Process for preparation of alogliptin

1. A process for the preparation of alogliptin, a compound of formula I, or a salt thereof, comprising:

a) methylating a compound of formula IV, to obtain a compound of formula V

wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group, wherein the aromatic ring of the phthalimido group is unsubstituted or substituted with one or more R 3 substituents selected from the group consisting of halogen, alkyl, nitro and amino; and

b) deprotecting the compound of formula V to obtain compound of formula I.

2. The process of claim 1 , wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group and wherein R 3 on the aromatic ring of the phthalimido group is alkyl.

3. The process of claim 2 , wherein the deprotection is carried out in presence of an amine.

4. A compound of formula IV having a purity of 90 to 95%:

wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group, wherein the aromatic ring of the phthalimido group is substituted with one or more R 3 substituents selected from the group consisting of halogen, alkyl, nitro and amino.

5. The compound of claim 4 , wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group and wherein R 3 on the aromatic ring of the phthalimido group is alkyl.

6. The compound of claim 5 , wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group and wherein R 3 on the aromatic ring of the phthalimido group is methyl, represented by compound of Formula Iva

7. The process of claim 1 , wherein the compound of formula IV is prepared by a process comprising

reacting a compound of formula II with a compound of formula III

wherein R 1 and R 2 together with the nitrogen to which they are attached form a phthalimido group, wherein the aromatic ring of the phthalimido group is unsubstituted or substituted with one or more R 3 substituents selected from the group consisting of halogen, alkyl, nitro and amino.

8. A compound of Formula Va having a purity more than 99%:

9. The process of claim 1 , further comprising;

(a) treating alogliptin with an acid to form an acid addition salt of alogliptin; and

(b) treating the acid addition salt of alogliptin with a base followed by addition of benzoic acid to obtain alogliptin benzoate.

10. The process of claim 9 , further comprising isolating alogliptin benzoate from a solvent selected from the group consisting of n-propanol, hexane, ethylene dichloride, methyl tertiary butyl ether, xylene, methyl tetrahydrofuran, propyl acetate, methyl acetate or mixtures thereof.

11. The process of claim 10 , wherein the step of isolating comprises

a) subjecting alogliptin benzoate to slurrying in a solvent selected from the group consisting of n-propanol, hexane, ethylene dichloride, methyl tertiary butyl ether, xylene, methyl tetrahydrofuran, propyl acetate, methyl acetate or mixtures thereof to obtain solid alogliptin benzoate; and

b) filtering out the solid alogliptin benzoate, obtained in step a.