BACKGROUND OF INVENTION
Ribociclib succinate (1) is a selective cyclin-dependent kinase inhibitor that help to slow the progression of cancer by inhibiting two proteins called cyclin-dependent kinase 4 and 6 (CDK4/6). It is used for the treatment of certain kinds of breast cancer and is being studied for the treatment for other drug-resistant cancers. Chemically, it is 7-cyclopentyl-N, N-dimethyl-2-(5-(piperazin-1-yl) pyridin-2-ylaminuteso)-7H-pyrrolo[2,3-D] pyrimidine-6-carboxamide succinate (1). The following patents and applications describes the synthesis of Ribociclib succinate (1) and its different salts and polymorphs.
US2012115878 discloses the synthesis of intermediates 2-chloro-7-cyclopentyl-N,
N-dimethyl-7H-pyrrolo[2,3-d] pyrimidine-6-carboxamide and 4-(6-nitro-pyridin-3-
yl)-piperazine-1-carboxylic acid tert-butyl ester used for the preparation of
Ribociclib free base (1). 2-chloro-7-cyclopentyl-N,N-dimethyl-7H-pyrrolo[2,3-
d]pyrimidine-6-carboxamide was coupled with 4-(6-nitro-pyridin-3-yl)-
piperazine-1-carboxylic acid tert-butyl ester using palladium (II) acetate, (2,2'-
bis(diphenylphosphino)-1,1'-binaphthyl) (BINAP) and cesium carbonate to form the
protected intermediate tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-
pyrrolo[2,3-d]pyrimidin-2-ylaminuteso)pyridin-3-yl)piperazine-1-carboxylate
which on deprotection with aqueous hydrochloric acid formed Ribociclib free base.
Ribociclib free base was further treated with succinic acid to form Ribociclib
succinate (1). It further discloses different forms of succinate salt of Ribociclib
including non-hydrate, hydrate forms, or mixtures thereof.
US2017342075 discloses form A of hemi-succinate, adipate, maleate and glycolate salts of Ribociclib. It further discloses the mono-succinate crystalline form-I of Ribociclib along with the XRD and DSC data.
Thus, based on prior art and literatures, very less information is available regarding stable forms of Ribociclib succinate. Hence, the present inventors hereby report an

improved process for the preparation of Ribociclib succinate (1) and its novel polymorphs which are stable by using safe and commercially viable reagents under mild reaction conditions which can be industrially feasible.
OBJECTIVE OF THE INVENTION
Accordingly, one objective of the invention is to provide an improved process for the preparation of Ribociclib succinate (1) with purity greater than 99.5% by HPLC. Another objective of the invention is to provide novel crystalline forms of Ribociclib succinate (1)
Yet, another objective of the invention is to provide a process for the preparation of novel crystalline forms of Ribociclib succinate (1)
SUMMARY OF THE INVENTION
Accordingly, in one embodiment the present invention relates to an improved process for the preparation of Ribociclib succinate (1), which comprises of the following steps:
a) coupling of 2-chloro-7-cyclopentyl-N, N-dimethyl-7H-pyrrolo[2,3-d] pyrimidine-6-carboxamide (5) with tert-butyl 4-(6-aminutesopyridin-3-yl) piperazine-1-carboxylate (4) in presence of a suitable base and isolated from a suitable protic solvent to form tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-d] pyrimidin-2-ylaminuteso) pyridin-3-yl) piperazine-1-carboxylate (3)
b) deprotecting the amine protecting group of the intermediate (3) in presence of suitable acid to form Ribociclib free base (2)
c) converting Ribociclib free base (2) to succinate salt of Ribociclib (1) using succinic acid in a suitable protic solvent.
Accordingly, the present invention provides novel crystalline forms of Ribociclib succinate (1).

In another aspect, the invention provides a process for preparation of crystalline forms of Ribociclib succinate (1) comprising the steps of:
I. contacting Ribociclib succinate (1) with a solvent or mixture of solvents;
II. optionally, heating the solvent or solvents mixture with Ribociclib
succinate (1)
III. stirring the reaction mixture at 25-30⁰C and
IV. precipitating Ribociclib succinate (1) from solvent or solvents mixture by using conventional techniques viz. slow or fast cooling, addition of crystallization solvent, distillation under reduced pressure, drying at atmospheric or reduced pressure, to obtain the desired crystalline form of Ribociclib succinate (1);
wherein the crystalline forms of Ribociclib succinate (I) produced by the process is any of polymorphic forms form I, form II, form II and form IV, each crystalline form is characterized by XRPD peaks patterns as depicted in figure-1, figure-2, figure-3 and figure-4 respectively.
wherein the solvent or solvents mixture can be selected from the protic solvents selected from the group comprising water, methanol, ethanol, propanol, isopropyl alcohol, butanol, benzyl alcohol or the like, preferably methanol, benzyl alcohol and water were used in the present invention.
In another embodiment the aprotic solvents used for the preparation of crystalline forms of Ribociclib succinate (1), was selected from the group comprising acetone, acetonitrile, nitromethane, 1,4-dioxane, diethyl ether, dichloromethane, ethyl acetate, 3-butyl acetate, N, N-dimethylformamide, methyl tertiary butyl ether, hexane, cyclohexane, toulene, tetrahydrofuran or the like, preferably acetonitrile, nitromethane, butyl acetate and dichloromethane were used in the present invention.
Yet another embodiment, the crystalline forms of Ribociclib succinate obtained in the present invention is having purity greater than 99.5% by High-performance liquid chromatography, (HPLC).

BRIEF DESCRIPTION OF DRAWINGS
Figure 1: X-Ray powder diffraction (XPRD) pattern of crystalline form I of
Ribociclib succinate (1) as prepared in example-4a
Figure 2: X-Ray powder diffraction (XPRD) pattern of crystalline form II of
Ribociclib succinate (1) as prepared in example-4b
Figure 3: X-Ray powder diffraction (XPRD) pattern of crystalline form III of
Ribociclib succinate (1) as prepared in example-4c
Figure 4: X-Ray powder diffraction (XPRD) pattern of crystalline form IV of
Ribociclib succinate (1) as prepared in example-4d
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, in one embodiment the present invention provides an improved
process for the preparation of Ribociclib succinate (1) with purity greater than or
equal to 99.5% by HPLC.
In another embodiment of the invention provides the novel crystalline forms of
Ribociclib succinate (1)
Ribociclib succinate (1) prepared in the present invention is as represented in
Scheme-1 below:

Step a) proceeds with the coupling of 2-chloro-7-cyclopentyl-N, N-dimethyl-7H-
pyrrolo[2,3-d] pyrimidine-6-carboxamide (5) with tert-butyl 4-(6-
aminutesopyridin-3-yl) piperazine-1-carboxylate (4). Intermediate (5) was added to
the reaction mass containing intermediate (4) dissolved in an aprotic solvent and a
suitable base at a temperature range of 10-30 ⁰C. Reaction completion time ranges
from 10-14 hrs. On completion of reaction, reaction mass was cooled to 10-15 0C
and suitable protic solvent was added. The aqueous layer was extracted with a
suitable aprotic solvent. The residue was then treated with a protic solvent at 60-65
0C to obtain tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-
d] pyrimidin-2-ylaminuteso) pyridin-3-yl) piperazine-1-carboxylate (3)
The suitable base used in step a) was selected from a group comprising lithium bis(trimethylsilyl)amide (LiHMDS), potassium bis(trimethylsilyl)amide (KHMDS) and sodium bis(trimethylsilyl)amide (NaHDMS) or the like; preferably lithium bis (trimethylsilyl)amide (LiHMDS) was used in the present invention.
Step b) proceeds with the deprotection of amine protecting group of tert-butyl 4-(6-
(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-d] pyrimidin-2-
ylaminuteso) pyridin-3-yl) piperazine-1-carboxylate (3). Intermediate (3) was
treated with a suitable deprotecting agent in a protic solvent. Preferably the
deprotecting agent is an acid, more preferably an organic acid. The reaction
temperature ranges from 25 to 65 0C, preferably 60 to 65⁰C. On completion of the
reaction, the reaction mass was cooled to 10-15 0C and pH was adjusted to an
optimum range in between 10 to 11 using a suitable base. The solid so formed was
then filtered and optionally treated with a protic solvent to obtain Ribociclib free
base (2).
The acid used for deprotection in step b) was selected from a group comprising of organic or inorganic acids. The organic acid may be selected form the group consisting of carboxylic acid or sulphonic acid such as trifluoroacetic acid, trifluoromethanesulphonic acid, methanesulphonic acid, formic acid, tartaric acid,

p-touenesulphonic acid or the like. The inorganic acid may be selected from the group consisting of hydrochloric acid, hydrobromic acid, sulphuric acid, phosphoric acid or the like. More preferably p-touenesulphonic acid was used in the present invention.
The base used in step b) was selected from a group comprising sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, lithium bicarbonate, cesium bicarbonate, sodium methoxide, sodium ethoxide; potassium methoxide, potassium ethoxide or the like. Preferably sodium hydroxide was used in the present invention.
Step c) involves the conversion of Ribociclib free base (2) to succinate salt of Ribociclib (1). Ribociclib free base (2) was added to a suitable protic solvent and heated to 60 to70 0C. Succinic acid was added to the reaction mass. The temperature of the reaction may range from 15-85 0C. The reaction completion time range from 1hr to 3 hr., preferably 1hr to 2 hr. The final compound was isolated from a protic solvent to obtain pure Ribociclib succinate (1).
The suitable protic solvent used in step a), step b) and step c) were selected from a group comprising of methanol, ethanol, isopropyl alcohol (IPA), n-propanol, n-butanol, water or the like, preferably methanol, water and isopropyl alcohol were used in the present invention.
The suitable aprotic solvents used in step a) were selected from a group comprising of acetone, acetonitrile, 1,4-dioxane, diethyl ether, dichloromethane, ethyl acetate, N, N-dimethylformamide, methyl tertiary butyl ether, hexane, cyclohexane, toulene, tetrahydrofuran or the like; preferably tetrahydrofuran, toulene and ethyl acetate were used in the present invention.
Ribociclib succinate (1) obtained by the above process was having purity greater than equal to 99.5% by HPLC.

In another aspect, the invention provides a process for preparation of crystalline forms of Ribociclib succinate (1) comprising the steps of:
I. contacting Ribociclib succinate (1) with a solvent or mixture of solvents;
II. optionally, heating the solvent or solvents mixture with Ribociclib succinate
(1)
III. stirring the reaction mixture at 25-30⁰C and
IV. precipitating Ribociclib succinate (1) from solvent or solvents mixture by using conventional techniques namely slow or fast cooling, addition of crystallization solvent, distillation under reduced pressure, drying at atmospheric or reduced pressure, to obtain the desired crystalline form of Ribociclib succinate (1);
In another embodiment the protic solvents used for the preparation of crystalline forms of Ribociclib succinate (1) was selected from a group comprising of water, methanol, ethanol, propanol, isopropyl alcohol, butanol, benzyl alcohol or the like, preferably methanol, benzyl alcohol and water were used in the present invention.
In another embodiment the aprotic solvents used for the preparation of crystalline forms of Ribociclib succinate (1), was selected from a group comprising of acetone, acetonitrile, nitromethane, 1,4-dioxane, diethyl ether, dichloromethane, ethyl acetate, 3-butyl acetate, N, N-dimethylformamide, methyl tertiary butyl ether, hexane, cyclohexane, toulene, tetrahydrofuran or the like, preferably acetonitrile, nitromethane, 3-butyl acetate and dichloromethane were used in the present invention.
In another aspect, the crystalline forms of Ribociclib succinate (1) obtained in the present invention was having purity greater than equal to 99.5% by HPLC.

In another aspect, the crystalline forms I, II, III and IV of Ribociclib succinate (1) may produce an X-ray diffraction (XRD) pattern as illustrated in figure 1, figure 2, figure 3 and figure 4 and whose 2 theta values are tabulated in table 1, table 2, table 3 and table 4 below.
The crystalline form I of Ribociclib succinate (1) may produce an X-Ray diffraction (XRD) pattern comprising one or more of the following characteristic reflections: 4.51 ,10.57, 13.00, 13.82, 16.13, 16.44, 18.18, 19.95, 21.41, 21.93, 23.42, 25.18 and 26.23±2θ or that produces an X-ray powder diffraction pattern further comprising one or more of the following additional reflections at 8.40, 8.84, 9.23, 11.91, 24.39, 25.18, 27.88, 28.65, 29.83, 30.52 and 34.06±2θ or that produces an X-ray powder diffraction pattern comprising the 2 theta values tabulated in Table-1
The crystalline form II of Ribociclib succinate (1) may produce an X-Ray diffraction (XRD) pattern comprising one or more of the following characteristic reflections at 6.45, 7.60, 11.19, 12.62, 13.92, 14.68, 15.13, 16.54, 17.52, 18.46, 18.95, 19.30, 19.78, 20.58, 21.24, 21.79, 22.19, 23.72, 25.16, 25.34, 25.58, 26.26, 26.62, 28.05, 28.59, 30.05 and 30.61±2θ or that produces an X-ray powder diffraction pattern further comprising one or more of the following additional reflections at 10.09, 24.83, 29.37, 31.18, 32.04, 34.21 and 35.06 ±2θ or that produces an X-ray powder diffraction pattern comprising the 2 theta values tabulated in Table-2
The crystalline form III of Ribociclib succinate (1) may produce an X-Ray diffraction (XRD) pattern comprising one or more of the following characteristic reflections at 4.41, 6.91, 11.16, 12.37, 12.76, 14.86, 15.79, 17.55, 18.13, 19.22, 19.68, 21.16, 21.43, 21.81, 22.51 and 23.79 ±2θ or that produces an X-ray powder diffraction pattern further comprising one or more of the following additional reflections at 4.73, 6.15, 8.85, 9.26, 9.63, 10.11, 10.59, 13.49, 24.65, 25.86, 29.41,

30.18, 30.76, 31.60 and 36.02 ±2θ or that produces an X-ray powder diffraction pattern comprising the 2 theta values tabulated in Table-3
The crystalline form IV of Ribociclib succinate (1) may produce an X-Ray diffraction (XRD) pattern comprising one or more of the following characteristic reflections at 5.22,9.18, 9.60, 10.20, 10.44, 13.81, 16.88, 17.30, 17.83, 18.08, 20.32, 20.79, 21.41, 22.70, 23.05, 23.79 and 25.15 ±2θ or that produces an X-ray powder diffraction pattern further comprising one or more of the following additional reflections at 4 .83, 8.25, 11.85, 12.48, 12.96, 14.31, 15.44, 15.75, 16.620, 18.37, 19.33, 24.97, 26.02, 26.88, 27.39, 28.10, 28.40, 29.86, 32.30, 33.48, 37.48 and 39.67 ±2θ or that produces an X-ray powder diffraction pattern comprising the 2 theta values tabulated in Table-4
In another embodiment,
-the crystalline form I of Ribociclib succinate (1) is obtained by heating
Ribociclib succinate in methanol and isolating by cooling to 25-30°C
-The crystalline form II of Ribociclib succinate (1) is obtained by stirring in
benzyl alcohol at 25-30°C for 10hrs to 12hrs
-The crystalline form III of Ribociclib succinate (1) is obtained by 3-butyl
acetate at 25-30°C for 10hrs to 12hrs
- the crystalline form IV of Ribociclib succinate (1) is obtained by heating
Ribociclib succinate in methanol and isolating by distilling off the solvent
under vacuum
The X-Ray diffraction data of the Ribociclib succinate forms obtained are tabulated
below

The following examples further illustrate the present invention, but should not be construed in anyway, as to limit its scope.
EXAMPLE -1
Preparation of tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-
pyrrolo[2,3-d] pyrimidin-2-ylaminuteso) pyridin-3-yl) piperazine-1-
carboxylate (3)
209.5g of tert-butyl 4-(6-aminutesopyridin-3-yl) piperazine-1-carboxylate (4) was added to 1000mL of toulene and stirred for 10-15 mins. The reaction mixture was then cooled to 10-15 0C and a solution of 1.0M lithium bis(trimethylsilyl)amide in tetrahydrofuran was added to the reaction mass. The temperature of the reaction mixture was raised to 20-35 0C and stirred for 1hr. 100g of 2-chloro-7-cyclopentyl-N, N-dimethyl-7H-pyrrolo[2,3-d] pyrimidine-6-carboxamide (5) was added to the reaction mass and stirred for 22-24hrs at 25-30 0C. On completion of reaction, the reaction mass was cooled to 10-15 0C and water was added. The temperature of the

reaction mixture was again raised to 25-30 0C and the layers were separated. The aqueous layer was extracted with ethyl acetate and the total organic layer was distilled under vacuum below 50 0C. The residue was then treated with methanol and heated for 1hr at 60-65 ⁰C. The reaction mixture was cooled to 5-10 0C and filtered. The solid so obtained was washed with methanol and dried below 650C to obtain tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-d] pyrimidin-2-ylaminuteso) pyridin-3-yl) piperazine-1-carboxylate (3) Yield: 60% Purity: 97.0%
EXAMPLE-2
Preparation of Ribociclib free base (2)
100g of tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-d] pyrimidin-2-ylamino) pyridin-3-yl) piperazine-1-carboxylate (3) was added to 1000mL of isopropyl alcohol and acidified with p-toluenesulfonic acid at 25-30 0C. The reaction mixture was heated at 60-65 0C for 8-10 hrs. On completion of reaction, the reaction mixture was cooled to10-15 0C and the pH was adjusted to 10-11 using 20% sodium hydroxide solution. The reaction mixture was stirred for 1hr at 25-30 0C and filtered to obtain the solid. The solid so obtained was washed with water and dried below 65 0C to obtain Ribociclib free base (2) Yield: 86% Purity: 98.0%
EXAMPLE-3
Preparation of Ribociclib succinate (1)
100g of Ribociclib free base (2) was dissolved in 2500mL of methanol, stirred for 10 minutes and heated to 60-65 0C. 28.5g of succinic acid was added to the reaction mass and the reaction mass heated to 75-80 0C for 2hrs. The reaction mixture was cooled to 15-20 0C, stirred for 2hrs and filtered. The solid so obtained was then washed with 100 mL of cold methanol (0-50C) and dried below 65 0C to obtain Ribociclib succinate (1)

Yield: 90%
Purity: 99.85%
XRD: figure 1; table 1
EXAMPLE-4
a) Preparation of crystalline form of Ribociclib succinate (1)
5.0g of Ribociclib succinate (1) was suspended in 125mL of methanol at 25-30 0C, heated to 60-65 0C and stirred for 10-15 mins. 2.0mL of water was added to the reaction mixture and stirred to form a clear solution. The clear solution was then cooled to 25-30 0C and stirred for 30 mins to form a solid mass. The solid so formed was filtered, washed with 10mL of methanol and dried under vacuum for 15 mins to obtain crystalline of Ribociclib succinate (1) Yield: 71% XRD: figure 1; table 1
b) Preparation of crystalline form of Ribociclib succinate (1)
1.0g of Ribociclib succinate (1) was charged with 20mL of benzyl alcohol at 25-30 0C and stirred for 10-15mins to form a clear solution. The reaction mixture was maintained for 12hrs at 25-30 0C. The slurry so formed was then filtered and the residue was washed with 2mL of benzyl alcohol. The wet cake so obtained was dried under vacuum for 10-15 mins to obtain crystalline Ribociclib succinate (1) Yield: 73% XRD: figure 2; table 2
c) Preparation of crystalline form of Ribociclib succinate (1)
1.0g of Ribociclib succinate (1) was charged 25mL of 3-butyl acetate and stirred for 10 mins at 25-30 0C. The reaction mixture was maintained for 12hrs at 25-30 0C. The slurry so formed was then filtered and the residue so obtained was dried under vacuum for 15 mins to obtain crystalline form of Ribociclib succinate (1) Yield: 78% XRD: figure 3; table 3

d) Preparation of crystalline form of Ribociclib succinate (1)
3.0g of Ribociclib succinate (1) was charged in 300mL of methanol and stirred for
30 mins at 25-30 0C. The reaction mixture was then heated to 60-65 0C for 30mins
to form a clear solution. The clear solution was then distilled off under vacuum to
obtain crystalline form of Ribociclib succinate (1)
Yield: 75%
XRD: figure 4; table 4

We claim:
1. A process for the preparation of Ribociclib succinate (1) having purity of greater than 99.5%
said process comprising the steps of;
a) coupling of 2-chloro-7-cyclopentyl-N, N-dimethyl-7H-pyrrolo[2,3-d] pyrimidine-6-carboxamide (4)
with tert-butyl 4-(6-aminutesopyridin-3-yl) piperazine-1-carboxylate (5)
in presence of suitable base to form tert-butyl 4-(6-(7-cyclopentyl-6-(dimethyl carbamoyl)-7H-pyrrolo[2,3-d] pyrimidin-2-ylaminuteso) pyridin-3-yl) piperazine-1-carboxylate (3);

b) deprotecting intermediate (3) in presence of suitable acid to form Ribociclib free base (2);
c) converting Ribociclib free base (2) to succinate salt of Ribociclib (1) using succinic acid in a suitable protic solvent.
2. The process as claimed in claim 1, wherein the suitable base employed in step
a) is selected from the group comprising lithium bis(trimethylsilyl)amide
(LiHMDS), potassium bis(trimethylsilyl)amide (KHMDS) and sodium
bis(trimethylsilyl)amide (NaHDMS) or the like.
3. The process as claimed in claim 1, wherein the suitable acid employed in step
b) is selected from the group comprising sulphuric acid, nitric acid,
hydrochloric acid, orthophosphoric acid, p-toluene sulfonic acid or the like.
4. The process as claimed in claim 1, wherein the suitable protic solvents employed in step c) is selected from the group comprising water, methanol, ethanol, isopropyl alcohol (IPA), n-propanol, n-butanol or the like.
5. A process for preparation of crystalline forms of Ribociclib succinate (1) with more than 99.5% purity comprising the steps of:

said process comprising the steps of;
a) contacting Ribociclib succinate (1) with a solvent or mixture of solvents;
b) optionally, heating the solvent or solvents mixture with Ribociclib succinate (1)
c) stirring the reaction mixture at 25-30⁰ C and
d) precipitating Ribociclib succinate (1) from solvent or solvents mixture by using conventional techniques viz. slow or fast cooling, addition of crystallization solvent, distillation under reduced pressure, drying at atmospheric or reduced pressure, to obtain the desired crystalline form of Ribociclib succinate (1);
-wherein the solvent or solvents mixture can be selected from protic
or aprotic solvents. The suitable protic solvent is selected from a
group comprising water, methanol, ethanol, isopropyl alcohol (IPA),
n-propanol, n-butanol, benzyl alcohol or the like. The suitable aprotic
solvents employed is selected from a group comprising acetone,
acetonitrile, nitromethane, 1,4-dioxane, diethyl ether,
dichloromethane, ethyl acetate, 3-butyl acetate, N, N-dimethylformamide, methyl tertiary butyl ether, hexane, cyclohexane, toulene, tetrahydrofuran or the like.
-wherein the crystalline forms of Ribociclib succinate (1) produced by the process is any of polymorphic forms form I form II, form III and form IV, each polymorphic form is characterized by XRPD peaks as depicted in figure-1, figure-2, figure-3 and figure-4 respectively.

6. A process for preparing crystalline form I of Ribociclib succinate (1) characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at value 4.51, 8.40, 8.84, 9.23, 10.57, 11.91, 13.00, 13.82, 16.13, 16.44, 18.18, 19.95, 21.41, 21.93, 23.42, 24.39, 25.18, 26.23, 27.88, 28.65, 29.83, 30.52 and 34.06 ±0.2 degrees 2 theta and by X-ray powder diffraction pattern as shown in figure 1, comprising the steps of heating Ribociclib succinate in methanol and isolating form I of Ribociclib succinate (1) by cooling to 25-30⁰ C.
7. The process as claimed in claim 5, wherein said crystalline form II of Ribociclib succinate (1) obtained by the process is characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 6.45, 7.60, 10.09, 11.19, 12.62, 13.92, 14.68, 15.13, 16.54, 17.52, 18.46, 18.95, 19.30, 19.78, 20.58, 21.24, 21.79, 22.19, 23.72 ,24.83, 25.16, 25.34, 25.58, 26.26, 26.62, 28.05, 28.59, 29.37, 30.05, 30.61, 31.18 ,32.04, 34.21 and 35.06 ± 0.2 degrees 2 theta and which has X-ray powder diffraction pattern as shown in figure 2.
8. The process as claimed in claim 5, wherein said crystalline form III of Ribociclib succinate (1) obtained by the process is characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 4.41, 4.73, 6.15,6.91, 8.85, 9.63, 10.11, 10.59, 11.16, 12.37, 12.76, 13.49, 14.86, 15.79, 17.55, 18.13, 19.22, 19.68, 21.16, 21.43, 21.81, 22.51, 23.79, 24.65, 25.86, 29.41, 30.18, 30.76, 31.60 and 36.02 ±0.2 degrees 2 theta and which has X-ray powder diffraction pattern as shown in figure 3.
9. The process as claimed in claim 5, wherein said crystalline form IV of Ribociclib succinate (1) obtained by the process is characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 4.83, 5.22, 8.25, 9.18, 9.60, 10.20, 10.44, 11.85, 12.48, 12.96, 13.81, 14.31,, 15.44,, 15.75, 16.60, 16.88, 17.30, 17.83, 18.08, 18.37, 19.33, 20.32, 20.79, 21.41, 22.70, 23.05, 23.79, 24.97, 25.15, 26.02, 26.88, ,27.39, 28.10, 28.40, 29.86, 32.30, 33.48, 37.48 and 39.67 ± 0.2 degrees 2 theta and which has X-ray powder diffraction pattern as shown in figure 4.

10. A process for preparing crystalline form II of Ribociclib succinate (I) characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 6.45, 7.60, 10.09, 11.19, 12.62, 13.92, 14.68, 15.13, 16.54, 17.52, 18.46, 18.95, 19.30, 19.78, 20.58, 21.24, 21.79, 22.19, 23.72 ,24.83, 25.16, 25.34, 25.58, 26.26, 26.62, 28.05, 28.59, 29.37, 30.05, 30.61, 31.18 ,32.04, 34.21 and 35.06 ± 0.2 degrees 2 theta and which has X-ray powder diffraction pattern as shown in figure 2, comprising the steps of by stirring in benzyl alcohol at 25-30⁰C for 10hrs to 12hrs and isolating form II by filtering the solid under reduced pressure
11. A process for preparing crystalline form III, Ribociclib succinate (I) characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 4.41, 4.73, 6.15,6.91, 8.85, 9.63, 10.11, 10.59, 11.16, 12.37, 12.76, 13.49, 14.86, 15.79, 17.55, 18.13, 19.22, 19.68, 21.16, 21.43, 21.81, 22.51, 23.79, 24.65, 25.86, 29.41, 30.18, 30.76, 31.60 and 36.02 ±0.2 degrees 2 theta and by X-ray powder diffraction pattern as shown in figure 3, comprising the steps of stirring Ribociclib succinate 3-butyl acetate and isolating form III by filtering the solid under vacuum
12. A process for preparing crystalline form IV, Ribociclib succinate (I) characterized by X-ray powder diffraction (XRPD) comprising one or more of the reflections at values 4.83, 5.22, 8.25, 9.18, 9.60, 10.20, 10.44, 11.85, 12.48, 12.96, 13.81, 14.31,, 15.44,, 15.75, 16.60, 16.88, 17.30, 17.83, 18.08, 18.37, 19.33, 20.32, 20.79, 21.41, 22.70, 23.05, 23.79, 24.97, 25.15, 26.02, 26.88, ,27.39, 28.10, 28.40, 29.86, 32.30, 33.48, 37.48 and 39.67 ± 0.2 degrees 2 theta and X-ray powder diffraction pattern as shown in figure 4, comprising the steps of heating Ribociclib succinate (I) in methanol and isolating form IV by distillation under hot condition.