A NOVEL METHOD OF PREPARATION OF IMATINIB
Imatinib base (I) is used in the treatment of Chronic Myeloid Leukemia in the form of its mesylate salt. The drug acts by inhibiting Tyrosine Kinase and is indicated for Philadelphia chromosome positive leukemia and also for malignant gastrointestinal stromal tumours
The free base of the drug substance 'imatinib base' is usually prepared by condensation of N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) and 4-[(4-Methylpiperazin-l-yl) methyl]benzoylchloride dihydrochloride (III). A novel, industrially feasible and environmentally friendly method of preparation of the intermediate amine N-(5-Amino-2-methyl phenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) and its condensation with the acid chloride (III) is described in the current invention.

The amine intermediate N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) is usually prepared from the corresponding nitro derivative N-(2-Methyl-5-nitrophenyl)-4-(3-

pyridyl)-2-pyrimidineamine (IV), This conversion is effected by reduction of the nitro group by catalytic hydrogenation (H2/Pd/C) as described in US 5522184 and EP 0564409. But this method suffers from the disadvantages like longer reaction times, inconsistency of product composition and requirement of large volume of solvent. In our hands in some batches the reduction did not proceed to yield the desired product.
Reducing agents like SnCl2 have been used successfully as described in the US patent 2004/0248918. These methods are beset with problems like use of heavy metal salts leading to problems in effluent streams rich in tin salts. Also purification of the resulting product free of heavy metal salts is rather difficult. In continuation of our Research & Development efforts to develop a simple method of preparation of the imatinib base and also useful amine intermediate (II) free of the disadvantages mentioned, we developed a simple method of reducing the nitro fimction of the intermediate (IV) by employing reagents like sodium disulphide or sodium polysulphide. The reduction of the nitrocompound (IV) may also be carried out in alkaline polysulphide solutions prepared by dissolving elemental sulphur in caustic alkali solutions like aq. NaOH, aq. KOH, alcoholic NaOH, alcoholic KOH or aq/alcoholic NaOH or aq. Alcoholic KOH.
During the condensation of the N-(5-Amin0"2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) and 4-[(4-Methylpiperazin-l-yl) methyl]benzoylchloride dihydrochloride (III), organic bases like pyridine have been employed in prior art methods (EP0564409). Use of pyridine is not feasible for industrial scale operation and is now replaced with environmentally friendly potassium carbonate, sodium carbonate, dilute aq. NaOH or aq. KOH


Example 1:
(A) Preparation of N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (II)
To a solution of commercial sodium sulphide nonahydrate (Na2S.9H2O, 20g) in ethanol (200ml) is charged sulphur (3g) and the mass refluxed for 2 hr. the resulting solution of sodium disulphide is treated with the nitro compound N-(2-Methyl-5-nitrophenyl)-4-(3-pyridyl)-2-pyrimidineamine (12.5g) in one lot. The reaction mixture is refluxed for 1hr and the solvent ethanol is distilled off under reduced pressure. The reaction mixture is diluted with water (100ml) and extracted with chloroform (2x100ml). The chloroform layer is washed with water (2x50ml)5 dried over anhy. Na2S04 (2g) and the solvent distilled off. The cooled mass is crystallized from ethylacetate (40ml) to yield the intermediate amine N-(5-Amino-2-methyl phenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) (10g).mp:142-147°C
(B) Preparation of imatinib base (I):
4-[(4-Methylpiparazin-l-yl)methyl]benzoylchloride dihydrochloride (7.2g) is suspended in isopropanol (100ml), and anhy. potassium carbonate (5.3g) is added and the mixture
stirred for 30 minutes at 25-30°C.

The resulting mixture is treated with N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (5g) and the reaction slurry is refluxed for 1h when absence of the amine (IV) is observed by TLC, The reaction mixture is filtered and washed with hot isopropanol (30ml). The residual solid cake is suspended in water (100ml) extracted with chloroform (2xl00ml). The chloroform layer is subjected to vacuum distilled and the residue treated with ethylacetate (50ml) and the slurry filtered and dried to get imatinib base (7.5g).mp.: 205-208°C
Advantage of the invention:
• Use of sodium disulphide / or sodium polysulfide for conversion of nitro intermediate (IV) is novel and is environmentally friendly and avoids the use of heavy metal like stannous chloride.
• Considerable amount of time to the extent of 70% is saved in this conversion and the reduction is very fast and the entire procedure of reduction, work-up and isolation of the amine intermediate (II) is greatly simplified.
• Replacement of pyridine with environmentally friendly reagents like K2CO3 during the condensation of amine (II) and aroyl chloride (III) rendered the process of isolation of imatinib. Very elegant and operator friendly
• The total process of conversion of nitro compound to imatinib base is novel leading to an industrially feasible and economical manufacturing process for imatinib

We claim:
1) A novel high yielding method of reduction of the nitro compound, N-(2-Methyl-5-nitrophenyl)-4-(3-pyridyl)-2-pyrimidineamine (IV) employing sodium disulphide in an alkaline medium to get the pharmaceutically useful intermediate N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidineamine (II) in alcoholic or aqueous alcoholic media or aqueous media.
2) A novel high yielding method of preparation of the amine, N-(5-Amino-2-methyIphenyl)-4-(3-pyridyl)-2-pyrimidinamine from the nitro compound (II) N-(2-Methyl-5-nitrophenyl)-4-(3-pyridyl)-2-pyrimidine amine (IV) by employing sodium polysulphide in alcoholic or aq. alcoholic or aqueous media.
3) A method of preparation of the amine intermediate N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidinamine (II) as in claim 1 and wherein the solvent is chosen from a lower alcohols like methanol, ethanol, isopropanol or n-butanol.
4) A method of preparation of the amine intermediate N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidinamine (II) as in claim 2 wherein the alcoholic solvent is chosen from lower alcohols like methanol, ethanol, isopropanol or n-butanol.
5) A method of condensation of the amine intermediate 4-[(4-Methylpiperazin-l-yl) methyl]benzoylchloride dihydrochloride (III) wherein the acid scavenging agent is potassium carbonate and the solvent is a lower alcohol like methanol, ethanol, isopropanol or n-butanol,
6) A method of preparation of the amine N-(5-Amino-2-methylphenyl)-4-(3-pyridyl)-2-pyrimidinamine (II) essentially as described in the example cited above.

7) A method of preparation of imatinib base (I) essentially as described in example cited above.

To
The Controller of Patents
Chennai Patent Office
Chennai.