Abstract:
Method for preparing cinacalcet hydrochloride having the steps of heating (R)-1-naphthyl ethylamine (Formula I) and 3-(trifluoromethyl)benzene (Formula II) 
                                 
wherein L is a halogen atom, methanesulfonate group (OMs), p-Toluenesulfonate (OTs), or triflate (OTf), in an organic solvent in presence of an inorganic base, refluxing until 3-(trifluoromethyl)benzene is completely consumed, obtaining a reaction mixture containing cinacalcet, and after treatment, obtaining cinacalcet hydrochloride having a formula of
 
                                 
The post treatment separates (R)-1-naphthyl ethylamine hydrochloride and cinacalcet hydrochloride by adjusting pH value, extraction, and other simple operations, and the (R)-1-naphthyl ethylamine obtained is recycled for preparing the next batch of cinacalcet hydrochloride.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject application is a continuation-in-part of PCT international application PCT/CN2013/000066 filed on Jan. 21, 2013, which in turn claims priority on Chinese patent applications CN 201210170026.1 filed on May 29, 2012. The contents and subject matter of the PCT and Chinese priority applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The subject application relates to a process for preparing drug substance, particularly, for preparing a calcimimetic agent, cinacalcet hydrochloride. 
     BACKGROUND OF THE INVENTION 
     (R)—N-(1-(naphthalen-1-yl)ethyl)-3-(3-(trifluoromethyl)phenyl)propan-1-amine has the international non-proprietary name as cinacalcet [CAS number 226456-56-0] and chemical structure as follows: 
                                
Cinacalcet is the free base of cinacalcet hydrochloride [CAS Number, 364782-34-3], and the chemical structure of cinacalcet hydrochloride is shown as follows:
 
                                
It is reported by NPS Pharma. Inc. that cinacalcet hydrochloride (the brand name is Sensipar) is a calcimimetic agent, which is a drug substance that can effectively treat the primary hyperparathyproidism (PHPT). Currently, it has been reported to have the following preparation methods for cinacalcet:
 
(1) Reductive Amination
 
     U.S. Pat. No. 6,211,244 and Drugs of the future (27), 9, 931, 2002, disclose a process to prepare cinacalcet by reductive amination as illustrated below: 
     
       
                 
         
             
             
         
      
     
     However, the method is unsuitable for industrial production due to the toxicity of the reductant sodium cyanoborohydride, the high cost and easy hydrolysis of tetraisopropyl titanate, and unavoidable over-reductive impurities produced in the post-production process, which results in difficult operation, tedious purification and low yield, etc. The over-reductive impurities are difficult to be avoided even by catalytic hydrogenation reduction using heavy metals palladium and platinum as catalysts. 
     (2) Amide Reduction 
     Alternatively, WO2007127445 and WO 2008117299 disclose the process as illustrated below: 
     
       
                 
         
             
             
         
      
     
     First, 3-trifluoromethylphenyl propionic acid is used to prepare acyl chloride; then, acyl chloride and (R)-1-naphthyl ethylamine are condensed to obtain amide; finally, carbonyl in amide is reduced to obtain cinacalcet. In the reduction of carbonyl, the reagents used, such as BF3, LiAlH4, or NaBH4/I2, NaBH4/AlCl3 bring difficulties in the operation and cause post treatment problems, so the method is not suitable for scale-up production. Additionally, the process is disfavored for industrial implementation due to the use of hazardous chemicals such as NaBH4/I2, NaBH4/AlCl3, protonic acid, as the large quantity of the chemicals will cause the difficulties of obtaining the high yield as claimed in the articles and too much trouble in work up and purification. 
     (3) Alkylation 
     A method of direct alkylation of mesylate (a compound of Formula II, L is methanesulfonate group (OMS)) is published in Chinese Patent No. CN101180261: 
     
       
                 
         
             
             
         
      
     
     In the process, residual (R)-1-(naphthalen-1-yl)ethan-1-amine is not effectively removed from the product because of its similar properties with cinacalcet, as both are alkaline substances. And (R)-1-naphthyl ethylamine is obtained by resolution or asymmetric synthesis, so the cost is high. In order to reduce the cost, the reported synthesis method by direct alkylation uses excessive amount of formula II compound to consume (R)-1-naphthyl ethylamine at maximum, and salify the product by adjusting pH. The unconsumed formula II compound and product could be separated due to the non-salification of excessive formula II compound. But the excessive amount of formula II compound may result in the large amount of dialkylation impurity (Formula IV Compound) present in the final product of alkylation (in the mixtures of end reaction, the content of dialkylation impurity may reach about 7%), while this impurity is an alkaline substance and hard to be separated from cinacalcet. In another aspect, the excessive amount of formula II compound results in the formation of large amount of impurity carbamic acid ester (Formula III Compound), which makes the post treatment of separation and purification more difficult, the yield decreases, and the impurity is difficult to be removed by simply adjusting pH or re-crystallization. See below for formulae II, III, and IV. 
                                
Where L is a halogen atom, methanesulfonate group (OMs), p-Toluenesulfonate (OTs), or triflate (OTf).
 
     
       
                 
         
             
             
         
      
     
     A Forster-Deker method which is improved from direct alkylation to avoid the by-products of dialkylation, is reported in Org. Process Res. Dev, 2011, 15 (2), P455-461, but due to the solubility problem of intermediate imine, big steric hindrance and little nucleophilicity, the yield may not reach expectation, and the increased steps and operations make the improvement of the method loss outweigh the gain. Similar problems are reported in WO2010004588, such as by the method first forms sulfamide, followed by alkylation and de-protection group, and in WO2010010359, first forms benzylamine, then alkylation and de-benzylation, etc. All these methods are difficult to be industrialized because of the prolongation of steps, difficult group protection and de-protection, abruptly increased environment protection pressure and costs. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to solve the deficiencies of the above methods, research and design a preparation method for cinacalcet hydrochloride, which is simple for operation and recovery of (R)-1-naphthyl ethylamine yet with high yield and low impurities. 
     The present invention provides a method for preparing cinacalcet hydrochloride having the following steps: 
     charging (R)-1-naphthyl ethylamine (Formula I Compound) and 3-(trifluoromethyl) benzene compound (Formula II Compound) at a ratio of (1.0-5.0):1, heating the mixture in an organic solvent in presence of an inorganic base, refluxing and reacting until formula II compound disappears, obtaining a cinacalcet-containing reaction mixture, and obtaining cinacalcet hydrochloride after acidification with hydrochloride and extraction from the reaction mixture. 
                                
In Formula II, L is a halogen atom, methanesulfonate group (OMs), p-Toluenesulfonate (OTs), or triflate (OTf).
 
     
       
                 
         
             
             
         
      
     
     In the method of the present invention, the molar ratio of (R)-1-naphthyl ethylamine (Formula I Compound) to Formula II Compound may be (1.0-3.0): 1, preferably, (1.0-2.0):1. 
     The molar ratio of the inorganic base and (R)-1-naphthyl ethylamine (Formula I Compound) is (1.0-2.0):1. 
     The inorganic base is potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium hydroxide, or sodium hydroxide. 
     Another purpose of the present invention is to provide a post treatment method for the above-mentioned mixture containing cinacalcet, including: 
     {circle around (1)} Washing the cinacalcet mixture with water, separating and discarding the water phase, adding hydrochloric acid into the organic phase. 
     {circle around (2)} Heating the mixture of the organic layer with the hydrochloric acid layer (40° C. −80° C.) until clear, separating the organic phase and the hydrochloric acid phase before cooling. 
     {circle around (3)} Allowing the organic layer as obtained in step {circle around (2)} cooled to 0° C.-30° C., crystallizing and filtering to obtain cinacalcet hydrochloride. 
     {circle around (4)} Adjusting pH value of the hydrochloric acid layer as obtained in step {circle around (2)} to 8-14 with an inorganic base, extracting with an organic solvent from one to five times, each time with a solvent 1 to 10 times the quantity of (R)-1-naphthyl ethylamine (W/V), combining the organic phases and discard solvents to recover the (R)-1-naphthyl ethylamine (Formula I Compound). 
     The molar ratio of hydrochloric acid used in post treatment step {circle around (1)} to raw material (R)-1-naphthyl ethylamine (Formula I Compound) is (1.0-5.0):1. 
     The inorganic base used in step {circle around (4)} is potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, potassium hydroxide, or sodium hydroxide. The organic solvent used in extraction is toluene, ethyl acetate, dichloromethane, methyl tert-butyl ether, pinacolone, or acetonitrile, and preferably, toluene, ethyl acetate, or dichloromethane. 
     In the present invention, the generation of the by-products of dialkylation (Formula IV Compound) is ultimately controlled by over charge of (R)-1-naphthyl ethylamine. It is surprising to find that, because of the over charge of (R)-1-naphthyl ethylamine, the content of the by-products of dialkylation (Formula IV Compound) and by-products of dialkylation (Formula IV Compound) are greatly decreased from more than 7% to not more than 1% in the final mixture of alkylation reaction. What&#39;s more, with the charge ratio, the content of the by-products of carbamate (Formula III Compound) is also decreased to below 0.1%. The present invention greatly simplifies the post treatment process and the impurity control method, and enables the impurity control easily to be carried out. Meanwhile, the solubility of excessive unconsumed (R)-1-naphthyl ethylamine hydrochloride and of cinacalcet hydrochloride in slightly heated organic solvents is apparently different. In the post treatment process, the (R)-1-naphthyl ethylamine hydrochloride and cinacalcet hydrochloride are easily separated by simple operation of extraction, and the purity of (R)-1-naphthyl ethylamine obtained by extraction is sufficient to be recycled for preparation of next batch cinacalcet hydrochloride after adjusting pH. 
     The present invention is easy to operate and convenient in the post treatment, the resulted yield is high, the (R)-1-naphthyl ethylamine is easily recycled, and cinacalcet hydrochloride obtained is of good quality with low content of related substance. The present invention is suitable to be used in industrialized production with great application value. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following examples further describe the present invention in details but do not limit the scope of the present invention. One of ordinary skill in the art knows how to make modifications based on the examples without departing from the scope of the present invention. 
     Example 1 
     3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (4 g), toluene (57 mL), R-(−)-1-naphthyl ethylamine (2.91 g) and potassium carbonate (1.96 g) were added into the reactor, the mixture was refluxed for 7 hours, The mixture was cooled to 20° C.-25° C., water (100 mL) and toluene (10 mL) were added. The organic phase was separated, and washed with HCl (1 M, 20 mL×3) at 50° C., then organic phase was stirred at 5° C.-10° C. for one hour. filter and obtain 4.58 g cinacalcet hydrochloride, the yield is 82%. The aqueous layer was combined, adjusted to pH=14 with NaOH (10%) and extracted with toluene (30 mL). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 0.33 g. 
     Cinacalcet hydroxide obtained in this implement is confirmed by tests: 
     HPLC purity (purity): 99.0%; Chiral purity (purity): 99.0%; MS (ESI): m/z=358 [M+H + ];  1 HNMR (400 MHz, CDCl 3 ): δ=1.97-1.99 (d, 3H), 2.21-2.32 (m, 2H), 2.46-2.57 (m, 2H), 2.72-2.79 (m, 2H), 5.17-5.21 (t, 1H), 7.16-7.27 (m, 3H), 7.33-7.31 (d, J=7.2 Hz, 2H), 7.54-7.65 (m, 3H), 7.88-7.98 (m, 3H), 8.23-8.25 (d, J=7.2 Hz, 1H), 10.07-10.09 (d, J=7.2 Hz, 1H), 10.61 (s, 1H);  13 C NMR (400 MHz, CDCl 3 ): δ=21.32 (CH 3 ), 27.30 (CH 2 ), 32.51 (CH 2 ), 45.49 (CH 2 ), 53.53 (CH), 121.26, 122.62, 123.09, 124.88, 125.03, 125.33 (CF 3 ), 126.13, 126.27, 127.35, 128.04, 128.85, 129.51, 129.56, 130.19, 130.69, 131.55, 132.10, 133.87, 140.78. The structure of R-(−)-1-naphthyl ethylamine as recovered is confirmed by the test result of MS (ESI): m/z=172[M+H+]. 
     Example 2 
     R-(−)-1-naphthyl ethylamine (0.33 g recovered from example 1, +2.58 g), toluene (57 mL), 3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (4.0 g), and potassium carbonate (1.96 g) were charged and refluxed for 10 hours. The mixture was cooled to 20° C.-25° C., water (20 mL) and toluene (20 ml) were added. Organic phase was separated and washed with hydrochloric acid (1 mol/L, 20 mL×3) at 50° C., chilled and stirred at 0° C.-5° C. for one hour. Solid was collected by filtration to afford cinacalcet hydrochloride at 4.50 g, and confirmed as Example 1 to have HPLC purity (Purity) at 99.2% and Chiral purity (Purity) at 99.0%. 
     Example 3 
     R-(−)-1-naphthyl ethylamine (4 g), toluene (65 mL), 3-(3-(trifluoromethyl)phenyl) propyl methanesulfonate (4.86 g), and potassium carbonate (1.96 g) were charged and refluxed for 16 hours. The mixture was cooled to 20° C.-30° C., water (150 mL) and toluene (10 ml) were added. Organic phase was separated and washed with hydrochloric acid (2 mol/L, 20 mL×3) at 60° C., chilled and stirred at 10° C.-15° C. for one hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.4 g, 79%, and confirmed that HPLC purity (Purity) is 99.0% and Chiral purity (Purity) is 99.0%. 
     The aqueous layer was combined, adjusted to pH=13 with NaOH (10%) and extracted with acetonitrile (12 ml×3). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 2.0 g. The results were confirmed as in Example 1 MS (ESI): m/z=172[M+H+]. 
     Example 4 
     3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (5.1 g), dimethylbenzene (32 ml), R-(−)-1-naphthyl ethylamine (2.91 g), and potassium hydroxide (0.80 g) were charged and refluxed for 5 hours, the mixture was cooled to 20° C.-30° C., water (20 ml) and dimethylbenzene (32 ml) were added, organic phase was separated and washed with hydrochloric acid (2 mol/L, 10 mL×3) at 40° C., chilled and stirred at 0° C.-5° C. for one hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.24 g, 76%. Cinacalcet hydroxide obtained in this example was tested and confirmed with the same method as used in example 1: 
     HPLC purity (Purity): 98.5%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=12 with NaOH (10%) and extracted with acetonitrile (20 ml×4). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 3.8 g. The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 5 
     3-(3-(trifluoromethyl)phenyl)propyl trifluoromethanesulfonate (4.8 g), toluene (16 ml), R-(−)-1-naphthyl ethylamine (2.91 g), and potassium hydroxide (1.14 g), was charged and refluxed for 6 hours, The mixture was cooled to 20° C.-25° C., water (20 ml) and toluene (20 ml) were added, Organic phase was separated and washed with hydrochloric acid (1 mol/L, 20 mL×3) at 50° C., chilled and stirred at 20° C.-25° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.4 g, 79%. Cinacalcet hydrochloride obtained in this example was tested and confirmed with the same method as used in example 1: HPLC purity (Purity): 99.0%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=14 with NaOH (10%) and extracted with toluene (30 ml×4). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 0.34 g. The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 6 
     3-(3-(trifluoromethyl)phenyl)propyl trifluoromethanesulfonate (4.0 g), toluene (50 ml), R-(−)-1-naphthyl ethylamine (7.28 g), and potassium hydroxide (1.96 g), was charged and refluxed for 16 hours, the mixture was cooled to 20° C.-25° C., water (50 ml) and toluene (50 ml) were added, organic phase was separated and washed with hydrochloric acid (3 mol/L, 20 mL×3) at 80° C., chilled and stirred at 0° C.-5° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.9 g, 89%. Cinacalcet hydrochloride obtained in this example was tested and confirmed with the same method as used in Example 1: HPLC purity (Purity): 99.0%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=13 with NaOH (10%) and extracted with ethyl acetate (15 ml×5 mL). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 4.4 g. The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 7 
     3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (4 g), toluene (32 ml), R-(−)-1-naphthyl ethylamine (4.86 g), and potassium carbonate (3 g) was charged and refluxed for 16 hours, the mixture was cool to 20° C.-25° C., water (30 ml) and toluene (30 ml) were added, Organic phase was separated and washed with hydrochloric acid (1 mol/L, 50 mL×3) at 70° C., chilled and stirred at 0° C.-5° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.7 g, 85%. 
     Cinacalcet hydroxide obtained in this example is tested and confirmed with the same method as used in example 1: HPLC purity (Purity): 99.0%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=14 with NaOH (10%) and extracted with toluene (15 mL×2). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine, 2.1 g. 
     The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 8 
     1-(3-bromopropyl)-3-(trifluoromethyl)benzene (3.8 g), toluene (30 ml), R-(−)-1-naphthyl ethylamine (2.91 g), and potassium carbonate (3.92 g) was charged and refluxed for 7 hours, The mixture was cooled to 20° C.-25° C., water (100 ml) and toluene (30 ml) were added, organic phase was separated and washed with hydrochloric acid (1 mol/L, 40 mL×3) at 50° C., chilled and stirred at 5° C.-10° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.6 g, 83%. Cinacalcet hydroxide obtained in this example was tested and confirmed with the same method as used in Example 1: HPLC purity (Purity): 98.7%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=13 with NaOH (10%) and extracted with toluene (15 mL×3). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine 0.33 g. 
     The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 9 
     1-(3-chloropropyl)-3-(trifluoromethyl)benzene (3.15 g), toluene (50 ml), R-(−)-1-naphthyl ethylamine (2.91 g), and potassium carbonate (1.96 g) was charged and refluxed for 15 hours, the mixture was cooled to 15° C.-20° C., water (50 ml) and toluene (50 ml) were added, organic phase was separated and washed with hydrochloric acid (2 mol/L, 10 mL×3) at 60° C., chilled and stirred at 5° C.-10° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4 g, 73%. Cinacalcet hydroxide obtained in this example was tested and confirmed with the same method as used in Example 1: HPLC purity (Purity): 97.0%; Chiral purity (Purity): 98.0%. 
     The aqueous layer was combined, adjusted to pH=12 with NaOH (10%) and extracted with toluene (20 mL×1). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford recovered R-(−)-1-naphthyl ethylamine 0.3 g. 
     The R-(−)-1-naphthyl ethylamine recovered in this example was tested and confirmed with the same method as used in Example 1. 
     Example 10 
     3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (4.0 g), toluene (50 ml), R-(−)-1-naphthyl ethylamine (2.42 g), and sodium bicarbonate (1.53 g) was charged and refluxed for 16 hours, the mixture was cooled to 20° C.-25° C., water (50 ml) and toluene (50 ml) were added, organic phase was separated and washed with hydrochloric acid (2 mol/L, 10 mL×3) at 80° C., chilled and stirred at 0° C.-5° C. for 1 hour. Solid was collected by filtration to afford cinacalcet hydrochloride, 4.1 g, 73%. 
     Cinacalcet hydroxide obtained in this example was tested and confirmed with the same method as used in Example 1: HPLC purity (Purity): 99.0%; Chiral purity (Purity): 99.0%. 
     The aqueous layer was combined, adjusted to pH=14 with NaOH (10%) and extracted with toluene (20 mL×1). the organic layer was dried with anhydrous sodium sulfate, distill and remove toluene, basically no R-(−)-1-naphthyl ethylamine was recovered. 
     Example 11 
     3-(3-(trifluoromethyl)phenyl)propyl methanesulfonate (4.0 g), toluene (50 ml), of R-(−)-1-naphthyl ethylamine (2.0 g), and sodium carbonate (3.0 g), was charged and refluxed for 16 hours, The mixture was cooled to 5° C.-10° C., water (50 ml) and toluene (50 ml) were added, Organic phase was separated. Extract water phase with toluene 30 mL×3, combine the organic phases and dry with anhydrous sodium sulfate, filter and distill the solvent, then cinacalcet is obtained. Add 30 ml of 2 mol/L hydrochloric acid, stir to formulahydrochloride, distill the solvent, afford cinacalcet hydrochloride, 3.0 g, 55%. 
     Cinacalcet hydroxide obtained in this example was tested and confirmed with the same method as used in Example 1: HPLC purity (Purity): 88.0%; Chiral purity (Purity): 99.0%. 
     The result of the example shows that the contents of dialkylation compound (Formula IV Compound) and carbamate impurity (Formula III Compound) in the product are respectively 10.0% and 1.5%, the cause is that the excessive amount of Formula II Compound will result in the large amount of dialkylation impurity (Formula IV Compound) existing in end product of alkylation reaction, which is hard to be separated from cinacalcet because it&#39;s an alkaline substance. In another aspect, excessive Formula II Compound results in the formation of large amount of carbamate impurity (Formula III Compound), finally increase the hardship of separation and purification in the post treatment, the yield decreases.