CLIAMS:1) Process for the preparation of crystalline Form-SL of Lenalidomide (I),
(I)
comprising the steps of:
a) Providing a solution of 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione (II)
(II)
in methanol;
b) Subjecting the solution obtained from step a) to selective catalytic hydrogenation;
c) Treating the reaction product obtained in step b) with methanol or solvent mixture containing methanol as one of the solvent;
d) Isolating the crystalline Form-SL of Lenalidomide.

2) Process for the preparation of crystalline Form-SL of Lenalidomide (I) according to claim 1, wherein selective catalytic hydrogenation is carried out in presence of catalyst Pd/C or Raney Ni, at temperature ranging between 20-35°C.

3) Process for the preparation of crystalline Form-SL of Lenalidomide (I) according to claim 1, wherein step c) solvent mixture contains other organic solvent selected from C2-C4 alcohol or C2-C5 ester solvent.

4) Process for the preparation of crystalline Form-SL of Lenalidomide (I) according to claim 3, wherein treatment of the reaction product with methanol or solvent mixture containing methanol as one of the solvent, comprises-
a) providing the solution of the reaction mass obtained in step b) of claim-1 with methanol or solvent mixture containing methanol as one of the solvent;
b) heating the reaction mixture to recover 50 % or more volume of the solvent, without reaching the stage of complete dryness;
c) optionally repeating the steps a) and b).

5) Process for the preparation of crystalline Form-SL of Lenalidomide (I) according to claim 1, wherein isolation of the crystalline Form-SL of Lenalidomide, comprises the steps of-
a) optionally cooling the reaction mixture to a temperature of 40 °C or below;
b) filtering the reaction mixture;
c) washing the reaction mass with an alcoholic or ester solvent;
b) drying the wet solid material to obtain crystalline Form-SL of Lenalidomide.

6) Crystalline Form-SL of Lenalidomide (I) obtained by the process according to any of the claims 1 to 5.

7) Crystalline Form-SL of Lenalidomide characterized by X-ray powder diffraction pattern comprising of at least seven 2?° peaks selected from 7.061, 12.860, 14.284, 16.531, 18.698, 27.925, 33.212, 34.187, 35.253, 35.921 and 38.765 ± 0.01 2?°; a single un-split 2?° peak at 7.813± 0.01 2?°; and a three-way-split 2?° peak at 20.467 ± 0.10 2?°.

8) Crystalline Form-SL of Lenalidomide according to claim-7, further characterized by DSC isotherm having an endothermic peak at 268 °C.

9) Substantially pure crystalline Form-SL of Lenalidomide according to claim-7, with HPLC purity of at least 99.8 % and moisture content less than 0.2 % (by KF method).

10) A pharmaceutical composition comprising crystalline Form-SL of Lenalidomide obtained by the process according to any of the preceding claims, and at least one or more pharmaceutically acceptable excipients. ,TagSPECI:FIELD OF THE INVENTION

The present invention relates to a process for preparation of crystalline Form-SL of Lenalidomide (I).
(I)
The invention also relates to crystalline Form-SL obtained by the process of the present invention, the said Form-SL being substantially pure and characterized by X-ray powder diffraction pattern comprising of at least seven 2?° peaks selected from 7.061, 12.860, 14.284, 16.531, 18.698, 27.925, 33.212, 34.187, 35.253, 35.921 and 38.765 ± 0.01 2?°; a single un-split 2?° peak at 7.813± 0.01 2?°; and a three-way-split 2?° peak at 20.467 ± 0.01 2?°.
The invention further relates to pharmaceutical compositions comprising crystalline Form-SL of Lenalidomide, which may be useful for the treatment of cancer.

INTRODUCTION

Lenalidomide is an immunomodulatory agent with antiangiogenic and antineoplastic properties. Lenalidomide is chemically known as 3-(4-amino-l-oxo-1,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione of Formula I.
(I)
Lenalidomide has been used to successfully treat both inflammatory disorders and cancers for the past 10 years. Lenalidomide is a thalidomide analogue used in the treatment of multiple cancers and is sold under the trade name REVLIMID® by Celgene.
REVLIMID is indicated for the treatment of patients with- i) Multiple myeloma (MM), in combination with dexamethasone, in patients who have received at least one prior therapy; ii) Transfusion-dependent anemia due to low- or intermediate-1-risk myelodysplastic syndromes (MDS) associated with a deletion 5q abnormality with or without additional cytogenetic abnormalities; iii) Mantle cell lymphoma (MCL) whose disease has relapsed or progressed after two prior therapies, one of which included Bortezomib. Lenalidomide is off-white to pale-yellow solid powder known to exist as a hemihydrate form.
Lenalidomide and its process were disclosed initially in U.S. patent no. 5,635,517. Further various polymorphic forms of Lenalidomide have been disclosed in US 2005/0096351 Al by Jaworsky et al. Polymorphic forms of Lenalidomide disclosed in this application are designated as Form-A, Form-B, Form-C, Form-D, Form-E, Form-F, Form-G and Form-H. It is reported in this patent application that the polymorphic Form-A is anhydrous form and polymorphic Form-B is hemi hydrate. Polymorphic Form-C is disclosed to be a hemi- solvate of acetone and Form-D is solvated with water and acetonitrile. Form-E is apparently dihydrate and Form-F is an unsolvated material obtained by dehydration of Form-E. Form-G is also an unsolvated material obtained by slurrying Form-B and Form-E in THF solvent. Form-H is a crystalline solid hydrated with about 0.26 moles of water. Lenalidomide in its hemihydrate form exists as stable crystalline-Form-B which has been described to be the preferred polymorphic form which has been used in the formulation of API into drug product.
Amorphous polymorphic form of Lenalidomide and its methane sulfonic acid salt have been reported in patent application WO 2009/114601 A2. Further strong acid addition salts of Lenalidomide and their polymorphic forms are disclosed in patent application WO 2009/111948 Al. Konakanchi et al in WO2011/111053 A1 have disclosed preparation of anhydrous lenalidomide Form I utilizing either Azeotropic distillation in hydrocarbon solvents or distilling in nitrile or DMF etc., while the prior reduction step is carried out at a temperature exceeding 50°C or more beside also using formic acid or its salt resulting in large number of impurities formation and subsequently involving further multiple-step purifications .
Lenalidomide being an important anticancer therapeutic agent, additional and improved ways of preparing Lenalidomide and its polymorphs may be of immense value to pharmaceutical science and the healthcare of cancer patients. Further exploring new forms of pharmaceutically active / useful compounds such as Lenalidomide may provide an opportunity to improve the drug performance characteristics of such products. Hence, there exists a need for the further development of new stable crystalline form of Lenalidomide and economically viable processes for its preparation, which may be commercially up scalable, safer for handling, less time consuming and with better and consistent quality parameters.
The inventors of this application have developed a commercially viable process involving room temperature conditions during reduction steps, which provides a highly pure Lenalidomide and its stable polymorphic crystalline form, designated as Form-SL, which is non-hygroscopic and has easy handling properties. The process of this invention provides the crystalline Form-SL of Lenalidomide in a substantially pure form, which is free from any detectable impurities/ contamination of any other previously known crystalline forms of Lenalidomide.

SUMMARY OF INVENTION
Particular aspects of the present invention relate to a process for preparation of crystalline Form-SL of Lenalidomide (I). Crystalline Form-SL of Lenalidomide obtained by the process of the present invention is found to be substantially pure and stable.
(I)
In one aspect according to the present invention, it provides process for the preparation of crystalline Form-SL of Lenalidomide (I), comprising the steps of:
a) Providing a solution of 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione (II) in methanol;
(II)
b) Subjecting the solution obtained from step a) to selective hydrogenation;
c) Treating the reaction product obtained in step b) with methanol or solvent mixture containing methanol as one of the solvent;
d) Isolating the crystalline Form-SL of Lenalidomide.

In another aspect, the present invention provides crystalline Form-SL of Lenalidomide, which is characterized by-
i. X-ray powder diffraction pattern comprising of at least seven 2?° peaks selected from 7.061, 12.860, 14.284, 16.531, 18.698, 27.925, 33.212, 34.187, 35.253, 35.921 and 38.765 ± 0.01 2?°; a single un-split 2?° peak at 7.813± 0.01 2?°; and a three-way-split 2?° peak at 20.467 ± 0.10 2?°;
ii. DSC isotherm having an endothermic peak at 268 °C;
iii. HPLC purity of at least 99.8 % ;
iv. Moisture content less than 0.2 % (by KF method).
The crystalline Form-SL of Lenalidomide as obtained by the process of the present invention is free from any detectable impurities/ contamination of any other previously known crystalline forms of Lenalidomide.
In a further aspect, the present application also relates to a pharmaceutical composition comprising crystalline Form-SL of Lenalidomide of the present application and at least one or more pharmaceutically acceptable excipients. Such composition is substantially free of any other previously known crystalline forms of Lenalidomide. Further particular aspects of the invention are detailed in the description part of the specification, wherever appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an example of X-ray powder diffraction (“XRPD”) pattern of crystalline Form-SL of Lenalidomide
Fig. 2 is an example of a Differential Scanning Calorimetry (“DSC”) curve of Form-SL of Lenalidomide

DETAILED DESCRIPTION
As set forth herein, embodiments of the present invention relate to a reproducible and efficient process for preparation of crystalline Form-SL of Lenalidomide (I) in high yield. Crystalline Form-SL of Lenalidomide obtained by the process of the present invention is found to be substantially pure and stable.
A substantially pure product in the context of the present invention means product having purity exceeding 99.8% by HPLC.
In view of mention of free from any detectable impurities/ contamination in the context of the present invention means- total impurities not exceeding 0.2% by HPLC.
In one embodiment of the present application, it provides a process for the preparation of crystalline Form-SL of Lenalidomide (I), comprising the steps of:
(I)
a) Providing a solution of 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione (II) in methanol;
(II)
b) Subjecting the solution obtained from step a) to selective catalytic hydrogenation;
c) Treating the reaction product obtained in step b) with methanol or solvent mixture containing methanol as one of the solvent;
d) Isolating the crystalline Form-SL of Lenalidomide.

The individual steps of the process according to the present invention for preparing crystalline Form-SL of Lenalidomide (I) are detailed separately herein below.

Step a) comprises providing a solution of 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione in methanol;

3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione is initially added to 25-75 times (v/w) methanol to provide a heterogeneous reaction mass. This heterogeneous mass after stirring for 10-20 mins is then added to 150-250 volumes of methanol w.r.t. weight of 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione initially taken. Optionally the reaction mixture may be degassed by using Nitrogen gas purging for suitable duration of time.

Step b) comprises subjecting the solution obtained from step a) to selective catalytic hydrogenation;

The solution obtained from step a) is subjected to selective hydrogenation in presence of catalyst Pd/C or Raney Ni, at room temperature (20-35 °C). Addition of the catalyst to the reaction mixture may be carried out along with continuous nitrogen purging. Treatment of reaction mixture with Hydrogen gas may be carried out at 40-60 PSI, which shall be maintained for time duration of 10 mins- 1 hr. Hydrogen gas treatment may be repeated as per the progress of the reaction which may be monitored intermittently by HPLC. Crude form of Lenalidomide is achieved in reaction mixture at the end of this reaction.

Step c) comprises treating the reaction product obtained in step b) with methanol or solvent mixture containing methanol as one of the solvent;

The reaction product obtained from step b) may be subjected to filtration, which may be carried out using any conventional technique known to the person skilled in art, such as but not limiting to the use of celite bed (wherein washing of the celite bed with methanol may also be carried out post filtration). Filtrate provides the solution of the reaction product of step b) with methanol. The reaction mixture is heated to recover at least 50 % or more volume of the solvent. It’s worth noting that recovery of the solvent from the reaction mixture is stopped well before reaching the stage of complete dryness, so as to achieve the desired end product characteristics.

In further embodiment of the present application, another solvent is added to the concentrated reaction mixture obtained after partial recovery of the methanol solvent, thereby providing reaction mass with solvent mixture containing methanol as one of the solvent. The other solvent besides methanol may comprise of organic solvent selected from C2-C4 alcohol or C2-C5 ester solvent. In a preferred embodiment, the other organic solvent is selected to be isopropyl alcohol (IPA) or ethyl acetate. The reaction mass with solvent mixture containing methanol as one of the solvent, is heated to recover at least 50 % or more volume of the solvent, wherein, recovery of the solvent from the reaction mixture is stopped well before reaching the stage of complete dryness.

Solvent recovery mentioned above may be optionally carried out under reduced pressure conditions and at temperature of 50 °C or above. As per the end product characteristic requirements and matching the desired purity level of the end product, this cycle of addition of solvent to the concentrated reaction mixture and again recovering the solvent to provide concentrated reaction mass may be repeated.

Step d) comprises recovering the crystalline Form-SL of Lenalidomide.

The concentrated reaction mixture obtained from step c) may be optionally cooled to a temperature of 40 °C or below, if in the previous step its temperature was raised to a higher scale. The concentrated reaction mixture is filtered under vacuum and given washing with a C1-C4 alcoholic or C2-C5 ester solvent. The wet solid material is then dried at a temperature of 50-65 °C, wherein drying may be optionally carried out under reduced pressure conditions. Drying may be carried out for time duration ranging from 3-20 hrs depending upon achieving the anhydrous end-product as crystalline Form-SL of Lenalidomide.
Process of recovering the crystalline Form-SL of Lenalidomide may further comprise processes but not limited to conventional processes including scrapping and if required filtering from slurry which may be carried out at room temperature for the suitable durations to retain the crystalline form characteristics of Form-SA.
The process related impurities that appear in the impurity profile of Lenalidomide may be substantially removed by the process of the present invention resulting in the formation of crystalline Form-SL of high purity, without involving any cumbersome processes like acid-base treatment. The merit of the process according to the present invention resides in that - product isolated after drying is directly obtained as crystalline Form-SL of Lenalidomide. There is no involvement of any prior art known form to obtain the crystalline Form-SL of Lenalidomide according to the process of the present invention, thereby reducing any chance of polymorphic contamination.
The crystalline Form-SL of Lenalidomide described herein may be characterized by X-ray powder diffraction pattern (XRPD) and Thermal techniques such as differential scanning calorimetry (DSC) analysis. The samples of crystalline Form-SL of Lenalidomide were analyzed by XRPD on a Bruker AXS D8 Advance Diffractometer using X-ray source - Cu Ka radiation using the wavelength 1.5418 Å and lynx Eye detector. DSC was done on a Perkin Elmer Pyris 7.0 instrument. Illustrative examples of analytical data for the crystalline Form-SL of Lenalidomide obtained in the examples are set forth in the Figs. 1-2.
Another embodiment of the present invention provides crystalline Form-SL of Lenalidomide obtained by the process according to the present invention. Form-SL of Lenalidomide is found adequately stable to handle and store for longer time without any significant or measurable change in its morphology and physicochemical characteristics. Crystalline Form-SL of Lenalidomide obtained according to the process of the present invention is substantially pure i.e. it is found to have final API HPLC purity of more than 99.8 % w/w, with moisture content of not more than 0.2% (by KF method).
Crystalline Form-SL of Lenalidomide, is a non-hygroscopic crystalline solid, which is further characterized by-
i. X-ray powder diffraction pattern comprising of at least seven 2?° peaks selected from 7.061, 12.860, 14.284, 16.531, 18.698, 27.925, 33.212, 34.187, 35.253, 35.921 and 38.765 ± 0.01 2?°; a single un-split 2?° peak at 7.813± 0.01 2?°; and a three-way-split 2?° peak at 20.467 ± 0.01 2?°;
ii. DSC isotherm having an endothermic peak at about 268 °C.
Minor variations in the observed 2 ?° angles values may be expected based on the analyst person, the specific XRPD diffractometer employed and the sample preparation technique. Further possible variations may also be expected for the relative peak intensities, which may be largely affected by the non-uniformity of the particle size of the sample. Hence, identification of the exact crystalline form of a compound should be based primarily on observed 2 theta angles with lesser importance attributed to relative peak intensities. The 2 theta diffraction angles and corresponding d-spacing values account for positions of various peaks in the X-ray powder diffraction pattern. D-spacing values are calculated with observed 2 theta angles and copper K a wavelength using the Bragg equation well known to those of having skill in the art of XRPD diffractometry science.
The crystalline Form-SL of Lenalidomide as obtained by the process of the present invention is free from any detectable impurities/ contamination of any other previously known crystalline forms of Lenalidomide. This stable form thus, offers various advantages in terms of storage, shelf life, solubility, safety profile, improved physical and/or chemical properties.
In a further embodiment according to this specification, the invention also relates to a composition containing Crystalline Form-SL of Lenalidomide, which is substantially free of any other known forms of Lenalidomide.
The Crystalline Form-SL of Lenalidomide obtained by the process of the present application may be formulated as solid compositions for oral administration in the form of capsules, tablets, pills, powders or granules. In these compositions, the active product is mixed with one or more pharmaceutically acceptable excipients. The drug substance can be formulated as liquid compositions for oral administration including solutions, suspensions, syrups, elixirs and emulsions, containing solvents or vehicles such as water, sorbitol, glycerin, propylene glycol or liquid paraffin.
In one embodiment of the present invention, it also includes premix comprising one or more pharmaceutically acceptable excipients in the range of 1 to 50% w/w with crystalline Form-SL of Lenalidomide, while retaining the crystalline nature of the premix.
The compositions for parenteral administration can be suspensions, emulsions or aqueous or non-aqueous sterile solutions. As a solvent or vehicle, propylene glycol, polyethylene glycol, vegetable oils, especially olive oil, and injectable organic esters, e.g. ethyl oleate, may be employed. These compositions can contain adjuvants, especially wetting, emulsifying and dispersing agents. The sterilization may be carried out in several ways, e.g. using a bacteriological filter, by incorporating sterilizing agents in the composition, by irradiation or by heating. They may be prepared in the form of sterile compositions, which can be dissolved at the time of use in sterile water or any other sterile injectable medium.
Pharmaceutically acceptable excipients used in the compositions comprising crystalline Form-SL of Lenalidomide according to the present application include, but are not limited to diluents such as starch, pregelatinized starch, lactose, powdered cellulose, microcrystalline cellulose, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar and the like; binders such as acacia, guar gum, tragacanth, gelatin, pre-gelatinized starch and the like; disintegrants such as starch, sodium starch glycolate, pregelatinized starch, Croscarmellose sodium, colloidal silicon dioxide and the like; lubricants such as stearic acid, magnesium stearate, zinc stearate and the like; glidants such as colloidal silicon dioxide and the like; solubility or wetting enhancers such as anionic or cationic or neutral surfactants, waxes and the like. Other pharmaceutically acceptable excipients that are of use include but not limited to film formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants and the like.
Pharmaceutically acceptable excipients used in the compositions of crystalline Form-SL of Lenalidomide of the present application may also comprise to include the pharmaceutically acceptable carriers used for the preparation of solid dispersion, wherever utilized in the desired dosage form preparation.

EXAMPLES

Example-01: Process for preparation of crystalline Form-SL of Lenalidomide

In a 500 mL single necked round bottomed flask was charged 500 mL methanol and 10 g 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione and the heterogeneous mass (slurry) was stirred for 10 min. To a clean 5 L autoclave, 2000 mL methanol and the slurry obtained above were charged along with stirring. The reaction mass was degassed for 15 min using Nitrogen purging under stirring. 10% Pd/C (50% wet) was then charged to the reaction mass with nitrogen purging.
The reaction mixture was then degassed twice with Hydrogen at 50-55 PSI. The reaction mixture was maintained at 50-55 PSI Hydrogen pressure for about 30 min and then the Hydrogen pressure was released. On completion of the reaction as confirmed by intermittent reaction monitoring by HPLC, the reaction mixture was filtered through celite bed and the bed was washed with 200 mL Methanol.
The filtrate was concentrated at 50 oC under vacuum of 400-500 PSI till about only 200 mL vol. of reaction mixture is left. The reaction mass was then filtered under vacuum, washed with 50 mL Methanol and suck dried for 1 h. The solid material was further dried at 55 °C under vacuum (10-15 mm of Hg) for about 12 h, to obtain the crystalline Form-SL of Lenalidomide having XRPD similar to Fig.-1 and DSC thermogram similar to Fig.-2.
Yield: 5.9 g HPLC purity: 99.90 %

Example-02: Process for preparation of crystalline Form-SL of Lenalidomide

In a 500 mL single necked round bottomed flask was charged 500 mL methanol and 10 g 3-(4-nitro-1-oxoisoindolin-2-yl)piperidine-2,6-dione and the heterogeneous mass (slurry) was stirred for 15 min. To a clean 5 L autoclave, 2000 mL methanol and the slurry obtained above were charged along with stirring. The reaction mass was degassed for 20 min using Nitrogen purging under stirring. 10% Pd/C (50% wet) was then charged to the reaction mass with nitrogen purging.
The reaction mixture was then degassed thrice with Hydrogen at 50-55 PSI. The reaction mixture was maintained at 50-55 PSI Hydrogen pressure for about 35 min and then the Hydrogen pressure was released. On completion of the reaction as confirmed by intermittent reaction monitoring by HPLC, the reaction mixture was filtered through celite bed and the bed was washed with 200 mL Methanol.
The filtrate was concentrated at 55oC under vacuum of 400-500 PSI till about only 200 mL vol. of reaction mixture is left. To this reaction mixture, 200 mL isopropyl alcohol was added and again concentration of the reaction mixture was carried out under atmospheric pressure till about only 200 mL vol. of reaction mixture is left.
To the reaction mixture obtained, 200 mL isopropyl alcohol was added and again concentration of the reaction mixture was carried out under atmospheric pressure at 80oC till about only 200 mL vol. of reaction mixture is left. This procedure was repeated once again.
The reaction mass was cooled to 40 oC, filtered under vacuum with nitrogen blanket, washed with 50 mL isopropyl alcohol and suck dried for 1 h. The solid material was further dried at 60°C under vacuum (10-15 mm of Hg) for about 15 h, to obtain the crystalline Form-SL of Lenalidomide having XRPD similar to Fig.-1 and DSC thermogram similar to Fig.-2.
Yield: 6.9 g HPLC purity: 99.81 % Moisture Content: < 0.17% (by KF)

While the foregoing pages provide a detailed description of the preferred embodiments of the invention, it is to be understood that the description and examples are illustrative only of the principles of the invention and not limiting. Furthermore, as many changes can be made to the invention without departing from the scope of the invention, it is intended that all material contained herein be interpreted as illustrative of the invention and not in a limiting sense.