The present invention relates to an improved and industrially advantageous process for the purification of saxagliptin monohydrate. In particular, the present invention provides an effective method for preparation of highly pure saxagliptin monohydrate, wherein each impurity specifically corresponding amide impurity or cycline amidine impurity is present in an amount less than 0.01% and more preferably less than 0.05%.
BACKGROUND OF THE INVENTION
Saxagliptin (lS,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo [3.3.1.13,7] dec-l-yl)-l-oxoethyl]-2-azabicyclo [3.1.0] hexane-3-carbonitrile has the following chemical structure (Formula I).

N
"'H
)
OH NH2
N
Formula -1
Saxagliptin, in the form of its hydrochloride salt, is marketed under the trade name ONGLYZA® by Bristol-Myers Squibb for the treatment of type 2 diabetes mellitus.
Saxagliptin (ONGLYZA) is a highly potent, oral hypoglycemic reversible dipeptidyl peptidase IV (DPPIV) inhibitor recently approved by the FDA for the treatment of type 2 diabetes mellitus.

Saxagliptin and its pharmaceutical^ acceptable salts thereof have been disclosed first time in US 6395767B2. The patent also discloses the process for the preparation of saxagliptin and its pharmaceutically acceptable salts thereof as depicted in Scheme-1:
Scheme—t

The above process in scheme-1 involves the reduction of methyl ester with lithium aluminum hydride (LAH) to yield adamantly methanol, which is then oxidized under swern conditions to provide adamantly formaldehyde. The aldehyde is then treated with R-(-)-2-phenyl glycinol followed by potassium cyanide to provide nitrile compound. The nitrile compound on hydrolysis in a mixture of concentrated HCl and acetic acid provided the hydrochloride salt of its corresponding acid, n-deprotection of the hydrochloride salt under hydrogenolysis condition using Pearlman's catalyst (20% Pd (OH)2) provides adamantly glycine as its hydrochloride salt, which on treatment with di-tert-butyl dicarbonate in the presence of
3

potassium carbonate provides Boc protected adamantly glycine. The resulting N-Boc adamantly glycine is hydroxylated by treating with potassium permanganate in aqueous potassium hydroxide to provide hydroxy adamantly glycine which on condensation with (ls,3s,5s)-2-azabicyclo [3.1.0] hexane-3-carboxamide trifluoroacetic acid salt in presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), 1-hydroxybenzotriazole (HOBT) and triethylamine (TEA) provides amide derivative of hydroxy adamantly glycine. The obtained product is treated with triethylsilyl triflate in the presence of diisopropylethylamine (DIPEA) at -78°C to provide o-triethylsilyl protected amide compound. The o-silyl protected amide on treatment with phosphorous oxychloride in presence of imidazole in pyridine results in corresponding nitrile derivative which on reaction with aqueous trifluoroacetic acid (TFA) at 0°C furnishes saxagliptin as trifluoroacetic acid salt. In the said patent application, preparation of saxagliptin monohydrate has not been exemplified.
Another patent, US7186846B2 discloses a process for the preparation of saxagliptin through the hydrolytic cleavage of O-trifluoroacetyl saxagliptin as shown below in Scheme-2.

CM HCI
Scheme-2

H3.

KjCOCtf NHOQCFa

FjQOCHN l*C .-: i :■: , i . L i | .■ ■
in

The product obtained is purified using acid base treatment in methylene dichloride, ethyl acetate and water is reported in example 6. The product isolated has only 98.5% purity.
US7214702 also discloses process for saxagliptin and its hydrochloride salt. The exemplified process discloses the isolation of saxagliptin using methylene dichloride as solvent and isolated product has purity of 95%.
US7420079 discloses a process for preparing saxagliptin, its hydrochloride, trifluoroacetic
acid and benzoate salts, as well gliptin monohydrate. In this patent too, saxagliptin is
purified using acid base treatment in methylene dichloride, ethyl acetate and water and the
end product is isolated gliptin monohydrate. But the document is silent about the
purity.
The purity of final active pharmaceutical ingredient plays an important role for commercialization of a product. Impurities in saxagliptin monohydrate, or any active pharmaceutical ingredients ("API") are undesirable and, in extreme cases, might even be harmful to a patient being treated with a dosage form containing the API. Saxagliptin may contain impertinent compounds or impurities. These impurities may be, for example, starting materials; impurities carry forward from starting materials, by-products of the reaction, product of side reactions or degradation products.
The regulatory authorities of all major countries like U.S. Food and Drug Administration ("FDA"), Medicines and Healthcare Products Regulatory Agency ("MHRA") and European Medicines Agency ("EMEA") require that impurities be maintained below set limits. For example, in ICH Q7A guidance for API manufacturers, preferred limits for the quality of raw

materials that may be used are specified. The general impurities of saxagliptin reported in literature are given below:

3-Hydrxoyadamentylglycine-L-cis-4,5-methanoprolinamide


OH

NH

6-Amino-4-(3-hydroxytricyclo[3.3.1.13,7]dec-l-yl)-l,la,4,6a,7,7a-hexahydro-3H-cyclopropa[4,5]pyrrolo[l,2-a]pyrazin-3-one

HO NHBoc
O^^NH2
N-Boc-3-hydrxoyadamentyl glycine-L-cis-4,5-Methanoprolinamide

HO BocHN CN
N-Boc-(S)-3-hydroxyadamentyl glycine -L- cis -4,5-methano prolinenitrile
6

o1^
Ethyl 3-pyridinecarboxylate
Among these, the most important impurities are unreacted amide intermediate compound of formula II and cyclic amidine impurity of formula III as presented below:
HO H^ A
Formula II

Formula III
Various references also disclose such impurities. An article, Organic Process Research and Development 2009, 13, 1169-1176 discloses a process (Scheme-3). It is reported that the side reactions may occur due to the presence of the residual HOBt and trifluoroacetic anhydride (TFAA) used for the amide dehydration, therefore the complete conversion of the amide to nitrile is found to be very difficult and amide impurity may remain present in the desired compound.

It further discloses that acid salts of saxagliptin have proven to be stable in a solution, but the synthesis of the desired free base monohydrate was challenging due to the thermodynamically favourable conversion of the free amine to the six-membered cyclic amidine impurity.
Schemc-3

N ■'_
2l*f\ * CMJSOJM HNT3 ~
^S/ NMBC Y

EOC.HO«T
OffA

TFAA.
Etfiyl ntootrula
ElOAc

NMBM I NC
MCI. Ittpfopanoi
1
(T\ 1 A
AzrrT'O
HT7 "'«• Y
"° MO NC
■ u J

K,CO. MeOH LiOAc
N»OM. K/:O>
CH/C1,

Q NC
>-CF,

The process comprises the coupling of 3-hydroxy adamantly glycine with (lS,3S,5S)-2-azabicyclo [3.1.0] hexane-3-carboxamide methane sulphonic acid salt in presence of l-ethyl-3-(3dimethylaminopropyl) carbodiimide), hydrolysis of O-protected nitrile compound was done with aqueous potassium carbonate in presence of catalytic amount of methanol to get Boc saxagliptin. Methanol is added to improve the phase transfer of the 25 weight % potassium carbonates into ethyl acetate layer to facile the hydrolytic cleavage of trifluoroacetyl group. Boc Saxagliptin on treatment with concentrated hydrochloric acid in

aqueous isopropanol at 65°C resulted in situ formation of saxagliptin hydrochloride (la) which was basified with aqueous sodium hydroxide in a presence of methylene chloride followed by adjustment of pH to ~9 with potassium carbonate. The obtained methylene chloride solution was partially distilled to a constant volume under atmospheric conditions. The remaining methylene chloride was chased with enough ethyl acetate and the moisture content was adjusted in ethyl acetate solution to -1.5-2.0%. If the moisture content in ethyl acetate solution was less, then additional water was added to induce crystallization. The resulting solid was filtered and washed with wet ethyl acetate to obtain saxagliptin monohydrate.
In view of the above, in most of the prior art processes, either the impurities are controlled during reaction or involves acid base treatment to purify saxagliptin monohydrate. We have not found any purification process wherein saxagliptin is purified either by recrystalhzation or by using solvent /antisolvent system. Few disclosures are silent about the purity of saxagliptin monohydrate so there is an urgent need in the art to provide a purification process wherein the presence of individual impurity to be controlled to a level of less than 0.1% , more preferably less than 0.05% and total impurities to a minimal level. The present invention aims to provide an efficient purification process to obtain highly pure saxagliptin monohydrate which is unique with respect to simplicity, cost effectiveness and convenient to operate on industrial scale.
OBJECT OF THE INVENTION
The principal object of the present invention is to provide an efficient and industrially advantageous process for purification of saxagliptin monohydrate.

Another object of the present invention is to provide an efficient and industrially advantageous process for purification of saxagliptin monohydrate wherein individual impurity to be controlled to a level of less than 0.1% and total impurities to a minimal level.
One other object of the present invention is to provide a cost-effective and industrially advantageous process for purification of saxagliptin monohydrate wherein of formula I, individual impurity to be controlled to a level of less than 0.05% and total impurities to a minimal level.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an improved and industrially advantageous process for preparation of highly pure saxagliptin monohydrate of formula (I) having amide impurity of formula II in an amount less than 0.1%> more preferably less than 0.05% and cyclic amidine impurity of formula III, in an amount less than 0.05%.
According to one embodiment, the present invention provides a novel process for the purification of saxagliptin monohydrate of formula I,
OH NH2 ) 1
N7 .H20
Formula -1
which comprises steps of:
i. providing a suspension of saxagliptin in a suitable solvent such as aliphatic nitrile; ii. heating the susoension at a temoerature ranse of 50°C- 90°C to obtain a clear solution:

iii. adding of water;
iv. cooling the reaction mass to a temperature of 0-20;
v. filtering the product followed by washing with DI water;
vi. drying at 20-60; and
vii. isolating highly pure saxagliptin monohydrate.
One other embodiment of the present invention provides an improved process for the purification of saxagliptin monohydrate which comprises steps of:
i. dissolving saxagliptin in an aliphatic nitrile solvent at a temperature range of 50- 90
°C to obtain a clear solution; ii. adding an aliphatic ether to the above solution; iii. cooling the reaction mass to a temperature of -10-10 °C; iv. filtering the resulting solid followed by washing with aliphatic ether; v. drying at 20-60°C; and vi. isolating highly pure saxagliptin monohydrate.
Another embodiment of the present invention provides a novel process for purification of saxagliptin which comprises steps of:
i. dissolving saxagliptin in a mixture of aliphatic nitrile and DI water;
ii. heating the suspension at a temperature range of 50- 90°C to obtain a clear solution;
iii. adding an aliphatic ether to the above solution;
iv. cooling the reaction mass to a temperature of 0-20°C;
v. filtering the product followed by washing with aliphatic ether;
vi. drying at 20-60°C; and

vii. isolating highly pure saxagliptin monohydrate.
BRIEF DESCRIPTION OF DRAWINGS
1. Figure 1 represents PXRD pattern of saxagliptin monohydrate.
2. Figure 2 represents PXRD pattern of saxagliptin monohydrate
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides an efficient and industrially advantageous process for the purification of saxagliptin monohydrate of formula I by removing the cyclic amidine impurity and amide impurity within the prescribed limit.
As used herein, the term 'highly pure' represents a compound having purity greater than 99.5% w/w by HPLC, preferably greater than 99.7% w/w by HPLC, more preferably greater than 99.9% w/w by FIPLC and any individual impurity present in an amount of less than 0.1% more preferably less than 0.05% w/w by HPLC.
As used herein, the term 'ambient temperature' represents a temperature 25°C+ 5°C. DI represents demineralized water.
The present invention relates to an efficient process for purification of saxagliptin monohydrate by using specific solvent systems. The basic idea of the invention is to specifically develop an industrially viable cost-effective process to remove amide impurity namely, 3-hydrxoyadamentyl glycine-L-cis-4,5-methanoprolinamide of formula II and cyclic amidine impurity namely 6-amino-4-(3-hydroxytricyclo[3.3.1.13,7]dec-l-yl)-l,la,4,6a,7,7a-hexahydro-3H-cyclopropa [4,5] pyrrolo [l,2-a]pyrazin-3-one of formula III.

The present invention provides a process to reduce the amide impurity of Formula II (3-hydrxoyadamentyl glycine-L-cis-4,5-methanoprolinamide impurity) from 0.30% to less than 0.1% or 0.05% and cyclic amidine impurity of Formula III to less than 0.05%.
The process comprises the step of dissolving saxagliptin, namely 3-hydroxyadamentyl glycine -L-cis -4,5-methanoprolinenitrile, in a suitable organic solvent system under mild reaction conditions. The dissolution of saxagliptin in a suitable organic solvent may be achieved by heating the reaction mixture at a temperature range of 50-90°C. The suitable solvent system used in the reaction can be selected from any suitable aliphatic nitrile, or its mixture with water. In general, aliphatic nitrile used herein includes but not limited to acetonitrile or propionitrile. After obtaining clear solution, the reaction mixture can be optionally charcolized using activated carbon in order to remove colored impurities, if any present.
The reaction mass can then be further diluted using a suitable solvent in which saxagliptin has less solubility. The suitable solvent can be aliphatic ether selected from diisopropylether, methyl tert butyl ether, dimethyl ether and diethyl ether.
Then, the resulting reaction mixture can be cooled to a temperature of 0-20°C with stirring for complete crystallization. The resulting solid can be isolated by any method known in the art such as filtration and can be washed with the solvent used for dilution of reaction mass after obtaining clear solution. Thereafter, the solid obtained can be dried at a temperature range of 20-60°C for a period of 4-6 hours to obtain highly pure saxagliptin monohydrate.
The highly pure saxagliptin monohydrate obtained by using the purification process of present invention has purity greater than 99.5 %, preferably > 99.9% w/w as determined by HPLC

and having the amide impurity of Formula II (3-hydrxoyadamentyl glycine-L-cis-4,5-methanoprolinamide impurity) in less than 0.1% or 0.05% and cyclic amidine impurity of Formula III in less than 0.05% w/w by HPLC.
The crude saxagliptin having amide impurity and amidine impurity can be prepared by the methods reported in literature or by the process as given in the present specification. Specifically, crude saxagliptin can be prepared by the coupling of 3-hydroxy adamantly glycine with (lS,3S,5S)-2-azabicyclo [3.1.0] hexane-3-carboxamide trifluoroacetic acid salt in presence of l-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), 1-hydroxybenzotriazole (HOBT) and N, N-Diisopropylethylamine (DIPEA) to provide an amide derivative of hydroxy adamantly glycine. After the coupling reaction, the solvent was added to allow an acidic aqueous workup to remove the basic by products of the process. The solvent used herein includes ethyl acetate but not limited to methanol, ethanol, n-propanol, acetone, tert-butyl alcohol, benzyl alcohol and alike. The obtained product is treated with trifluoracetic anhydride in the presence of ethyl nicotinate to provide trifluoroacetate adamantly. After the coupling reaction, the suitable solvent such as ethyl acetate can be added to allow an acidic aqueous workup to remove the basic by products of the process.
The trifluoracetic acid salt of ethyl nicotinate formed after the reaction proves to be more difficult to remove, as it is freely soluble in ethyl acetate. In order to remove it, TMEDA and water is charged after the dehydration reaction with a subsequent phase split. Hydrochloric acid is charged to extract the corresponding ethyl nicotinate hydrochloric salt. Hydrolysis of O-protected nitrile compound is done with aqueous potassium carbonate in the presence of catalytic amount of methanol to get Boc saxagliptin. Methanol is added to improve the phase

transfer of the 25 weight % potassium carbonates into the ethyl acetate layer to facile the hydrolytic cleavage of trifluoro acetyl group. Boc Saxagliptin on treatment with concentrated hydrochloric acid in aqueous isopropanol at a temperature range of 40-70°C results in situ formation of saxagliptin hydrochloride which was basified with aqueous sodium hydroxide in a presence of methylene chloride followed by adjustment of pH to 8.75-9.25 with sodium hydroxide. The resulting methylene chloride solution is distilled under atmospheric conditions to get crude saxagliptin.
Major advantages realized in the present invention is that the solvent systems described herein was able to reduce the amide impurity of Formula II from 0.30% to less than 0.1% or less than 0.05% w/w by HPLC and also the cyclic amidine impurity of Formula III to less than 0.05% w/w by HPLC. None the less by the use of this particular purification process as set out in disclosure, saxagliptin monohydrate may be conveniently obtained in high purity having acceptable limits of impurities that is suitable for use in medicament.
Although, the following examples illustrate the practice of the present invention in some of its embodiments, the examples should not be construed as limiting the scope of invention. Other embodiments will be apparent to one skilled in the art from consideration of the specification and examples.
EXAMPLES
Example 1: Process for purification of saxagliptin
To a suspension of 1 OOg of saxagliptin having amide impurity of Formula II in an amount of 0.30%; cyclic amidine impurity > 0.20% in acetonitrile (180ml) and heated at 70-80°C to get a clear solution. To the reaction mixture, activated carbon was added and the mixture was

stirred. The solution was filtered through hyflo filter and the filtrate was diluted with DI water (20 ml). The reaction mass was cooled to an ambient temperature with stirring. After reaction completion, the resulting mass was further cooled to 5-15°C with stirring for 1-2 hours. The product was filtered, washed with DI water, and dried at 40-50°C for 4-6 hours to obtain highly pure saxagliptin having HPLC purity 99.94 % w/w having amide impurity of Formula 11= 0.05% and cyclic amidine of Formula 111= 0.01%. The XRD of resulting product matches with XRD reported for saxagliptin monohydrate.
Example 2: Process for purification of saxagliptin
To a suspension of lOOg of (S)-3-hydroxyadamentyl glycine -L-cis -4,5-methanoprolinenitrile or saxagliptin (having amide impurity in an amount of 0.30%); cyclic amidine impurity ~ 0.20% in acetonitrile (200 ml) and heated at 70-80°C to get a clear solution followed by addition of activated carbon and the solution was stirred. The solution was filtered through hyflo filter and isopropyl ether (20 ml) was added to the filtrate. The filtrate was cooled to an ambient temperature with stirring. The resulting mass was further cooled to -10 -10°C with stirring for 1-2 hours. The product was filtered, washed, chilled di isopropyl ether and dried at 40-50°C for 4- 6 hours to obtain highly pure saxagliptin having HPLC purity 99.96 %w/w; amide impurity of Formula II =Not detected; cyclic amidine impurity of Formula II = 0.04% and XRD similar to saxagliptin monohydrate.
Example 3: Process for the purification of saxagliptin
To a suspension of lOOg of (S)-3-hydroxyadamentyl glycine -L-cis -4,5-methanoprolinenitrile or saxagliptin (having amide impurity in an amount of 0.30%; cyclic amidine impurity ~ 0.20%) in acetonitrile (180ml) and heated at 65-80°C to get a clear solution. The solution was

filtered and the filtrate was diluted with DI water (20ml). The reaction mass was cooled to an ambient temperature followed with stirring. After reaction completion, the resulting mass was further cooled to 5-15°C with stirring for 1-2 hours. The product was filtered, washed with DI water and dried at 40-50°C for 4-6 hours to obtain highly pure saxagliptin (89g) having HPLC purity 99.94% w/w; amide impurity of Formula 111=0.04%; cyclic amidine impurity of Formula 111= 0.02% and having XRD similar to saxagliptin monohydrate.
Example 4: Process for purification of saxagliptin
To a suspension of 1 OOg of saxagliptin (having amide impurity of formula II in an amount of 0.30%; cyclic amidine impurity ~ 0.20%) in acetonitrile (180ml) and heated at 65-80°C to get a clear solution. To the reaction mixture, activated carbon was added and the mixture was stirred. The solution was filtered through hyflo filter and the filtrate was diluted with DI water. The reaction mass is cooled to 5-15°C with stirring for 1-2 hours. The product was filtered, washed with DI water and dried at 40-50°C for 4-6 hours to obtain highly pure saxagliptin (91 g) having HPLC purity 99.92%; amide impurity of Formula II =0.05%; cyclic amidine impurity of formula III =0.02% and having XRD similar to saxagliptin monohydrate as presented.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention and specific examples provided herein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of any claims and their equivalents.

WE CLAIM:

1. A process for the purification of saxagliptin monohydrate of formula I,
OH NH2 ) '
N H20
Formula -1
which comprises steps of:
i. providing a suspension of saxagliptin in a suitable solvent such as
aliphatic nitrile;
ii. heating the suspension at a temperature range of 50°C- 90°C to obtain a
clear solution;
iii. adding of water;
iv. cooling the reaction mass to a temperature of 0-20°C;
v. filtering the product followed by washing with DI water;
vi. drying at 20-60°C; and
vii. isolating highly pure saxagliptin monohydrate.
2. The process as claimed in claim 1, wherein in step i), the aliphatic nitrile is selected from acetonitrile or propionitrile.
3. The process as claimed in claim 1, wherein in step ii), the temperature is selected from 65°C- 80°C.
4. A process for the purification of saxagliptin monohydrate of formula I,


H
OH NH2
N H20
Formula -1
which comprises the steps of:
i. dissolving saxagliptin in an aliphatic nitrile solvent, at a temperature
range of 50- 90°C to obtain a clear solution;
ii. adding an aliphatic ether to the above solution;
iii. cooling the reaction mass to a temperature of -10-10°C;
iv. filtering the resulting solid followed by washing with aliphatic ether;
v. drying at 20-60°C; and
vi. isolating highly pure saxagliptin monohydrate.
5. The process as claimed in claim 4, wherein in step i), the aliphatic nitrile is selected from acetonitrile or propionitrile.
6. The process as claimed in claim 4, wherein in step ii), the aliphatic ether is selected from diisopropylether, methyl tert butyl ether, dimethyl ether, diethyl ether.
7. A process for purification of saxagliptin comprises the steps of:
i. dissolving saxagliptin in a mixture of aliphatic nitrile and DI water;
ii. heating the suspension at a temperature range of 50- 90°C to obtain a
clear solution;
iii. adding an aliphatic ether to the above solution;

v. filtering the product followed by washing with aliphatic ether;
vi. drying at 20-60°C; and
vii. isolating highly pure saxagliptin monohydrate.
8. The process as claimed in claim 7, wherein in step i), the aliphatic nitrile is selected from acetonitrile or propionitrile.
9. The process as claimed in claim 7, wherein in step ii), the temperature is selected from 65°C- 80°C.
10. The process as claimed in claim 7, wherein in steps iii) and v), the aliphatic ether is selected from diisopropylether, methyl tert butyl ether, dimethyl ether, diethyl ether.