A NOVEL PROCESS FOR THE PREPARATION OF TAPENTADOL

Abstract

The present invention relates to a novel process for the preparation of Tapentadol and intermediate compound 2R,3R)-3-(-methoxyphenyl)-N,N,2-trimethylpentanamine (compound of formula IIa).

Claims

1. A process for the preparation of a compound of formula IIa or salt thereof from compound of formula IIIa or a salt thereof, comprising: a) performing deoxygenation of the compound of formula IIIa or a salt thereof in the presence of at least one hydrosilane reagent and at least one first acid selected from the group consisting of Lewis acids and protic acids, to provide the compound of formula IIa, optionally in the form of a diastereomeric mixture ##STR00007##

2. The process according to claim 1, wherein the at least one hydrosilane reagent is selected from the group consisting of triethylsilane, trimethylsilane, dimethylphenylsilane, phenyl silane, triphenylsilane, trichlorosilane, tris(trimethylsilyl)silane, polymethylhydrosiloxane, and mixtures thereof.

3. The process according to claim 1, wherein the at least one first acid is selected from the group consisting of titanium tetrachloride, aluminium chloride, aluminium bromide, boron trifluoride, boron tribromide, tin tetrachloride, tin tetrabromide, stannous chloride, ferric chloride, zinc chloride, trifluoroacetic acid, p-toluolosulfonic acid, methanesulfonic acid, and mixtures thereof.

4. (canceled)

5. The process according to claim 1, wherein the compound of formula IIIa is in the form of an acid addition salt.

6. The process according to claim 5, wherein the acid addition salt is a hydrochloride salt or a hydrobromide salt.

7. (canceled)

8. The process according to claim 2, wherein the at least one first acid is selected from the group consisting of titanium tetrachloride, aluminium chloride, aluminium bromide, boron trifluoride, boron tribromide, tin tetrachloride, tin tetrabromide, stannous chloride, ferric chloride, zinc chloride, trifluoroacetic acid, p-toluolosulfonic acid, methanesulfonic acid, and mixtures thereof.

9. The process according to claim 1, further comprising: treating the compound of formula IIa with at least one second acid to form an acid addition salt via the amine group, wherein the at least one second acid is selected from the group consisting of hydrochloric acid, hydrobromic acid, nitric acid, oxalic acid, succinic acid, maleic acid, fumaric acid, sulfuric acid, phosphoric acid, acetic acid, priopionic acid, benzenesulfonic acid, toluenesulfonic acid, citric acid, tartaric acid, di-aroyl-tartaric acid, malic acid, mandelic acid, camphorosulfonic acid, and mixtures thereof.

10. The process according to claim 9, wherein the acid addition salt is (2R,3R)[3-(3-methoxyphenyl)-2-methyl-pentyl]dimethylamine.

11. The process according to claim 9, wherein the at least one second acid is selected from hydrochloric acid, hydrobromic acid, sulfuric acid, benzenesulfonic acid, toluenesulfonic acid, tartaric acid, mandelic acid, and mixtures thereof.

12. The process according to claim 1, further comprising demethylating the compound of formula IIa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0017] In a first embodiment, the present invention relates to a process for the preparation of a compound of formula IIa or salt thereof from compound of formula IIIa or a salt thereof, comprising the steps of: [0018] a) performing deoxygenation of compound of formula IIIa or a salt thereof in the presence of a hydrosilane reagent and an acid to provide compound of formula IIa, optionally in the form of a diastereomeric mixture;

##STR00005## [0019] b) optionally treating the product of step a) with a chiral or achiral acid or a mixture thereof, forming an acid addition salt via the amine group, and separating the salt of the desired (2R,3R)-[3-(3-methoxyphenyl)-2-methyl-pentyl]dimethylamine (compound of formula IIa).

[0020] Compound of formula IIIa or its salt is prepared according to prior art procedures, as disclosed for example in EP2046724 (or the respective WO2008012047). Compound of formula IIIa, ie the 2S,3R diastereomer of compound of formula III, is accessible in a reliable and reproducible manner, as extensively shown in said prior art disclosures. It is also commercially available either as a free base or in the form of an acid addition salt.

[0021] The deoxygenation performed in step a typically employs a hydrosilane reducing agent, which may be selected from triethylsilane, trimethylsilane, dimethylphenylsilane, phenyl silane, triphenylsilane, trichlorosilane, tris(trimethylsilyl)silane, polymethylhydrosiloxane.

[0022] In order for the deoxygenation to be performed, the hydrosilane reducing agent requires also the presence of an acid (hereinafter referred to as acid of step a). The acid of step a may be any acid capable of activating compound of formula IIIa. The acid may be a Lewis acid or a protic acid. In the case of Lewis acids, the acid may be selected from titanium tetrachloride, aluminium chloride, aluminium bromide, boron trifluoride, boron tribromide, tin tetrachloride, tin tetrabromide, stannous chloride, ferric chloride, zinc chloride. In the case of a protic acid, the acid may be selected from trifluoroacetic acid, p-toluolosulfonic acid or methanesulfonic acid.

[0023] The solvent of the reaction may be selected from hydrocarbons, such as toluene, xylenes, halogenated hydrocarbons, such as dichloromethane, 1,2 dichloroethane, chloroform, chlorobenzene, dichlorobenzene. Preferable is dichloromethane.

[0024] The temperature may range from about (−50)° C. to boiling point of the solvent of the reaction. Preferable temperature range is (31 10)-50° C. More preferable is 0-25° C. Even more is preferable 5-10° C.

[0025] The hydrosilane used may range from 1.5 to 10 equivalents. Preferably, the equivalents used may be 2.0.

[0026] The acid used may range from 2 to 10 equivalents. Preferably, the equivalents used may be 2.1.

[0027] The deoxygenation reaction converts compound of formula IIIa into compound of formula IIa. Compound of formula IIa may be optionally formed as part of a diastereomeric mixture, ie a mixture of compound of formula IIa and its diastereomer, compound of formula IIb.

##STR00006##

[0028] The ratio of the two diastereomers depends on various factors such as the temperature of the reaction and the solvent.

[0029] Where the diastereomeric purity is not satisfactory, the diastereomeric mixture may be subjected to treatment with an acid, upon which the acid addition salt formed allows separation of the two diastereomers.

[0030] The acid used in step b is selected from chiral or achiral acids and may be any of the following: hydrochloric acid, hydrobromic acid, nitric acid, oxalic acid, succinic acid, maleic acid, fumaric acid, sulfuric acid, phosphoric acid, acetic acid, priopionic acid, benzenesulfonic acid, toluenesulfonic acid, citric acid, tartaric acid and its derivatives, malic acid, mandelic acid and its derivatives, camphorosulfonic acid and its derivatives. Preferable acids are hydrochloric acid, hydrobromic acid, sulfuric acid, benzenesulfonic acid, toluenesulfonic acid, tartaric acid and its derivatives and mandelic acid.

[0031] The acid selected to effect the separation of diastereomers may vary and depend on the diastereomeric ratio of the diastereomeric mixture produced in step a. In addition, step b may be performed more than once and the acid used in each cycle may not necessarily be the same.

[0032] The solvent that may be used in step b depends on the selection of the acid used to effect the separation of the diastereomers. In general, commonly used polar organic solvents or water are suitable, such as ketones, alcohols, esters, ethers, halogenated hydrocarbons and mixtures thereof. In case of hydrohalic acid salts, ketone solvents are preferable, such as acetone, butanone, methyl isobutyl ketone. On the other hand, in case of tartaric acid derivatives' addition salts, aqueous alcoholic solvents are preferable.

[0033] The appropriate solvent of step b depends on the selection of the acid used to effect the separation of diastereomers. For instance, for the separation of a diastereomeric mixture of HCl addition salts of IIa the solvent is selected among acetone, butanone-2, methyl isobutyl ketone and related ketones. On the other hand for the separation of a mixture of tartaric acid derivatives addition salts the most appropriate solvent is aqueous methanol, aqueous ethanol or similar solvents.

[0034] The resolution of the diastereomeric mixture may generally be performed according to well-established prior art procedures, such as the one using hydrochloride salts in WO2008012047 or the one using diaroyl tartaric acid derivatives in WO2016023913 or according to the present invention.

[0035] In a preferred embodiment the deoxygenation reaction of compound of formula IIIa into compound of formula IIa, as describe in step a, results in a diastereomeric mixture which is then separated as described in step b to provide compound of formula IIa.

[0036] Compound of formula IIIa may be employed either as the free amine base, or as its acid addition salt. In a preferred embodiment, compound of formula IIIa is in the form of its acid addition salt. The counter ion of the acid addition salt may originate from an acid, as defined above. Preferably, the acid is selected from hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, trihaloacetic acid (e.g., trifluoroacetic acid), maleic acid, sulfonic acids such as methanesulfonic acids, toluenesulfonic acids and camphorsulfonic acids, propionic acids such as (R)-chloropropionic acid, phthalamic acids such as N-[(R)-1-(1-naphthyl) ethyl]phthalamic acid, tartaric acids such as L-tartaric acid and dibenzyl-L-tartaric acid, lactic acids, camphoric acids, aspartic acids, citronellic acids. More preferable are hydrochloric and hydrobromic acid.

[0037] In a second embodiment of the present invention, there is provided a process for the preparation of Tapentadol or a pharmaceutically acceptable salt thereof, comprising steps a and b as defined in previous embodiments and further comprising demethylating compound of formula IIa, to provide compound of formula I and optional conversion of compound of formula I into a pharmaceutically acceptable salt thereof.

[0038] The demethylation reaction may be performed according to methods disclosed in the prior art. The reagents used therein include but are not limited to hydrobromic acid, methanesulfonic acid, hydrochloric acid, trifluoroacetic acid, aluminium chloride, aluminium bromide, or combination thereof. Hydrobromic acid is preferable.

EXAMPLES

Example 1

[0039] 50 mg of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol are charged in 10 ml RB flask, along with 1.0 ml dichloromethane. 0.32 ml triethylsilane are added under stirring and the mixture is cooled to 0-5° C. 67 mg aluminium trichloride are added at this temperature and the mixture is stirred for 2 hours at 0-5° C. Mixture is then allowed to reach ambient temperature and further stirred for 2 hours.

[0040] Mixture is cooled down again to 0-5° C. and diluted with 3.0 ml of ethyl acetate, quenched with 2.0 ml of 10% w/v aq. solution of sodium hydroxide and allowed to reach ambient temperature again. The organic phase is separated and the aqueous one is extracted with another portion of 3.0 ml of ethyl acetate. Organic phase is separated again and combined with the first one, to be dried over sodium sulfate. After filtration, solvents are distilled off to provide 55 mg of crude product.

Example 2

[0041] 50 mg of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol are charged in 10 ml RB flask, along with 1.0 ml toluene. 0.32 ml triethylsilane are added under stirring and the mixture is cooled to 0-5° C. 67 mg aluminium trichloride are added at this temperature and the mixture is stirred for 2 hours at 0-5° C. Mixture is then allowed to reach ambient temperature and further stirred for 2 hours.

[0042] Mixture is subjected to workup as above, to provide 57 mg of crude product.

Example3

[0043] 250 mg of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol are charged in a 10 ml RB flask, along with 10 ml dichloromethane. The mixture is then cooled under stirring to 0-5° C. At this temperature 0.5 ml triethylsilane are added, followed by 0.76 ml trifluoroacetic acid. Mixture is warmed to room temperature and stirring is continued for 1 hour. Mixture is heated at about 50° C. and temperature is maintained for 2 hours.

[0044] Mixture is subjected to workup as above, to provide 223 mg of crude product.

Example 4

[0045] 250 mg of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol are charged in a 10 ml RB flask, along with 10 ml dichloromethane. The mixture is then cooled under stirring to 0-5° C. At this temperature 0.5 ml triethylsilane are added, followed by 1.23 ml boron trifluoride etherate. Mixture is warmed to room temperature and stirring is continued for 1 hour. Mixture is heated at about 50° C. and temperature is maintained for 2 hours. Mixture is subjected to workup as above, to provide 238 mg of crude product.

Example 5

[0046] A 1 L 3-necked RB flask equipped with a stir bar and a thermometer is charged with 10.0 g of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol, followed by 80 ml DCM and 12.7 ml triethylchlorosilane. The mixture is then cooled under stirring to 0-5° C. 10.61 g of aluminium trichloride are added portionwise. Reaction mixture is stirred at 0-5° C. for 1-2 hours. Upon completion of reaction (TLC), 100 ml of DM water are added and mixture is stirred for 30 minutes at ambient temperature. Organic phase is separated and solvent is stripped off. Residue is partitioned between 50 ml t-butyl methyl ether and 10 ml HCl 1.0 N. Aqueous phase is transferred to 500 ml RB flask and 7.0 ml NaOH 50% w/v are added, followed by 50 ml DCM. Organic phase is separated, dried over sodium sulfate and filtered. Solvent is stripped off to provide 8.53 g of crude product. HPLC: 81.2% for the two diastereomers (IIa and IIb).

Example 6

[0047] A 250 ml 3-necked RB flask equipped with a stir bar and a thermometer is charged with 10.0 g of (2S,3R)-1-(Dimethylamino)-3-(3-methoxyphenyl)-2-methylpentan-3-ol hydrochloride salt, followed by 80 ml DCM and 22.2 ml triethylchlorosilane. The mixture is then cooled under stirring to 0-5° C. 11.58 g of aluminium trichloride are added portionwise. Reaction mixture is stirred at ambient temperature for 1-2 hours. Upon completion of reaction (TLC), reaction mixture is poured into an aq. solution of 100 ml sodium potassium tartrate 20% w/v and stirred for a few minutes. Then 25 ml of 50% w/v aq. solution of sodium hydroxide is added and the mixture is filtered. Organic phase is collected. Aqueous phase is extracted with 50 ml DCM. Organic phase is separated, combined with previous one and solvent is stripped off. To the residue 50 ml t-butyl methyl ether are added, followed by 80 ml of 1.0 N HCl. Aqueous phase is collected, 9.0 ml aq. solution 50% w/v sodium hydroxide is added and aq. phase is extracted twice with 50 ml dichloromethane. Combined organic phases are dried over sodium sulfate, filtered and solvents are stripped off to provide 7.9 g of crude product. HPLC: 98.1% for the two diastereomers (IIa and IIb).

Example 7

[0048] A 25 ml RB flask equipped with a magnet bar is charged with 1.0 g of the crude product of example 6, followed by 5.0 ml butanone at ambient temperature. 0.59 mL of chlorotrimethylsilane are added followed by 84 μL of DM water. The mixture is further stirred for 1-2 hours and filtered through Buchner funnel. The wet cake is washed twice with 1.0 ml butanone and dried to afford 378 mg of (2R,3R)-3-(3methoxyphenyl)-N,N,2-trimethylpentane-1-amine hydrochloride salt. HPLC: 74.8% IIa, 23.7% compound of formula IIb.

Example 8

[0049] A 25 ml RB flask equipped with a magnet bar is charged with 1.07 g of the crude product of example 6, followed by 8.0 ml butanone at ambient temperature. 40 μL of DM water are added, followed by dropwise addition of 280 μL of chlorotrimethylsilane. The mixture is further stirred for 2 hours and filtered through Buchner funnel. The wet cake is washed with 2.0 ml butanone and dried to afford 290 mg of (2R,3R)-3-(3-methoxyphenyl)-N,N,2-trimethylpentane-1-amine hydrochloride salt. HPLC: 87.0% IIa, 10.6% IIb.

Example 9

[0050] A 25 ml RB flask equipped with a magnet bar is charged with 550 mg of the crude product of example 6, followed by 2.2 ml acetone at ambient temperature. 21 μL of DM water are added, followed by dropwise addition of 148 μL of chlorotrimethylsilane. The mixture is further stirred for 24 hours. 2.2 ml of t-butyl methyl ether are added and suspension forms. The mixture is stirred for 2 hours and then filtered through Buchner funnel. The wet cake is washed with 2.0 ml t-butyl methyl ether and dried to afford 190 mg of (2R,3R)-3-(3-methoxyphenyl)-N,N,2-trimethylpentane-1-amine hydrochloride salt. HPLC: 91.2% compound of formula IIa and 7.7% compound of formula IIb.

Example 10

[0051] A 50 ml RB flask equipped with a thermometer and a stirring bar is charged with 1.0 g of the crude product of example 6, followed by 1.5 ml aqueous methanol 10%. To the resulting solution is added 1.8 g di-p-touolyl-tartaric acid-L. The mixture is heated up to reflux for 30 minutes. It is then gradually cooled down to 5-10° C. and further stirred for 1.5 hours. Mixture is filtered under vacuum and the cake is washed with 2.0 ml aq. methanol 10%, to provide 1.78 g of (2R,3R)-3-(3-methoxyphenyl)-N,N,2-trimethylpentane-1-amine hydrochloride with diastereomeric purity 75.8% compound of formula IIa and 22.0% compound of formula IIb as a white solid.