Abstract:
The present invention relates to magnesium salts of HMG-CoA reductase inhibitors, processes for their preparation, pharmaceutical compositions thereof and methods of using compositions to treat mammals suffering from hypercholesterolemia.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to crystalline and amorphous magnesium salts of atorvastatin of structural formula I, processes for their preparation, pharmaceutical compositions thereof and methods of using compositions to treat mammals suffering from hypercholesterolemia. 
         [0000]    
       
                 
         
             
             
         
       
     
       BACKGROUND OF THE INVENTION 
       [0002]    Atorvastatin is represented by Formula II and is a member of the class of drugs called statins. Statins are currently the most therapeutically effective drugs available for reducing low-density lipoprotein (LDL) particle concentration in the blood stream of patients at risk for cardiovascular disease. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0003]    Statins&#39; mechanism of action of has been elucidated in some detail. They interfere with the synthesis of cholesterol and other sterols in the liver by competitively inhibiting the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase enzyme (“HMG-CoA reductase”). HMG-CoA reductase catalyses the conversion of HMG to mevalonate, which is the rate determining step in the biosynthesis of cholesterol. This inhibition leads to a reduction in the concentration of cholesterol in the liver. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect there is provided a crystalline form of a magnesium salt of atorvastatin having XRD pattern essentially as shown in  FIG. 1 . 
         [0005]    In another aspect there is provided a crystalline form of a magnesium salt of atorvastatin having IR spectrum as shown in  FIG. 2 . 
         [0006]    In yet another aspect there is provided a process for the preparation of a crystalline form of a magnesium salt of atorvastatin comprising contacting an alkali metal salt of atorvastatin salt with magnesium salt of an acid in a suitable solvent to form atorvastatin magnesium. 
         [0007]    In another embodiment there is provided amorphous form of a magnesium salt of atorvastatin having XRD pattern as shown in  FIG. 3 . 
         [0008]    In yet another embodiment there is provided amorphous form of a magnesium salt of atorvastatin having IR spectrum as shown in  FIG. 4 . 
         [0009]    In a further aspect there is provided a process for the preparation of an amorphous atorvastatin magnesium comprising dissolving a crystalline form of a magnesium salt of atorvastatin in one or more solvents, and removing the solvent from the solution to obtain an amorphous atorvastatin magnesium. One or more co-solvents may be added to the solution before solvent removal. 
         [0010]    In another aspect there is provided a process for the preparation of an amorphous atorvastatin magnesium. The process comprises dissolving a crystalline form of a magnesium salt of atorvastatin in one or more solvents, and adding an anti-solvent(s) to obtain an amorphous atorvastatin magnesium. 
         [0011]    In another aspect there is provided a pharmaceutical composition that comprises crystalline or amorphous form of atorvastatin magnesium and one or more of pharmaceutically acceptable excipients, diluents and carriers. 
         [0012]    In another aspect there is provided a method of inhibiting HMG-CoA reductase comprising administering to a mammal, in need thereof, a therapeutically effective amount of a crystalline or amorphous form of atorvastatin magnesium. 
         [0013]    In another aspect there is provided a method of treating primary hypercholesterolemia, dysbetalipoproteinemia or homozygous familial hypercholesterolemia. The method includes administering to a mammal, in need thereof, a therapeutically effective amount of crystalline and/or amorphous form of atorvastatin magnesium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1   a  is an XRD pattern showing peaks characteristic of crystalline form of magnesium salt of atorvastatin. 
           [0015]      FIG. 1   b  is a listing of peak values and intensities of the XRD pattern of  FIG. 1   a.    
           [0016]      FIG. 2  is an infrared spectrum showing characteristic absorption bands of crystalline form of magnesium salt of atorvastatin. 
           [0017]      FIG. 3  is an XRD pattern showing a halo that is characteristic of amorphous atorvastatin magnesium. 
           [0018]      FIG. 4  is an infrared spectrum showing characteristic absorption bands of amorphous atorvastatin magnesium. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The term “atorvastatin magnesium” as used herein refers to a salt, which includes atorvastatin anions and magnesium cations, in either a crystalline or amorphous form. 
         [0020]    Further, the term “atorvastatin magnesium” also encompasses stoichiometric, as well as non-stoichiometric ratios, of atorvastatin anions and magnesium cations. The ratio of atorvastatin to magnesium is not required to be 1:1 in order to be termed atorvastatin magnesium. Atorvastatin magnesium may be formed as a salt having a 2:1 molar ratio between atorvastatin anions and magnesium cations (i.e., atorvastatin hemi-magnesium). Atorvastatin hemi-magnesium may be formed even when an excess of atorvastatin or an excess of magnesium salt of an acid is used in the salt formation. 
         [0021]    Atorvastatin magnesium and particularly atorvastatin hemi-magnesium may exist in anhydrous, hydrated and solvated forms. 
         [0022]    The crystalline form of magnesium salt of atorvastatin can be characterized by XRD, with a pattern which can be expressed in terms of the 2θ, d-spacings and relative intensities. An illustrative example is shown in  FIG. 1 . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 2θ (±0.2) 
                 d-spacing 
                 Intensity 
                 I/I o   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 8.600 
                 10.2733 
                 5346 
                 61 
               
               
                   
                 8.800 
                 10.0403 
                 4882 
                 55 
               
               
                   
                 9.660 
                 9.1483 
                 4493 
                 51 
               
               
                   
                 9.880 
                 8.9451 
                 3591 
                 41 
               
               
                   
                 11.340 
                 7.7965 
                 3405 
                 39 
               
               
                   
                 11.520 
                 7.6750 
                 3131 
                 36 
               
               
                   
                 11.800 
                 7.4935 
                 2832 
                 32 
               
               
                   
                 12.080 
                 7.3205 
                 2808 
                 32 
               
               
                   
                 12.200 
                 7.2487 
                 2813 
                 32 
               
               
                   
                 16.140 
                 5.4870 
                 5228 
                 59 
               
               
                   
                 16.760 
                 5.2854 
                 3179 
                 36 
               
               
                   
                 17.960 
                 4.9349 
                 8817 
                 100 
               
               
                   
                 18.480 
                 4.7972 
                 5997 
                 68 
               
               
                   
                 18.620 
                 4.7614 
                 5777 
                 66 
               
               
                   
                 19.940 
                 4.4491 
                 3855 
                 44 
               
               
                   
                 20.320 
                 4.3667 
                 3605 
                 41 
               
               
                   
                 21.260 
                 4.1757 
                 5888 
                 67 
               
               
                   
                 21.440 
                 4.1411 
                 6280 
                 71 
               
               
                   
                 21.600 
                 4.1108 
                 5955 
                 68 
               
               
                   
                 22.460 
                 3.9553 
                 3572 
                 41 
               
               
                   
                 22.860 
                 3.8870 
                 3684 
                 42 
               
               
                   
                 22.980 
                 3.8669 
                 3864 
                 44 
               
               
                   
                 23.120 
                 3.8438 
                 3678 
                 42 
               
               
                   
                 23.720 
                 3.7479 
                 3357 
                 38 
               
               
                   
                 23.960 
                 3.7109 
                 3336 
                 38 
               
               
                   
                 24.200 
                 3.6747 
                 3107 
                 35 
               
               
                   
                 25.200 
                 3.5311 
                 2418 
                 27 
               
               
                   
                 25.460 
                 3.4956 
                 2319 
                 26 
               
               
                   
                 26.720 
                 3.3336 
                 2484 
                 28 
               
               
                   
                 27.440 
                 3.2477 
                 2476 
                 28 
               
               
                   
                 27620 
                 3.2269 
                 2564 
                 29 
               
               
                   
                 27.720 
                 3.2155 
                 2560 
                 29 
               
               
                   
                 27.940 
                 3.1907 
                 2519 
                 29 
               
               
                   
                 29.160 
                 3.0599 
                 2243 
                 25 
               
               
                   
                 29.500 
                 3.0254 
                 2287 
                 26 
               
               
                   
                 29.640 
                 3.0115 
                 2313 
                 26 
               
               
                   
                 29.920 
                 2.9839 
                 2348 
                 27 
               
               
                   
                 30.060 
                 2.9703 
                 2360 
                 27 
               
               
                   
                   
               
             
          
         
       
     
         [0023]    The crystalline form of a magnesium salt of atorvastatin can be characterized by its IR spectrum. An illustrative example of such a spectrum in potassium bromide is shown in  FIG. 2 . Characteristic absorption bands of the crystalline form of atorvastatin magnesium are observed at 510.0, 525.0, 614.3, 692.0, 716.4, 755.9, 811.9, 847.4, 885.9, 916.9, 970.6, 1014.0, 1031.7, 1076.2, 1092.0, 1110.7, 1155.4, 1222.5, 1313.0, 1435.8, 1506.1, 1524.4, 1594.4, 1654.4, 1898.2, 1947.3, 2954.3, 3283.6, 3405.8, and 3667.3 cm −1 . 
         [0024]    Also, the present invention provides processes for preparing a crystalline atorvastatin magnesium. The process comprises contacting an atorvastatin alkali metal salt with the magnesium salt of an acid in a suitable solvent to form a crystalline atorvastatin magnesium. 
         [0025]    Atorvastatin alkali metal salts, to be used in the process, may be obtained from a compound of Formula III, for example, by using methods known in the literature. For example, they may be obtained by processes comprising contacting the compound of Formula III with an acid to hydrolyse the ketal group, followed by addition of an alkali metal hydroxide to remove the tertiary butyl group along with the formation of a metal salt. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0026]    Suitable acids include mineral acids, such as hydrochloric acid. Suitable hydroxides of alkali metals include sodium hydroxide, lithium hydroxide and potassium hydroxide. 
         [0027]    Suitable solvents for preparing atorvastatin magnesium include any solvent capable of dissolving an alkali metal atorvastatin salt and from which crystalline atorvastatin magnesium may be isolated. 
         [0028]    Suitable solvents for carrying out the process include hydroxylic solvents, such as water, lower alkanols or mixtures thereof. The hydroxylic solvents may be made acidic or basic by the addition of a mineral acid or alkali metal hydroxide if desired. 
         [0029]    Suitable lower alkanols include primary, secondary and tertiary alcohols having one to six carbon atoms; primary, secondary and tertiary alcohols having one to four carbon atoms, for example methanol, ethanol, n-propyl alcohol, isopropyl alcohol, isobutanol, n-butanol, t-butanol and mixtures thereof. 
         [0030]    Suitable magnesium salts of an acid to be used in the processes may be a salt of any inorganic or organic acid, such as magnesium chloride, magnesium nitrate, magnesium sulphate, magnesium phosphate, magnesium carbonate, magnesium dihydrogenphosphate, magnesium oxalate, magnesium acetate, magnesium lactate, magnesium succinate, magnesium citrate or mixtures thereof. 
         [0031]    Once atorvastatin magnesium is crystallized, either spontaneously, upon cooling, upon seeding, or by any other inducement, the crystal may be isolated by filtration or any other conventional means known in the art. The isolated crystals are dried by conventional means. 
         [0032]    Also provided in the present invention is atorvastatin magnesium in an amorphous form. The amorphous atorvastatin magnesium may be characterized by its IR spectrum in potassium bromide, for example, as shown in  FIG. 2 . Characteristic absorption bands of amorphous atorvastatin magnesium are observed at about 507.5, 574.3, 624.0, 691.6, 734.0, 752.2, 817.9, 841.9, 884.8, 1054.5, 1092.6, 1155.5, 1221.3, 1311.3, 1435.6, 1508.5, 1527.2, 1560.2, 1594.8, 1653.7, 1948.4, 2870.0, 2958.4, 3056.3, and 3406.5 cm −1 . 
         [0033]    The amorphous atorvastatin magnesium may be prepared by dissolving a crystalline form of a magnesium salt of atorvastatin in one or more suitable organic solvents and adding an anti-solvent(s) to the solution to obtain an amorphous atorvastatin magnesium. 
         [0034]    Suitable organic solvents include one or more solvents that have the ability to dissolve crystalline atorvastatin magnesium. These solvents include, for example, tetrahydrofuran, dimethylsulphoxide, chloroform or mixtures thereof. 
         [0035]    Any organic solvent in which atorvastatin magnesium is not soluble may be used as an anti-solvent. These anti-solvents include, for example, n-hexane, n-heptane, cyclohexane, hexane fraction, heptane fraction and mixtures thereof. For example, the solvent used for dissolving crystalline atorvastatin magnesium may be tetrahydrofuran and the anti-solvent may be cyclohexane. 
         [0036]    The product can then be recovered by filtration at ambient temperature. The filtered material can be further dried to remove surface solvents in one or more of vacuum tray drier, tray drier, fluid bed drier or a rotary vacuum drier to obtain the amorphous atorvastatin magnesium. 
         [0037]    Amorphous atorvastatin magnesium may be characterized by its XRD pattern. Such an illustrative example of a spectrum is shown in  FIG. 3 . This XRD pattern ( FIG. 3 ) shows no peaks which are characteristic of a crystalline form of atorvastatin calcium ( FIG. 1 ), thus demonstrating an amorphous nature in the product. Also provided in the present invention is another process for the preparation of amorphous atorvastatin magnesium. The process includes dissolving a crystalline form of a magnesium salt of atorvastatin in one or more solvents, and removing the solvent from the solution to obtain an amorphous atorvastatin magnesium. One or more co-solvents may be added to obtain or augment the solution. 
         [0038]    Suitable solvents used to dissolve a crystalline form of a magnesium salt of atorvastatin are described above. 
         [0039]    Suitable co-solvents may be those in which a magnesium salt of atorvastatin is not readily dissolved but is sparingly or moderately soluble, or the anti-solvents described above but added in quantities which are not sufficient to substantially precipitate atorvastatin magnesium. Suitable co-solvents include cyclohexane and toluene. 
         [0040]    The process of solvent removal includes, for example, concentration, evaporation, flash evaporation, spray drying, freeze drying or lyophilization of a solution of atorvastatin magnesium. 
         [0041]    The atorvastatin magnesium may be formulated into pharmaceutical compositions. The pharmaceutical compositions include crystalline or amorphous forms of a magnesium salt of atorvastatin as an active ingredient, along with one or more pharmaceutically acceptable excipients, diluents and/or carriers. The pharmaceutical composition may be in the form of oral, buccal, rectal, topical and parenteral (including subcutaneous, intramuscular, and ophthalmic administration) dosage forms. These dosage forms also include solid dosage forms, such as powder, tablets, capsules, suppositories, sachets, troches and lozenges, as well as liquid suspensions and elixirs. 
         [0042]    A method of inhibiting HMG-CoA reductase comprising administering to a mammal, in need thereof, a therapeutically effective amount of a crystalline or amorphous form of atorvastatin magnesium is provided. 
         [0043]    Also provided is a method of treating primary hypercholesterolemia, dysbetalipoproteinemia or homozygous familial hypercholesterolemia. The method includes administering to a mammal in need thereof, a therapeutically effective amount of a crystalline and/or amorphous form of a magnesium salt of atorvastatin. The therapeutically effective amount of a crystalline and/or amorphous form of a magnesium salt of atorvastatin may be administered as a component of any of the pharmaceutical compositions described herein. 
         [0044]    While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are included within the scope of the present invention. The following examples illustrate various implementations of the invention without being limiting. 
       EXAMPLES 
     Example 1 
     Preparation of Crystalline Atorvastatin Magnesium 
       [0045]    To a solution of (4R-cis)-1,1-dimethylethyl-6-{2[2-(4-fluorophenyl)-5-(1-methylethyl)-3-phenyl-4-[(phenyl amino)-carbonyl]-1H-pyrrol-1-yl]ethyl-2,2-dimethyl-1,3-dioxane-4-acetate in methanol, 1N hydrochloric acid (90.3 ml) was added at 20-26° C. in 15 minutes. The reaction mixture was stirred for 6 hours at the same temperature until the reaction was completed. 
         [0046]    The pH of the resulting mixture was adjusted to about 12 by adding 10% w/v aqueous sodium hydroxide solution (107.5 ml) at 25-30° C. and the resulting mixture was stirred for 6 hours at 25-30° C. The pH of the reaction mixture was monitored and maintained at about 12 throughout the course of the reaction by adding 10% w/v aqueous sodium hydroxide solution as needed. After the reaction was completed, the mass was filtered and concentrated. 
         [0047]    Water, methanol and methyl tertiary butyl ether were added to the concentrated mass at room temperature. The reaction mixture was stirred and then allowed to settle. 
         [0048]    The organic layer was separated and discarded. The aqueous layer was washed with methyl tertiary butyl ether (170 ml) and 6N hydrochloric acid was slowly added to adjust the pH to 7.8 to 8.0. The reaction mixture was heated to 45-55° C. and an aqueous solution of magnesium acetate tetrahydrate in deionized water was slowly added at the same temperature. The reaction mixture was stirred for 1 hour at room temperature, filtered and washed with deionized water. The product was dried under vacuum (30 mm Hg) at 50-55° C., till the moisture content was about 3-7% w/w, to get 38 grams of crystalline atorvastatin magnesium. 
       Example 2 
     Preparation of Crystalline Atorvastatin Magnesium from Atorvastatin Calcium 
       [0049]    1N Hydrochloric acid (50 ml) was added gradually to a suspension of [R—(R*, R*)]-atorvastatin calcium (50 g) in deionized water (750 ml) at room temperature to adjust the pH to 3.5 to 4.0. The mixture was extracted with ethyl acetate. The organic layer was washed with 20% aqueous brine (150 ml) and concentrated under vacuum at 40-45° C. to get the residue. To the resulting residue, methanol was added and then recovered completely under vacuum at 40-45° C. twice to remove traces of ethyl acetate. Methanol (500 ml) was again added to the residue at room temperature. An aqueous sodium hydroxide solution (8 g in 400 ml deionized water) was added gradually to it and the mixture was stirred for 2 hours at room temperature. The pH of the reaction mixture was adjusted to 7.8 to 8.0 by adding 1N hydrochloric acid (25 ml) slowly at room temperature. An aqueous solution of magnesium acetate tetrahydrate (10 g in 1200 ml deionized water) was added in 60 minutes at room temperature and stirred for 1 hour at room temperature. The solid separated was filtered and dried to get 45 g of crystalline atorvastatin magnesium 
         [0050]    A suspension of atorvastatin magnesium in methanol (169 ml) and water (957 ml) was stirred for 12 hours at room temperature. The suspension was filtered and washed with a mixture of methanol (67.5 ml) and water (382.5 ml) and dried to get 44 g of pure crystalline atorvastatin magnesium. 
       Example 3 
     Preparation of Amorphous Atorvastatin Magnesium 
       [0051]    Crystalline atorvastatin magnesium (70 g) was dissolved in tetrahydrofuran (182 ml) at room temperature and stirred for 30 minutes. The solution was filtered through a celite bed and the bed was washed with tetrahydrofuran (28 ml). The above solution was added to cyclohexane (2100 ml taken in a separate vessel) slowly for 2 hours while stirring moderately at 22-25° C. It was then stirred vigorously for 30 minutes at 22-25° C., and the separated solid was filtered and washed with cyclohexane (70 ml). The material was dried under vacuum at 60-70° C. to get 66 g of the amorphous atorvastatin magnesium. 
       Example 4 
     Preparation of Amorphous Atorvastatin Magnesium 
       [0052]    Crystalline atorvastatin magnesium (70 g) was dissolved in tetrahydrofuran (182 ml) at room temperature and was stirred for 30 minutes. The solution was filtered through a celite bed and was washed with tetrahydrofuran (28 ml). The solvent was evaporated under vacuum at 60-70° C. to give 66 g of the amorphous atorvastatin magnesium.