DESC:The following specification describes the invention.

INTRODUCTION
Aspects of the present application relate to solid state form of Ruxolitinib phosphate. Specific aspects relate to crystalline Form S5 of Ruxolitinib phosphate and process for its preparation.
Ruxolitinib is useful as inhibitor of the Janus Kinase family of protein tyrosine kinases (JAKs) for treatment of inflammatory diseases, myeloproliferative disorders, and other diseases and is represented by below chemical structure.

Ruxolitinib phosphate is approved and marketed as JAKAFI (USA) / JAKAVI (Europe) oral tablets for the treatment of as the myelofibrosis, polycythaemia vera (PV) and steroid-refractory acute graft-versus-host disease (GVHD).
WO2007070514A1 first discloses Ruxolitinib, its preparation and use in the treatment of diseases related to activity of Janus kinases including immune-related diseases, skin disorders, myeloid proliferative disorders, cancer, and other diseases.
WO2008157208A2 discloses the phosphate salt of Ruxolitinib and its crystalline form. However, the PXRD pattern of crystalline Ruxolitinib phosphate was disclosed only during the prosecution of corresponding US patent application. Further, the CMHP assessment report elucidates that, crystalline Ruxolitinib phosphate present in marketed product, JAKAVI is anhydrous.
Further, patent applications viz., CA2928286A1, WO 2016063294 A2 and WO 2017125097 A1, reported various crystalline forms and amorphous form of Ruxolitinib Phosphate.
The existence and possible numbers of polymorphic forms for a given compound cannot be predicted, and there are no “standard” procedures that can be used to prepare polymorphic forms of a substance. This is well-known in the art, as reported, for example, by A. Goho, “Tricky Business,” Science News, Vol. 166(8), August 2004. Hence, there remains a need for an alternate and viable solid state form of Ruxolitinib phosphate.

SUMMARY
In an aspect, the present application provides a crystalline Form S5 of Ruxolitinib phosphate, characterized by a PXRD pattern comprising the peaks at about 18.21, 26.96 ± 0.2° 2?.
In another aspect, the present application provides a process for the preparation of crystalline Form S5 of Ruxolitinib phosphate, comprising the step of drying Form S3 of Ruxolitinib phosphate at about 50-100oC for at least 4 hours or by humidification of Form S3 of Ruxolitinib phosphate at about 60-80% Relative Humidity.
In another aspect, the present application provides pharmaceutical composition comprising crystalline Form S5 of Ruxolitinib phosphate together with atleast one pharmaceutically acceptable excipient.

BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is an illustrative X-ray powder diffraction pattern of crystalline Form S5 of Ruxolitinib phosphate, prepared by the method of Examples 1 and 2.

DETAILED DESCRIPTION
In an aspect, the present application provides a crystalline Form S5 of Ruxolitinib phosphate, characterized by a PXRD pattern comprising the peaks at about 18.21, 26.96 ± 0.2° 2?. In an embodiment, the crystalline Form S4 is characterized by one or more additional peaks at about 16.68, 20.95, 27.41 ± 0.2°2?. In an embodiment, the application provides crystalline Form S5, characterized by a PXRD pattern of Figure 1.
In another aspect, the present application provides a process for the preparation of crystalline Form S5 of Ruxolitinib phosphate, comprising the step of drying Form S3 of Ruxolitinib phosphate at 60-80 oC, for 4-12 hours or by humidification of Form S3 of Ruxolitinib phosphate at about 60-80% RH.
In embodiments, Ruxolitinib phosphate used in this aspect may be obtained by any methods known in the art or any process comprising the reaction of Ruxolitinib with phosphoric acid under suitable conditions to form phosphate salt of Ruxolitinib.
In embodiments, drying Form S3 of Ruxolitinib phosphate can be done at temperatures 50-100oC, preferably 60-80 oC, for 4-12 hours, preferably 6-8 hours.
In another embodiment, humidification of Form S3 of Ruxolitinib phosphate at about 60-80% RH can be done at room temperature for about 1-6 hours
In embodiments, the isolated solids may be dried under suitable drying conditions such as aerial drying, drying under vacuum or inert gas at a suitable temperature of about 25°C or above.
In embodiments, the crystalline Form S5 of Ruxolitinib phosphate obtained by the process of this aspect may be characterized by a DSC and TGA.
In another aspect, the present application provides pharmaceutical composition comprising crystalline Form S5 of Ruxolitinib phosphate together with atleast one pharmaceutically acceptable excipient.
In another aspect, the present application provides crystalline Form S5 of Ruxolitinib phosphate, according to instant application and pharmaceutical compositions thereof, wherein the chemical purity of Ruxolitinib phosphate may be more than 99% by HPLC or more than 99.5% by HPLC or more than 99.9% by HPLC.
Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. Variations of the described procedures, as will be apparent to those skilled in the art, are intended to be within the scope of the present application.

Definitions
The term "about" when used in the present application preceding a number and referring to it, is meant to designate any value which lies within the range of ±10%, preferably within a range of ±5%, more preferably within a range of ±2%, still more preferably within a range of ±1 % of its value. For example "about 10" should be construed as meaning within the range of 9 to 11 , preferably within the range of 9.5 to 10.5, more preferably within the range of 9.8 to 10.2, and still more preferably within the range of 9.9 to 10.1.

EXAMPLES
Example-1: Preparation of crystalline Form S5 of Ruxolitinib phosphate
Ruxolitinib phosphate Form S3 was subjected to drying in VTD at ~70oC for about 4 hours to afford the title polymorph.

Example-2: Preparation of crystalline Form S5 of Ruxolitinib phosphate
Ruxolitinib phosphate Form S3 was subjected to humidification at ~80% RH at room temperature to afford the title polymorph.
,CLAIMS:We claim

Claim 1: A crystalline Form S5 of Ruxolitinib phosphate, characterized by a PXRD pattern comprising the peaks at about 18.21, 26.96 ± 0.2° 2?.

Claim 2: A process for the preparation of crystalline Form S5 of Ruxolitinib phosphate, comprising the step of drying Form S3 of Ruxolitinib phosphate at about 50-100oC for at least 4 hours or by humidification of Form S3 of Ruxolitinib phosphate at about 60-80% Relative Humidity.

Claim 3: A process for the preparation of crystalline Form S5 of Ruxolitinib phosphate, comprising the step of humidification of Form S3 of Ruxolitinib phosphate at about 60-80% Relative Humidity.

Claim 4: A pharmaceutical composition comprising crystalline Form S5 of Ruxolitinib phosphate and at least one pharmaceutically acceptable excipient.