Field of the invention:
The present invention relates to a novel process for the preparation of 7-cyclopentyl-N,N-dimethyl-2-{[5-(piperazin-1-yl)pyridin-2-yl]amino}-7H-pyrrolo[2,3-d]pyrimidine-6-carboxamide succinate (1/1) compound of formula-1a. The said compound of formula-1a is represented by the following structural formula:

Formula-1a

Background of the Invention:
The 7-cyclopentyl-N,N-dimethyl-2-{[5-(piperazin-1-yl)pyridin-2-yl]amino}-7H-pyrrolo [2,3-d]pyrimidine-6-carboxamide succinate (1/1) is commonly known as Ribociclib succinate. Ribociclib succinate was developed by Novartis and Astex Pharmaceuticals which is an anticancer agent useful for the treatment of certain kinds of breast cancers. The trade name of Ribociclib succinate is Kisqali, dosage form is tablet.
WO20100020675 A1 and its equivalent patent US 8415355B2 first disclosed the Ribociclib freebase of formula-1 and its process for the preparation. According to the process, 2-chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid of formula-2 was reacted with dimethylamine in ethanol in the presence of N,N,N',N'-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate (HBTU) and N,N-diisopropylethyl amine to get compound of formula-8. Then the compound of formula-8 is coupled with 4-(6-amino-pyridine-3-yl)-piperazine-1-carboxylic acid tert-butyl ester of formula-4 by Buchwald method using tris(dibenzylideneacetone) dipalladium(0) (Pd2(dba)3), (+/-)-2,2’-Bis(diphenylphosphino)-1,1’-binaphthyl (BINAP) and sodium tert-butoxide to yield compound of formula-7. Further, the resulting compound of formula-7 is treated with HCl in dioxane in the solvent of methanol and/ or chloroform to afford Ribociclib freebase compound of formula-1. Synthetic scheme is depicted below:

Scheme-1:

The said process involves the usage of highly expensive and less stable reagents like N,N,N',N'-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate (HBTU), Tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), (+/-)-2,2’-Bis (diphenylphosphino)-1,1’-binaphthyl (BINAP) and sodium tert-butoxide, which are not suitable for the commercial scale process.
In view of the above, the present inventors have developed a novel process for the preparation Ribociclib succinate which utilizes the simple, easily available raw materials and low cost reagents thereby reduces the cost of production.
In the present invention, the expensive and less stable reagents such as tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), (+/-)-2,2’-Bis(diphenyl phosphino)-1,1’-binaphthyl (BINAP) and sodium tert-butoxide are replaced with lithium hexamethyldisilazane (1M solution in tetrahydrofuran) to give compound of formula-6. And another expensive coupling reagent N,N,N',N'-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate (HBTU) has been replaced with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC HCl) and hydroxybenzotriazole (HOBt) to achieve compound of formula-7.

Brief description of the Invention:
The first aspect of the present invention is to provide a novel process for the preparation of Ribociclib succinate compound of formula-1a.
The second aspect of the present invention is to provide novel intermediate compounds, which are useful in the preparation of Ribociclib compound of formula-1.

Detailed description of the Invention:
The term "suitable solvent" used in the present invention refers to "hydrocarbon solvents" selected from aliphatic hydrocarbon solvents such as n-hexane, n-heptane, cyclohexane, petroleum ether and aromatic hydrocarbon solvents such as benzene, toluene, xylene and the like; "ether solvents" such as dimethyl ether, diisopropyl ether, diethyl ether, methyl tert-butyl ether, 1 ,2-dimethoxy ethane, tetrahydrofuran, 1,4-dioxane, monoglyme, diglyme and the like; "ester solvents" such as methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate and the like; "polar-aprotic solvents such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone (NMP) and the like; "chloro solvents" such as dichloromethane/Methylene chloride, dichloroethane, chloroform, carbon tetrachloride and the like; "ketone solvents" such as acetone, methyl ethyl ketone, methyl isobutyl ketone and the like; "nitrile solvents" such as acetonitrile, propionitrile, isobutyronitrile and the like; "alcoholic solvents" such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol and the like; "polar solvents" such as water or mixtures thereof.
As used herein the present invention the term “suitable base” refers to “alkali metal carbonates” such as sodium carbonate, potassium carbonate, lithium carbonate and the like; “alkali metal bicarbonates” such as sodium bicarbonate, potassium bicarbonate and the like; “alkali metal hydroxides” such as sodium hydroxide, potassium hydroxide, lithium hydroxide and the like; “alkali metal alkoxides” such as sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, sodium tert.butoxide, potassium tert.butoxide, lithium tert.butoxide and the like; alkali metal hydrides such as sodium hydride, potassium hydride, lithium hydride and the like; alkali metal amides such as sodium amide, potassium amide, lithium amide and the like; and organic bases like dimethylamine, diethylamine, diisopropylamine, diisopropylethylamine, diisobutylamine, triethylamine, pyridine, 2-picoline, 3-picoline, 4-picoline, 4-dimethylaminopyridine (DMAP), N-methyl morpholine (NMM), 2,6-lutidine, lithium diisopropylamide; organosilicon bases such as lithium hexamethyldisilazide (LiHMDS), sodium hexamethyldisilazide (NaHMDS), potassium hexamethyldisilazide (KHMDS) or mixtures thereof.

The first aspect of the present invention is to provide a novel process for the preparation of Ribociclib succinate compound of formula-1a, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid compound of formula-2 with a suitable chlorinating agent in a suitable alcoholic solvent to provide alkyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-3,
b) reacting the compound of general formula-3 with 4-(6-amino-pyridin-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4 in the presence of a suitable base in a suitable solvent to provide alkyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-5,
c) hydrolyzing the compound of general formula-5 in the presence of a suitable base in a suitable solvent to provide 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid of formula-6,
d) reacting the compound of formula-6 with dimethylamine in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC HCl) and hydroxybenzotriazole (HOBt) in a suitable solvent to provide tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethylcarbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl] amino]-3-pyridyl]piperazine-1-carboxylate compound of formula-7,
e) deprotecting the Boc moiety of compound of formula-7 using a mineral acid in gaseous state or its aqueous solution in a suitable solvent, followed by basification to provide Ribociclib freebase of formula-1,
f) treating the Ribociclib compound of formula-1 with succinic acid in a suitable solvent to provide Ribociclib succinate compound of formula-1a.
Wherein, in step-a), the suitable chlorinating agent is selected from SO2Cl2, SOCl2, (COCl)2, POCl3, PCl3 and PCl5; the suitable alcoholic solvent is selected from C1-C4
alcohols.
In step-b), the suitable base is selected from organosilicon bases defined as above.
In step-c), the suitable base is selected from inorganic base such as sodium hydroxide,
lithium hydroxide, potassium hydroxide or its aqueous solution.
In step-e), the suitable acid is selected from inorganic acid such as HCl in gaseous state
or its aqueous solution.
In step a) to f), the suitable solvent is selected from ether solvents, chloro solvents, ester solvents, alcohol solvents, ketone solvents, polar aprotic solvents, hydrocarbon solvents, nitrile solvents and polar solvents such as water or mixtures thereof.

In a preferred embodiment of the present invention provides a novel process for the preparation of Ribociclib succinate compound of formula-1a, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidin-6-carboxylic acid compound of formula-2 with thionyl chloride in methanol provides methyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-3a,
b) reacting the compound of formula-3a with 4-(6-amino-pyridine-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4 in the presence of Lithium hexamethyldisilazane in toluene provides methyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-5a,
c) hydrolyzing the compound of formula-5a in the presence of aqueous lithium hydroxide in tetrahydrofuran and methanol provides 2-[[5-(4-tert-butoxy carbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d] pyrimidine-6-carboxylic acid of formula-6,
d) reacting the compound of formula-6 with dimethylamine in ethanol in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC HCl) and hydroxybenzotriazole (HOBt) and N-methylmorpholine provides tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethylcarbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl]amino]-3-pyridyl]piperazine-1-carboxylate compound of formula-7,
e) deprotecting the Boc moiety of compound of formula-7 using 1,4-dioxane-HCl in methylene chloride (or) aq.HCl in dioxane, followed by basification provides Ribociclib compound of formula-1,
f) treating the Ribociclib compound of formula-1 with succinic acid in tetrahydrofuran provides Ribociclib succinate of formula-1a.

The second aspect of the present invention is to provide novel intermediate compounds, which are useful in the preparation of Ribociclib compound of formula-1.
The said novel intermediate compounds are represented by the following structural formulas:

Formula-3 Formula-5
Wherein, ‘R’ = C1-C4 alkyl;

Formula-6

The present invention i.e., process for the preparation of Ribociclib succinate compound of formula-1a is schematically represented in Scheme-2 as below:

Scheme-2:

The alternate novel processes for the preparation of Ribociclib succinate compound of formula-1a is schematically represented in the following schemes:

Scheme-3:

Scheme-4:

Scheme-5:

Scheme-6:

The best mode of carrying out the present invention was illustrated by the below mentioned examples. These examples provides as illustration only and hence should not be construed as limitation of the scope of the invention.
Examples:
Exampe-1: Preparation of methyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d] pyrimidine-6-carboxylate (Formula-3)
Methanol (500 mL) and 2-chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid (2) (25.0g, 0.0943 moles) were charged into 1L four necked round bottomed flask under nitrogen atmosphere, and stirred of 5-10 min to get brown colored suspension. Reaction mass was cooled to 0±50C. Thionyl chloride (24.7g, 0.2075 moles) was added dropwise to the reaction mass through addition funnel by maintaining mass temperature at 0 ±5°C and then stirred for 25-30 min. Reaction mass temperature was raised to 65±5°C and stirred for 13-14h for reaction completion.
After completion of reaction (by TLC) solvent was distilled off under vacuum on rotavapor at 50°C to yield brown colored solid. The resulting crude was suspended in DM water (500 mL) and stirred for 5-10min at 25-35°C to get brown colored suspension. pH of the resulting suspension was adjusted to 8.0-8.5 with saturated aqueous sodium bicarbonate solution (64.0 mL) and stirred for 20-30 min. Product was filtered off under suction with the help of DM water (250 mL). The wet product was dried in hot air oven at 55-60°C and purified by flash chromatography to afford title compound. Wt. of the product 16.5g (63.0% by theory).

Example-2: Preparation of methyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate (Formula-5)
Toluene (96 mL) and 4-(6-amino-pyridine-3-yl)-piperazine-1-carboxylic acid tert-butyl ester (4, 8.8g, 0.0315 moles) were charged into 500 mL four necked round bottomed flask under nitrogen atmosphere at 30±5°C and stirred for 5-10 min to get brown colored suspension. Reaction mass was cooled to 0±5°C. Lithium hexamethyldisilazane 1M solution in THF (60.0 mL, 0.060 moles) was added dropwise to the reaction mass through addition funnel by maintaining the reaction mass temperature at 0 ±5°C and stirred the reaction mass for 15 min to get clear brown colored solution. The suspension of methyl 2-chloro-7-cyclopentyl pyrrolo[2,3-d]pyrimidine-6-carboxylate (3, 8.0g, 0.0286 moles) in 64.0 mL of toluene was added to the reaction mass at 0 ±5°C. Reaction mass temperature was raised to 25-35°C and stirred for 1h for reaction completion.
After completion of reaction (by TLC), aq. sodium bicarbonate solution (8.0g of sodium bicarbonate was dissolved in 96 mL of DM water) and DM water (96 mL) were added to the above reaction mass and stirred for 10-15 min. Layers were separated. Organic layer was washed with DM water (96 mL) and layers were separated. Organic layer was dried over sodium sulphate and filtered. Solvent was distilled off from filtrate completely under vacuum at 50-55°C on rotavapor to obtain brown colored solid. The solid was leached with ethyl acetate (24.0 mL) at 30 ± 5°C to afford title compound as pale brown colour solid. Weight of the product: 10.1g (67.6% by theory).

Example-3: Preparation of 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid (Formula-6)
Methanol (50.0 mL), tetrahydrofuran (100.0mL) and methyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate (5) (5.0g, 0.0096 moles) were charged into 250 mL four necked round bottomed flask at 30±5°C and stirred for 5-10 min to get pale yellow colored suspension. Aq.Lithium hydroxide solution (1.21g, 0.0288 moles, dissolved in DM water (5.0 mL)) was added dropwise to the reaction mass through addition funnel and stirred the reaction mass for 1h for reaction completion. After completion of reaction (by TLC), solvent was distilled off under vacuum on rotavapor at 45°C to yield yellow colored solid. The resulting crude was suspended in DM water (200 mL) and stirred for 5-10min at 25-35°C to get yellow colored suspension. pH of the resulting suspension was adjusted to 6.0-6.5 with aqueous hydrochloric acid solution (4 mL Conc.Hydrochloric acid was diluted with 36 mL of DM water) and stirred for 1h. Product was filtered off under suction with the help of DM water (10 mL). The wet product was dried in hot air oven at 60-65°C to afford title compound. Weight of the product: 4.8g (98.76% by theory).

Example-4: Preparation of tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethyl carbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl]amino]-3-pyridyl]piperazine-1-carboxylate (Formula-7)
Methylene chloride (20 mL) and 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid (6, 1.0g, 0.00197 moles) were charged into 100 mL four necked round bottomed flask under nitrogen atmosphere, and stirred for 5-10 min to get pale orange colored suspension. Reaction mass was cooled to 0±20C. HOBt (0.29g, 0.00216 moles), EDC.HCl (0.41g, 0.00216 moles) were charged into the reaction mass and stir for 5-10 min at 0 ± 2°C. Dimethylamine 2M solution in ethanol (1.1 mL, 0.282 moles) added dropwise to the reaction mass through addition funnel by maintaining mass temperature at 0 ±2°C and then reaction mass was stirred for 5-10 min. Then N-methylmorpholine (0.59g, 0.0059 moles) was added dropwise to the above reaction mass by maintaining the reaction mass temperature at 0 ± 2°C and stirred for 5-10 min. Then the reaction mass was allowed to 30±5°C and stirred for 7-8h for reaction completion.
Solvent was distilled off under vacuum on rotavapor at 45°C to yield brown colored oily crude. The resulting crude was dissolved in ethyl acetate (30 mL) and stirred for 5-10min at 25-35°C to get pale orange colored clear solution. The above solution was washed with DM water (10 mL) followed by aq.potassium carbonate solution (2g of potassium carbonate was dissolved in 10 mL of DM water) and DM water (10 mL). Layers were separated. Organic layer was dried over sodium sulphate and filtered. Solvent from the filtrate was distilled off completely under vacuum at 50°C on rotavapor to obtain pale brown colored solid. The resulting brown colored solid was leached with n-heptane (5.0 mL) at 30 ± 5°C for 1h. Product was filtered under suction with the help of n-heptane (2.0 mL). The wet product was dried in hot air oven at 50-55°C for 6h to afford title compound. Wt. of the product 0.82g (78% by theory).

Example-5: Preparation of Ribociclib (Formula-1).
Methylene chloride (7.0 mL) and tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethylcarbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl]amino]-3-pyridyl]piperazine-1-carboxylate(7) (0.7g, 0.0013 moles) were charged into 50 mL two necked round bottomed flask at 30±5°C and stirred for 5-10 min to get brown colored clear solution. 1,4-dioxane-HCl (3.1 mL, 0.01309 moles) was added as dropwise to the reaction mass through addition funnel at 30 ±5°C and stirred for 1h for reaction completion.
Reaction mass was diluted with DM water (7.0 mL) and stirred for 5-10min. Layers were separated. Aqueous layer pH was adjusted to 10-11 using aq.NaOH (0.62g of NaOH was dissolved in 12 mL of DM water) and stirred the reaction mass for 30 min at 30 ±5°C. Product was filtered under suction with the help of DM water (1.4 mL) and dried in hot air oven for 6h at 65-70°C. Weight of the product: 0.35g (62.5% by theory).

Example-6: Preparation of Ribociclib succinate (Formula-1a)
Tetrahydrofuran (7.2 mL) and Ribociclib (1), (0.3g, 0.00069 moles) were charged into 50 mL three necked round bottomed flask at 30±5°C and stirred for 5-10 min. to get cream colored suspension. Reaction mass was heated to 65-70°C and stirred for 15 min. to get clear solution. The solution of succinic acid (0.08g, 0.00072moles) in tetrahydrofuran (3 mL) was added to the above reaction mass dropwise through addition funnel at 65-70°C. After addition of succinic acid solution, cream coloured suspension was formed in the reaction mass and was stirred for 30 min. Then the reaction mass was cooled to 25-35°C and stirred for 1h. Product was filtered off under suction. Product was dried in vacuum oven at 65-70°C to afford title compound as cream coloured solid. Weight of the product: 0.35g (92.1% by theory).
,CLAIMS:1. A process for the preparation of Ribociclib succinate compound of formula-1a, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid compound of formula-2

Formula-2
with a suitable chlorinating agent in a suitable alcoholic solvent to provide alkyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-3,

Wherein, R is C1-4 alkyl group;
Formula-3
b) reacting the compound of general formula-3 with 4-(6-amino-pyridin-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4

Formula-4
in the presence of a suitable base in a suitable solvent to provide alkyl 2-[[5-(4-tert-
butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]
pyrimidine-6-carboxylate compound of general formula-5,

Wherein, R is C1-4 alkyl group;
Formula-5
c) hydrolyzing the compound of general formula-5 in the presence of a suitable base in a suitable solvent to provide 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid of formula-6,

Formula-6
d) reacting the compound of formula-6 with dimethylamine in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC HCl) and hydroxybenzotriazole (HOBt) in a suitable solvent to provide tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethylcarbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl] amino]-3-pyridyl]piperazine-1-carboxylate compound of formula-7,

Formula-7
e) deprotecting the Boc moiety of compound of formula-7 using a mineral acid in gaseous state or its aqueous solution in a suitable solvent, followed by basification to provide Ribociclib freebase of formula-1,
f) treating the Ribociclib compound of formula-1 with succinic acid in a suitable solvent to provide Ribociclib succinate compound of formula-1a.

2. The process as claimed in claim-1, wherein:
In step-a), the suitable chlorinating agent is selected from SO2Cl2, SOCl2, (COCl)2,
POCl3, PCl3 and PCl5; the suitable alcoholic solvent is selected from C1-C4
Alcohols;
In step-b), the suitable base is selected from organosilicon bases selected from lithium
hexamethyldisilazide (LiHMDS), sodium hexamethyldisilazide (NaHMDS), potassium hexamethyldisilazide (KHMDS) or mixtures thereof.
In step-c), the suitable base is selected from inorganic base such as sodium hydroxide,
lithium hydroxide, potassium hydroxide or its aqueous solution.
In step-e), the suitable acid is selected from inorganic acid such as HCl in gaseous state
or its aqueous solution.
In step a) to f), the suitable solvent is selected from ether solvents, chloro solvents,
ester solvents, alcohol solvents, ketone solvents, polar aprotic solvents, hydrocarbon solvents, nitrile solvents and polar solvents such as water or mixtures thereof.

3. A process for the preparation of Ribociclib succinate compound of formula-1a, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidin-6-carboxylic acid compound of formula-2 with thionyl chloride in methanol provides methyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-3a,
b) reacting the compound of formula-3a with 4-(6-amino-pyridine-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4 in the presence of Lithium hexamethyldisilazane in toluene provides methyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d] pyrimidine-6-carboxylate compound of formula-5a,
c) hydrolyzing the compound of formula-5a in the presence of aqueous lithium hydroxide in tetrahydrofuran and methanol provides 2-[[5-(4-tert-butoxy carbonyl piperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid of formula-6,
d) reacting the compound of formula-6 with dimethylamine in ethanol in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC HCl) and hydroxybenzotriazole (HOBt) and N-methylmorpholine provides tert-butyl 4-[6-[[7-cyclopentyl-6-(dimethylcarbamoyl)pyrrolo[2,3-d]pyrimidin-2-yl]amino]-3-pyridyl]piperazine-1-carboxylate compound of formula-7,
e) deprotecting the Boc moiety of compound of formula-7 using 1,4-dioxane-HCl in methylene chloride (or) aq.HCl in dioxane, followed by basification provides Ribociclib compound of formula-1,
f) treating the Ribociclib compound of formula-1 with succinic acid in tetrahydrofuran provides Ribociclib succinate of formula-1a.

4. Compounds having the following structural formulae:

Wherein, ‘R’ = C1-C4 alkyl;

5. A process for the preparation of alkyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-5, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid compound of formula-2 with a suitable chlorinating agent in an alcoholic solvent provides alkyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-3,
b) reacting the compound of general formula-3 with 4-(6-amino-pyridin-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4 in the presence of organosilicon base in hydrocarbon solvent provides alkyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of general formula-5.

6. The process as claimed inclaim-5, comprising of:
a) Reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidin-6-carboxylic acid compound of formula-2 with thionyl chloride in methanol provides methyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-3a,
b) reacting the compound of formula-3a with 4-(6-amino-pyridine-3-yl)-piperazine-1-carboxylic acid tert-butyl ester compound of formula-4 in the presence of Lithium hexamethyldisilazane in toluene provides methyl 2-[[5-(4-tert-butoxycarbonylpiperazin-1-yl)-2-pyridyl]amino]-7-cyclopentyl-pyrrolo[2,3-d] pyrimidine-6-carboxylate compound of formula-5a.

7. A process for the preparation of alkyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d] pyrimidine-6-carboxylate compound of formula-3, comprising of reacting 2-chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidin-6-carboxylic acid compound of formula-2 with chlorinating agent in an alcoholic solvent provides alkyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-3.

8. The process as claimed in claim-7, comprising of reacting 2-Chloro-7-cyclopentyl-7H-pyrrolo[2,3-d]pyrimidin-6-carboxylic acid compound of formula-2 with thionyl chloride in methanol provides methyl 2-chloro-7-cyclopentyl-pyrrolo[2,3-d]pyrimidine-6-carboxylate compound of formula-3a.