Process for preparing quinoline-3-carboxamide derivatives

1. A process for the preparation of substituted quinoline-3-carboxamide compound of formula I:

wherein

R is selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec,-butyl and allyl;

R 1 is selected from methyl, ethyl, n-propyl, iso-propyl, methoxy, ethoxy, methylthio, ethylthio, n-propylthio, methylsulphinyl, ethylsulphinyl, fluoro, chloro, bromo, trifluoromethyl, difluoromethoxy and trifluoromethoxy;

R 2 is hydrogen; or

R 1 and R 2 together can be methylenedioxy, ethylenedioxy and isopropylidenedioxy;

R 3 is selected from hydrogen, methyl, ethyl, n-propyl, iso-propyl, methoxy, ethoxy, fluoro, chloro, bromo, trifluoromethyl, difluoromethoxy and trifluoromethoxy; and

R 4 is selected from hydrogen, fluoro and chloro, with the proviso that R 4 is selected from fluoro and chloro only when R 3 is selected from fluoro and chloro;

comprising:

reacting a quinoline-3-carboxylic acid derivative of formula II:

wherein R 1 and R 2 are as defined in formula I;

with an aniline derivative of formula III:

wherein R, R 3 and R 4 are as defined in formula I; in the presence of a coupling agent in a solvent to provide a substantially pure compound of formula I and optionally converting the compound of formula I obtained into a pharmaceutically acceptable salt thereof; wherein the coupling agent is selected from the group consisting of dichlorotriphenyl phosphorane, phosphorous oxychloride, O-benzotriazole-N,N,N′,N′-tetramethyl-uronium-hexafluoro-phosphate (HBTU), and combinations comprising one or more of the foregoing coupling agents.

2. The process of claim 1 , wherein the coupling agent is dichlorotriphenyl phosphorane; and wherein the solvent used in the coupling reaction is selected from the group consisting of methylene chloride, ethylene dichloride, chloroform, carbon tetrachloride, n-pentane, n-hexane, n-heptane, cyclohexane, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, acetonitrile, ethyl acetate, methyl acetate, isopropyl acetate, tert-butyl methyl acetate, ethyl formate, tetrahydrofuran, dioxane, diethyl ether, diisopropyl ether, monoglyme, diglyme, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, and mixtures thereof.

3. The process of claim 1 , wherein R 1 , in the compound of formula II is chloro, and R 2 is hydrogen; wherein R 3 and R 4 in the compound of formula III are hydrogen, and R is ethyl; wherein R 2 , R 3 and R 4 in the compound of formula I are hydrogen, R 1 is chloro, and R is ethyl; and wherein the compound of formula I obtained is laquinimod of formula I(i):

or a pharmaceutically acceptable salt thereof:.

4. The process of claim 1 , wherein the solvent used in the coupling reaction is a chlorinated hydrocarbon solvent selected from the group consisting of methylene chloride, ethylene dichloride, chloroform, carbon tetrachloride, and mixtures thereof; and wherein the reaction is carried out in the presence or absence of a base, wherein the base is an organic or inorganic base.

5. The process of claim 4 , wherein the solvent is methylene chloride or chloroform; wherein the organic base is selected from the group consisting of tributylamine, triethylamine, diisopropylethylamine, diethylamine, tert-butyl amine, pyridine, N-methylmorpholine and 4-(N,N-dimethylamino)pyridine; and wherein the inorganic base is selected from the group consisting of sodium hydroxide, calcium hydroxide, magnesium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, sodium tert-butoxide, sodium isopropoxide and potassium tert-butoxide.

6. The process of claim 1 , wherein the reaction is carried out at a temperature of about 0° C. to the reflux temperature of the solvent used for at least 20 minutes; wherein the coupling agent is used in a molar ratio of about 1 to about 6 moles per 1 mole of the quinoline-3-carboxylic acid derivative of formula II; and wherein the substituted quinoline-3-carboxamide compound of formula I obtained has a purity of about 99% to about 99.95% as measured by HPLC.

7. The process of claim 6 , wherein the reaction is carried out at the reflux temperature of the solvent used for about 1 hour to about 5 hours; and wherein the coupling agent is used in a molar ratio of about 2 to about 4 moles per 1 mole of the quinoline-3-carboxylic acid derivative of formula II.

8. The process of claim 1 , wherein the reaction mass containing the substituted quinoline-3-carboxamide compound of formula I obtained is subjected to a washing, an extraction, an evaporation and/or a pH adjustment; followed by isolating as a solid from a solvent by cooling, seeding, partial removal of the solvent from the solution, by adding an anti-solvent to the solution, evaporation, vacuum drying, spray drying, freeze drying, or a combination thereof.

9. The process of claim 8 , wherein the solvent used for isolation is selected from the group consisting of water, acetone, methanol, ethanol, n-propanol, isopropanol, ethyl acetate, methylene chloride, n-pentane, n-hexane, n-heptane, cyclohexane, toluene, and mixtures thereof.

10. A process for the preparation of laquinimod of formula I(i) or a pharmaceutically acceptable salt thereof, comprising reacting 1,2-dihydro-4-hydroxy-5-chloro-l-methyl-2-oxo-quinoline-3-carboxylic acid with N-ethyl aniline in the presence of thionyl chloride and a base selected from the group consisting of diisopropylethylamine and pyridine; and isolating pure laquinimod from a suitable solvent and optionally converting the laquinimod obtained into a pharmaceutically acceptable salt thereof.

11. The process of claim 10 , wherein the reaction is carried out in the presence of a solvent, wherein the solvent is selected from the group consisting of methylene chloride, ethylene dichloride, chloroform, carbon tetrachloride, n-pentane, n-hexane, n-heptane, cyclohexane, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, acetonitrile, ethyl acetate, methyl acetate, isopropyl acetate, tert-butyl methyl acetate, ethyl formate, tetrahydrofuran, dioxane, diethyl ether, diisopropyl ether, monoglyme, diglyme, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, and mixtures thereof.

12. The process of claim 11 , wherein the solvent is selected from the group consisting of methylene chloride, ethylene dichloride, chloroform, n-pentane, n-hexane, n-heptane, cyclohexane, toluene, xylene, and mixtures thereof.

13. The process of claim 12 , wherein the solvent is methylene chloride or toluene.

14. The process of claim 10 , wherein the base is used in a molar ratio of about 1.5 to about 5 moles per 1 mole of 1,2-dihydro-4-hydroxy-5-chloro-l-methyl-2-oxo-quinoline-3-carboxylic acid.

15. The process of claim 14 , wherein the base is used in a molar ratio of about 2 to about 3.5 moles per 1 mole of 1,2-dihydro-4-hydroxy-5-chloro-l-methyl-2-oxo-quinoline-3-carboxylic acid.