The invention relates to process for the preparation of regadenoson. The invention further relates to the use of novel intermediates for the preparation of regadenoson, wherein the process is simple, efficient and economical.
Background of the Invention
Regadenoson, chemically known as (1-{9-[(4S,2R,3R,5R)-3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl]-6-aminopurin-2-yl}pyrazol-4-yl)-N-methyl carboxamide is represented as compound of Formula I,

Formula I
Regadenoson is an A2A adenosine receptor agonist that is a coronary vasodilator. It produces maximal hyperemia quickly and maintains it for an optimal duration that is practical for radionuclide myocardial perfusion imaging.
U.S. Pat. No. 6,403,567 discloses process for the preparation of regadenoson starting from commercially available 2-aminoadenosine, which is sequentially converted to 2-chloroadenosine using phosphorus oxychloride and then to 2-hydrazinoadenosine. 2-hydrazinoadenosine is then reacted with ethyl diformyl acetate to yield 2-(4-methoxycarbonylpyrazol-1-yl)adenosine. The resulting product is reacted with excess of methyl amine for about 24 hours to obtain regadenoson, which is purified using prep TLC. The disclosed process involves use of highly corrosive phosphorus oxychloride which makes the handling operations very difficult on large scale application. Further the final step requires use of excess of methyl amine and the reaction time is too long (24 hrs) at 65oC, which leads to higher consumption of energy making the process economically inefficient. Also the use of preparative thin layer chromatography for purification of final product is not suitable for industrial scale preparation of an active pharmaceutical ingredient. The disclosed process conditions not only are economically burdensome but also involves methods, which are not at all suitable for purification of a compound to reach desired purity level of active pharmaceutical ingredient at industrial scale.
U.S. Pat. No. 8,859,522 discloses a process for the preparation of regadenoson, wherein the process involves contacting 2-haloadenosine with 4-N-alkylcarboxamide pyrazole or a 4-carboxylate pyrazole in the presence of a copper metal catalyst, iminodiacetic acid resin-copper(II) and a base. The process further discloses purification of regadenoson using reverse phase chromatography using water/methanol as eluent. The process disclosed is not feasible for large scale application since use of column chromatography is only feasible at small scale and is highly inoperable and very expensive for industrial application. Further, the copper catalyst used for the preparation of intermediate can be difficult to remove which may lead to high metal content in final product.
U.S. Pat. No. 9,580,457 discloses a process for the preparation of regadenoson. The process involves reaction of 2,6-dichloropurine with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribose to obtain 2,6-dichloro-9-beta-D-(2,3,5-tri-O-benzoyl)-ribofuranosylpurine which is recrystallized from 1-butanol. The product is further treated with methanolic ammonia in an autoclave at 100oC for 24 hrs and the resulting compound crystallized from acetone to get 2-chloro-9-(beta-D-ribofuranosyl) adenine which is subsequently reacted with 1H-pyrazole-4-carboxylic acid amide in presence of N-methylpyrrolidine, treated with potassium carbonate in a sealed reactor at 100-150oC under inert atmosphere to obtain regadenoson. Regadenoson obtained is then purified by column chromatography and again recrystallized from methanol to get pure compound. The disclosed process involves use of crystallization of intermediates at each step and finally column chromatography is used for the purification of final product, thus it is quite evident that the process is incapable of providing intermediates of desirable purity. Also the column chromatography is highly infeasible to be applicable on industrial scale due to operational difficulties and generation of large quantities of effluent.
U.S. Pat. No. 9,771,390 discloses another process for the preparation of regadenoson wherein the process involves reaction of 2-chloroadenosine with hydroxyl protecting groups in the presence of acid, the intermediate 2-chloro hydroxyl protected adenosine. The intermediate is then reacted with pyrazole-4-carboxamide in the presence of base to obtain hydroxyl protected regadenoson, which is treated with perchloric acid to obtain regadenoson. The invention points out the probability of formation of impurities when unprotected hydroxyl group intermediates are used for the preparation of regadenoson, whereas its own process the invention aims to protect two germinal hydroxyl groups during the reaction leaving behind one methylene hydroxyl unprotected, which being free may lead to generation of other probable impurities. Further, the process involves use of perchloric acid at final step of deprotection, perchloric acid is a known explosive hazard and is difficult to handle at large scale application. Thus, probability of impurity formation and operational difficulty of disclosed process makes it infeasible for large scale production.
Thus, there remains a need in the art to provide a simple, safe and efficient method for the preparation of regadenoson for industrial application. The present invention provides a process for the preparation of regadenoson in a simple, safe and efficient manner, wherein the process involves use of novel intermediates.
Object and summary of the Invention
The principal object of the present invention is to provide a process for the preparation of regadenoson, which alleviates one or more drawbacks of the prior art processes.
It is another object of the present invention to provide a simple, safe and efficient process for the synthesis of regadenoson.
A yet another object of the present invention is to provide novel intermediates of regadenoson.
It is yet another object of the present invention to provide an efficient process for the preparation of regadenoson by use of novel intermediates.
In an embodiment, the present invention provides a novel intermediate of regadenoson of Formula II.

Formula II
wherein R1 is hydroxyl protecting group; R2 is group forming activated ester
In another embodiment, the present invention provides a process for the preparation of regadenoson intermediate of Formula II as depicted in Scheme 1.

wherein R1 is hydroxyl protecting group; R2 is group forming activated ester.
Scheme 1
In yet another embodiment, the present invention provides a process for the preparation of regadenoson by using intermediate compound of Formula II, as depicted in Scheme 2.

wherein R1 is hydroxyl protecting group; R2 is group forming activated ester
Scheme 2
In another embodiment, the present invention provides a process for the preparation of regadenoson using hydroxyl protected intermediate of Formula IV, as depicted in Scheme 3.

wherein R1 is hydroxyl protecting group;
Scheme 3
In yet another embodiment, the present invention provides a novel intermediate of regadenoson of Formula IIa.

Formula IIa
wherein R2 is group forming activated ester.
In yet another embodiment, the present invention provides a process for the preparation of regadenoson novel intermediate compound of Formula IIa, as depicted in Scheme 4.

wherein R2 is group forming activated ester
Scheme 4
In yet another embodiment, the present invention provides a process for the preparation of regadenoson using intermediate compound of Formula IIa, as depicted in Scheme 5.

wherein R2 is group forming activated ester
Scheme 5

Description of the Invention
While this specification concludes with claims particularly pointing out and distinctly claiming that, which is regarded as the invention, it is anticipated that the invention can be more readily understood through reading the following detailed description of the invention and study of the included examples.
The conventionally used processes for the preparation of regadenoson are very much prone to the formation of multiple impurities. The formation of impurities or the control on formation of impurities is dependent upon the reagents, solvents and conditions used for carrying out various reactions, therefore it is a challenge for the present inventors to reach at such reaction conditions, selection of solvents and reagents such that they provide regadenoson with required purity standards, wherein the process should not involve working difficulties, involve high costs, expensive techniques/reagents, rather the process should be simple, easy to operate and economical.
In view of above requirements, the present invention provides processes that are simple, convenient, environment friendly and economical for industrial application. The method utilizes operationally easy techniques and novel intermediates that avoids formation of multiple impurities, which thereby reduces the additional requirements of purifying intermediates at various stages and accordingly reduces the use of solvents and reagents. Further, it also avoids use of column chromatography for the purification of intermediates and that of final product which results in decrease in costs attributed to a more efficient use of reagents and solvents and at the same time makes process more environment friendly with highly reduced effluent generation. Also the developed process involves use of such intermediates which results in the shorter reaction duration owing to their enhanced reactivity as compared to traditional intermediates used in the literature for similar reactions. The enhanced rate of reaction resulting in shorter reaction time, not only is energy efficient but also reduces the chances of impurity formation many folds thus providing dual advantage at same time.
In an embodiment, the present invention provides a novel intermediate of regadenoson of Formula II.

Formula II
wherein R1 is hydroxy protecting group; R2 is group forming activated ester.
According to the present invention, the R1 is “hydroxyl protecting group” which refers to a functional moiety that renders a hydroxyl group unreactive. The examples of such protecting groups include, but are not limited to, methyl ethers, benzyl ethers, silyl ethers, esters and the like. The group R2 that refers to “group forming activated ester” which refers to a moiety that results in ester formation which can be substituted more easily. The examples of such activating esters include, but are not limited to, p-nitrophenol, N-hydroxysuccinimide, ethyl chloroformate, pivaloyl chloride and the like.
In another embodiment, the present invention provides a process for the preparation of novel intermediate of Formula II comprising, reacting 2-hydrazinoadenosine of Formula VI with ethoxycarbonyl malondialdehyde of Formula VII to produce compound of Formula V. The hydroxyl groups of compound of Formula V is protected with appropriate/suitable protecting group to produce compound of Formula IV, which is hydrolyzed to corresponding acid of Formula III using a base. The acidic group of compound of Formula III is then converted to activated ester by reaction with suitable reagent to get novel intermediate of Formula II (Scheme 1).
According to present invention, the 2-hydrazinoadenosine of Formula VI reacts with ethoxycarbonyl malondialdehyde of Formula VII. The reaction is carried out in solvent in presence of an acid, wherein the solvent is selected from the group comprising of alcohols such as methanol, ethanol, propanol, butanoland the like, halogenated hydrocarbons such as dichloromethane, chloroformand the like, esters such as ethyl acetate, isopropyl acetateand the like, nitrile such as acetonitrile and the like, water and mixtures thereof. The acid used for the reaction is selected from the group comprising of alkanoic acids such as formic acid, acetic acid, oxalic acid and the like, mineral acids such as hydrochloric acid, hydrobromic acid, sulfuric acid and the like. The reaction is carried out at 40-90° C for about 2 to 5 hours to give compound of Formula V.
The compound of Formula V is then treated with hydroxyl protecting reagent to produce compound of Formula IV, wherein the reaction is carried out in solvent selected from the group comprising of esters such as ethyl acetate and the like, nitrile such as acetonitrile and the like, aromatic hydrocarbons such as toluene, xylene, chlorobenzene and the like, amides such as dimethylsulphoxide, dimethylformamide, dimethylacetamide and the like and mixtures thereof. The hydroxyl protecting group used is selected from the group comprising of methyl ethers such as methoxymethyl, benzyloxymethyl and the like, benzyl ethers such as p-methoxybenzyl, 3,4-dimethoxybenzyl and the like, silyl ethers such as trimethyl silyl, tertiary butyl methyl silyl, tertiary butyl diphenyl silyl and the like and esters such as acetyl, benzoyl and the like. The reaction is carried out in the presence of catalyst selected from the group comprising of imidazole and the like. The reaction is carried out at up to reflux temperature to produce compound of Formula IV. The compound of Formula IV is subsequently hydrolyzed using a base in a solvent to form the compound of Formula III. The base used is selected from the group comprising of metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide and the like, metal carbonate such as potassium carbonate, sodium carbonate lithium carbonate, calcium carbonate, magnesium carbonate and the like. The solvent used to carry out the reaction is selected from the group comprising of alcohols such as methanol, ethanol and the like, esters such as ethyl acetate and the like, water and mixtures thereof. The reaction is carried out at 15-35° C for about 1-5 hours to get acid compound of Formula III.
According to the present invention, the compound of Formula III is then treated with a suitable reagent in a solvent to get an activated ester compound of Formula II. The suitable reagent used is selected from the group comprising of p-nitrophenol, N-hydroxysuccinimide, ethyl chloroformate, pivaloyl chloride and the like. The solvent used is selected from the group comprising of alcohols such as methanol, ethanol, propanol and the like, halogenated hydrocarbons such as dichloromethane and the like, esters such as ethyl acetate and the like, nitrile such as acetonitrile and the like, water and mixtures thereof. The reaction is carried out in the presence of suitable catalysts selected from the group comprising of N,N'-dicyclohexylcarbodiimide (DCC), dimethylamino pyridine (DMAP), (2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU), hydroxybenzotriazole (HOBt) and the like. The reaction is carried out at 15-35° C for about 18-30 hours to obtain compound of Formula II.
In another embodiment, the present invention provides a process for the preparation of regadenoson using novel intermediate of Formula II, comprising treating compound of Formula II with methylamine to produce regadenoson (Scheme 2).
According to the present invention, the compound of Formula II is treated with methylamine to obtain regadenoson. The reaction is carried out at 15-40 ° C for about 3-6 hours to obtain regadenoson.
In yet another embodiment, the present invention provides a process for the preparation of regadenoson comprising, reacting compound of compound VI with ethoxycarbonyl malondialdehyde of Formula VII to produce compound of Formula V. The hydroxyl groups of compound of Formula V is protected with appropriate/suitable protecting reagent/groups to produce compound of Formula IV, which is hydrolyzed using methylamine to obtain regadenoson (Scheme 3).
According to present invention, the 2-hydrazinoadenosine of Formula VI reacts with ethoxycarbonyl malondialdehyde of Formula VII. The reaction is carried out in solvent in presence of an acid, wherein the solvent is selected from the group comprising of alcohols such as methanol, ethanol, propanol, butanol and the like, halogenated hydrocarbons such as dichloromethane, chloroform and the like, esters such as ethyl acetate, isopropyl acetate and the like, nitrile such as acetonitrile and the like, water and mixtures thereof. The acid used for the reaction is selected from the group comprising of alkanoic acids such as formic acid, acetic acid, oxalic acid and the like, mineral acids such as hydrochloric acid, hydrobromic acid, sulfuric acid and the like. The reaction is carried out at 40-90° C for about 2 to 4 hours to give compound of Formula V.
The compound of Formula V is then treated with hydroxyl protecting reagent to produce compound of Formula IV, wherein the reaction is carried out in solvent selected from the group comprising of esters such as ethyl acetate, isopropyl acetate and the like, nitrile such as acetonitrile and the like, aromatic hydrocarbons such as toluene, xylene chlorobenzene and the like, amides such as dimethylformamide, dimethylacetamide and the like and mixtures thereof. The hydroxyl protecting reagent/group used is selected from the group comprising of methyl ethers such as methoxymethyl, benzyloxymethyl and the like, benzyl ethers such as p-methoxybenzyl, 3,4-dimethoxybenzyl and the like, silyl ethers such as trimethyl silyl, tertiary butyl methyl silyl and the like and esters such as acetyl, benzoyl and the like. The reaction is carried out in the presence of catalyst selected from the group comprising of imidazole and the like. The reaction is carried out at 60-90° C for about 24-28 hours to give to produce compound of Formula IV.
According to the present invention, the compound of Formula IV is treated with methylamine to obtain regadenoson. The reaction is carried out at 15-60 °C for about 3-6 hours to obtain regadenoson.
In an embodiment, the present invention provides a novel intermediate of regadenoson of Formula IIa.

Formula IIa
wherein R2 is group forming activated ester.
According to the present invention, the group R2 refers to “group forming activated ester” which refers to a moiety that results in ester formation that is highly susceptible toward nucleophilic attack. The examples of such activating esters include, but are not limited to, p-nitrophenol, N-hydroxysuccinimide, ethyl chloroformate, pivaloyl chloride and the like.
In another embodiment, the present invention provides a process for the preparation of novel intermediate of Formula IIa comprising, reacting 2-hydrazinoadenosine of Formula VI with ethoxycarbonyl malondialdehyde of Formula VII to produce compound of Formula V. The compound of Formula V is subjected to hydrolysis to obtain compound of Formula VIII. The acidic group of compound of Formula VIII is then converted to activated ester by reaction with suitable reagent to get novel intermediate of Formula IIa (Scheme 4).
According to present invention, the 2-hydrazinoadenosine of Formula VI reacts with ethoxycarbonyl malondialdehyde of Formula VII. The reaction is carried out in solvent in presence of an acid, wherein the solvent is selected from the group comprising of alcohols such as methanol, ethanol, propanol, butanol and the like, halogenated hydrocarbons such as dichloromethane chloroform and the like, esters such as ethyl acetate isopropyl acetate and the like, nitrile such as acetonitrile and the like, water and mixtures thereof. The acid used for the reaction is selected from the group comprising of alkanoic acids such as formic acid, acetic acid, oxalic acid and the like, mineral acids such as hydrochloric acid, hydrobromic acid, sulfuric acid and the like. The reaction is carried out at 40-90° C for about 2 to 4 hours to give compound of Formula V.
According to present invention, the compound of Formula V is hydrolyzed to compound of Formula VIII. The reaction is carried out in solvent in presence of a base, wherein the solvent is selected from the group comprising of alcohols such as methanol, ethanol, propanol, butanol and the like, halogenated hydrocarbons such as dichloromethane, chloroform and the like, esters such as ethyl acetate, isopropyl acetate and the like, nitrile such as acetonitrile and the like, water and mixtures thereof. The base used for the reaction is selected from the group comprising of inorganic and organic. The organic base is selected from the group comprising of methylamine, dimethylamine, trimethylamine and the like. The inorganic base used is selected from the group comprising of hydroxide, carbonate, bicarbonate salt of alkali and alkaline earth metals. The alkali and alkaline earth metal is selected from the group comprising of sodium, potassium, calcium, magnesium and the like. The reaction is carried out at 50-90° C for about 2 to 8 hours to give compound of Formula VIII.
According to the present invention, the compound of Formula VIII is then treated with a suitable reagent in a solvent to get an activated ester compound of Formula IIa. The suitable reagent used is selected from the group comprising of p-nitrophenol, N-hydroxysuccinimide, ethyl chloroformate, pivaloyl chloride and the like. The solvent used is selected from the group comprising of alcohols such as methanol, ethanol, propanol, butanol and the like, halogenated hydrocarbons such as dichloromethane, chloroform and the like, esters such as ethyl acetate, isopropyl acetate and the like, nitrile such as acetonitrile and the like, N-methyl pyrrolidine, dimethylsulfoxide, dimtheylacetamide, water and mixtures thereof. The reaction is carried out in the presence of suitable catalysts selected from the group comprising of 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and its hydrochloride salt, N,N'-dicyclohexylcarbodiimide (DCC), dimethylamino pyridine (DMAP), (2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU), hydroxybenzotriazole (HOBt) and the like. The reaction is carried out at 15-35° C for about 18-30 hours to obtain compound of Formula IIa.
According to the present invention, the ethoxycarbonyl malondialdehyde of Formula VII used is prepared as per the process known in the prior art.
In another embodiment, the present invention provides a process for the preparation of regadenoson using novel intermediate of Formula IIa, comprising treating compound of Formula IIa with methylamine to produce regadenoson (Scheme 5).
According to the present invention, the compound of Formula IIa is treated with methylamine to obtain regadenoson. The methylamine used is selected from methylamine and aqueous methylamine. The reaction is carried out at 15-40 ° C for about 3-6 hours to obtain regadenoson.
According to the present invention, the compound of Formula II, III, IV, V and regadenoson are isolated using one or more work-up processes such as extraction, washing, filtration and the like. The intermediates used for the preparation of regadenoson and regadenoson obtained is then optionally crystallized from suitable organic solvent to increase/enhance purity. The suitable organic solvent for crystallization is selected from the group comprising of alcohols, esters, ketones, ethers, water or mixtures thereof; particularly methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, methyl acetate, ethyl acetate, isopropyl acetate, tertiary butyl acetate, acetone, methyl ethyl ketone, diisopropyl ether, tetrahydrofuran, water or mixtures thereof.
According to the present invention, the regadenoson obtained is optionally converted into pharmaceutically acceptable salts. The pharmaceutically acceptable salt is selected from the group comprising of hydrochloride, hydrobromide, sulfate, acetate, phosphate, succinate, methanesulfonate and the like.
Examples:
Example 1: Preparation of compound of Formula V
To a solution of 2-hydrazinoadenosine of Formula VI (25 g) in ethanol/acetic acid (10:0.2 v/v), is added (ethoxycarbonyl) malondialdehyde (Formula VII, 19.0 g). The reaction mixture is heated at 80° C for 3 hours. On completion of reaction, the reaction mixture is cooled to room temperature and stirred for another 3 hour. The solid obtained is filtered and washed with ethanol to afford compound of Formula V.
Example 2: Preparation of compound of Formula IV
The compound of Formula V (5.0 g) obtained in Example 1 is dissolved in dimethylformamide. To the reaction mixture is added tertiary-butyl dimethyl silyl chloride (15 g) along with imidazole (6.8 g) and the mixture is heated at 80° C for 24 hours. The reaction mass is cooled to 25-30° C to precipitate the product which is filtered to obtain compound of Formula IV.
Example 3: Preparation of compound of Formula III
The trisilyl hydroxyl protected compound of Formula IV (8.0 g) is suspended in 10 mL of water and is treated with one equivalent of IN NaOH. The solution was allowed to stir at room temperature and is then acidified to pH 4. The resulting precipitate is filtered and washed with water and ether to afford the compound of Formula III.
Example 4: Preparation of compound of Formula II, wherein R2 is p-nitrophenyl
The compound of Formula III (1.4 g) is dissolved in dichloromethane (50 ml). To the solution is added HBTU (1.9 g), HOBt (0.76 g), p-nitro phenol (0.55 g) and catalytic amount of dimethylaminopyridine. The mixture is allowed to stir at room temperature for 24 hour. The solid so obtained is filtered and dried to obtain compound of Formula II.
Example 5: Preparation of Regadenoson from compound of Formula II
The compound of Formula II is reacted with excess aqueous methylamine at room temperature, for about 4 hours. The product is isolated by filtration and washed with cold ethanol to get regadenoson.
Example 6: Preparation of Regadenoson from compound of Formula IV
The compound of Formula IV is reacted with excess aqueous methylamine at room temperature, for about 4 hours. The product is isolated by filtration and the solid is washed with cold ethanol to get regadenoson.

Example 7: Preparation of compound of Formula VIII
To a suspension of compound of Formula V (25 g) in ethanol/water (50 ml, 5:14, v/v), added sodium hydroxide (3.98 g). The reaction mixture is heated to about 80°C and stirred for 3 hours. On completion of reaction solvent is distilled under pressure and the pH of reaction mixture is adjusted to about 5.0 using hydrochloric acid. The reaction mixture is then stirred for another 5 hours at room temperature. The solid obtained is filtered, treated with acetone to obtain compound of Formula VIII.

Example 8: Preparation of compound of Formula IIa
To a mixture of compound of Formula VIII (10 g), N-methyl-2-pyrrolidine (100 ml) and p-nitrophenol (4.4 g), added 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC.HCl) (7.6 g), raised the temperature to about 50°C and stirred for about 10 hour. On completion of reaction, the reaction mixture is cooled to 15°C and added a mixture of acetonitrile/water (400 ml, 1:4 v/v) and stirred for another 2 hour. The solid so obtained is filtered and dried to obtain compound of Formula IIa.

Example 9: Preparation of regadenoson from compound of Formula IIa
A mixture of compound of Formula IIa (6 g) and 40% aqueous methylamine (30 ml) was stirred at room temperature for about 2 hour. On completion of reaction, the reaction mixture is diluted with water (30 ml), heated to about 50°C and stirred for about 2 hour. The reaction mixture is then cooled to about 15°C, the solid obtained is filtered, washed with water and dried to obtain regadenoson.
HPLC purity: greater than 99.0%

We claim:

1.A compound of Formula II,

Formula II
wherein R1 is hydroxyl protecting group; R2 is group forming activated ester.
2. The process for the preparation of compound of Formula II, as claimed in claim 1, comprising the steps of:
(i) reacting 2-hydrazinoadenosine of Formula VI with ethoxycarbonyl malondialdehyde of Formula VII to obtain compound of Formula V;
(ii) protecting hydroxyl groups of compound of Formula V suitable protecting group to obtain compound of Formula IV;
(iii) hydrolyzing compound of Formula IV to obtain compound of Formula III using a base; and
(iv) esterifying compound of Formula III to obtain compound of Formula II.

wherein R1 is hydroxyl protecting group; R2 is group forming activated ester.

3. The process for preparation of regadenoson using compound of Formula II by reacting compound of Formula II with methylamine.

4. A process for preparation of regadenoson, comprising the steps of:
(i) reacting compound of compound VI with ethoxycarbonyl malondialdehyde of Formula VII to obtain compound of Formula V;
(ii) protecting hydroxyl groups of compound of Formula V with suitable protecting reagent to obtain compound of Formula IV
(iii) hydrolyzing compound of Formula IV using methylamine to obtain regadenoson.

wherein R1 is hydroxyl protecting group.

5. A compound of Formula IIa

Formula IIa
wherein R2 is group forming activated ester.

6. The process for preparation of compound of Formula IIa, as claimed in claim 1, comprising the steps of:
(i) reacting 2-hydrazinoadenosine of Formula VI with ethoxycarbonyl malondialdehyde of Formula VII to obtain compound of Formula V;
(ii) hydrolyzing compound of Formula V to obtain compound of Formula VIII; and
(iii) esterifying compound of Formula VIII suitable reagent to get compound of Formula IIa.

wherein R2 is group forming activated ester.

7. The process for preparation of regadenoson using compound of Formula IIa by reacting compound of Formula IIa with methylamine.

8. The process as claimed in claim 1, 2, 4 and 6, wherein the hydroxyl protecting group used is selected from the group comprising of methyl ethers, benzyl ethers, silyl ethers and esters.

9. The process as claimed in claim 1, 2, 5 and 6, wherein the group forming activated ester used for esterification is selected from the group comprising of p-nitrophenol, N-hydroxysuccinimide, ethyl chloroformate and pivaloyl chloride.