodiment, the below process illustrates a method for the preparation of 2-aminohypoxanthine of Formula (I) by Scheme-I.
Schematic representation of Scheme-I is depicted below:

Scheme-I
In aspects, conversion of Guanidinium nitrate to crude 2-aminohypoxanthine using alkyl cyanoacetate may be performed in a one pot synthesis method using suitable base and suitable nitrosation, reducing reagent and cyclization reagents, which comprises all the reaction steps performed in a single continuous method without isolating and purifying any intermediates.
Conversion of Guanidinium nitrate to 2,6-diaminopyrimidin-4-ol may be performed using a suitable alkyl cyanoacetate and base in a suitable solvent. Suitable alkyl cyanoacetate used include but not limited to C1 to C8 cyanoacetates, preferably, methyl cyanoacetate or ethyl cyanoacetate. Bases used include but not limited to sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium ethanoate, potassium ethanoate, sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and the like or mixtures thereof. Preferably, sodium methoxide. The solvents used include but not limited to toluene, xylene, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, dichloromethane, chloroform, isopropyl ether, ethyl acetate, isopropyl acetate, acetonitrile, DMF, ethanol, methanol, water and like or a mixture thereof. Specifically, the solvent may be methanol.
In aspects, conversion of Guanidinium nitrate to 2,6-diaminopyrimidin-4-ol may be performed using suitable molar ratios of alkyl cyanoacetate to Guanidinium nitrate. The molar ratio of the alkyl cyanoacetate to guanidine nitrate is preferably in between 1: 1 to 1: 2, and more preferably 1: 1.
The product 2,6-diaminopyrimidin-4-ol is optionally may convert to next step without further isolation and purification to obtain crude 2-aminohypoxanthine using suitable nitrosation, reducing and cyclization reagents. Nitrosating reagents used include but not limited sodium nitrite, potassium nitrite, nitrous acid, nitrous anhydride, nitric oxide (NO), nitrosyl halides (e.g. ClNO, BrNO), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4) and organic nitrites (e.g. t-BuONO) and like or a mixture thereof. Specifically, sodium nitrite. Reducing reagents used include but not limited to sodium bisulfite, Zn-acid, Sn-HCl, sodium hydrosulphite, stannous chloride and like or a mixture thereof. Preferably, sodium bisulfite. Reagents used for cyclization to form 2-aminohypoxanthine from corresponding reduced product are formamide and formic acid.
In aspects, purification of crude 2-aminohypoxanthine to pure 2-aminohypoxanthine may be performed using suitable polar aprotic solvent. The polar aprotic solvents used in step b) include but not limited to methanol, ethanol, isopropyl alcohol, ammonia, acetic acid, hydrogen fluoride, formic acid, water and like or a mixture thereof. Preferably, water.
Advantages of the present invention over prior art:
• Isolation/ Purification: The present invention overcomes the problems associated in terms of impurity formation and isolation procedures by a single continuous method without isolating and purifying any intermediates.
• Safety: The present invention replaced the usage of pyrophoric sodium or potassium metal by a non-pyrophoric base such as sodium methoxide in methanol solution, which is low in cost and safe in handling and thus suitable for industrial usage.
• Yield and Cost: Applicant conducted extensive studies for screening the molar ratios and volumes of the reagents and solvents with respect to starting materials and have developed a commercial process to prepare the final product in higher yields in less reaction time.
• Purities: The usage of polar protic solvent such as water for the recrystallization of crude 2-aminohypoxanthine drastically removes the salts formed during reaction and increases the assay purity remarkably from around 70 – 75% to 97- 98%, and thus meets the regulatory requirements.
• Impurity profile: Since the process disclosed in prior art involves usage of formamide in higher volumes and the reaction was performed at high temperatures, impurities were formed because of the decomposition of formamide. Applicant tried multiple reactions and reduces the volumes of formamide to lesser volumes for smooth proceedings of the reaction. Also, applicant executed number of reactions with various molar ratios of Guanidinium nitrate to alkyl cyanoacetate and developed a new and improved process for preparation of 2-aminohypoxanthine with higher yields and purities.
• The process is not only new and improved but also has technical advancement and economical significance compared to prior arts.
The details of the invention are given in the examples provided below, which are given to illustrate the invention only and therefore should not be construed to limit the scope of the invention.
Examples:
Preparation of 2-aminohypoxanthine (Formula-I) by Scheme-I:

Example 1:
Preparation of crude 2-aminohypoxanthine using methyl cyanoacetate:
To a stirred solution of 30% sodium methoxide in methanol solution (2.0 eq.) in methanol (1.0 vol) was added Guanidinium nitrate (1.0 eq.) at 25 – 35°C. Added methyl cyanoacetate ((1.0 eq.) slowly and stirred the reaction mixture at reflux temperature. Evaporated the reaction mass under vacuum and diluted the resulting residue product in formamide (6.3 vol). Added sodium nitrite (1.17 eq.) at 0 -5°C and stirred for 10 to 15 minutes. Added a mixture of formamide
(1.7 vol) and formic acid (1.6 vol) to the reaction mass and raised the temperature to 90 to 100°C. Now added sodium bisulfite (0.57 eq.) slowly and further raised the reaction mass temperature to 170 to 180°C. On completion, cooled the reaction mass and filtered the resulting precipitate under vacuum to get crude 2-aminohypoxanthine (16.3 g) with crude HPLC assay 71.645%).
Example 2:
Preparation of crude 2-aminohypoxanthine using ethyl cyanoacetate:
To a stirred solution of 30% sodium methoxide in methanol solution (2.0 eq.) in methanol (1.0 vol) was added Guanidinium nitrate (1.0 eq.) at 25 – 35°C. Added ethyl cyanoacetate ((1.0 eq.) slowly and stirred the reaction mixture at reflux temperature. Evaporated the reaction mass under vacuum and diluted the resulting residue product in formamide (6.3 vol). Added sodium nitrite (1.17 eq.) at 0 -5°C and stirred for 10 to 15 minutes. Added a mixture of formamide (1.7 vol) and formic acid (1.6 vol) to the reaction mass and raised the temperature to 90 to 100°C. Now added sodium bisulfite (0.57 eq.) slowly and further raised the reaction mass temperature to 170 to 180°C. On completion, cooled the reaction mass and filtered the resulting precipitate under vacuum to get crude 2-aminohypoxanthine (15.4 g).
Example 3:
Purification of crude 2-aminohypoxanthine using water:
Crude 2-aminohypoxanthine (16.3 g) obtained in above step was suspended in water (146.7 mL) at 20 to 30°C. Heated the reaction mass to 90 to 100°C and stirred for 30 to 60 minutes. Cooled the reaction mass to 25 to 35°C and filtered the resulting precipitate under vacuum to get the desired 2-aminohypoxanthine (10.74 g, yield: 86.6%) with HPLC assay 97.820%).

Dated this Nov, 3rd 2023

Signature:
VINOD SAGAR TIRUMALARAJU
Patent Agent Reg. No.: IN/PA-5328
, Claims:We claim:

1. An improved process for preparation of 2-aminohypoxanthine of Formula-I, which comprising,
a) reaction of Guanidinium nitrate with alkyl cyanoacetate in a suitable molar ratio in presence of a suitable base and solvent to obtain 2,6-diaminopyrimidin-4-ol;
b) subjecting the 2,6-diaminopyrimidin-4-ol obtained in step a) optionally without isolation to further nitrosation, reduction and cyclization reactions using suitable reagents respectively to obtain crude 2-aminohypoxanthine;
c) purification of crude 2-aminohypoxanthine obtained in step b) using a suitable polar protic solvent to obtain 2-aminohypoxanthine.
2. The process as claimed in claim 1, wherein the suitable alky cyanoacetate used in step a) is selected from C1 to C8 cyanoacetates, preferably, methyl cyanoacetate or ethyl cyanoacetate.
3. The process as claimed in claim 1, wherein the suitable molar ratio of ethyl cyanoacetate to guanidine nitrate in step a) is about 1: 1.4; preferably, 1: 1.
4. The process as claimed in claim 1, wherein the suitable base used in step a) is selected from sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium ethanoate, potassium ethanoate, sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide and like or mixtures thereof.
5. The process as claimed in claim 1, wherein the suitable solvent used in step a) is selected from methanol, ethanol, isopropyl alcohol, toluene, xylene, tetrahydrofuran, 2-methyltetrahydrofuran, isopropyl ether, ethyl acetate, isopropyl acetate, acetone, acetonitrile, Dimethylformamide and like or a mixture thereof.
6. The process as claimed in claim 1, wherein the suitable reagent used in step b) for nitrosation is selected from sodium nitrite, potassium nitrite, nitrous acid, nitrous anhydride, nitric oxide (NO), nitrosyl halides (e.g. ClNO, BrNO), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4) and organic nitrites (e.g. t-BuONO) and like or a mixture thereof; suitable reagent for reduction is selected from sodium bisulfite, Zn-acid, Sn-HCl, sodium hydrosulphite, stannous chloride and like or a mixture thereof; suitable reagent used for cyclization is formamide and formic acid mixture.
7. The process as claimed in claim 1, wherein the polar protic solvent used in step c) is water.

Dated this Nov, 3rd 2023

Signature:
VINOD SAGAR TIRUMALARAJU
Patent Agent Reg. No.: IN/PA-5328