FIELD OF THE INVENTION:
The present invention relates to robust, safe and industrially applicable process for preparing sitagliptin phosphate.
BACKGROUND OF THE INVENTION:
Sitagliptin, 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3-(trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate of formula-1, is dipeptidyl peptidase-4 inhibitor class and used for treatment of diabetes metlitus type-2.
Sitagliptin is white, crystalline, slightly hygroscopic solid.
US 6699871 discloses class of beta-amino tetrahydrotriazolo [4,3-a] pyrazines. It also describes process for preparation of sitagliptin or a salt thereof comprises coupling of (3R)-3-[N-(tert- butoxycarbonyOaminoJ^^^jS-trifluorophenyObutanoic acid with 3-trifluoromethyl-S^^^-tetrahydro-fl^^triazolo^^-aJpyrazine hydrochloride to afford Boc-protected Sitagliptin, which was deprotected using methanolic hydrochloride to obtain Sitagliptin hydrochloride.
The process is given below scheme.

WO2006081151 describes a process for preparation of Sitagliptin via enamine compound which is reduced by employing a rhodium metal precursor completed to a ferrocenyl diphosphine ligand, followed by treatment with phosphoric acid to obtain Sitagliptin phosphate.
WO2009064476 describes process for preparing sitagliptin comprises reacting (R)-3-(t-butoxycarbonylamino)-4-(2,4)5-trifluorophenyl)butanoic acid with 3-(trifluoromethyl)r 5,6,7,8-tetrahydro-[l,2,4]triazolo[4,3-a]pyrazine hydrochloride in the presence of N,N'-dicyclohexylcarbodiimide (DCC), 4-dimethylaminopyridine(DMAP), and triethylamine in dimethylformamide to give sitagliptin.
WO 2005097733 discloses the process of asymmetric hydrogenation is carried out in the presence of a rhodium metal precursor complexed with a chiral mono- or biphosphine ligand.
Most of the prior art process involves use of costly metal catalyst makes process uneconomical. Further tedious workups make process more complex at industrial scale. The major disadvantages of above said processes are using hazardous chemicals such as butyl lithium, diazomethane and silver benzoate. Moreover, the processes involve multiple step synthesis which results in lower yield.
Hence it is necessary to develop cost-effective and safe process for preparation of Sitagliptin.
The present invention provides, economical, safe and industrially feasible process for preparing Sitagliptin phosphate monohydrate.

OBJECT OF THE PRESENT INVENTION:
1. The main object of the present invention is the elimination of enamine reaction and isolation of its product.
2. Another object of the present invention is to avoid high pressure hydrogenation and use of specialized equipment
3. Another object of the present invention is to avoid use of heavy metals and carbon treatment for its removal.
4. Another object of the present invention is that the present invention provides higher enantioselectivity with high yield.
5. one another object of the present invention is that the bio-catalytic process is economically cheaper and better than prior art processes.
SUMMARY OF THE INVENTION:
The present invention relates to bio-catalytic process for the preparation of 7-[(3R)-3-amino-
l-oxo-4-(2,4,5-trifluorophenyl) butyl]-536,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-
triazolo[4,3-a] pyrazine phosphate monohydrate of formula-1
One embodiment of the present invention provides preparing of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate of formula-2.

Another embodiment of the present invention provides purification of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate.
- DETAIL DESCRIPTION OF THE INVENTION: *
The present invention relates to improved, safe, economical and industrially applicable process for the preparation of 7-[(3R)-3-amino-l-oxo-4-(2)4]5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-ls2,4-triazolo[4,3-a] pyrazine phosphate monohydrate of formula-2
One aspect of the present invention provides preparing of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate of formula-2 comprises;
(a) Dissolving coenzyme in water
(b) Reacting l-(3-(trifluoromethyl)-5)6-dihydro-[l)2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butane-l,3-dione with biocatalyst in presence of amino group donor and organic solvent
(c) Isolating 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3-(trifluorornethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate
The process for preparation of 7-[(3R)-3-amino-l-oxo-4-(254,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,254-triazolo[4,3-a] pyrazine phosphate monohydrate of Formula-2 given in the below reaction scheme-1

The co-enzyme for step (a) is selected from the group consisting of Vitamin B6 family,
pyridoxal, pyridoxamine and their phosphorylated counterparts, pyridoxine phosphate and
pyridoxamine phosphate.
In transamination reactions using transaminase enzymes, the amino group of the amino group
donor is transferred to the coenzyme to produce a keto byproduct, while pyridoxal-5'-
phosphate is converted to pyridoxamine phosphate. Pyridoxal-5'-phos phate is regenerated by
reaction with a different keto compound (the amino group acceptor). The transfer of the
amino group from pyridoxamine phosphate to the amino acceptor produces a chiral amine
and regenerates the coenzyme.
The bio-catalyst is CDX-036.
The organic solvent is selected from the group consisiting of methanol, ethanol, THF,
DMSO, acetone, toluene, isopropylacetate, hexanes, propanol, benzene, acetone, Xylene,
methylethyl ketone, ether and ethyl acetate.
The amino group donor for step (b) is selected from the group consisting of isopropylamine
(also referred to as 2-aminopropane), L, D or DL alanine, phenylalanine, glutamate,
glutamine, leucine, 3-aminobutyric acid and methylbenzylamine, C-phenethylamine (also
termed 1-phenylethanamine), and its enantiomers (S)-l-phenylethanamine and (R)-l-phenyle
thanamine, 2-amino-4-phenylbutane, glycine, L-glutamic acid, L-glutamate, monosodium
glutamate, L-aspartic acid, L-lysine, L-ornithine, B-alanine, taurine, n-octylamine,

cyclohexylamine, 1,4-butanediamine, 1.6-hexanediamine, 6-aminohexanoic acid, 4-
aminobutyric acid, tyramine, benzyl amine, 2-aminobutane, 2-amino-l-butanol, 1-amino 1-
phenylethane, 1 -amino-1 -(2-methoxy-5-fluorophenyl)ethane, 1 -amino-1 -phenylpropane, 1 -
amino-1 -(4-hydroxyphenyl)propane, 1 -amino-1 -(4-bromophenyl)propane, 1 -amino 1 -(4-
nitrophenyl)propane, - l-phenyl-2-aminopropane, l-(3-trifluoromethylphenyl)-2-
aminopropane, 2-aminopropanol, 1-amino-1-phenylbutane, l-phenyl-2-aminobutane, l-(2,5-
dimethoxy-4-methylphenyl)-2-aminobutane, l-phenyl-3- aminobutane, l-(4-hydroxyphenyl)-
3-aminobutane, l-amino-2-methylcyclopentane, l-amino-3-methylcyclopentane, l-amino-2-
methylcyclohexane, l-amino-l-(2- naphthyl)ethane, 3-methylcyclopentylamine, 2-methylcy
clopentylamine, 2-ethylcyclopentylamine, 2-methylcyclohexylamine, 3-
methylcyclohexylamine, 1-aminotetralin, 2-aminotetralin, 2-amino-5-methoxytetralin, and l-aminoindan.
Most of the prior art process for preparing 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyO-l^^-triazoIo^^-a] pyrazine phosphate involves use of heavy metals, high pressure hydrogenation, special equipment for tedious work ups that makes the process uneconomical, difficult to handle.
The present invention provides bio-catalytic process for preparing 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate with higher enantioselectivity with high purity and higher yield. Moreover, bio-catalytic process is economical and industrially feasible as compare to prior art processes.
One aspect of the present invention provides purification of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,758-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate comprises;
(a) suspending crude 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-
tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate into water and
heating the mixture
(b) adding organic solvent
(c) isolating pure 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyO-l^^-triazolo^^-a] pyrazine phosphate

The organic solvent for step (b) is selected from the group consisting of methanol, ethano isopropyl alcohol, butanol.
The heating temperature for step (a) is 60-80°C.
The following examples explain various other embodiments without limiting the scope of th present invention.
Example-1: Preparation of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl 5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphal monohydrate
The Pyridoxal phosphate (PLP) dissolved in process water. Isopropyl amine, Biocataly: were charged. The reaction mass stirred for 5 min then DMSO and diketo intermediate addec The reaction mass stirred for lOmin then the reaction mass heated to 60-80°C. Maintained th reaction mass for 35 hrs. After completion of reaction, process water charged. The produ< extracted with isopropyl acetate and treated with orthophosphoric acid and IPA to get * [(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyf l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate crude. HPLC purity: 99.8%
Example-2: Purification of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl 5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphal monohydrate
The crude 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3 (trifluorornethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate material suspended in proces water at 25-40°C. The reaction mass heated to 30-40°C for 24 hrs. Then cooled the mass t 25-40°C. The reaction mass further cooled to 0-10°C and charged isopropyl alcohc maintained for 2 hrs, filtered, washed and dried to get pure 7-[(3R)-3-amino-l-oxo-4-(2,4,f trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazin phosphate monohydrate. HPLC purity: 99.95%

Example-3: Preparation of 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-I,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate
The Pyridoxal phosphate (PLP) dissolved in process water. Isopropyl amine, Biocatalyst ' were charged. The-reaction mass stirred for 5 min then acetone and diketo intermediate added. The reaction mass stirred for lOmin then the reaction mass heated to 30-40°C. Maintained the reaction mass for 35 hrs. After completion of reaction, process water charged. The product extracted with isopropyl acetate and treated with orthophosphoric acid and IPA to get 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-3-(trifluoromethyl)-l52,4-triazolo[4,3-a] pyrazine phosphate monohydrate crude. HPLC purity: 99%

Claims:
(1) An improved process for preparing 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butylJ-S^^S-tetrahydro^- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate of formula-2 comprises;
(a) Dissolving co-enzyme in water
(b) Reacting 1 -(3-(trirluoromethyl)-5,6-dihydro-[ 1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butane-l,3-dione with biocatalyst in presence of amino group donor and organic solvent
(c) Isolating 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyI) butyl]-5,6,7,8-tetrahydro-3-(trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate

(2) The process according to claim 1, wherein the co-enzyme is selected from the group consisting of Vitamin B6 family, pyridoxal, pyridoxamine and their phosphorylated counterparts, pyridoxine phosphate and pyridoxamine phosphate or mixture thereof.
(3) The process according to claim 1, wherein the bio-catalyst is CDX-036.
(4) The process according to claim 1, wherein the amino group donor is selected from the group consisting of isopropylamine (also referred to as 2-aminopropane), L, D or DL alanine, phenylalanine, glutamate, glutamine, leucine, 3-aminobutyric acid and methylbenzylamine, C-phenethylamine (also termed 1-phenylethanamine), and its enantiomers (S)-l-phenylethanamine and (R)- 1-phenylethanamine, 2-amino-4-phenylbutane, glycine, L-glutamic acid, L-glutamate, monosodium glutamate, L-aspartic acid, L-lysine, L-ornithine, B-alanine, taurine, n-octylamine, cyclohexylamine, 1,4-butanediamine, 1.6-hexanediamine, 6-aminohexanoic acid, 4-aminobutyric acid, tyramine, benzyl amine, 2-ami no butane, 2-amino-1-butanol, 1-amino 1-phenylethane, 1 -amino- l-(2-methoxy-5-rluorophenyl)ethane, 1-amino-1 -phenylpropane, 1 -amino-1 - (4-hydroxyphenyl) propane, 1 -amino-1 -(4-bromophenyl)propane, 1-amino l-(4-nitrophenyl)propane, l-phenyl-2-aminopropane, l-(3-

trifluoromethylphenyl)-2-aminopropane, 2-aminopropanol, 1 -amino-1 -phenylbutane, 1 -phenyl-2-aminobutane, l-(2,5-dimethoxy-4-methylphenyl)-2-aminobutane, l-phenyl-3-aminobutane, l-(4-hydroxyphenyl)-3-aminobutane, l-amino-2-methylcyclopentane, 1-amino-3-methylcyclopentane, l-amino-2-methylcyclohexane, 1-amino-1-(2- naphthyl)ethane, 3-methylcyclopentylamine, 2-methylcyclopentylamine, 2-ethylcyGlopentylamine, 2-methylcyclohexylamine, 3-methylcyclohexylamine, 1 -aminotetralin, 2-aminotetraIin, 2-amino-5-methoxytetralin, and 1-aminoindan or mixture thereof.
(5) The process according to claim 1, wherein the organic solvent is selected from the group
consisiting of methanol, ethanol, THF, DMSO, acetone, toluene, i so propyl acetate, hexanes,
propanol, benzene, acetone, Xylene, methylethyl ketone, ether and ethyl acetate or mixture
thereof.
(6) An improved purification process for 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl)
butyl]-5,6,7,8-tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate
monohydrate of formula-2 comprises;
(a) suspending crude 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-
tetrahydro-3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate into water and
heating the mixture
(b) adding organic solvent
(c) isolating pure 7-[(3R)-3-amino-l-oxo-4-(2,4,5-trifluorophenyl) butyl]-5,6,7,8-tetrahydro-, 3- (trifluoromethyl)-l,2,4-triazolo[4,3-a] pyrazine phosphate monohydrate

(7) The process according to claim 6, wherein the organic solvent is selected from the group consisting of methanol, ethanol, isopropyl alcohol, butanol or mixture thereof.
(8) The process according to claim 6, wherein the heating temperature is 60-80°C .