1. Filed of the Invention
The present invention relates to a novel process for the preparation of (1S-cis)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-N-methyl-1-naphthalenamine(sertraline) comprising hydrogenation of N-[4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenylidene]methanamine.
2. Discussion of the Background
Sertraline, (1S-cis)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-N-methyl-1-naphthalenamine, which has a structure of formula I 
is marketed in the form of its hydrochloride for the treatment of depression, obsessive-compulsive disorder and panic disorder.
The synthesis of sertraline is described in U.S. Pat. No. 4,536,518, which is incorporated herein by reference. The process described comprises a condensation reaction of 4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone of formula II with 
monomethylamine yielding N-[4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenylidene]methanamine. This is further hydrogenated in the presence of palladium on carbon catalyst to form a mixture of cis- and trans-racemates of 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-N-methyl-1-naphthalenamine with the isomeric ratio of 70:30. The desired product is the cis isomer, and accordingly the trans isomer is a not desired by-product which is classified as an impurity in the final product. Other impurities formed in the reaction are, e.g., dehalogenation products, the amount of which depends, e.g., on the temperature and pressure used in the hydrogenation and the quality of the imine starting material. The removal of the dehalogenation products is difficult.
Different solutions have been suggested to increase the formation of the cis isomer and to prevent the dehalogenation reaction in the hydrogenation. In the process described in U.S. Pat. No. 5,082,970, the trans-isomer is treated with a basic equilibration agent like potassium tert-butoxide to convert it to the cis-isomer. This approach, however, requires an additional step in the synthesis. In WO 99/47486, copper containing catalysts are used to improve the ratio, and results as high as 98.5% in favor of the cis compound have been achieved. Nothing has, however, been said about the dehalogenation products formed. In WO 99/57093, a hydrogenation process with a palladium catalyst which has been pretreated with alkali halide has been described. The process described gives a cis/trans ratio of 85-95/15-5 (in %), and the amount of dehalogenation side products is said to be below 0.5%.
In U.S. Pat. No. 3,474,144, there has been described the use of triphenyl phosphite or tritolyl phosphite as dehalogenation inhibitors in the catalytic reduction of aromatic chloronitro compounds. It has also been mentioned that the use of the inhibitors does not affect the original isomer ratio. EP 292 682 discloses the use of organic esters of phosphoric acid together with hydrocarbyl-silanes to inhibit the dehalogenation during the catalytic reduction of aromatic nitro-halo-derivatives. A degree of dehalogenation lower than 1% was reported. In Kosak, Catal. Org. Synth., 1980, vol. date 1978, p. 107-117, there has been described the use of phosphorous acid and some related compounds as dehalogenation inhibitors in the hydrogenation of haloaromatic nitro compounds. However, the use of the inhibitors of the present invention in the preparation of sertraline or in the hydrogenation of imine compounds has not been described.
Accordingly, it is one object of the present invention to provide an improved preparation method for cis-sertraline and/or a pharmaceutically acceptable acid addition salt thereof.
It is another object of the present invention to provide an improved preparation method for cis-sertraline and/or a pharmaceutically acceptable acid addition salt thereof, which affords sertraline having a high content of the cis isomer.
It is another object of the present invention to provide an improved preparation method for cis-sertraline and/or a pharmaceutically acceptable acid addition salt thereof, which produces the undesirable dehalogenated side products in a reduced amount.
It is another object of the present invention to provide pharmaceutical compositions comprising cis-sertraline or a pharmaceutically acceptable acid addition salt thereof made by the process of the invention.
These and other objects, which will become apparent during the following detailed description, have been achieved by the inventor""s surprising discovery that if some phosphorus compounds, especially esters of phosphorous acid, are used as dehalogenation inhibitors in the hydrogenation of the imine in the production of sertraline, the cis-trans ratio is improved. In addition, the amount of dehalogenation products is diminished. The produced racemic cis-sertraline can be further resolved or crystallized directly to a pharmaceutically acceptable acid addition salt, e.g., hydrochloride.
The present invention provides a process for the preparation of cis-sertraline comprising hydrogenating N-[4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenylidene]methanamine in the presence of a catalyst and a dehalogenation inhibitor to obtain cis-racemate of 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-N-methyl-1-naphthalenamine.
By using the hydrogenation process of the present invention, the ratio of cis:trans isomers is improved to as high as 97:3, and the formation of the dehalogenation by-products may be reduced to even less than 0.1%. No further purification process is needed before resolution or crystallization. These results are achieved by using the inhibitors of the invention in the hydrogenation process.
Cis-sertraline is prepared starting from 4-(3,4-dichlorophenyl)-3,4-dihydro-1-(2H)-naphthalenone (tetralone), which can be prepared by methods known in the art, e.g., as described in U.S. Pat. No. 5,019,655, which is incorporated herein by reference in its entirety. Tetralone is then reacted with monomethylamine to form an imine, which can be performed by methods known in the art, e.g., as described in U.S. Pat. No. 4,536,518, which is incorporated herein by reference in its entirety. The imine obtained is further hydrogenated to the cis-racemate of 4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-N-methyl-1-naphthalenamine in the presence of a catalyst and a dehalogenation inhibitor of the invention. From this mixture, the cis-compound can be either resolved by, e.g., mandelic acid or 10-camphorsulphonic acid to afford cis-(+)-sertraline and crystallized as a base or a pharmaceutically acceptable acid addition salt, e.g., hydrochloride, or the racemic cis-sertraline can be crystallized as a base or as a pharmaceutically acceptable salt.
The hydrogenation of the imine is performed in the presence of a catalyst and an inhibitor, which is selected from the group consisting of hypophosphorous acid, esters of hypophosphorous acid, phosphorous acid, esters of phosphorous acid, phosphine and substituted phosphines. Suitable inhibitors are, e.g., mono-, di-, and triesters of phosphorous acid, preferably trimethyl phosphite, triphenyl phosphite, or tritolyl phosphite. Examples suitable phosphines are, e.g., trimethylphosphine, triethylphosphine, triisopropylphosphine, tritolylphosphine, and tribenzylphosphine. The amount of the inhibitor used in the process is typically 0.5-10 mol %, preferably 3-5 mol %, based on the number of moles of the metal in the catalyst used.
The catalyst used can be any suitable catalyst known in the art, e.g., palladium on carbon, palladium on graphite, palladium on carbon paste or PtO2. The catalyst is typically used in an amount of 0.1-1.0% (w/w, calculated as the pure metal in the catalyst) based on the weight of the imine used. The hydrogenation may be carried out in an organic solvent, which can be any suitable protic or aprotic solvent or mixtures thereof. Examples of solvents are, e.g., dimethylformamide (DMF), esters like ethyl acetate, chlorinated hydrocarbons like methylene chloride or chloroform, or alcohols like methanol, ethanol or isopropanol. Preferably a lower alcohol, e.g., methanol or ethanol or their mixtures with DMF is used as the solvent.
The reaction can be carried out at a temperature of 0-100xc2x0 C., preferably at 20-50xc2x0 C. The hydrogen pressure used is typically from 1 to 50 bar, preferably from 2 to 5 bar.
The reaction time can vary from half an hour to 24 hours depending on the catalyst used, on hydrogen pressure, on the reaction temperature and on the equipment used. Preferably the hydrogenation time is about 2 to 6 hours.
The following examples merely illustrate the invention and they are not to be construed as limiting.