Field of Invention
The present invention encompasses improved processes for the preparation of(1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)-1-oxoethyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile or its salts or hydrates thereof, which is acyclopropyl-fused pyrrolidine-baseddipeptidyl peptidase (DPP) IV inhibitor. The present invention also provided novel intermediate compounds which can be used further for the preparation of (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)-1-oxoethyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile or its salts or hydrates thereof. Further, present invention also provides processes for the preparation of those novel intermediate compounds.

Background of the Invention

Saxagliptin, (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)-1-oxoethyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile is having the following chemical structure:

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. Each film coated tablet of ONGLYZA for oral use contains either 2.79mg saxagliptin hydrochloride (anhydrous) equivalent to 2.5mg saxagliptin, or 5.58mg saxagliptin hydrochloride (anhydrous) equivalent to 5 mg saxagliptin and the following inactive ingredients: lactose monohydrate, microcrystalline cellulose, croscarmellose sodium, and magnesium stearate.

Saxagliptin is used as an adjunct to diet and exercise to improve glycemic controls in adults with type 2 diabetes mellitus. Saxagliptin is understood to slow the breakdown of incretin hormones, thereby increasing the levels of these hormones in the body, which in turn increases the production of insulin in response to meals and decreases the amount of glucose produced by the liver.

The US6395767 discloses the process for the preparation of saxagliptin and its pharmaceutically acceptable salts thereof as depicted in Scheme-1:

Scheme-1

The above disclosed process in scheme-1 involves the reduction of methyl ester with lithium aluminium hydride (LAH) to yield adamantyl methanol, which is then oxidized under Swern conditions to provide adamantylformaldehyde. The aldehyde is then treated with R-(-)-2-phenylglycinol followed by potassium to provide nitrile compound. The nitrile compound on hydrolysis in a mixture of conc. 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 adamantyl glycine as its hydrochloride salt, which on treatment with di-tert-butyl dicarbonate in presence of potassium carbonate to provide Boc protected adamantyl glycine. The resulting N-Boc adamantyl glycine is hydroxylated by treating with potassium permanganate in aq. potassium hydroxide to provide hydroxyadamantyl glycine which on condensation 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 triethylamine (TEA) provides amide derivative of hydroxyadamantyl glycine. The obtained product is treated with triethylsilyltriflate in presence of diisopropylethylamine (DIPEA) at -78oC to provide O-triethylsilyl protected amide compound.The O-silyl protected amide on treatment with phosphorous oxychloride in presence of imidazole in pyridine resulted corresponding nitrile derivative which on reaction with aqueous trifluoroacetic acid (TFA) at 0oC furnished saxagliptin as trifluoroacetic acid salt.

The process disclosed in US6395767B2 has certain disadvantages.The process uses highly carcinogenic reagent like potassium cyanide and also involves the usage of lithium aluminium hydride for the reduction of adamantane-l-carboxylic acid methyl ester, which is hygroscopic, pyrophoric and highly reactive.

US7186846B2 disclosed a process for the preparation of saxagliptin base through the hydrolytic cleavage of O-trifluoroacetylsaxagliptin as shown below in Scheme-2.

Scheme-2

US7420079 discloses a process for preparing saxagliptin, its hydrochloride, trifluoroacetic acid and benzoate salts, as well as Saxagliptin monohydrate.

US7214702 and US2006/035954 also discloses process for saxagliptin.

Organic Process Research and Development 2009, 13, 1169-1176 discloses a process (Scheme-3) where 3-hydroxy adamantyl glycine is coupled with (lS,3S,5S)-2-azabicyclo[3.1.0] hexane-3-carboxamide methanesulphonic acid salt in presence of l-ethyI-3-(3-dimethylaminopropyl)carbodiimide), 1-hydroxybenzotriazole, and diisopropylethylamine in a mixture of ethylacetate and acetonitrile to get corresponding glycine amide derivative which is then treated with trifluoroacetic anhydride (TFAA) in presence of ethyl nicotinate at -10oC to get the O-trifluoroacetyl protected saxagliptin. 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 wt % potassium carbonate into the ethyl acetate layer to facile the hydrolytic cleavage of trifluoroacetyl group. Boc-Saxagliptin on treatment with conc. hydrochloric acid in aqueous isopropanol at 65°Cresulted in-situ formation of saxagliptin hydrochloride (Ia) 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 sufficient amount of ethyl acetate and adjusted the moisture content in ethyl acetate solution to ~1.5-2.0%. If moisture content in ethyl acetate solution is less then additional water was added to induce crystallization. The resulting solid was filtered and washed with wet ethyl acetate to obtain saxagliptin monohydrate (Ib).
Scheme-3

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15. 5025-5037 discloses a process (Scheme-4) where the hydroxylation of N-Boc-adamantylglycine at the bridgehead was accomplished using potassium permanganate in 2% aqueous potassium hydroxide at elevated temperature to give N-Boc hydroxyadamantyl glycine. The obtained N-Boc hydroxyadamantyl glycine was then coupled with methanoprolinamide intermediate in presence of l-ethyl-3-(3-dimethylaminopropyl)carbodiimide, 1-hydroxybenzotriazole, and triethylamine to get amide intermediate in high yield. This amide intermediate was on treatment with TFFA in presence of pyridine in THF at 0oC resulted O-trifluoroacetyl nitrile whichwas in-situ hydrolyzed with 10% K2CO3 in methanol at room temperature to afford Boc-protected nitrile which was deprotected using TFA in methylene chloride at room temperature to provide saxagliptin as trifluoroacetic acid salt.

Scheme-4

The processes reported for preparing saxagliptin, its salts or hydrates thereof as mentioned vide supra suffer from drawbacks such as involving use of carcinogenic reagents such as DCC or EDC or mesyl chloride during coupling reaction which also generates genotoxic product like DCU/EDCU. Use of expensive, hazardous and carcinogenic reagents like TFAA or pyridine/ethyl nicotinate made these processes unsuitable in production in commercial scale. Removal of pyridine or ethyl nicotinate is very tedious which significantly lower the yield. Also, prior art process generates potential impurities like cyclic amidine and diketopyrazine impurity during isolation of saxagliptin free base from saxagliptin HCl salt. Hence, there is a continuous need in the art to develop a simple, safe, efficient, robust, environment friendly and commercially viable process for the synthesis of (lS,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxyadamantan-l-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile to avoid the problems associated with prior-art.

Summary of the Invention
The principal object of the present invention is to provide an improved process for the production of cyclopropyl-fused pyrrolidine-based inhibitors of dipeptidyl peptidase IV specifically, saxagliptin free base or its pharmaceutically acceptable salts or a hydrate thereof, which alleviatesone or more drawbacks of prior art process.

One object of the invention provides the process for the preparation of enantiomerically enriched intermediates, which will be useful for the synthesis of enantiomerically enriched saxagliptin free base or its pharmaceutically acceptable salts or hydrates thereof, by a simple, reliable, convenient and commercially acceptable process
It is an another object of the present invention to provide a simple, reliable, convenient and commercially viable, environment and industrial friendly process for synthesizing saxagliptin free base or its pharmaceutically acceptable salts or hydrates thereof.

It is an another object of the present invention to provide novel intermediate of compounds of formula (4a) and formula (5a).

In yet another embodiment the invention provides a process for producing novel intermediate of compounds of formula (4a) and formula (5a).

A yet another object of the present invention provides a process for producing saxagliptin free base or its pharmaceutically acceptable salts or hydrates thereof employing the use of the novel of compounds of formula (4a) and formula (5a).

The present invention can be useful for mass production by reducing the production cost using cheaper reagents in the reaction, simplifying the isolation techniques and improving the yield.

In an embodiment, the present invention provides a process for the preparation of saxagliptin or its salts or/and hydrates thereof, comprising the steps of (a) coupling (S)-N-Boc-3-hydroxyadamantyl glycine with L-cis-4,5-methanoprolinamide or salts thereof in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide; (b) protection of N-Boc hydroxy amide with suitable protecting group to provide O- and N-protected amide in a single step or number of steps; (c) dehydration of O- and N-protected amide in the presence of a dehydrating agent and in a suitable solvent to produce O- and N-protected nitrile; (d) optionally, converting O- and N-protected nitrile to saxagliptin or its salts or/and hydrates thereof; wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates. In the preferred embodiment suitable O-protecting group is formyl group (Scheme 6a) yielding saxagliptin hydrochloride dihydrate (Ia’).

In an another embodiment, the present invention provides another method for manufacturing
of an intermediate of saxagliptin i.e (S)-N-Boc-3-hydroxyadamantylglycine (1) comprising steps of: (a) 2-(adamantan-1-yl)acetic acid (9) is treated with S-benzyl oxazolidinone to get 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10); (b) 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10) is treated with lithium diisopropylamide (LDA) in a suitable solvent to produce an intermediate enolate compound which may be used further with or without isolation; (c) intermediate enolate compound obtained in step “b” is treated with di-tert-butyl azodicarboxylate to get N,N-di-Boc-hydrazinocarboximide (11a); (d) hydrolysis of N,N-di-Boc-hydrazinocarboximide(11a) in a suitable solvent to get N,N-di-Boc-hydrazino acid (12a); (e) deprotection of N,N-di-Boc-hydrazino acid (12a) followed by salt formationin presence of an acid to get hydrazino acid addition salt (13), with or without isolation of intermediate compound; (f) hydrogenolysis of hydrazino acid addition salt (13) in the presence of Raney Nickel in a suitable solvent to get adamantyl glycine acid addition salt (14); (g) Boc protection of adamantyl glycine acid addition salt (14) to get an intermediate compound followed by the subsequent hydroxylation to obtain N-Boc-3-hydroxyadamantyl glycine (1), with or without isolation of an intermediate compound; and (h) optionally, purifying compound (1) in a suitable solvent.

In an another embodiment, the present invention provides another method for manufacturing
of an intermediate of saxagliptin i.e (S)-N-Boc-3-hydroxyadamantylglycine (1) comprising steps of: (a) esterification of 2-(3-hydroxyadamantyl-1-yl)-2-oxo-acetic acid (15) in a suitable solvent to get methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a); (b) reacting methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a); (c) diastereoselective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(3-hydroxyadamantan-1-yl)acetate (18a), wherein, compound (17a) can be used further with or without isolation for the preparation of compound (18a); (d) removal of chiral auxiliary (18a) using Pd(OH)2-C in presence of Boc anhydride to obtain an intermediate compound (19a), which may be used further with or without isolation; (e) hydrolyzing an intermediate compound (19a) obtained in step “d” to obtain 3-hydroxyadamantyl N-Boc glycine (1) and (f) optionally, purifying compound (1) in a suitable solvent.

In yet another embodiment, the present invention provides another method for manufacturing
of an intermediate of saxagliptin i.e (S)-N-Boc-3-hydroxyadamantylglycine (1) comprising steps of: (a) esterification of 2-(adamant-1-yl)-2-oxo-acetic acid (20) in a suitable solvent to get methyl 2-(adamant-1-yl)-2-oxo acetate (21a); (b) reacting methyl 2-(adamant-1-yl)-2-oxo acetate (21a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a); (c) diastereoselective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(adamantan-1-yl)acetate (23a), wherein, compound (22a) can be used further with or without isolation for the preparation of compound (23a); (d) removal of chiral auxiliary (23a) using Pd(OH)2-C in presence of Boc anhydride to obtain an intermediate compound (24a), which may be used further with or without isolation; (e) hydrolyzing an intermediate compound (24a) obtained in step “d” to obtain (2S)-N-Boc-2-(adamant-1-yl) glycine (14); (f) hydroxylation of (2S)-N-Boc-2-(adamant-1-yl)-glycine (14) to produce 3-hydroxyadamantyl N-Boc glycine (1) and (g) optionally, purifying compound (1) in a suitable solvent.
Saxagliptin or its salt, preferably hydrochloride salt of saxagliptin of the formula (I) obtained according to the process of the present invention may be substantially free of one or more impurities. Substantially free as described herein refers to the purity of compound saxagliptin or its salt, preferably hydrochloride salt of saxagliptin of the formula (I) to be more than 99%, preferably 99.5%, more preferably 99.7%.
In yet another embodiment of the present invention provides a pharmaceutical composition and their use, wherein the compositions comprise saxagliptin free base or its salts or/and hydrates thereof, obtained by the processes of the present invention.

Brief description of the drawings
FIG.1 shows the X-ray powder diffractogram (XRPD) of N-Boc hydroxy amide (3).
FIG.2 shows the X-ray powder diffractogram (XRPD) of O-formyl N-Boc amide (4a).
FIG.3 shows the X-ray powder diffractogram (XRPD) of O-formyl N-Boc nitrile (5a).
FIG.4 shows the X-ray powder diffractogram (XRPD) of Saxagliptin crude.
FIG.5 shows the X-ray powder diffractogram (XRPD) of Saxagliptin Hydrochloride dihydrate (Ia’).
Detailed description of Invention
The present invention encompasses a process for the preparation of a saxagliptin free base its pharmaceutically acceptable salts or hydrates thereof.
A first aspect of the present invention encompasses a method for manufacturing saxagliptin or its salts or hydrates thereof through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycinewith L-cis-4,5-methanoprolinamide or salts thereof in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide;
(b) protection of N-Boc hydroxy amide with suitable protecting group to provide O- and N-protected amide in a single step or number of steps;
(c) dehydration of O- and N-protected amide in the presence of a dehydrating agent and in a suitable solvent to produce O- and N-protected nitrile;
(d) optionally, converting O- and N-protected nitrileto saxagliptin or its salts or/and hydrates thereof
wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates.
A second aspect of the present invention encompasses a method for manufacturing saxagliptin or its salts or hydrates thereof [Scheme-5 wherein P1= formyl group and P2= Boc] through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) formylating N-Boc hydroxy amide (3) in the presence of suitable formylating agent to produce O-formyl N-Boc amide (4a);
(c) dehydration of O-formyl N-Boc amide (4a) in the presence of a dehydrating agent in a suitable solvent to produce O-formyl N-Boc nitrile (5a);
(d) optionally, converting O-formyl N-Boc nitrile (5a)to saxagliptin,its salts or/and hydrates thereof
wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates.

A third aspect of the present invention encompasses a method for manufacturing saxagliptin or its salts or hydrates thereof [Scheme-5 wherein P1= acetyl group and P2= Boc] through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) acetylating N-Boc hydroxy amide (3) in the presence of suitable acetylating agent to produce O-acetyl N-Boc amide (4b);
(c) dehydration of O-acetyl N-Boc amide (4b) in the presence of a dehydrating agent and a basein a suitable solvent to produce O-acetyl N-Boc nitrile (5b);
(d) optionally, converting O-acetyl N-Boc nitrile (5b) to saxagliptin or its salts or/and hydrates thereof
wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates.

Scheme-5

A fourth aspect of the present invention encompasses a method for manufacturing saxagliptin its salts or hydrates thereof [Scheme-6 wherein P1 and P2 is acetyl group] through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride, and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) Boc-deprotection of N-Boc hydroxy amide (3) to produce amino amide hydrochloride (6);
(c) acylating amino amidehydrochloride (6) to produce diacetyl amino amide (7a);
(d) dehydration of diacetyl amino amide (7a) in the presence of a dehydrating agent and in a suitable solvent to produce diacetyl amino nitrile (8a);
(e) optionally, converting diacetyl amino nitrile (8a) to saxagliptin or its salts or/and hydrates thereof
wherein, one or more steps from (b) to (e) may be performed in-situ or by isolation of the respective intermediates.

A fifth aspect of the present invention encompasses a method for manufacturing saxagliptin its salts or hydrates thereof [Scheme-6 wherein P1= H and P2= trityl group] through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride, and a base and in a suitable solvent to produce N-Bochydroxy amide (3);
(b) Boc-deprotection of N-Bochydroxy amide (3) to produce amino amide hydrochloride (6);
(c) tritylation of amino amidehydrochloride (6) to furnish N-trityl hydroxy amide (7b);
(d) dehydration of N-trityl hydroxy amide (7b) in the presence of a dehydrating agent and in a suitable solvent to produce N-trityl hydroxy nitrile (8b);
(e) optionally, converting N-trityl hydroxy nitrile (8b) to saxagliptin, its salts or/and hydrates thereof
wherein, one or more steps from (b) to (e) may be performed in-situ or by isolation of the respective intermediates.

Scheme-6

In yet another aspect of the present invention, it encompasses a method for manufacturing saxagliptin hydrochloride dihydrates (Ia’) [Scheme-6a] through, the method comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide hydrochloride (2a) in presence of coupling agent and a base in a suitable solvent, optionally in presence of additive, to produce N-Boc hydroxy amide (3);
(b) formylating N-Bochydroxy amide (3) in the presence of suitable formylating agent to produce O-formyl N-Boc amide (4a);
(c) dehydration ofO-formyl N-Boc amide (4a) in the presence of a dehydrating agent in a suitable solvent to produce O-formyl N-Boc nitrile (5a);
(d) converting O-formyl N-Boc nitrile (5a) to saxagliptin hydrochloride dihydrates
wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates,

Scheme-6a

wherein P1 and P2 of scheme 5 and scheme 6 can independently be ‘H’ or ‘O-protecting group’ or ‘amine protecting group’. The O-protecting group or amine protecting group ‘P1 and P2’ of the present invention can be independently selected from but not limited to tert-butoxycarbonyl (Boc), 3,4-dihydro-2H-pyran (DHP), formyl, acetyl, benzyl, benzoyl, benzylidinecarboalkoxy, carboaryloxy, carboaralkyloxytrifluoroacetyl, pivaloyl, tri(C1-C6 alkyl) silyl (eg. trimethylsilyl, triethsilyl, tert-butyldimethylsilyl and the like), triphenylmethyl (trityl) groups and the like and it can be removed by treating the corresponding O-protected compound or amino-protected compound with a suitable acid or a suitable base or by hydrogenolysis depending on the nature of the protecting group employed.
Acylation reagents employed in scheme 5 and scheme 6 can preferably be acetic anhydride, acetyl chloride, pentafluorophenyl acetate and the like.

Formylating reagents employed in schemes 5 and 6a can preferably be formic acid or 2,2,2-trifluoroethyl formate and the like.
Tritylation reagents employed in scheme 6 can preferably be trityl chloride, 4,4’-dimethoxytrityl chloride and the like.

The compound N-Boc-L-cis-4,5-methanoprolinamide (2) or unprotected (2) may be used either in its free base form or as its acid addition salt. Suitable acid addition salts include, but not limited to, salts with inorganic acids such as hydrochloric acid, hydrobromic acid, hydro iodic acid,sulphuric acid, nitric acid; organic acids such as formic acetic, acetic acid, propanoic acid, tartaric acid, oxalic acid, maleic acid, mandelic acid, malonic acid, methane sulphonic acid, p-toluene sulphonic acid or trifluoroacetic acid or any other suitable acid.

Coupling agents as used in schemes 5, 6and 6a, with or without additives, can be independently selected from the group comprising of pivaloyl chloride, N,N’-dicyclohexylcarbodiimide (DCC), N,N’-diisopropylcarbodiimide (DPCI), N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC / DED), N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), isobutylchloroformate, diisopropylcarbodiimide (DIC), N,N’-dicarbonyldiimidazole (CDI), benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP), (7-azabenzotriazol-1-yloxy)tripyrrolidinophosphoniumhexafluorophosphate (PyAOP), N,N-Disuccinimidyl carbonate (DSC), O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluroniumtetrafluoroborate (TBTU), 1H-benzotriazolium 1-[bis(dimethylamino)methylene]-5chloro-hexafluorophosphate (1-),3-oxide (HCTU) and O-(benzotriazol-1-yl)-N,N,N’,N’-tetramethyluroniumhexafluorophosphate (HBTU).

The additives used for the coupling reaction in Schemes 5, 6 and 6a can be selected from a group comprising of 4-dimethylaminopyridine (4-DMAP), diisopropylethylamine (DIPEA), 2-methylpyridine, 2,6-dimethylpyridine (lutidine), 2,4,6-trimethylpyridine (collidine), 4-(tetrahydropyrrolidinyl)pyridine, imidazole, N-methylimidazole, diazabicycloundecane (DABCO), N-hydroxysuccinimide (HOSu), N-hydroxy-5-norbornene-2,3-dicarboximide (HONB), 1-hydroxybenzotriazole (HOBt), 6-chloro-1-hydroxybenzotriazole (Cl-HOBt), 1-hydroxy-7-azabenzotriazole (HOAt) and 3-hydroxy-4-oxo-3,4-dihydro-1,2,3-benzotriazine (HODhbt), its aza derivative (HODhat) and the like, preferably 4-dimethylaminopyridine (4-DMAP).

Deprotection of N-Boc hydroxy amide (3) to produce amino amide hydrochloride (6) in scheme 6 can be achieved by using acid; preferably hydrochloric acid.

Dehydrating reagents employed in schemes 5, 6 and 6a can be independently selected from the group comprising of phosphorus oxychloride, trifluoroacetic anhydride, acetic anhydride, p-toluenesulfonyl chloride thionyl chloride, cyanuric chloride and benzenesulfonyl chloride; preferably phosphorus oxychloride.

A suitable base for the coupling reaction as defined above in scheme 5, 6 and 6a can be independently selected from organic bases, whereas for hydrolysis reaction and neutralization reaction inorganic bases can be used. The inorganic base is selected from group comprising of ammonia, carbonates, bicarbonates, hydroxides of alkali and alkaline earth metals and the like. Organic base is selected from the group comprising methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine (TEA), N,N-diisopropylethylamine, tributylamine, triisopropylamine, pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (4-DMAP), 1,8-bis-(dimethylamino)naphthalene, 1-ethylpiperidine, 1-methylmorpholine, lutidine and mixtures thereof. Carbonates are selected from the group comprising of K2CO3, Cs2CO3 and Na2CO3 etc. Bicarbonates are selected from the group comprising of NaHCO3, KHCO3 etc. Hydroxides are selected from the group comprising ofNaOH, KOH, LiOH, CsOH etc.

A sixth aspect of the present invention encompasses a method for the preparation of (S)-N-Boc-3-hydroxyadamantylglycine (1) [Scheme-7 wherein R= COOBut] through, the method comprising the steps of:
(a) 2-(adamantan-1-yl)acetic acid (9) is treated with S-benzyl oxazolidinone to get 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10);
(b) 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10) is treated with lithium diisopropylamide (LDA) in a suitable solvent to produce an intermediate enolate compound which may be used further with or without isolation;
(c) intermediate enolate compound obtained in step “b” is treated with di-tert-butyl azodicarboxylate to get N,N-di-Boc-hydrazinocarboximide (11a);
(d) hydrolysis of N,N-di-Boc-hydrazinocarboximide(11a) in a suitable solvent to get N,N-di-Boc-hydrazino acid (12a);
(e) deprotection of N,N-di-Boc-hydrazino acid (12a) followed by salt formation in presence of an acid to get hydrazino acid addition salt (13), with or without isolation of intermediate compound;
(f) hydrogenolysis of hydrazino acid addition salt(13)in the presence of Raney Nickel in a suitable solvent to get adamantyl glycine acid addition salt (14);
(g) Boc protection of adamantyl glycine acid addition salt (14) to get an intermediate compound followed by the subsequent hydroxylation to obtain N-Boc-3-hydroxyadamantylglycine (1), with or without isolation of an intermediate compound; and
(h) optionally, purifying compound (1)in a suitable solvent.

Scheme-7

wherein R is COOR’ and R’ is C1-C6 alkyl.

A seventh aspect of the present invention encompasses a method for the preparation of (S)-N-Boc-3-hydroxyadamantylglycine (1) [Scheme-8 wherein R’= Methyl] through, the method comprising the steps of:
(a) esterification of 2-(3-hydroxyadamantyl-1-yl)-2-oxo-acetic acid (15) in a suitable solvent to get methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a);
(b) reacting methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a);
(c) diastereo selective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(3-hydroxyadamantan-1-yl)acetate (18a),wherein, compound (17a) can be used further with or without isolation for the preparation of compound (18a);
(d) removal of chiral auxiliary (18a) using Pd(OH)2-C in presence of Boc anhydride to obtain an intermediate compound (19a), which may be used further with or without isolation;
(e) hydrolyzing an intermediate compound (19a) obtained in step “d” to obtain 3-hydroxyadamantyl N-Boc glycine (1) and
(f) optionally, purifying compound (1)in a suitable solvent.
Scheme-8

wherein R’ is C1-C6 alkyl.
An eighth aspect of the present invention encompasses a method for the preparation of (S)-N-Boc-3-hydroxyadamantylglycine (1) [Scheme-9 wherein R’=Methyl] through, the method comprising the steps of:
(a) esterification of 2-(adamant-1-yl)-2-oxo-acetic acid (20) in a suitable solvent to get methyl 2-(adamant-1-yl)-2-oxo acetate (21a);
(b) reacting methyl 2-(adamant-1-yl)-2-oxo acetate (21a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a);
(c) diastereoselective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(adamantan-1-yl)acetate (23a), wherein, compound (22a) can be used further with or without isolation for the preparation of compound (23a);
(d) removal of chiral auxiliary (23a) using Pd(OH)2-C in presence of Boc anhydride to obtain an intermediate compound (24a), which may be used further with or without isolation;
(e) hydrolyzing an intermediate compound (24a) obtained in step “d” to obtain (2S)-N-Boc-2-(adamant-1-yl) glycine (14);
(f) hydroxylation of (2S)-N-Boc-2-(adamant-1-yl)-glycine (14) to produce 3-hydroxyadamantyl N-Boc glycine (1) and
(g) optionally, purifying compound (1) in a suitable solvent.
Scheme-9

wherein R’ is C1-C6 alkyl.
The reducing agent used in scheme-8 and scheme-9 for the reductive amination can be selected from the group comprising of sodium borohydride, sodium triacetoxyborohydride sodium cyanoborohydride and trialkylsilane in acidic medium or palladium carbon or platinum on carbon, platinum oxide, palladium hydroxide on carbon and Raney nickel under H2 atmosphere; acid is selected from acetic acid, formic acid, trifluoroacetic acid, propanoic acid, pivaloic acid isobutyric acid and the like; preferably, reducing agent is sodium borohydride in acetic acid

Bases as used above in scheme 7, scheme 8 and scheme 9 can be independently selected from organic bases, whereas for hydrolysis reaction and neutralization reaction inorganic bases can be used. The inorganic base is selected from group comprising of ammonia, carbonates, bicarbonates, hydroxides of alkali and alkaline earth metals and the like. Organic base is selected from the group comprising methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine (TEA), N,N-diisopropylethylamine, tributylamine, triisopropylamine, pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (4-DMAP), 1,8-bis-(dimethylamino)naphthalene, 1-ethylpiperidine, 1-methylmorpholine, lutidine and mixtures thereof. Carbonates are selected from the group comprising of K2CO3, Cs2CO3 and Na2CO3 etc. Bicarbonates are selected from the group comprising of NaHCO3, KHCO3 etc. Hydroxides are selected from the group comprising of NaOH, KOH, LiOH, CsOH etc.

Oxidizing agent used in scheme 7 and scheme 9 can be independently selected from potassium permanganate, hydrogen peroxide, sulfuric acid, peroxymonosulfuric acid, peroxydisulfuric acid, sodium perborate, nitrous oxide, silver oxide, potassium nitrate etc.

The solvents as used above in any of the schemes can be independently selected from the group comprising of nitriles, alcohols, ketones, esters, halogenated hydrocarbons, ethers, amides, dialkylsulfoxides, hydrocarbons, organic acids, water or the mixtures thereof. Nitriles are selected from the group comprising of acetonitrile, propionitrile, butyronitrile, valeronitrile and the like. Alcohols are selected from the group comprising of methanol, ethanol, n-propanol, isopropanol, n-butanol and the like. Ketones are selected from the group comprising of acetone, methyl ethyl ketone, methyl isobutyl ketone and the like. Esters are selected from the group comprising of ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate and the like. Halogenated hydrocarbons are selected from the group comprising of dichloromethane (DCM), chloroform, dichloroethane, chlorobenzene and the like. Ethers are selected from the group comprising of diethyl ether, methyl tert-butyl ether (MTBE), diisopropyl ether, tetrahydrofuran (THF), dioxane and the like. Amides are selected from the group comprising of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylformamide, N-methylpyrrolidone and the like. Dialkylsulfoxides can be selected from the group comprising of dimethylsulfoxide, diethylsulfoxide, dibutylsulfoxide and the like. Aliphatic hydrocarbons are selected from the group comprising of alkanes or cycloalkanes such as pentane, hexane, heptane, octane, cyclohexane, cyclopentane and the like. Aromatic hydrocarbons are selected from the group comprising of toluene, xylene and the like. Organic acids are selected from the group comprising of acetic acid, formic acid, propionic acid and the like. The selection of the solvent is appropriate with proviso that for the reduction reaction, the solvents such as alcohols and ketones are not used.

In another aspect there is provided a pharmaceutical composition that includes a therapeutically effective amount of saxagliptin its pharmaceutically acceptable salts or hydrates thereof according to the process of the present invention and one or more pharmaceutically acceptable carriers, excipients or diluents.

In yet another aspect there is provided a use of a pharmaceutical composition that includes a therapeutically effective amount of saxagliptin its pharmaceutically acceptable salts or hydrates thereof according to the process of the present invention and one or more pharmaceutically acceptable carriers, excipients or diluents useful in the treatment of diabetes and complications thereof, hyperglycemia, Syndrome X, hyperinsulinemia, obesity, and atherosclerosis and related diseases as well as immunomodulatory diseases and chronic inflammatory bowel disease.

Saxagliptin or its salt, preferably hydrochloride salt of saxagliptin of the formula (I) obtained according to the process of the present invention may be substantially free of one or more impurities selected from the following compounds or their salts or O- or N-protected / deprotected forms or isomers thereof. Substantially free as described herein refers to the purity of compound saxagliptin or its salt, preferably hydrochloride salt of saxagliptin of the formula (I) to be more than 99%, preferably 99.5%, more preferably 99.7%.

The details of the process of the invention are provided in the Examples given below, which are provided by way of illustration only and therefore should not be construed to limit the scope of the invention.

Examples:

Example-1 (as per scheme 5)
Example 1(a): (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolin-amide i.e.(1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-hydroxytricyclo-[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Boc hydroxy amide)
To a stirred solution of N-Boc-L-cis-4,5-methanoprolinamide (9.1 g) in dichloromethane (200 mL) was added trifluoroacetic acid (58.8 mL) drop wise at 25-30°C and stirred for 3-4 hrs. The reaction mass was concentrated under vacuum at 45-50°C to obtain TFA salt of L-cis-4,5-methanoprolinamide which was dissolved in ethyl acetate (100 mL) at 25-30°C. In a separate flask to a stirred cooled (-20°C) solution of (S)-N-Boc-3-hydroxyadamantylglycine (25 g) in ethyl acetate (200 mL) was added dropwise pivaloyl chloride (10.18 g). After 30 min, triethylamine (38.8g) was added to the reaction mixture and stirred for 2 hrs at -15 to -20°C. To this reaction mixture was added the above ethyl acetate solution of TFA salt of L-cis-4,5-methanoprolinamide at -15 to -20°C in 15-20 min. The reaction was warmed to 25-30°C and stirred for 16 hrs. Reaction was quenched with 10% aqueous hydrochloric acid (100 mL). Organic layer was washed successively with saturated sodium bicarbonate solution (2x100 mL) followed by brine (100 mL) and concentrated under vacuum at 45-50°C. The residue obtained was crystallized in a mixture of methyl tert-butyl ether (125 mL) and cyclohexane (250 mL) at 25-30°C. The precipitated solid was filtered, washed with cyclohexane (2x50 mL) and dried under vacuum at 25-30°C to furnish the title compound.
Weight: 27g
Yield: 81%

Example 1(b): (S)-N-Boc-3-formyloxyadamantylglycine-L-cis-4,5-methanoprolinamide i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-formyloxytricyclo[3.3.1.13,7]
dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (O-Formyl N-Boc amide)
To a mixture of acetic anhydride (14.1 mL) and formic acid (10.6 mL) was added N-Boc hydroxy amide (10 g) at 25-30°C and stirred for 16 hrs. The reaction mass was concentrated to dryness under vacuum at 45-50°C to obtain a residue which was dissolved in toluene (150 mL) and successively washed with water (100 mL), saturated sodium bicarbonate solution (100 mL) followed by brine (100 mL). Solvent was distilled completely under vacuum at 45-50°C to afford the title compound, O-formyl N-Boc amide.
Weight: 10.5g
Yield: 99%
1H NMR (400 MHz) : (CDCl3, d): 0.82-0.83 (m. 1H), 0.85-0.87 (m, 1H), 1.43-1.46 (m, 9H), 1.52-1.58 (M, 2H), 1.68-1.83 (m, 4H), 1.99-2.15 (m, 6H), 2.22-2.37 (m, 4H), 2.55-2.59 (d, J=13.2 Hz, 1H), 3.68 (bs, 1H), 4.55-4.57 (d, J=9.6 Hz, 1H), 4.91-4.93 (m, 1H), 5.38-5.40 (d, J=8 Hz, 1H), 5.50 (bs, 1H), 6.93 (bs, 1H), 7.18-7.27 (m, 1H) , 8.03 (s, 1H)
MS(m/z) : 484 (M+Na).

Example 1(c): (S)-N-Boc-3-formyloxyadamantylglycine-L-cis-4,5-methanoprolinenitrile i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-formyloxytricyclo[3.3.1.13,7]
dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile (O-Formyl N-Boc nitrile)
To a stirred and cooled (0-5°C) solution of O-formyl N-Boc amide(5 g) and triethylamine (7.54 mL) in dichloromethane (120 mL) was added phosphorus oxychloride (1.5 mL) then warmed to 25-30°C and stirred for 1 hr. The reaction mass was diluted with dichloromethane (50 mL) and made basic with cold (0°C) 5% aqueous sodium hydroxide solution. The organic layer was washed successively with 20% aqueous potassium bisulfate solution (2x50 mL), saturated sodium bicarbonate solution (50 mL) followed by brine (120 mL). The separated organic layer was treated with silica gel (5 g) and activated charcoal (1 g) for 30 min and filtered through hyflo. Solvent was evaporated off completely under vacuum at 45-50°C to furnish the title compound, O-formyl N-Boc nitrile.
Weight: 4.1g
Yield: 85%
1H NMR (400 MHz) : (CDCl3, d): 1.06-1.11 (m. 2H), 1.44 ( s, 9H), 1.55-1.68 (m, 4H), 1.77-1.80 (m, 2H), 1.90-1.97 (m, 2H), 2.04-2.16 (m, 4H), 2.21-2.24 (m, 1H), 2.32-2.41 (m, 3H), 2.55-2.63 (m, 1H), 3.84-3.85 (m, 1H), 4.47-4.50 (d, J=10 Hz, 1H), 5.04-5.07(dd, J=2 Hz, 2 Hz, 1H), 5.30-5.32 (d, J= 9.6 Hz,1H), 8.04 (s, 1H).
MS(m/z) : 442.19 (M_H).

Example 1(d): (S)-3-hydroxyadmantylglycine-L-cis-4,5-methanoprolinenitrile HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride, (Saxagliptin hydrochloride dihydrate – Ia’ )
To a stirred solution of O-formyl N-Boc nitrile (4.0 g) in ethyl acetate (40 mL) was added conc. hydrochloric acid (4.5 mL) at 25-30°C and stirred for 2 hrs. The reaction mass was diluted with ethyl acetate (40 mL) and stirred at 5-10°C for 2 hrs. The precipitated solid was filtered, washed with ethyl acetate (10 mL) and dried under vacuum at 25-30°C to furnish Saxagliptin hydrochloride (dihydrate) (Fig. 5).
Weight: 2.6g
Yield: 82%

Example 2 (as per scheme 5)
Example 2(a): (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolin-amide i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-hydroxytricyclo-[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Bochydroxy amide)
Preparation of compound N-Bochydroxy amide is same as described in Example 1; 1(a).

Example 2(b): (S)-N-Boc-2-(3-acetoxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolinamide i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-acetoxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (O-Acetyl N-Boc amide)
To a stirred solution of acetic anhydride (9.4 g) in dichloromethane (100 mL) and conc. sulfuric acid (1 mL) was added N-Boc hydroxy amide (10 g) at 25-30°C and stirred for 2-3 hrs. pH of the reaction mass was adjusted to 7-8 with aqueous sodium carbonate solution. Organic layer after washing with brine (50 mL) was concentrated to dryness under vacuum at 45-50°C to afford the title compound, O-acetyl N-Boc amide.
Weight: 10g
Yield: 91%

Example 2(c): (S)-N-Boc-3-acetoxyadamantylglycine-L-cis-4,5-methanoprolinenitrile i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-acetoxytricyclo[3.3.1.13,7]-dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile (O-Acetyl N-Boc nitrile)
To a stirred and cooled (0-5°C) solution of O-acetyl N-Boc amide(12 g) and triethylamine (17.6 mL) in dichloromethane (120 mL) was added phosphorus oxychloride (3.5 mL) then warmed to 25-30°C and stirred for 1 hr. The reaction mass was diluted with dichloromethane (120 mL) and made basic with cold (0°C) 5% aqueous sodium hydroxide solution. The organic layer was washed successively with 20% aqueous potassium bisulfate solution (2x120 mL), saturated sodium bicarbonate solution (120 mL) followed by brine (120 mL). The separated organic layer was treated with silica gel (12 g) and activated charcoal (1.2 g) for 30 min and filtered through hyflo. Solvent was evaporated off completely under vacuum at 45-50°C to furnish the title compound, O-acetyl N-Boc nitrile.
Weight: 9.5g
Yield: 82%

Example 2(d): (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinenitrile HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride, (Saxagliptin hydrochloride)
To a stirred solution of O-acetyl N-Boc nitrile (3.0 g) in methanol (30 mL) was added conc. hydrochloric acid (6.85 mL) at 25-30°C and stirred for 16 hrs. The reaction mass was concentrated under vacuum at 40-45°C to obtain an oily residue. To the stirred solution of the above residue in methanol (10 mL) was added methyl tert-butyl ether (MTBE) (40 mL) at 25-30°C and stirred for 2 hrs. The precipitated solid was filtered, washed with MTBE (10 mL) and dried under vacuum at 45-50°C to furnish Saxagliptin hydrochloride.
Weight: 1.8g
Yield: 78%

Example 3 (as per scheme 6)
Example 3(a): (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolin-amide i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Boc hydroxy amide)
Preparation of compound N-Boc hydroxy amide is same as described in Example 1; 1(a).

Example 3(b): (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinamide HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide Hydrochloride, (Amino amide hydrochloride)
To a stirred solution of N-Boc hydroxy amide (4g) in ethyl acetate (20 mL) was added saturated hydrochloric acid in ethyl acetate (20 mL) at 25-30°C and stirred for 16 hrs. During stirring solid was precipitated out from the reaction mixture. The solid was filtered, washed with ethyl acetate (8 mL) and dried under vacuum at 25-30°C to furnish the title compound, amino amide hydrochloride.
Weight: 2.8g
Yield: 82%

Example 3(c): (S)-N-Acetyl-3-acetoxyadamantylglycine-L-cis-4,5-methanoprolinamide i.e. (1S,3S,5S)-2-[(2S)-2-acetylamino-2-(3-acetoxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (di-acetyl amino amide)
A solution of amino amide hydrochloride (2 g) in acetic anhydride (20 mL) was stirred at 25-30°C for 24 hrs. The reaction mass was concentrated to dryness under vacuum at 45-50°C. Toluene solution (30 mL) of the obtained residue was successively washed with saturated sodium bicarbonate solution (2x20 mL) followed by brine (20 mL). Evaporation of solvent under vacuum at 45-50°C afforded the title compound, diacetyl amino amide.
Weight: 2 g
Yield: 88%

Example 3(d): (S)-N-Acetyl-3-acetoxyadamantylglycine-L-cis-4,5-methanoprolinenitrile i.e. (1S,3S,5S)-2-[(2S)-2-acetylamino-2-(3-acetoxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile (di-acetyl amino nitrile)
To a stirred and cooled (0-5°C) solution of diacetyl amino amide (2 g) and triethylamine (3.34 mL) in dichloromethane (20 mL) was added phosphorus oxychloride (0.66 mL) then warmed to 25-30°C and stirred for 1 hr. The reaction mass was diluted with dichloromethane (20 mL) and made basic with cold (0°C) 5% aqueous sodium hydroxide solution. The organic layer was washed successively with 20% aqueous potassium bisulfate solution (2x20 mL), saturated sodium bicarbonate solution (20 mL) followed by brine (20 mL). The separated organic layer was treated with silica gel (2 g) and activated charcoal (0.5 g) for 30 min and filtered through hyflo. Solvent was evaporated off completely under vacuum at 45-50°C to furnish the title compound, diacetyl amino nitrile.
Weight: 1.2 g
Yield: 63%

Example 3(e): (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinenitrile HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride, (Saxagliptin hydrochloride)
To a stirred solution of diacetyl amino nitrile (0.5 g) in methanol (5 mL) was added conc. hydrochloric acid (1.1 mL) at 25-30°C and stirred for 16 hrs. The reaction mass was concentrated under vacuum at 40-45°C to obtain an oily residue which was purified by column chromatography eluting with dichloromethane to 8% methanol in dichloromethane to afford pure Saxagliptin hydrochloride.
Weight: 0.18 g
Yield: 41%

Example-4 (as per scheme 6)

Example 4(a): (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolin-amide i.e. (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Boc hydroxy amide)
Preparation of compound N-Boc hydroxy amide is same as described in Example 1; 1(a).

Example 4(b): (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinamide HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide Hydrochloride, (Amino amide hydrochloride)
Preparation of compound Amino amide hydrochloride is same as described in example 3; 3(b).

Example 4(c): (S)-N-Trityl-3-hydroxyadamantylglycine-L-cis-4,5-methanoprolinamide i.e. (1S,3S,5S)-2-[(2S)-2-(tri-phenylmethyl)amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Trityl hydroxy amide)
To a stirred and cooled (5°C) solution of amino amide hydrochloride (2 g) in dichloromethane (20 mL) was slowly added triethylamine (1.36 g) followed by slow addition of trityl chloride (1.36 g) at 5-10°C. The reaction mass was then warmed to 25-30°C and stirred for 6 hrs. Reaction mass was quenched with water and the organic layer was successively washed with 20% aq. potassium bisulfate solution (20 mL) followed by brine (20 mL). Evaporation of solvent under vacuum at 40-45°C resulted in a solid mass which was recrystallized from a mixture of IPA (4 mL) and DIPE (40 mL). The solid was filtered, washed with DIPE (10 mL) and dried under vacuum at 40-45°C to provide the title compound (trityl amide).
Weight: 2.5 g
Yield: 81%

Example 4(d): (S)-N-Trityl-3-hydroxyadamantylglycine-L-cis-4,5-methanoprolinenitrile i.e. (1S,3S,5S)-2-[(2S)-2-(tri-phenylmethyl)amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (N-Trityl hydroxy nitrile)
To a stirred and cooled (0-5°C) solution of N-trityl hydroxy amide(2 g) and triethylamine (2.1 g) in dichloromethane (20 mL) was added phosphorus oxychloride (1.06 g) then warmed to 25-30°C and stirred for 2 h. The reaction mass was diluted with dichloromethane (20 mL) and made basic with cold (0°C) 5% aqueous sodium hydroxide solution. The organic layer was washed successively with 20% aqueous potassium bisulfate solution (2x20 mL), saturated sodium bicarbonate solution (20 mL) followed by brine (20 mL). The resulting organic layer was treated with silica gel (5 g) and activated charcoal (1 g) for 30 min and filtered through hyflo. Solvent was evaporated off completely under vacuum at 45-50°C to furnish the title compound, N-trityl nitrile.
Weight: 1.8 g
Yield: 93%

Example 4(e): (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinenitrile HCl salt i.e. (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride, (Saxagliptin hydrochloride dihydrate- Ia’)
To a stirred solution of N-trityl nitrile (1.5 g) in ethyl acetate (15 mL) was added conc. hydrochloric acid (2.4 mL) at 25-30°C and stirred for 2 hrs. The reaction mass was diluted with ethyl acetate (7.5 ml) and stirred at 5-10°C for 2 hrs. The precipitated solid was filtered, washed with ethyl acetate (10 mL) and dried under vacuum at 25-30°C to furnish Saxagliptin hydrochloride (dihydrate).
Weight: 0.85 g
Yield: 89.8%

Preparation of (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine
Example-5 (as per scheme-7)
Example 5(a): (4S)-3-[2-(Adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one or (4S)-3-[1-oxo-2-(adamantan-1-yl)ethyl]-4-(phenylmethyl)oxazolidin-2-onei.e. (4S)-3-[2-(Adamantan-1-yl)-1-oxoethyl]-4-benzyloxazolidin-2-one
A mixture of 2-(adamantan-1-yl)acetic acid (24.15 g), dimethylformamide (DMF) (1 mL) and thionyl chloride (50 mL) was stirred at 25-30°C for 2 hrs. The reaction mass was concentrated to dryness under vacuum at 50-55°C. To the solution of residue obtained in toluene (200 mL) was successively added S-benzyl oxazolidinone (20 g), triethylamine (46.3 mL) followed by dimethylaminopyridine (DMAP) (1.4 g) at 25-30°C. The resulting mixture was stirred at 65-70°C for 16 hrs. After cooling to 25-30°C, the reaction mixture was quenched with 1N hydrochloric acid solution (200 mL). The organic layer was successively washed with 1N hydrochloric acid solution (2x200 mL), saturated sodium bicarbonate solution (200 mL) followed by water (200 mL). Evaporation of solvent under vacuum at 50-55°C resulted in an oily mass which was crystallized from a mixture of ethyl acetate (100 mL) and hexanes (300 mL) at 25-30°C. The precipitated solid was filtered, washed with hexanes (100 mL) and dried under vacuum at 45-50°C to furnish the title compound.
Weight: 25 g
Yield: 57%

Example 5(b): [3(2S), 4S]-3-{2-[1,2-bis-(tert-butoxycarbonyl)hydrazino]-2-(adamantan-1-yl)acetyl}-4-benzyloxazolidin-2-one i.e. [3(2S),4S]-3-{2-[N,N’-bis-(tert-butoxycarbonyl)hydrazino]-2-(adamantan-1-yl)-1-oxoethyl}-4-(phenylmethyl)-2-oxazolidinone i.e. [3(2S),4S]-3-{1-Oxo-2-[1,2-bis-(tert-butoxycarbonyl)hydrazino]-2-(adamantan-1-yl)ethyl}-4-benzyloxazolidin-2-one
To a freshly prepared solution of 0.102 mol of lithium diisopropylamide (LDA) in THF [Prepared by stirring a mixture of diisopropylamine (17.9 mL) and n-BuLi (2.5M in n-hexane (20.5 mL) in THF (100 mL) at 0 to 5°C for 1 hr] was added a solution of N-acyl oxazolidinone derivative of adamantanyl acetic acid (15 g) in THF (100 mL) at -78°C under nitrogen atmosphere and stirring was continued at -78° for 45 min. A solution of di-tert-butyl azodicarboxylate (11.75 g) in THF (100 mL) was added to the above enolate solution at -78°C and stirred for additional 10-15 min. The reaction was quenched by 10% aqueous ammonium chloride solution (150 mL), warmed to 25-30°C and extracted with ethyl acetate (2x250 mL). The combined organic phase was washed with brine (150 mL) and concentrated under vacuum at 50-55°C to afford the title compound.
Weight: 30 g

Example 5(c): (2S)-2-[1,2-bis-(tert-butoxycarbonyl)hydrazino]-2-(adamantan-1-yl)acetic acid i.e. (2S)-2-[N,N’-bis-(tert-butoxycarbonyl)hydrazino]-2-(adamantan-1-yl)ethanoic acid
To a stirred and cooled (5°C) solution of lithium hydroxide monohydrate (4.32 g) in water (50 mL) was added 30% hydrogen peroxide solution (34.8 mL) at 0-5°C and stirred for 1 hr. In a separate flask to a stirred and cooled (0-5°C) solution of the N,N-di-Boc hydrazinocarboximide (30 g) in a mixture of THF (300 mL) and water (120 mL) was added the above prepared lithium hydroperoxide solution at 0-5°C and stirred at the same temperature for 16 hrs. The reaction was quenched with 1.5N sodium sulphite solution (300 mL). Following removal of THF under vacuum, the mixture was extracted with cyclohexane (2x200 mL). The basic cyclohexane layer containing lithium salt of the product was acidified to pH ~4 with dilute hydrochloric acid. Concentration of cyclohexane layer under vacuum at 45-50°C provided a crude mass which was purified by column chromatography eluting with 5% to 10% ethyl acetate in hexanes to afford the title compound.
The acidic aqueous layer was made basic to pH 10-11 and extracted with DCM. Evaporation of DCM layer under vacuum provided the chiral auxiliary which could be used after purification, by recrystallization or chromatoghraphy.
Weight: 16.5 g
Yield: 93% (starting from Ex-5(b))

Example 5(d): (S)-2-Hydrazino-2-(adamantan-1-yl)acetic acid TFA salt i.e. (2S)-2-Hydrazino-2-(adamantan-1-yl)ethanoic acid TFA salt
To a stirred solution of N,N-di-Boc hydrazino acid (16 g) in DCM (160 mL) was added trifluoroacetic acid (14.5 mL) at 25-30°C and stirred for 18 hrs. After completion of reaction, solvents were evaporated under vacuum at 45-50°C. The obtained residue was crystallized in ethyl acetate (80 mL) and filtered. The solid was dried to afford the title compound.
Weight: 8.5 g
Yield: 65%

Example 5(e): (S)-2-(adamantan-1-yl)glycine OR (S)-2-Amino-2-(adamantan-1-yl)ethanoic acid trifluoroacetic acid salt
To a solution of hydrazino acid TFA salt (8.5 g) in methanol (100 mL) was added Raney Ni (3.2 g) and stirred under hydrogen atmosphere (5 Kg/cm2) at 25-30ºC for 6 hrs. The catalyst was removed by filtration over hyflo-bed, washed with methanol (2x50 mL) and the filtrate was concentrated under vacuum at 45-50°C. The obtained residue was stirred in ethyl acetate (80 mL) at 55-60°C for 30 min and then at 25-30°C for next 30 min. The solid was filtered, washed with ethyl acetate (2x20 mL) and dried under vacuum at 45-50°C to afford the title compound.
Weight: 5 g
Yield: 62%

Example 5(f): (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine i.e. (S)-2-[tert-butyloxycarbonylamino]-2-(3-hydroxyadamantan-1-yl)acetic acid i.e. (S)-2-[tert-butyloxycarbonylamino]-2-(3-hydroxyadamantan-1-yl)ethanoic acid
To a stirred solution of TFA salt of (2S)-(adamantan-1-yl)glycine (4.5g) in a mixture of THF (25 mL) and water (45 mL) was added sodium hydroxide (1.72 g) at 25-30°C. To the above solution was added Boc anhydride (5.63g) at 5-10°C then gradually warmed to 25-30°C and stirred for 3 hrs. After completion on TLC, the reaction mixture was acidified to pH 2-3 with 20% aqueous potassium bisulfate solution and extracted with ethyl acetate (4x50 mL), the combined organic layer was washed with water (50 mL). Evaporation of solvent under vacuum at 45-50°C afforded the desired (S)-N-Boc-2-(adamantan-1-yl)glycine (6 g).
A solution of potassium hydroxide (1.63 g) and potassium permanganate (4.6 g) in water (60 mL) was stirred to 55-60°C for 15 min and then the above isolated viscous mass (6 g) was added portion wise at 55-60°C. The resulting mixture was stirred at 85-90°C for 30 min. After completion the reaction mass was cooled to 25°C and then acidified to pH 2-3 at 0-5°C with 20% aqueous potassium bisulfate solution. The reaction mass was then extracted with ethyl acetate (3x60 mL), washed the combined organic layer with brine solution (50 mL). Concentration of ethyl acetate layer under vacuum at 45-50°C afforded crude product (4.6 g) which was purified by column chromatography eluting with dichloromethane to 4% methanol in dichloromethane to afford the title compound.
Weight: 2.5 g
Yield: 36%

Example-6 (as per scheme 8)
Example 6(a): Preparation of Methyl 2-(3-Hydroxyadamantan-1-yl)-2-oxo acetate
To a stirred solution of 2-(3-hydroxy-adamantan-1-yl)-2-oxo-acetic acid (10g) in methanol (100 mL) was added thionyl chloride (11.3 g) at 0-5°C. Reaction mass was gradually warmed to 25-30°C and stirred overnight till to completion on TLC. Concentration of reaction mass under vacuum at 45-50°C provided a residue which was dissolved in ethyl acetate (100 mL), washed with saturated sodium bicarbonate solution (100 mL) followed by brine (100 mL). Evaporation of solvent under vacuum at 45-50°C afforded the desired product.
Weight: 10g
Yield: 94%

Example 6(b): Preparation of (2S)-Methyl 2-{[(R)-1-phenylethyl]amino}-2-(3-hydroxyadamantan-1-yl)acetate
A mixture of (3-hydroxyadamantan-1-yl)-2-oxo acetic acid methyl ester (3 g), (R)-phenyl ethylamine (6.11 g) and acetic acid (3.8 g) in toluene (50 mL) was stirred under to reflux in Dean-Stark apparatus for 8-10hrs. After completion of (TLC and mass analysis), reaction mass was cooled to 25-30°C then acetic acid (3.8 mL) was added. To the resulting reaction mass was added sodium borohydride (0.97 g) at 0-5°C then it was gradually warmed to 25-30°C and stirred for 2hrs. After completion, the reaction (TLC & mass analysis) mass was diluted with water (50 mL) then made alkaline to pH to 9.0-9.5 using sodium carbonate solution. Separating the organic layer, aqueous layer was extracted with toluene (50 mL). The combined organic layer was washed with water (50 mL) followed by concentration under vacuum at 45-50°C afforded the title compound.
Weight: 4.3 g
Yield: 99%

Example 6(c): Preparation of (2S)-Methyl N-[tert-Butyloxycarbonylamino]-2-(3-hydroxyadamantan-1-yl)acetatei.e. (2S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine methyl ester
To a mixture of (2S)-Methyl 2-{[(R)-1-phenylethyl]amino}-2-(3-hydroxyadamantan-1-yl)acetate(15 g) and Boc anhydride (11.4 g) in THF (150 mL) was added Pd(OH)2-C and stirred under hydrogen pressure (3 Kg/cm2) for 15 hrs. After completion the reaction mass was filtered over hyflo and the bed was washed with THF (50 mL). The combined filtrate and washing was concentrated under vacuum at 45-50°C to half of the volume and directly used in the next step.

Example 6(d): Preparation of (S)-2-[tert-Butoxycarbonylamino]-(3-hydroxyadamantan-1-yl)acetic acid i.e. (2S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine
To the mixture of above obtained THF solution of (2S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine methyl ester and water (75 mL) was added sodium hydroxide (5.23 g) followed by lithium hydroxide monohydrate (5.5 g) at 25-30°C and stirred for overnight. After completion, the reaction mass was diluted with water (75 mL). The aqueous solution obtained after evaporation off THF under vacuum at 45-50°C was washed with ethyl acetate (2x75 mL). The aqueous layer was made acidic to pH 2-3 with 20% aqueous potassium bisulfate solution and then extracted with ethyl acetate (3x100 mL). The combined organic layer was washed with brine (100 mL) and concentrated under vacuum at 45-50°C to give an oily mass which was crystallized with a mixture of ethyl acetate (40 mL) and n-heptane (80 mL) to afford the title compound.
Weight: 6.2 g
Yield: 44%

Example-7 (as per scheme 9)
Example 7(a): Preparation of Methyl 2-(adamantan-1-yl)-2-oxo acetate
To a stirred solution of 2-(adamantan-1-yl)-2-oxo-acetic acid (10 g) in methanol (100 mL) was added thionyl chloride (11.3 g) at 0-5°C. Reaction mass was gradually warmed to 25-30°C and stirred overnight till to completion on TLC. Concentration of reaction mass under vacuum at 45-50°C provided a residue which was dissolved in ethyl acetate (100 mL), successively washed with saturated sodium bicarbonate solution (100 mL) brine (100 mL) followed by water (100 mL). Evaporation of solvent under vacuum at 45-50°C afforded the desired product.
Weight: 10 g
Yield: 94%

Example 7(b): Preparation of (2S)-Methyl 2-{[(R)-1-phenylethyl]amino}-2-(3-hydroxyadamantan-1-yl)acetatei.e. (2S)-N-[(R)-1-Phenylethyl]-2-(adamantan-1-yl)glycine methyl ester
To a stirred mixture of methyl 2-(adamantan-1-yl)-2-oxo acetate (6 g), (R)-phenyl ethyl amine (3.93 g) and triethylamine (TEA) (9.2 mL) in toluene (60 mL) was added titanium tetrachloride (1.57 mL) at 10-15°C. The reaction mass was stirred under reflux for 24 hrs. After completion, the reaction mixture was cooled to 25-30°C, filtered over hyflo and washed the bed with toluene (2x25 mL). The combined filtrate and washing was concentrated under vacuum at 45-50°C to afford the enamino ester (8.5 g).
To a mixture of above enamino ester and acetic acid (22.1g) in toluene (120 mL) was added sodium borohydride (2.8 g) at 0-5°C. The reaction mixture was gradually warmed to 25-30°C and stirred for 2 hrs. After completion the reaction mixture was diluted with water (50 mL) then acidified to pH 9.0-9.5 with 10% sodium hydroxide solution. Separating organic layer aqueous layer was extracted with toluene (120 mL) and the combined organic layers were washed with water (2x100 mL). Evaporation of solvent from the organic layer under vacuum at 45-50°C afforded the title compound.
Weight: 12 g

Example 7(c): Preparation of (2S)-N-Boc-2-(adamantan-1-yl)glycine methyl ester i.e. (S)-2-(tert-Butyloxycarbonylamino)-2-(adamantan-1-yl)acetic acid methyl ester
To a mixture of (2S)-N-[(R)-1-phenylethyl]-2-(adamantan-1-yl)glycine methyl ester (12 g) and Boc anhydride (9.6 g) in THF (120 mL) was added Pd(OH)2-C (2.5). The mixture was stirred under hydrogen pressure (3 Kg/cm2) for 20 hrs. After completion, the catalyst was filtered off over hyflo and the bed was washed with THF (60 mL). The combined filtrate and washing was concentrated under vacuum at 45-50°C to half of the volume and directly used in the next step.

Example 7(d): Preparation of (2S)-N-tert-butyloxycarbonyl-2-(adamantan-1-yl)glycinei.e. (S)-2-(tert-butoxycarbonylamino)-2-(adamant-1-yl)acetic acid
To the mixture of THF solution of (2S)-N-Boc-2-(adamantan-1-yl)glycine methyl ester (obtained in previous step) and water (60 mL) was added lithium hydroxide monohydrate (7.7 g) at 25-30°C and stirred for overnight. After completion the reaction mass was diluted with water (75 mL). The aqueous solution obtained after evaporating off THF under vacuum at 45-50°C was washed with ethyl acetate (2x75 mL). The aqueous layer was made acidic to pH 2-3 with 20% aqueous potassium bisulfate solution and then extracted with ethyl acetate (3x100 mL). The combined organic layer was washed with brine (100 mL) and then concentrated under vacuum at 45-50°C to give an oily residue which was crystallized with a mixture of ethyl acetate (45 mL) and n-heptane (90 mL) to afford the title compound.
Weight: 7 g
Yield: 90%

Example 7(e): Preparation of (2S)-N-tert-butyloxycarbonyl-2-(3-hydroxyadamantan-1-yl)glycinei.e. (S)-2-(tert-butoxycarbonylamino)-2-(3-hydroxyadamant-1-yl)acetic acid
To a stirred solution of potassium hydroxide (1.63 g) in water (60 mL) was added potassium permanganate (10.22 g) and stirred at 55-60°C for 30 min. To the above mixture was added N-Boc-2-(adamantan-1-yl)glycine (5g) portion wise at 55-60°C. The resulting mixture was stirred at 85-90°C for 2 hrs. After completion, the reaction mass was cooled to 25°C, acidified to pH 2-3 at 0-5°C with 20% aqueous potassium bisulfate solution and extracted with ethyl acetate (3x60 mL). The organic layer after washing with brine (50 mL) was concentrated under vacuum at 45-50°C to give an oily residue which was purified by column chromatography eluting with dichloromethane to 3% methanol in dichloromethane to afford the title compound.
Weight: 3.2g
Yield: 61%

Example-8
Preparation of (R)-N-Boc-2-(3-hydroxyadamantan-1-yl) glycine (Undesired (R) isomer KSM)
Example 8(a): 2-Bromo-2-(adamantan-1-yl) acetic acid
A mixture of 2-(adamantan-1-yl)acetic acid (50 g), DMF (1 mL) and thionyl chloride (100 mL) was stirred at 25-30°C for 2 hrs. After completion to the reaction mixture was added NBS (68.8 g) at 25-30°C and it was stirred at 65-70°C for 4 hrs. After completion, the reaction mass was concentrated to dryness under vacuum at 45-50°C and residual thionyl chloride was removed by azeotropic distillation with n-heptane under vacuum at 45-50°C. To the residue obtained was added water (500 mL) and extracted with n-heptane. The organic layer was washed with water and evaporated off completely under vacuum to obtain a residue which was stirred in a mixture of THF (500 mL) and water (250 mL) at 25-30°C for 16 hrs. The mixture was concentrated under vacuum at 45-50°C to obtain slurry which was diluted with a mixture of acetonitrile (250 mL) and water (250 mL) and stirred at 25-30°C for 2 hrs. The solid was filtered and washed with aq. acetonitrile (1:1) and dried under vacuum at 45-50°C to afford the title compound.
Weight: 62 g
Yield: 88.5%

Example 8(b): 2-Hydroxy-2-(adamantan-1-yl) acetic acid
A mixture of adamantylbromo acetic acid (50 g) and sodium hydroxide (18.4 g) in a mixture of THF (250 mL) and water (250 mL) was stirred at 70-75°C 15 hrs. After completion, the reaction mass was cooled to 25-30°C, acidified to pH ~2-3 with conc.HCl and extracted with ethyl acetate. The organic layer was washed with water and concentrated under vacuum at 45-50°C. The solid residue obtained was stirred in ethyl acetate (175 mL) at 55-60°C for 30 min to get a clear solution which was cooled to 25-30°C and was added hexanes (350 mL). The resulting mixture was stirred at 25-30°C for overnight. The precipitated solid was filtered, washed with hexanes (50x2 mL) dried under vacuum at 45-50°C to afford the title compound.
Weight: 30 g
Yield: 77.7%

Example 8(c): Methyl 2-hydroxy-2-(adamantan-1-yl) acetate
To a stirred and cooled (0-5°C) solution of adamantly hydroxyacetic acid (29 g) in methanol (232 mL) was added acetyl chloride (12 mL) and stirred at 25-30°C for 20 hrs. After completion, the reaction mass was concentrated under vacuum at 45-50°C. The residue obtained was stirred in mixture of ethyl acetate (290 mL) and saturated sodium bicarbonate solution (150 mL). The organic layer was successively washed with sodium bicarbonate (150 mL) and brine (150 mL). Solvent was evaporated off under vacuum at 45-50°C to afford the title compound.
Weight: 29 g
Yield: 94%

Example 8(d): Methyl 2-(adamantan-1-yl)-2-oxo acetate
To a cooled (-78°C) solution of oxalyl chloride (33.5 mL) in DCM (290 mL) was added a solution of dimethyl sulfoxide (55 mL) in DCM (55 mL) under nitrogen atmosphere. The reaction mixture was stirred at -78°C for 15-20 min and a solution of methyl adamantly hydroxy acetate (29 g) in DCM (120 mL) was added at -78°C. After 30 min stirring at -78°C to the reaction mixture was added triethylamine (162 mL) at the same temperature. The reaction mixture was slowly warmed to 25-30°C and stirred at for 1 hr. After completion the reaction mixture was quenched with DM water (150 mL), concentrated under vacuum at 45-50°C and extracted with ethyl acetate (450 mL). The organic layer was washed with water (100x2 mL) followed by brine (100 mL). Solvent was completely evaporated off under vacuum at 45-50°C to afford a residue which was purified by column chromatography eluting with hexanes to 2% ethyl acetate in hexanes to provide the title compound.
Weight: 23.5 g
Yield: 82%

Example 8(e): Methyl 2-(3-hydroxyadamantan-1-yl)-2-oxo acetate
To a stirred and cooled (0-5°C) conc. sulfuric acid (113.8 mL) was added 50% aq. nitric acid (10.9 mL). The mixture was stirred at 0-5°C for 15-20 min and adamantane keto methyl ester (23 g) was portionwise added at 0-5°C. The reaction mixture was stirred at 15-20°C for 1 hr. After completion, the reaction mass was quenched with water (500 mL) at -5 to -10°C and extracted with ethyl acetate. The organic layer was washed with saturated sodium bicarbonate solution (150x2 mL) and then solvent was evaporated off under vacuum at 45-50°C to afford the title compound.
Weight: 21 g
Yield: 85%

Example-9
Example 9(a): Preparation of Methyl 2-(3-hydroxyadamantan-1-yl)-2-oxo acetate
To a stirred solution of 2-(3-hydroxy-adamantan-1-yl)-2-oxo acetic acid (10 g) in methanol (100 mL) was added thionyl chloride (11.3 g) at 0-5°C. Reaction mass was gradually warmed to 25-30°C and stirred overnight till to completion on TLC. Concentration of reaction mass under vacuum at 45-50°C provided a residue which was dissolved in ethyl acetate (100 mL), washed with saturated sodium bicarbonate solution (100 mL) followed by brine (100 mL). Evaporation of solvent under vacuum at 45-50°C afforded the desired product.
Weight: 10 g
Yield: 94%

Example 9(b): Preparation of (2R)-Methyl 2-{[(S)-1-phenylethyl]amino}-2-(3-hydroxyadamantan-1-yl) acetate
A mixture of (3-hydroxyadamantan-1-yl)-2-oxo acetic acid methyl ester (10 g), (S)-phenyl ethylamine (6.11 g) and acetic acid (12.6 g) in toluene (100 mL) was stirred under reflux in Dean-Stark apparatus for 20-24 hrs. After completion the reaction mass was cooled to 25-30°C then acetic acid (12.6 g) was added. To the resulting reaction mass was added sodium borohydride (3.2 g) at 0-5°C then it was gradually warmed to 25-30°C and stirred for 2 hrs. After completion, the reaction mass was decomposed with water (50 mL) and made alkaline to pH ~9.0-9.5 with sodium carbonate solution. Separating the organic layer, aqueous layer was extracted with toluene (100 mL). The combined organic layer was washed with water (100 mL) followed by concentration under vacuum at 45-50°C afforded the title compound.
Weight: 14 g
Yield: 97%

Example 9(c): Preparation of (2R)-Methyl tert-Butyloxycarbonylamino-2-(3-hydroxyadamantan-1-yl) acetate i.e. (2R)-N-Boc-2-(3-hydroxyadamantan-1-yl) glycine methyl ester
To a mixture of (2R)-methyl 2-{[(S)-1-phenylethyl]amino}-2-(3-hydroxy-adamantan-1-yl) acetate (14 g) and Boc anhydride (10.65 g) in THF (150 mL) was added Pd(OH)2-C. The mixture was then stirred under hydrogen pressure (3 Kg/cm2) for 18 hrs. After completion the reaction mass was filtered over hyflo and washed the bed with THF (50 mL). The combined filtrate and washing was concentrated under vacuum at 45-50°C to half of the volume and directly used in the next step.

Example 9(d): Preparation of (2R)-tert-Butoxycarbonylamino-2-(3-hydroxyadamantan-1-yl) acetic acid i.e. (2R)-N-Boc-2-(3-hydroxyadamantan-1-yl) glycine
The THF solution of (2R)-N-Boc-2-(3-hydroxyadamantan-1-yl) acetic acid methyl ester (obtained in the previous step) was diluted in a mixture of water (50 mL) and methanol (50 mL) then lithium hydroxide monohydrate (8.5 g) at 25-30°C was added and stirred for overnight. After completion, the reaction mass was diluted with water (75 mL) and concentrated under vacuum at 45-50°C. The resulting reaction mass was washed with ethyl acetate (2x75 mL). The aqueous layer was made acidic to pH 2-3 with 20% aqueous potassium bisulfate solution and extracted with ethyl acetate (3x100 mL). The combined organic layer was washed with brine (100 mL). Concentration under vacuum at 45-50°C resulted in a residue which was crystallized with a mixture of ethyl acetate (50 mL) and n-heptane (100 mL) to afford the title compound.
Weight: 7.5 g
Yield: 57%

Example 10 (as per scheme 6a)
Preparation of (S)-3-hydroxydamantylglycine-L-cis-4,5-methanoprolinenitrile hydrochloride or (1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride, (Saxagliptin hydrochloride dihydrate – Ia’)

Example 10a: Preparation of (1S,3S,5S)-2-Azabicyclo[3.1.0]hexane-3-carboxamide hydrochloride or L-cis-methanoprolinamidehydochloride, (2a)

N-Boc L-cis-4,5-methanoprolinamide, 2 (10 g, 0.0442 mol) in IPA-HCl (60 mL) was stirred at 25-30°C for 12 hr. The reaction mixture was diluted with ethyl acetate (140 mL) and stirred for another 3 hr. The solid was filtered, washed with ethyl acetate (20 mL). The wet solid was suspended in ethyl acetate (50 mL) and stirred for 2 hr at 25-30°C. The solid was filtered, washed with ethyl acetate (20 mL) and dried under vacuum at 25-30°C for 16 hr to furnish the title compound 2a.
Weight: 6.1 g
Yield: 85%

Example 10b:
(S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolinamide or (1S,3S,5S)-2-[(2S)-2-(tert-butyloxycarbonyl)]amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide, (3)

To a stirred solution of (S)-N-Boc-3-hydroxyadamantylglycine, 1 (10 g, 0.0307 mol), EDC hydrochloride (6.49 g, 0.0339 mol), HOBt.monohydrate (4.71g, (0.0307 mol) and L-cis-4,5-methanoprolinamide hydrochloride (2a) (5.25 g, 0.0323 mol) in a mixture of acetonitrile (15 mL) and ethyl acetate (30 mL) was added a solution of diisopropylethylamine (8.74 g, 0.0676 mol) in ethyl acetate (15 mL) at 25-40°C. The reaction mass was stirred at 35-40°C for 6-8 hr. The reaction mixture was diluted with ethyl acetate (70 mL) followed by addition of 1N HCl (30 mL) and brine (30 mL) then stirred at 25-30°C for 15 min. Both the layers were collected. The organic layer was washed with 15% aqueous Na2CO3 solution and the combined aqueous layers was extracted with ethyl acetate. The combined organic layer was washed with brine and then solvent was recovered completely under vacuum at 45-50°C. The residual ethyl acetate was chased with cyclohexane (20 mL) under reduced pressure at 45-50°C. The obtained oily residue was stirred with cyclohexane (40 mL) at 25-30°C for 4-5 hr. The solid thus obtained was filtered, washed with cyclohexane (20 mL) and dried under vacuum at 45-50°C for 16 hr to furnish the title compound, 3.
Weight: 12.4g
Yield: 93%

Example 10c: Preparation of 3-((S)-1-((tert-Butoxycarbonyl)amino)-2-((1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxoethyl)adamantan-1-yl formate, (4a)

A mixture of formic acid (8.49 g, 0.1846 mol) and acetic anhydride (9.42 g, 0.0923 mol) was stirred for 2 hr at ambient temperature. A solution of (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolinamide, 3 (10 g, 0.0231 mol) in DCM (10 mL) was added and stirred for 16-18 hr. The reaction mass was concentrated under vacuum. The solution of the residue obtained in DCM (100 mL) was successively washed with saturated NaHCO3 solution and brine. DCM was recovered completely under vacuum at 35-40°C to get the title compound, 4a as a viscous oily mass which was used in the next step without further purification.

Example 10d: Preparation of 3-((S)-1-((tert-Butoxycarbonyl)amino)-2-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxoethyl)adamantan-1-yl formate, (5a)

A solution of compound, 4a obtained in example 10c and triethylamine (12.02g, 0.1188 mol) in DCM (80 mL) was cooled to -15°C. To the resulting solution was added a solution of POCl3 (7.32 g, 0.0478 mol) in DCM (20 mL) at -15 to -5°C in about 60-90 min and stirring was continued at -10 to -5°C for another 30 min then quenched by pouring the reaction mass to a pre-cooled solution of NaOH (6.93 g, 0.1732 mol) in water (100 mL) in about 30 min. The reaction mixture was warmed to room temperature in about 1 hr. Both layers were collected and the aqueous layer was stirred with DCM (50 mL) and water (50 mL). The combined organic layer was successively washed with 10% aq.KHSO4 solution (100 mL), 2% NaHCO3 solution (50 mL), 1% aq. NaBH4 solution (2x50 mL), 2% aq.KHSO4 solution (50 mL), 2% NaHCO3 solution (50 mL) followed by 8% brine (50 mL). The solvent was evaporated off under vacuum at 35-40°C to furnish the title compound, 5a as a viscous oily mass which was directly used in the next step without further purification.

Example 10e: Preparation of (S)-3-hydroxyadmantylglycine-L-cis-4,5-methanoprolinenitrile hydrochloride dihydrate or(1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxytricyclo[3.3.1.13,7]dec-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride dihydrate, (Saxagliptin monohydrochloride dihydrate), (Ia’)

To a stirred and cooled (15-20°C) solution of the compound, 5a obtained in example 10d in ethyl acetate (135 mL) was added Conc. HCl (10.8 mL, (0.1222 mol). The mixture was then stirred at 25-30°C for 3-4 hr. The precipitated solid was filtered, washed with ethyl acetate (2x18 mL). The wet solid was suspended in a mixture of ethyl acetate (58.2 mL) and water (1.8 mL) and stirred 10-12 hr. The solid was filtered, washed with ethyl acetate (2x18 mL) and dried at 30-35°C for 2-4 hr to obtain Saxagliptin monohydrochloride dihydrate Ia’.
Weight: 6.2 g
Yield: 69% (over 4 steps).

1H NMR (400 MHz, DMSO-d6, d): 0.73-0.77 (m, 1H), 1.0-1.05 (m, 1H), 1.40-1.66 (m, 12 H), 1.93-1.97 (m, 1H), 2.15 (brs,2H), 2.23-2.27 (dd, J=14 & 2.0 Hz, 1H), 4.09-4.13 (m, 1H), 4.23-4.24 brd, 1H), 4.28 (s, 1H), 5.21-5.24 (dd, J=10.8 & 2.0 Hz, 1H), 8.29 (brs, 3H)
13C NMR (100 MHz, DMSO-d6, d): 13.64, 17.85, 29.0, 29.95, 30.54, 35.27, 37.08, 37.15, 38.32, 39.58, 44.52, 44.66, 45.77, 45.83, 58.20, 66.86, 120.26, 166.63
MS(m/z): 316.11 (M+H)

Preparation of Impurities:
Example 11
Preparation of (1S,3S,5S)-2-[(1S,3S,5S)-2-azabicyclo[3.1.0]hex-3-ylcarbonyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide TFA salt

Example 11a: Preparation of tert-butyl (1S,3S,5S)-3-{[(1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hex-2-yl]carbonyl}-2-azabicyclo[3.1.0]hexane-2-carboxylate

To a stirred solution of N-Boc-L-cis-4,5-methanoproline (2.0 g, 0.0088 mol), EDC.HCl (1.85 g, 0.0097 mol), HOBt monohydrate (1.34 g, (0.0087 mol) and -L-cis-4,5-methanoprolinamide hydrochloride (1.5 g, 0.0092 mol) was added a solution of diisopropylethylamine (2.6 g, 0.0202 mol) in THF (10 mL) at 25-30°C. The reaction mixture was stirred at 25-30°C for 4 hr then concentrated under vacuum at 40-45°C to get an oily residue which was stirred in a mixture of ethyl acetate (30 mL) and 1N HCl (7 mL) at 25-30°C for 15 min. The solid thus obtained was collected by filtration. The organic layer separated from the mother liquor was washed with 20% aqueous KHCO3 solution (2x10 mL) followed by brine (10 mL). Concentartion of organic layer under reduced pressure at 40-45°C provided another lot solid. Both the solid were mixed and dried under vacuum at 45-50°C for 16 hr to furnish the title compound, which was used in the next step without further purification.
Weight: 2.4 g
Yield: 81%

Example 11b: (1S,3S,5S)-2-[(1S,3S,5S)-2-azabicyclo[3.1.0]hex-3-ylcarbonyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide (A) TFA salt

To a stirred solution of compound, obtained in Example11a (2.4 g) in DCM (4.8 mL) was added trifluoroacetic acid (4.8 mL) at 25-30°C and stirred at room temperature for 6 hr. Solvent was then evaporated off under reduced pressure at 40-45°C and the residue obtained was stirred with MTBE (30 mL) at 25-30°C for 12 hr. The solid obtained was filtered and dried under vacuum at 40-45°C for 16 hr to afford the title compound.
Weight: 1.7 g
Yield: 72%

1H NMR (400 MHz, DMSO-d6): 0.67-1.08 (m, 4H), 1.74-1.84 (m, 4H,), 2.54-2.67 (m, 2H), 3.31 (bs, 1H,), 3.47 (bs, 1H), 4.64 (d, 1H, 9.6 Hz), 5.02 (d, 1H, 9.6 Hz)
13C NMR (100 MHz, DMSO-d6) : 9.04, 13.15, 16.85, 18.17, 30.14, 30.69, 36.77, 36.96, 59.72, 61.44, 167.5, 173.3
MS (m/z) : 236.00 (M+ +1) , 257.97 (M+ +Na)

Example 12:
Preparation of tert-butyl ((S)-2-((1S,3S,5S)-3-((1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hexane-2-carbonyl)-2-azabicyclo[3.1.0]hexan-2-yl)-1-(3-hydroxyadamantan-1-yl)-2-oxoethyl)carbamate (B),

To a mixture of tert-butyl (1S,3S,5S)-3-{[(1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hex-2-yl]carbonyl}-2-azabicyclo[3.1.0]hexane-2-carboxylate (3.24 g, 0.0096 mol) in 6.5 mL DCM was added 6.5 mL of TFA at room temperature and stirred till to completion. Solvent was distilled off under reduced pressure at 40-45°C to get an oily residue which was dissolved in acetonitrile (9 mL) at 25-30°C and used for coupling in the following step.
In a separate flask to a stirred solution of (S)-N-Boc-3-hydroxyadamantylglycine (3 g, (0.0092 mol), EDC hydrochloride (1.94 g, 0.0101 mol) and HOBt monohydrate (1.4 g. 0.0092 mol) was added a solution of diisopropylamine (5.93 g, 0.0459 mol) in ethyl acetate (9 mL) followed by the above solution of (1S,3S,5S)-2-[(1S,3S,5S)-2-azabicyclo[3.1.0]hex-3-ylcarbonyl]-2-azabicyclo[3.1.0]hexane-3-carboxamide TFA salt and then stirred at room temperature for 12 hr. To the reaction mass was added ethyl acetate (30 mL), 1N HCl (15 mL) and stirred for 15 min. The solid thus obtained was collected by filtration. The organic layer separated from the mother liquor was washed with 20% aqueous KHCO3 solution (2x15 mL) followed by brine (15 mL). Concentartion of organic layer under reduced pressure at 40-45°C provided another lot solid. Both the solid were mixed and dried under vacuum at 45-50°C for 16 hr to furnish the title compound.
Weight: 3.7 g
Yield: 76%
1H NMR(400 MHz, DMSO-d6): 0.63-0.71 (m, 2H), 0.89 (m, 1H), 1.06 (m, 1H), 1.35-1.55 (m, 20H), 1.63-1.69 (m, 4H), 1.74-1.78 (m, 1H), 2.04-2.07 (m, 2H), 2.11-2.15 (m, 1H), 2.41-2.54 (m, 2H), 3.56 (m, 1H,), 3.68 (m, 1H), 4.35 (d, 1H, J=9.2 Hz), 4.53 (dd, 1H, J=11.2 Hz, 2.4 Hz), 5.23 (dd, 1H, J=11.2, 2.8 Hz), 6.41 (d, 1H, J=9.2 Hz), 6.81 (s, 1H), 7.31 (s, 1H).
13C NMR(100 MHz, DMSO-d6): 12.93, 13.38, 17.07, 17.19, 28.87, 29.05, 30.18, 30.33, 30.67, 35.77, 36.53, 37.18, 38.11, 39.06, 44.99, 45.08, 46.34, 59.26, 59.99, 60.70, 67.29, 78.59, 155.96, 168.91, 170.43, 174.22
MS (m/z) : 543.09 (M+ +1) , 565.22 (M+ +Na), 581.16 (M+ +K)

Example 13
Preparation of (1S,3S,5S)-2-{(1S,3S,5S)-2-[(S)-2-amino-2-(3-hydroxyadamantan-1-yl)acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonyl}-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride

Example 13a: Preparation of 3-((S)-1-((tert-butoxycarbonyl)amino)-2-((1S,3S,5S)-3-((1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0] hexane-2-carbonyl)-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxoethyl)adamantan-1-yl formate, (C)
A mixture of formic acid (2.02 g, 0.044 mol) and acetic anhydride (2.24 g, 0.022 mol) was stirred at room temperature for 2 hr then was added a solution of compound, B obtained in example 12 (3 g. 0.0055 mol) in DCM (3 mL). The reaction mixture was stirred for 20 hr and the solvent was evaporated off under reduced pressure at 40-45°C. The oily residue thus obtained was dissolved in 30 mL DCM and washed with saturated NaHCO3 solution followed by brine. Evaporation of solvent under reduced pressure at 40-45°C resulted a foam solid which was purified by column chromatography using ethyl acetate/hexanes (10:90% v/v) as eluant to obtain the title compound, 13 as a light brown solid.
Weight: 1.72g
Yield: 55%

Example 13b: Preparation of 3-((S)-1-((tert-butoxycarbonyl)amino)-2-((1S,3S,5S)-3-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0] hexane-2-carbonyl)-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxoethyl)adamantan-1-yl formate (E)
To a stirred and cooled (0°C) solution of compound, C obtained in example 13a (1.7 g, 0.0030 mol) and triethylamine (1.5 g, 0,0149 mol) in DCM (17 mL) was slowly added phosphorus oxychloride (0.91 g, 0.0059 mol) at 0-5°C and stirred at 5-10°C till to completion. In a separate RB flask, sodium hydroxide (0.95g) was dissolved in water (20 mL), cooled to 0-5°C and the above reaction mass was added at 0-5°C in about 1 hr. Reaction mixture was warmed to room temperature and stirred for 15 min. Layers separated and the organic layer was successively washed with 10% KHSO4 solution (20 mL) , saturated NaHCO3 solution (10 mL) followed by brine (10 mL). The organic layer was treated with a mixture of activated charcoal (0.2 g) and silica gel (0.4 g) for 20 min, filtered through hyflo, washed with DCM (5 mL). Concentration of filtrate under vacuum at 35-40°C provided the title compound, (14) as a foamy mass which was used in the next step without further purification.
Weight: 1.52g
Yield: 92%

Example 13c: Preparation of (1S,3S,5S)-2-((1S,3S,5S)-2-((S)-2-amino-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carbonyl)-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride
To a stirred solution of compound, E obtained in example 13b (1.5 g, 0.0027 mol) in ethyl acetate (15 mL) was added conc.HCl (1.0 mL) at room temperature and stirred till to completion. The precipitated solid was filtered, washed with ethyl acetate (4.5 mL) and dried at 30-35°C for 16 hr to furnish the title compound.
Weight: 1.07 g
Yield: 86%
1H NMR(400 MHz, DMSO-d6): 0.75-0.96 (m, 4H), 1.46-1.62 (m, 12H), 1.71-1.79 (m, 4H), 1.94-1.98 (m, 2H), 2.62-2.69 (m, 2H), 3.86 (m, 1H,), 4.00 (m, 1H), 4.23 (m, 1H), 4.53 (bs, 1H), 5.11-5.13 (d, 1H, 10 Hz), 5.30-5.33 (m, 1H), 8.01 (s, 3H)
13C NMR (100 MHz, DMSO-d6) : 12.11, 12.87, 16.9, 17.16, 28.66, 29.51, 29.56, 29.83, 34.89, 35.93, 36.04, 36.84, 38.70, 44.24, 44.24, 45.09, 45.29, 58.09, 59.55, 66.59, 66.59, 120.35, 165.44, 169.44
MS (m/z) : 425.23 (M+ +1)

Example 14
Preparation of Bis[3-{(S)-1-amino-2-((1S,3S.5S)-3-cyano-2-azabicyclo[3,1,0]hexan-2-yl)-2-oxoethyl}adamantan-1-yl] hydrogen phosphite

Example 14a: Preparation of di-tert-Butyl ((1S,1'S)-((1R,1'R,3R,3'R,5R,5'R,7S,7'S)-((hydroxyphosphanediyl) bis(oxy))bis(adamantane-3,1-diyl))bis(2-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxoethane-1,1-diyl))dicarbamate, (D)

To a stirred cooled (5°C) solution of (S)-N-Boc-2-(3-hydroxyadamantan-1-yl)glycine-L-cis-4,5-methanoprolinamide, 3 (2.0 g, 0.0046 mol) and triethyl amine (1.6 g, 0.0158 mol) in DCM (20 mL) was added phosphorus trichloride (0.63 g, 0.0046 mol). The reaction mixture was warmed to room temperature and stirred for 1 hr. Then it was quenched by pouring into cold (5°C) 10% sodium hydroxide solution (10 mL) at 5-10°C in about 30 min. Temperature was gradually raised to room temperature and layers separated. The organic layer was washed with 20% aq. KHSO4 solution (10 mL) and then treated with a mixture of activated charcoal and silica gel. Concentration of the filtrate under reduced pressure at 35-40°C resulted the title compound, which was used in the next step without further purification.
Weight: 1.5 g
Yield: 74%

Example 14b: Preparation of bis(3-((S)-1-amino-2-((1S,3S,5S)-3-cyano-2-azabicyclo[3,1,0]hexan-2-yl)-2-oxoethyl)adamatan-1-yl) hydrogen phosphate
To a stirred solution of compound, D (1.5 g) obtained in example 14a in ethyl acetate (15 mL) was added conc. HCl (1.8 mL) at 25-30°C and stirred for 4 hr.
The precipitated solid was filtered, washed with ethyl acetate (3 mL ) and dried under vacuum at 25-30°C for 16 hr to furnish the title compound.
Weight: 0.90 g
Yield: 70%

1H NMR (400 MHz, DMSO-d6): 0.75 (m, 2H), 1.00-1.05 (m, 2H,), 1.42-1.45 (m, 2H), 1.50-1.58 (m, 6H), 1.69-1.76 (m, 4H), 1.88-1.91 (m, 6H,), 1.93-2.0 (m, 2H), 2.03-2.11 (m, 6H), 2.23-2.26 (m, 6H), 2.53-2.56 (m, 2H),4.14(s, 2H), 4.32 (s, 2H), 5.22-5.25 (m, 2H), 8.46 (s, 6H)
13C NMR (100 MHz, DMSO-d6): 13.61, 17.88, 30.14, 30.19, 30.52, 34.58, 36.32, 36.57, 38.33, 42.79, 42.85, 44.50, 45.81, 57.80, 81.44, 81.51, 120.27, 166.42
MS (m/z) : 677.31 (M+ +1), 694.11 (M+ +NH4)

Example 15
Preparation of (S)-2-amino-N-((S)-2-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0]hexan-2-yl)-1-(3-hydroxyadamantan-1-yl)-2-oxoethyl)-2-(3-hydroxyadamantan-1-yl)acetamide (G) hydrochloride

To a stirred solution of (S)-N-Boc-3-hydroxyadamantylglycine, 1 (2.0 g, 0.0062 mol), EDC hydrochloride (1.31 g, 0.0068 mol), HOBt monohydrate (0.95 g, (0.0062 mol) and saxagliptin hydrochloridedihydrate, Ia’ (2.38 g, 0.0062 mol) in a mixture of acetonitrile (10 mL) and ethyl acetate (20 mL) was added a solution of diisopropylethylamine (1.75 g, 0.0135 mol) in ethyl acetate (10 mL) at 25-40°C. The reaction mass was stirred at 35-40°C till to completion (~6 hr). To the reaction mixture was added ethyl acetate (20 mL) followed by a mixture of 1N HCl (6.4 mL) and brine (3 mL). Layers were separated, the organic layer was washed with 15% aqueous Na2CO3 solution (2x10 mL) followed by brine (10 mL). Evaporation of solvent under vacuum at 45-50°C provided an oily residue. To the solution of the obtained oily residue in ethyl acetate (45 mL) was added conc. HCl (3.6 mL) at room temperature and stirred for 4 hr. The residue obtained after concentration of the reaction mass under reduced pressure at 35°C was redissolved in ethyl acetate (40 mL) and again concentrated under vacuum at 35°C. The residue obtained was stirred with MTBE (30 mL) at room temperature.. The solid thus obtained was filtered, washed with MTBE (10 mL) and dried under vacuum at 35°C for 4 hr to furnish the title compound.
Weight: 2.6 g
Yield: 90%
1H NMR (400 MHz, DMSO-d6): 0.74 (m, 1H), 1.04-1.06 (m, 1H,), 1.26-1.36 (m, 3H), 1.39-1.60 (m, 20H), 1.70-1.75 (m, 3H), 1.86-1.87 (m, 2H), 2.09-2.12 (m, 4H), 2.53-2.58 (m, 1H), 3.76-3.77 (m, 1H), 3.81-3.84 (m, 1H), 4.59-4.61 (d, 1H, 8 Hz), 5.05-5.08 (dd, 1H, J=10.8, 2,4 Hz), 8.19 (s, 3H), 8.40-8.42 (d, 1H, 8 Hz)
13C NMR (100 MHz, DMSO-d6): 13.48, 17.10, 21.08, 26.83, 29.45, 29.52, 29.64, 29.70, 30.19, 34.87, 35.17, 36.33, 36.61, 36.91, 37.13, 37.85, 37.96, 44.13, 44.21, 44.36, 44.58, 45.27, 45.57, 57.64, 66.48, 66.63, 120.09, 167.26, 168.26
MS (m/z): 522.94 (M+ +1)

Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(4-oxoadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride (H.HCl)

Example 16: Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(4-oxoadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride
Example 16a: Preparation of 5-hydroxyadamantan-2-one:

To a stirred and cooled (0-5°C) mass of conc. H2SO4 (250 mL) was added 50% aqueous HNO3( 25 mL) followed by adamantan-2-one (50.0 g, 0.3388 mol) at 0-5°C. Reaction mass was warmed to room temperature and stirred for 12 hr. After completion of reaction (TLC), it was cooled to 0-5°C and DM water (500 mL) was slowly added at 0-5°C. The heterogeneous mass was stirred at ambient temperature for 1 hr, solid was filtered and washed with DM water (50 mL). The mother liquor was extracted with DCM ( 4x500 mL), organic layer was mixed with the wet solid and concentrated under vacuum at 40-45°C. The crude residue was purified by column chromatography eluting with 10% ethyl acetate to 40% ethyl acetate in hexanes to afford the title compound.
Weight: 30.0 g
Yield: 55%

Example 16b: Preparation of Methyl 4-oxoadamantane-1-carboxylate

To a hot (60°C) oleum (180 mL) was slowly added a solution of 5-hydroxy adamantan-2-one (30.0 g, 0.1805 mol) in formic acid (90 mL) in 20-30 min at 60-65°C and further stirred for 1 hr. Additional formic acid (90 mL) was slowly added in 20-30 min and stirred at 60-65°C for another 1 hr and then warmed to room temperature. Cold (0°C) methanol (300 mL) was slowly added to it at 0-5°C. The reaction mass was then gradually warmed to room temperature and stirred for 3 hr. Solvent was distilled off under reduced pressure at 45-50°C to get an oily mass in which chilled water (500 mL) was slowly added at 0-5°C. The reaction mass was brought to room temperature and extracted with DCM (5x300 mL). The combined organic extract was concentrated under reduced pressure at 40-45°C. The crude residue thus obtained was purified using by column chromatography eluting with 5% to 20% ethyl acetate in hexanes to afford the title compound.
Weight: 24.5 g
Yield: 65%

Example 16c: Preparation of methyl spiro[adamantane-2,2'-[1,3]dioxolane]-5-carboxylate

To a stirred solution of methyl 4-oxoadamantane-1-carboxylate (24.0 g, 0.1152 mol) in toluene (360 mL) was added ethylene glycol (35.77 g, 0.577 mol) and p-toluenesulphonic acid (2.4 g) at 25-30°C. The reaction mass was stirred under reflux at 110-115°C till to completion (~3 hr) then cooled to room temperature and was successively washed with saturated sodium bicarbonate solution (2x120 mL) followed by brine (120 mL). Organic layer was concentrated to dryness under reduced pressure at 45-50°C to get title compound (32 g) which was used as such in the next step without further purification.

Example 16d: Preparation of (spiro[adamantane-2,2'-[1,3]dioxolan]-5-yl)methanol

To a stirred and cooled (0-5°C) solution of methyl spiro[adamantane-2,2'-[1,3]dioxolane]-5-carboxylate, (32.0 g, 0.0127 mol) in THF (200 mL) was slowly added a solution of vitride (110 mL, 0.381 mol) in THF (100 mL) in 30-40 min and stirred at 0-5°C till to completion (~1 hr). The reaction mass was quenched with 10% aqueous NaOH solution (300 mL) at 0-5°C in 25-30 min, then warmed to room temperature and stirred for 2 hr. Layers were separated and the aqueous layer extracted with ethyl acetate (2 x 320 mL). The combined organic layer was concentrated to dryness under reduced pressure at 45-50°C to get a crude mass which was purified by column chromatography eluting with 5% to 10% ethyl acetate in hexanes to afford the title compound , (21.0 g) as a thick oily mass.

Example 16e: Preparation of spiro[adamantane-2,2'-[1,3]dioxolane]-5-carbaldehyde

To a stirred and cooled (-78°C) solution of oxalyl chloride (56.7 g, 0.446 mol) in DCM (150 mL) was added a solution of dimethyl sulphoxide (69.6 g, 0.893 mol) in DCM (50 mL) under nitrogen atmosphere and then stirred at -75°C to -78°C for 30 min. A solution of spiro[adamantane-2,2'-[1,3]dioxolan]-5-yl)methanol (22) (20.0 g, 0.0893 mol) in DCM (100 mL) was added to the reaction mass at -75°C to -78°C and further stirred at same temperature for 30 min. Then triethyl amine (186.3 mL) was slowly added at -75°C to -78°C in 30-35 min and stirred for 1 hr then warmed to room temperature. After the completion of reaction DM water (200 mL) was added to the reaction mass, stirred for some time and separated the layers. Aqueous layer was extracted with DCM (200 mL) and the combined organic layer was washed the with DM water (3x100 mL). Solvents was evaporated under vacuum at 40-45°C and the crude mass thus obtained was purified by column chromatography eluting with 2% to 7% ethyl acetate in hexanes to afford the title compound .
Weight: 16.5g
Yield: 83%

Example 16f: Preparation of (S)-(((R)-2-hydroxy-1-phenylethyl)amino)-2-(spiro[adamantane-2,2'-[1,3]dioxolan]-5-yl)

To a stirred solution of sodium bisulphite (12.4 g) in DM water (250 mL) was added spiro[adamantane-2,2'-[1,3]dioxolane]-5-carbaldehyde (16.5 g, 0.0743 mol) at 25-30°C and stirred for 2 hr. To the resulting solution was added sodium cyanide (4.13 g) and stirred for 30 min and then a solution of R-phenyl glycinol (11.6 g) in methanol (85 mL) was added and warmed to 85°C. The reaction mass was stirred at 80-85°C for 18 hr. After cooling to room temperature ethyl acetate (400 mL) was added to the reaction mass, stirred and the layers separated. Aqueous layer was extracted with ethyl acetate (3x400 mL). The combined organic layer was washed with brine (400 mL) was concentrated under reduced pressure at 45-50°C to get the title compound, which was used in the next step without further purification.

Example 16g: Preparation of (S)-2-(((R)-2-hydroxy-1-phenylethyl)amino)-2-(4-oxoadamantan-1-yl)acetic acid

To a stirred solution of (S)-(((R)-2-hydroxy-1-phenylethyl)amino)-2-(spiro[adamantane-2,2'-[1,3]dioxolan]-5-yl)acetonitrile, (18.0 g) in acetic acid (50 mL) was added conc. HCl (85 mL) at 25-30°C and the mass was stirred at 80-85°C till to completion (~ 16 hr). The reaction mass was concentrated to dryness under vacuum at 45-50°C. After cooling to 25-30°C DM water (50 mL) was added to the residue and stirred then cooled to 0-5°C under stirring solid was precipitated. The suspended solution was stirred at 0-5°C for another 1 hr. The solid was filtered, washed with DM water (50 mL) and dried under vacuum at 45-50°C for 16 hr to afford the title compound.

Example 16g: Preparation of (S)-2-((tert-butoxycarbonyl)amino)-2-(4-oxoadamantan-1-yl)acetic acid

To a solution of (S)-2-(((R)-2-hydroxy-1-phenylethyl)amino)-2-(4-oxoadamantan-1-yl)acetic acid, (14.0 g, 0.0408 mol) in a mixture of methanol (140 mL) and acetic acid (140 mL) was added Pd(OH)2 (2.8 g) and stirred under hydrogen pressure of 5 Kg/cm2 at 45-50°C for 16 hr. After the completion of reaction on TLC, the reaction mass was cooled to room temperature, filtered through hyflo and washed the bed with methanol (50 mL). The filtrate was concentrated to dryness under reduced pressure at 45-50°C and crude mass was stirred with methyl tert butyl ether (70 mL) at room temperature for 2 hr. The precipitated solid was filtered, washed with methyl tert butyl ether (20 mL) and dried under vacuum at 45-50°C for 16 hr. To the solution of the above solid (8.0 g) in a mixture of THF (80 mL) and DM water (40 mL) was added potassium carbonate (12.32 g, 0.0893 mol). The reaction mass was cooled to 0-5°C and Boc anhydride (9.34 g, 0.0429 mol) was added drop wise at 0-5°C and stirred at 5-10°C for 2 hr. The reaction mass was concentrated to remove THF and stirred with ethyl acetate (100 mL). Aqueous layer was extracted with ethyl acetate (3x200 mL). The combined organic layer was washed the with brine (100 mL) and concentrated under vacuum at 45-50°C to get crude mass which was purified by column chromatography eluting with 10% to 40% ethyl acetate in hexanes to afford the title compound.
Weight: 5.0 g
Yield: 38%
1H NMR(400 MHz) : (DMSO-d6, ): 1.38 (s, 9H), 1.72-1.93 (m, 10H,), 2.06 (m, 1H), 2.38 (m, 2H), 3.74-3.76 (d, 1H, 9.2 Hz), 6.99-7.01(d, 1H, 9.2 Hz), 12.50 (bs, 1H)
MS (m/z) : 322.33 (M+ +1)

Example 16h: Preparation of tert-Butyl ((S)-2-((1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxo-1-(4-oxoadamantan-1-yl)ethyl)carbamate

To a stirred solution of tert-butyl (1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hexane-2-carboxylate, (3.82 g, 0.0169 mol) in DCM (40 mL) was added TFA (14.0 g, 0.123 mol) drop wise at 25-30°C and stirred for 3-4 hr.. The reaction mass was concentrated under vacuum at 45-50°C, residual TFA was removed using additional ethyl acetate (20 mL) by concentration under vacuum at 45-50°C. The residue thus obtained was cooled to 25-30°C and dissolved in ethyl acetate (20 mL).
In a another flask to a stirred and cooled (-20°C) solution of (S)-2-((tert-butoxycarbonyl)amino)-2-(4-oxoadamantan-1-yl)acetic acid (Oxo ABG), (5 g, 0.0153 mol) in ethyl acetate (40 mL) was added drop wise pivaloyl chloride (2.03 g, 0.0169 mol) and stirred for 30 min, then was added TEA (7.7 g, 0.0768 mol) and stirred at -15 to -20°C for 2 hr. To this solution was added the previously prepared ethyl acetate solution of deprotected product of (1) at -15 to -20°C in 15-20 min and stirred at 25-30°C for 16 hr. Reaction was quenched by adding 10% HCl (20 mL) and stirred for 15 min. Organic layer was separated, washed successively with saturated NaHCO3 solution (2x20 mL) and brine solution (20 mL) and concentrated to dryness under vacuum at 45-50°C to furnish the title compound.
Weight: 5.5 g
Yield: 83%

Example 16i: Preparation of tert-Butyl ((S)-2-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxo-1-(4-oxoadamantan-1-yl)ethyl)carbamate

To a stirred and cooled solution (0-5°C) of tert-butyl ((S)-2-((1S,3S,5S)-3-carbamoyl-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxo-1-(4-oxoadamantan-1-yl)ethyl)carbamate, (5 g, 0.011 mol) and triethyl amine (7.54 mL, 0.054 mol in DCM (50 mL) was slowly added phosphorus oxychloride (1.5 mL, 0.016 mol) and then warmed to 25-30°C and stirred for 1 hr. After completion of the reaction the reaction mass was diluted with DCM (50 mL) and quenched with cold aqueous NaOH solution (3.5g in 50 mL DM water, prepared and precooled to 0°C) at 0-5°C. The reaction mass was warmed to 25-30°C. The organic layer was successively washed with 20% aqueous KHSO4 solution (2x50 mL), saturated NaHCO3 solution (50 mL) and brine (2x50 mL). The organic layer was stirred with silica gel (5 g) and activated charcoal (1 g) for 30 min, filtered through hyflo and washed the bed with DCM (2x25 mL). Solvent was distilled off completely under vacuum at 45-50°C to furnish the title compound.
Weight: 3.0 g
Yield: 63%

Example 16j: Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(4-oxoadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carbonitrile hydrochloride

To a stirred solution of tert-butyl ((S)-2-((1S,3S,5S)-3-cyano-2-azabicyclo[3.1.0]hexan-2-yl)-2-oxo-1-(4-oxoadamantan-1-yl)ethyl)carbamate (3.0 g, 0.0072 mol) in ethyl acetate (45 mL) was added conc. HCl (3.6 mL, 0.043 mol) at 25-30°C. The reaction mass was stirred for ~2 hr). The solid was filtered, washed with ethyl acetate, sucked to dryness for 15 min and dried under vacuum at 25-30°C for 16 hr to furnish the title compound.
Weight: 1.5g
Yield: 60%
1H NMR(400 MHz) : (DMSO-d6, ): 0.74-0.77 (m, 1H), 1.02-1.05 (dd, 14.8 Hz, 6.4 Hz, 1H), 1.84-2.15 (m, 12H), 2.23-2.27(dd, 14.0 Hz, 2.4 Hz, 1H), 2.47-2.52 (m, 3H), 4.16-4.17 (m, 1H), 4.34 (s, 1H), 5.21-5.24 (dd, , 10.8 Hz, 2.2 Hz, 1H), 8.57 (s, 3H)
13C NMR (100 MHz) : (DMSO-d6, ) : 13.53, 17.93, 27.09, 30.43, 36.13, 36.13, 36.79, 37.96, 37.96, 38.34, 39.02, 45.51, 45.51, 45.85, 57.29, 120.21, 166.25, 215.99
MS (m/z) : 314.16 (M+ +1) , 330.91 (M+ +NH4)
Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid, TFA salt

Example 17: Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid, TFA salt

Example 17a: Preparation of Ethyl (1S,3S,5S)-2-((S)-2-((tert-butoxycarbonyl)amino)-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylate

To a stirred solution of 2-(tert-butyl)-3-ethyl (1S,3S,5S)-2-azabicyclo[3,1,0]hexane-2,3-dicarboxylate(4.94 g, 0.019 mol) in DCM (30 mL) was dropwise added TFA (21 g, 0.184 mol) at 25-30°C and stirred for 2-3 hr. The reaction mass was concentrated at 45-50°C under vacuum, chased with toluene (10 mL) and the residue thus obtained was stirred in MTBE (50 mL) for 2-3 hr. The solid was filtered, washed with MTBE (5 mL) and dried under vacuum at 35-40°C for 2-3 hr and stored.
In another flask to a stirred and cooled (-20°C) solution of (S)-2-((tert-butoxycarbonyl)amino)-2-(3-hydroxyadamantan-1-yl)acetic acid (1) (5 g, 0.076 mol) and TEA (4.65g, 0.046 mol) in ethyl acetate (60 mL) was slowly added pivaloyl chloride (2.44 g, 0.020 mol) at -20°C and stirred at -15 to -20°C for 1-1.5 hr and then a solution of previously stored deprotected compound of (30) in ethyl acetate was added at -15 to -20°C in 20-30 min and stirred at 25-30°C for 16 hr. Reaction was quenched with 10% HCl (2x30 mL) and stirred for 15 min. Organic layer was separated, successively washed with saturated NaHCO3 solution (2x30 mL) and brine (30 mL) and concentrated to dryness under reduced pressure at 45-50°C to furnish the title compound.
Weight: 6.0 g
Yield: 90%
Example 17b: Preparation of (1S,3S,5S)-2-((S)-2-((tert-butoxycarbonyl)amino)-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid

To a stirred and cooled (0-5°C) solution of ethyl (1S,3S,5S)-2-((S)-2-((tert-butoxycarbonyl)amino)-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylate in ethanol (20 mL) (5.0 g 0.0108 mole) was slowly added a solution of lithium hydroxide (0.54 g) in water (10 ml) at 0-5°C and stirred. The reaction mass was concentrated under vacuum at 45-50°C. To the distilled reaction mass was added ethyl acetate (25 ml) and water (75 ml), layers were separated. pH of aqueous layer was adjusted to 2.5-3.0 using 10% aq. HCl solution. Layers were separated, aq. layer was extracted with DCM (2x25 ml) and the combined DCM layer was washed with brine and concentrated to dryness under vacuum at 40-45°C to provide the title compound.
Weight: 4.5g
Yield: 97%

Example 17c: Preparation of (1S,3S,5S)-2-((S)-2-amino-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid TFA salt

To a stirred solution (1S,3S,5S)-2-((S)-2-((tert-butoxycarbonyl)amino)-2-(3-hydroxyadamantan-1-yl)acetyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid, (3.5 g 0.008 mole), in DCM (17.5 mL) was added TFA (9.19 g 0.080 mole) was added at 25-30°C and stirred further for 3-4 hr. The reaction mass was concentrated to dryness under vacuum at 45-50°C. To the distilled reaction mass MTBE (35 ml) was added and stirred for 2-3 hr. The solid was filtered, washed with MTBE (7 mL) and dried under vacuum at 35-40°C to furnish the title compound as a white solid.
Weight: 3.0 g
Yield: 86%

1H NMR(400 MHz) : (DMSO-d6, ): 0.75-0.76 (m, 1H), 0.77-0.84 (m, 1H), 1.45-1.60 (m, 10H), 1.63-1.71 (m, 2H), 1.76-1.81 (m, 1H), 1.95-1.99 (m, 1H), 2.14 (bs, 2H), 2.51-2.58 (m, 1H), 3.90-3.94 (m, 1H), 4.22(bs, 1H), 4.70-4.74 (dd, 11.6 Hz, 3.4 Hz, 1H), 8.03 (bs, 3H), 12.82 (bs, 1H)
13C NMR (100 MHz) : (DMSO-d6, ) : 13.82, 17.73, 29.70, 29.96, 35.18, 36.43, 37.01, 38.75, 40.27, 44.37, 44.45, 44.46, 58.36, 60.04, 67.05, 67.05, 165.98, 173.54
MS (m/z) : 335.14 (M+ +1)

CLAIMS:
We Claim:
1. A process for preparation of saxagliptin or its salts or hydrates thereof comprising the steps of:
(a) coupling (S)-N-Boc-3-hydroxyadamantyl glycine with L-cis-4,5-methanoprolinamide or salts thereof in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide;
(b) protection of N-Boc hydroxy amide with suitable protecting group to provide O- and N-protected amide in a single step or number of steps;
(c) dehydration of O- and N-protected amide in the presence of a dehydrating agent and in a suitable solvent to produce O- and N-protected nitrile;
optionally, converting O- and N-protected nitrile to saxagliptin or its salts or/and hydrates thereof wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates OR
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) formylating N-Boc hydroxy amide (3) in the presence of suitable formylating agent to produce O-formyl N-Boc amide (4a);
(c) dehydration ofO-formyl N-Boc amide (4a) in the presence of a dehydrating agent in a suitable solvent to produce O-formyl N-Boc nitrile (5a);
(d) optionally, converting O-formyl N-Boc nitrile (5a) to saxagliptin, its salts or/and hydrates thereof wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates OR
(a) coupling (S)-N-Boc-3-hydroxyadamantyl glycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) acetylating N-Boc hydroxy amide (3) in the presence of suitable acetylating agent to produce O-acetyl N-Boc amide (4b);
(c) dehydration of O-acetyl N-Boc amide (4b) in the presence of a dehydrating agent and a base in a suitable solvent to produce O-acetyl N-Boc nitrile (5b);
(d) optionally, converting O-acetyl N-Boc nitrile (5b) to saxagliptin its salts or/and hydrates thereof wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates OR

(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride, and a base in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) Boc-deprotection of N-Boc hydroxy amide (3) to produce amino amide hydrochloride (6);
(c) acylating amino amide hydrochloride (6) to produce diacetyl amino amide (7a);
(d) dehydration of diacetyl amino amide (7a) in the presence of a dehydrating agent and in a suitable solvent to produce diacetyl amino nitrile (8a);
(e) optionally, converting diacetyl amino nitrile (8a) to saxagliptin its salts or/and hydrates thereof wherein, one or more steps from (b) to (e) may be performed in-situ or by isolation of the respective intermediates OR
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide or salts thereof (2) in presence of pivaloyl chloride, and a base and in a suitable solvent to produce N-Boc hydroxy amide (3);
(b) Boc-deprotection of N-Boc hydroxy amide (3) to produce amino amide hydrochloride (6);
(c) tritylation of amino amide hydrochloride (6) to furnish N-trityl hydroxy amide (7b);
(d) dehydration of N-trityl hydroxy amide (7b) in the presence of a dehydrating agent and in a suitable solvent to produce N-trityl hydroxy nitrile (8b);
(e) optionally, converting N-trityl hydroxy nitrile (8b) to saxagliptin, its salts or/and hydrates thereof wherein, one or more steps from (b) to (e) may be performed in-situ or by isolation of the respective intermediates OR
(a) coupling (S)-N-Boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide hydrochloride (2a) in presence of coupling agent and a base in a suitable solvent, optionally in presence of additive, to produce N-Boc hydroxy amide (3);
(b) formylating N-Boc hydroxy amide (3) in the presence of suitable formylating agent to produce O-formyl N-Boc amide (4a);
(c) dehydration of O-formyl N-Boc amide (4a) in the presence of a dehydrating agent in a suitable solvent to produce O-formyl N-Boc nitrile (5a);
(d) optionally, converting O-formyl N-Boc nitrile (5a) to saxagliptin, its salts or/and hydrates thereof, wherein, one or more steps from (b) to (d) may be performed in-situ or by isolation of the respective intermediates.

2. The process according to claim 1, wherein acylation reagents is selected from acetic anhydride, acetyl chloride or pentafluorophenyl; formylation reagent is selected from formic acid or 2,2,2-trifluoroethyl formate; tritylation reagent is selected from trityl chloride or 4,4’-dimethoxytrityl chloride; coupling agent is selected from the group comprising ofpivaloyl chloride, N,N’-dicyclohexylcarbodiimide (DCC), N,N’-diisopropylcarbodiimide (DPCI), N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC / DED), N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), isobutylchloroformate, diisopropylcarbodiimide (DIC), N,N’-dicarbonyldiimidazole (CDI), benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP), (7-azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (PyAOP), N,N-Disuccinimidyl carbonate (DSC), O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU), 1H-benzotriazolium 1-[bis(dimethylamino)methylene]-5chloro-hexafluorophosphate (1-),3-oxide (HCTU) or O-(benzotriazol-1-yl)-N,N,N’,N’-tetramethyluronium hexafluorophosphate (HBTU);additive used for the coupling reaction is selected from a group comprising of 4-dimethylaminopyridine (4-DMAP), diisopropylethylamine (DIPEA), 2-methylpyridine, 2,6-dimethylpyridine (lutidine), 2,4,6-trimethylpyridine (collidine), 4-(tetrahydropyrrolidinyl)pyridine, imidazole, N-methylimidazole, diazabicycloundecane (DABCO), N-hydroxysuccinimide (HOSu), N-hydroxy-5-norbornene-2,3-dicarboximide (HONB), 1-hydroxybenzotriazole (HOBt), 6-chloro-1-hydroxybenzotriazole (Cl-HOBt), 1-hydroxy-7-azabenzotriazole (HOAt) and 3-hydroxy-4-oxo-3,4-dihydro-1,2,3-benzotriazine (HODhbt) and its aza derivative (HODhat); dehydrating reagents is selected from the group comprising of phosphorus oxychloride, trifluoroacetic anhydride, acetic anhydride, p-toluenesulfonyl chloride thionyl chloride, cyanuric chloride or benzenesulfonyl chloride; base for the coupling reaction is selected from organic bases, base for hydrolysis reaction and neutralization reactionis selected from organic bases and inorganic bases; inorganic base is selected from group comprising of ammonia, carbonates, bicarbonates, hydroxides of alkali and alkaline earth metals; organic base is selected from the group comprising methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine (TEA), N,N-diisopropylethylamine, tributylamine, triisopropylamine, pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (4-DMAP), 1,8-bis-(dimethylamino)naphthalene, 1-ethylpiperidine, 1-methylmorpholine, lutidine and mixtures thereof;carbonates are selected from the group comprising of K2CO3, Cs2CO3 and Na2CO3; bicarbonates are selected from the group comprising of NaHCO3and KHCO3; hydroxides are selected from the group comprising of NaOH, KOH, LiOH and CsOH.

3. The process according to claim 1, wherein compound N-boc-L-cis-4,5-methanoprolinamide (2)or unprotected (2)is used either in its free base form or as its acid addition salt with inorganic or organic acids; inorganic acid is selected from acid hydrochloric acid, hydrobromic acid, hydro iodic acid, sulphuric acid, nitric acid; organic acid is selected formic acetic, acetic acid, propanoic acid, tartaric acid, oxalic acid, maleic acid, mandelic acid, malonic acid, methane sulphonic acid, p-toluene sulphonic acid and trifluoroacetic acid.

4. A process for the preparation of (S)-N-boc-3-hydroxyadamantylglycine (1) comprising the steps of:
(a) 2-(adamantan-1-yl)acetic acid (9) is treated with S-benzyl oxazolidinone to get 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10);
(b) 3-[2-(adamantan-1-yl)acetyl]-4-benzyloxazolidin-2-one (10) is treated with lithium diisopropylamide (LDA) in a suitable solvent to produce an intermediate enolate compound which may be used further with or without isolation;
(c) intermediate enolate compound obtained in step “b” is treated with di-tert-butyl azodicarboxylate to get N,N-di-Boc-hydrazino carboximide (11a);
(d) hydrolysis of N,N-di-Boc-hydrazino carboximide (11a) in a suitable solvent to get N,N-di-Boc-hydrazino acid (12a);
(e) deprotection of N,N-di-Boc-hydrazino acid (12a) followed by salt formationin presence of an acid to get hydrazino acid addition salt (13), with or without isolation of intermediate compound;
(f) hydrogenolysis of hydrazino acid addition salt (13) in the presence of Raney Nickel in a suitable solvent to get adamantyl glycine acid addition salt (14);
(g) Boc protection of adamantyl glycine acid addition salt (14) to get an intermediate compoundfollowed by the subsequent hydroxylation to obtain N-Boc-3-hydroxyadamantyl glycine (1), with or without isolation of an intermediate compound; and
(h) optionally, purifying compound (1) in a suitable solvent OR

(a) esterification of 2-(3-hydroxyadamantyl-1-yl)-2-oxo-acetic acid (15) in a suitable solvent to get methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a);
(b) reacting methyl 2-(3-hydroxyadamantyl-1-yl)-2-oxo acetate (16a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a);
(c) diastereoselective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(3-hydroxyadamantan-1-yl)acetate (17a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(3-hydroxyadamantan-1-yl)acetate (18a), wherein, compound (17a) can be used further with or without isolation for the preparation of compound (18a);
(d) removal of chiral auxiliary (18a) using Pd(OH)2-Cinpresence of Boc anhydride to obtain an intermediate compound (19a), which may be used further with or without isolation;
(e) hydrolyzing an intermediate compound (19a) obtained in step “d” to obtain 3-hydroxyadamantyl N-Boc glycine (1) and
(f) optionally, purifying compound (1) in a suitable solvent OR
(a) esterification of 2-(adamant-1-yl)-2-oxo-acetic acid (20) in a suitable solvent to get methyl 2-(adamant-1-yl)-2-oxo acetate (21a);
(b) reacting methyl 2-(adamant-1-yl)-2-oxo acetate (21a) with (R)-1-phenylethylamine in suitable solvent to get an intermediate compound (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a);
(c) diastereoselective reduction of (R,E)-methyl 2-[(1-phenylethyl)imino]-2-(adamantan-1-yl)acetate (22a) to produce (2S)-methyl 2-{[(R)-1-phenylethyl]imino}-2-(adamantan-1-yl)acetate (23a), wherein, compound (22a) can be used further with or without isolation for the preparation of compound (23a);
(d) removal of chiral auxiliary (23a) using Pd(OH)2-Cinpresence of Boc anhydride to obtain an intermediate compound (24a), which may be used further with or without isolation;
(e) hydrolyzing an intermediate compound (24a) obtained in step “d” to obtain (2S)-N-Boc-2-(adamant-1-yl) glycine (14);
(f) hydroxylation of (2S)-N-Boc-2-(adamant-1-yl)-glycine (14) to produce3-hydroxyadamantyl N-Boc glycine (1) and
(g) optionally, purifying compound (1) in a suitable solvent.

5. The process according to claim 4, wherein reducing agent is selected from the group comprising of sodium borohydride, sodium triacetoxy borohydride sodium cyanoborohydride and trialkylsilane in acidic medium or palladium carbon or platinum on carbon, platinum oxide, palladium hydroxide on carbon and Raney nickel under H2 atmosphere; acid is selected from acetic acid, formic acid, trifluoroacetic acid, propanoic acid, pivaloic acid isobutyric acid; base is selected from organic bases, whereas for hydrolysis reaction and neutralization reaction inorganic bases can be used; inorganic base is selected from group comprising of ammonia, carbonates, bicarbonates, hydroxides of alkali and alkaline earth metals; organic base is selected from the group comprising methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine (TEA), N,N-diisopropylethylamine, tributylamine, triisopropylamine, pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (4-DMAP), 1,8-bis-(dimethylamino)naphthalene, 1-ethylpiperidine, 1-methylmorpholine, lutidine and mixtures thereof; carbonates are selected from the group comprising of K2CO3, Cs2CO3 and Na2CO3; bicarbonates are selected from the group comprising of NaHCO3, KHCO3; hydroxides are selected from the group comprising of NaOH, KOH, LiOH and CsOH; oxidizing agent is selected from potassium permanganate, hydrogen peroxide, sulfuric acid, peroxymonosulfuric acid, peroxydisulfuric acid, sodium perborate, nitrous oxide, silver oxide or potassium nitrate.

6. The process according to any of the proceeding claims, wherein solvents used is selected from the group comprising of nitriles, alcohols, ketones, esters, halogenated hydrocarbons, ethers, amides, dialkylsulfoxides, hydrocarbons, organic acids, water or the mixtures thereof; nitrileis selected from the group comprising of acetonitrile, propionitrile, butyronitrile and valeronitril; alcoholis selected from the group comprising of methanol, ethanol, n-propanol, isopropanol andn-butanol;ketone is selected from the group comprising of acetone, methyl ethyl ketone and methyl isobutyl ketone; ester is selected from the group comprising of ethyl acetate, propyl acetate, isopropyl acetate and butyl acetate; halogenated hydrocarbon is selected from the group comprising of dichloromethane (DCM), chloroform, dichloroethane and chlorobenzene; ether is selected from the group comprising of diethyl ether, methyl tert-butyl ether (MTBE), diisopropyl ether, tetrahydrofuran (THF) and dioxane; amide is selected from the group comprising of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylformamide and N-methylpyrrolidone; dialkyl sulfoxides is selected from the group comprising of dimethylsulfoxide, diethylsulfoxide and dibutylsulfoxide; aliphatic hydrocarbon is selected from the group comprising of alkanes or cycloalkanes such as pentane, hexane, heptane, octane, cyclohexane and cyclopentane; aromatic hydrocarbon is selected from the group comprising of toluene and xylene; organic acid is selected from the group comprising of acetic acid, formic acid and propionic acid; the selection of the solvent is appropriate with proviso that for the reduction reaction, the solvents alcohols and ketones are not used.

7. The process according to claim 1, wherein Saxagliptin or its hydrochloride salt or its hydrates is substantially free of one or more of the impurities selected from the following compounds or their salts or O- or N-protected / deprotected forms or isomers thereof

8. Compounds selected from the group comprising of the following compounds or their salts or O- or N-protected / deprotected forms or isomers thereof

9. A pharmaceutical composition that includes a therapeutically effective amount of saxagliptin its pharmaceutically acceptable salts or hydrates thereof prepared according to the process of claim 1 and one or more pharmaceutically acceptable carriers, excipients or diluents and its use in the treatment of diabetes and complications thereof, hyperglycemia, Syndrome X, hyperinsulinemia, obesity, and atherosclerosis and related diseases as well as immunomodulatory diseases and chronic inflammatory bowel disease.
10. A process for preparation of saxagliptin hydrochloride dihydrates comprising the steps of:
(a) coupling (S)-N-boc-3-hydroxyadamantylglycine (1) with L-cis-4,5-methanoprolinamide hydrochloride (2a) in presence of a coupling agent and a base in a suitable solvent and optionally in presence of an additive to produce N-boc hydroxy amide (3);
(b) formylating N-boc hydroxy amide (3) in the presence of suitable formylating agent to produce O-formyl N-boc amide (4a);
(c) dehydration of O-formyl N-boc amide (4a) in the presence of a dehydrating agent in a suitable solvent to produce O-formyl N-boc nitrile (5a);
(d) converting O-formyl N-boc nitrile (5a) to saxagliptin hydrochloride dihydrates
wherein, one or more steps (b) to (d) may be performed in-situ or by isolation of the respective intermediates.