Process for producing 1-[2-(dimethylamino)-1-(4-phenol)ethyl]cyclohexanol
The present invention relates to an improved, process for large scale production of 1-[2-(dimethylamino)-1-(4-phenol)ethyl]cyclohexanol (O-desmethylvenlafaxine) or its pharmaceutically acceptable salts with increased yield and minimal impurities.
1. A process for preparing 1-[2-(dimethylamino)-1-(4-phenol)ethyl]cyclohexanol (O-desmethylvenlafaxine) or its pharmaceutically acceptable salt thereof,
wherein the process comprises:
(a) reducing 1-[cyano(substituted benzyloxyphenyl) methyl] cyclohexanol of formula (II) with reducing agent sodiumborohydride-iodine or sodiumborohydride-trifluoroacetic acid in presence of a solvent to obtain 1-[2-amino-1-(substituted benzyloxyphenyl)ethyl]cyclohexanol of formula (III);
wherein R is selected from phenyl, nitrophenyl, hydroxyphenyl or halophenyl;
(b) alkylating the 1-[2-amino-1-(substituted benzyloxyphenyl)ethyl]cyclohexanol of formula (III) to obtain compound of formula IV; and
(c) deprotecting the compound of formula (IV) to obtain O-desmethylvenlafaxine.
2. The process according to claim 1 , wherein the reducing agent comprises sodium borohydride-iodine.
3. The process according to claim 1 , wherein the solvent is selected from ether, aliphatic hydrocarbon or alcohol or mixture thereof.
4. The process according to claim 2 , wherein the solvent is selected from tetrahydrofuran, hexane, cyclohexane, heptane, pentane, methanol, ethanol or isopropyl alcohol.
5. The process according to claim 1 , wherein the alkylation is performed employing an alkylating agent selected from formaldehyde and formic acid, methyl iodide or dimethyl sulphate.
6. The process according to claim 1 , wherein the deprotection is carried out in presence of metal catalyst under hydrogen pressure.
7. The process according to claim 6 , wherein the metal catalyst is selected from Raney nickel or palladium on carbon.
8. The process for preparing O-desmethylvenlafaxine according to claim 1 , wherein the 1-[cyano(substituted benzyloxyphenyl) methyl) cyclohexanol of formula (II) is prepared by reacting substituted benzyloxyphenyl acetonitrile of formula (I),
wherein R is selected from phenyl, nitrophenyl, hydroxyphenyl, or halophenyl, with cyclohexanone in presence of a base and a phase transfer catalyst (PTC) in a solvent.
9. The process according to claim 8 , wherein the base is selected from alkali metal hydroxide, alkali metal alkoxide, alkali earth metal hydroxide, alkali earth metal oxide, lithium hexmethylenedisilane or mixture thereof.
10. The process according to claim 9 , wherein the alkali metal hydroxide is selected from sodium hydroxide and potassium hydroxide or mixture thereof.
11. The process according to claim 9 , wherein the alkali metal alkoxide is selected from sodium methoxide, sodium tertiarybutoxide, potassium methoxide, and potassium tertiarybutoxide or mixture thereof.
12. The process according to claim 9 , wherein the alkali earth metal hydroxide is selected from magnesium hydroxide and calcium hydroxide or mixture thereof.
13. The process according to claim 9 , wherein the alkali earth metal oxide is selected from calcium oxide, magnesium oxide or mixture thereof.
14. The process according to claim 8 , wherein the phase transfer catalyst is selected from tetrabutylammonium hydrogensulphate, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutyl ammonium iodide, benzyltriethyl ammonium chloride, polyethylene glycol-400, or N-methyl-N,N-dioctyloctan-1-ammonium chloride.
15. The process according to claim 8 , wherein the solvent used is selected from alcohol, aliphatic hydrocarbons, aromatic hydrocarbons or ethers.
16. The process according to claim 15 , wherein the solvent is selected from methanol, ethanol, isopropyl alcohol, hexane, heptane, cyclohexane, toluene, xylene tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether or isopropyl ether.
17. The process according to claim 1 , wherein the process comprises optionally treating the 1-[2-amino-1-(substituted benzyloxyphenyl)ethyl] of formula (III) with an acid to obtain an acid addition salt having formula (IIIa),
wherein R is selected from phenyl, nitrophenyl, hydroxyphenyl or halophenyl.
18. The process according to claim 17 , wherein the acid used is selected from hydrochloric acid, hydrobromic acid, sulphuric acid, phosphoric acid, methane sulphonic acid or p-toluene sulphonic acid.
19. The process according to claim 1 , wherein the process further comprises treating the O-desmethylvenlafaxine with an acid in a solvent to give pharmaceutically acceptable acid addition salt of O-desmethylvenlafaxine.
20. The process according to claim 19 , wherein the acid comprises succinic acid.
21. The process according to claim 19 , wherein the solvent is selected from methanol, ethanol, n-propanol, isopropanol or mixture thereof.