Abstract:
A first solution and a second solution are supplied to the inlet conduit of a chamber. The chamber includes a stator formed of spaced stationery blades within which a rotor with spaced blades is rotatably received. As the rotor is rotated, high shear mixing forces are applied to the solutions and crystallization take place within the chamber. Additional mixing of the product can take place after it leaves the chamber. Seed material can be introduced to the chamber and recirculated from the inlet to the outlet as the process is performed. The process can be used to combine a solution of the material to be crystallized dissolved in a solvent and an anti-solvent solution. Alternatively, solutions containing first and second reactive intermediates in solvents can be combined under conditions of temperature and pressure that permit reaction of the first and second reactive intermediates to produce a reaction product of limited solubility in the solvent mixture.

Description:
[0001]    This application claims a benefit of priority from U.S. Provisional Application No. 60/379,351, filed on May 10, 2002 and No. 60/439,057, filed on Jan. 9, 2003, the entire disclosures of which are herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a process for crystallization of organic pharmaceutical compounds and more particularly to a crystallization process that utilizes homogenization and to the apparatus for practicing such a process.  
           [0004]    It is well known in the pharmaceutical industry that the bioavailability of a sparingly soluble organic compound is often enhanced when the compound is very pure and the molecules of the compound have a small, uniform particle size, high surface area and short dissolution time. Purification can be accomplished by crystallization of the compound from solution. However, when crystallization takes place directly in a high supersaturation environment, the resulting material is often unsatisfactory due to low purity, high friability and lack of stability because the crystal structure formation is inadequate. Further, oils commonly produced during processing of supersaturated material may solidify without sufficient structure.  
           [0005]    It is possible to slow down the crystallization process to obtain a higher purity, more stable product. However, slowing the process decreases crystallizer productivity and produces particles which are too large, having low surface area. Such particles require high intensity milling to create a useable product.  
           [0006]    2. Description of Related Art  
           [0007]    To overcome those problems, and provide crystalline particles of high surface area, high chemical purity and high stability, without the need for post-crystallization milling, a crystallization process, known as the “impinging fluid jet” process, has been developed.  
           [0008]    One well known version of the “impinging fluid jet” process is disclosed in detail in U.S. Pat. No. 5,314,506 entitled “Crystallization Method To Improve Crystal Structure And Size” issued May 24, 1994, to Midler, et al, owned by Merck &amp; Co., Inc. of Rahway, N.J. The reader is referred to that patent for background information and the details of the process.  
           [0009]    Basically, the impinging fluid jet process utilizes a supersaturated solution of the compound to be crystallized in solvent and an appropriate “anti-solvent” solution. Diametrically opposed high velocity jet streams of these solutions are formed by nozzles and micro mixed in a jet chamber. The mixed solutions are then transferred into a vessel where they are stirred to produce the end product. The product, such as a neutral molecule or a salt, is crystallized out by mixing the solutions which reduces the solubility of the compound in the solvent mixture.  
           [0010]    The impinging fluid jet stream process has also been used for conducting reactive crystallization wherein a chemical reaction and controlled crystallization take place simultaneously. Patent Application Publication No.: U.S. 2002/0016,498 A1 of Feb. 7, 2002, entitled “Reactive Crystallization Method to Improve Particle Size” in the name of Am Ende et al., owned by Pfizer Inc., provides further information in this regard.  
           [0011]    Reactive crystallization involves two reactive intermediates. Fluid streams of solutions of the reactive intermediates are impinged in a chamber under appropriate reactive conditions. For example, a first solution containing one reagent (for example, an acid) in a solvent is reacted with a second solution containing another reagent (for example, a base) in a solvent are reacted to form a product, such as a salt. The product is not soluble in the solvent mixture and thus it rapidly crystallizes out. In the pharmaceutical industry, the drug substance is often in a salt form, so reactive crystallization is commonly used.  
           [0012]    The impinging fluid jet process produces a satisfactory result in terms of purity, particle size and stability. However, several major drawbacks of this process have been observed. For example, the nozzles used to form the fluid streams must be very accurately aligned so that the streams impinge correctly. The ratio of the flow rates of the two streams is limited by the size of the nozzles. The process cannot be used for low flow rates as the impingement would not offer a sufficient degree of mixing. Further, the apparatus used to practice the process is time consuming to set up and difficult to control.  
           [0013]    The present invention entails a different crystallization system that can be used with both non-chemically reactive constituents and chemically reactive constituents, and which overcomes the drawbacks of the impinging fluid jet process by eliminating the need for forming fluid streams and for accurately aligning the nozzles. The ratio of the flow rates are not limited by the nozzle size and low flow rates can be accommodated. Moreover, the apparatus used to perform the process is easy to set up and control.  
           [0014]    This system produces particles of purity, surface area and stability that are comparable to or better than obtained with the impinging fluid jet process. Like the impinging fluid jet process, the product obtained with the process of this invention does not require post-crystallization milling.  
           [0015]    It is, therefore, a prime object of the present invention to provide a method for crystallizing an organic pharmaceutical compound using homogenization which results in particles of high purity, high stability and high surface area, without the necessity of post-crystallization milling.  
           [0016]    It is another object of the present invention to provide a system for crystallizing an organic pharmaceutical compound using homogenization wherein the necessity for critical alignment of fluid jet streams is entirely eliminated.  
           [0017]    It is another object of the present invention to provide a system for crystallizing an organic pharmaceutical compound using homogenization wherein the ratio of the solutions fed to the apparatus can be easily controlled.  
           [0018]    It is another object of the present invention to provide a system for crystallizing an organic pharmaceutical compound using homogenization wherein the apparatus for performing the process can be set up relatively rapidly.  
           [0019]    It is another object of the present invention to provide a system for crystallizing an organic pharmaceutical compound using homogenization that can be used with non-chemically reactive constituents or chemically reactive constituents.  
         BRIEF SUMMARY OF THE INVENTION  
         [0020]    The process of the present invention utilizes homogenization and takes place in a chamber consisting of an enclosed stator and a rotor assembly. The energy for crystallization is obtained from the stator and rotor assembly, instead of a collision of high velocity jet streams. The solutions are combined in the chamber by the rotation of the rotor assembly, resulting in fast crystallization. Shear forces are applied, and mixing and crystallization take place simultaneously in the chamber.  
           [0021]    When non-chemically reactive constituents are combined, a first solution may be a supersaturated solution containing the material to be crystallized, such as a neutral molecule or a salt, dissolved in a solvent. That material-containing solution is homogenized with a second solution, which is an anti-solvent solution. Homogenizing the solutions reduces the solubility of the material in the solvent mixture, causing it to crystallize out.  
           [0022]    As used herein, the terms “first” and “second” are not intended to denote order or to limit the invention to a particular sequence of the combination of the constituents. Further, the term “solution” is used generically and should be understood to include dispersions, emulsions, multi-phase systems and pure solvents, as well as solutions.  
           [0023]    The process may also be used for reactive crystallization, for example, to prepare pharmaceutical salts. In that case, a first solution may contain a first reactive intermediate, such as an acid, and solvent and the second solution may contain a second reactive intermediate, such as a base, and a solvent. The solvents used for the first and second reactants may be the same or different. The reaction product is not soluble in the solvent mixture and thus rapidly crystallizes out as the solutions are mixed.  
           [0024]    Since the process of our invention does not depend upon using nozzles to create fluid jet streams, the problem associated with the critical alignment of the opposing fluid jets is entirely eliminated. The ratio of the first and second solutions is easy to accurately control. It takes much less time to set up the apparatus to perform our process. Moreover, tests indicate that the resulting product is at least as pure, with particles that are as stable and have as high a surface area as those obtained by the impinging fluid jet process.  
           [0025]    In accordance with one aspect of the present invention, a process is provided for crystallization of a chemical material from a first solution and a second solution. The process is performed in an apparatus including a chamber having a stator and a rotatable rotor. The process begins with the introduction of the first and the second solutions into the chamber. A high shear mixing force is applied to the solutions in the chamber to form the crystallized product by rapidly rotating the rotor relative to the stator. The crystallized product is then removed from the chamber.  
           [0026]    The first solution may include the material to be crystallized dissolved in a solvent. The second solution may include an anti-solvent.  
           [0027]    Alternatively, the first solution may include a solvent and a first reactive intermediate. The second solution may include a solvent and a second reactive intermediate. The mixing force is applied under conditions of temperature and pressure that permit the first and second reactive intermediates to form a product of limited solubility in the solvent mixture.  
           [0028]    In accordance with another aspect of the present invention, non-reactive constituents are utilized in a process for the crystallization of a chemical material from a solution containing the material to be crystallized dissolved in a solvent and an anti-solvent solution. The process takes place in an apparatus with a chamber including a stator and rotor. The material-containing solution and the anti-solvent solution are introduced into the chamber. A high shear mixing force is applied to the solutions in the chamber to form the crystallized product by rapidly rotating the rotor relative to the stator. The crystallized product is removed from the chamber.  
           [0029]    In accordance with another aspect of the present invention, reactive constituents are utilized in a process for the crystallization of a chemical material from a first solution comprising a solvent and a first reactive intermediate and a second solution comprising a solvent and a second reactive intermediate. The process takes place in apparatus including a chamber having a stator and a rotatable rotor. The first solution and the second solution are introduced into the chamber. A high shear mixing force is applied to the solutions in the chamber under conditions of temperature and pressure that permit reaction of the first and second reactive intermediates to form a product of limited solubility in the solvent mixture by rapidly rotating the rotor relative to the stator. The product is then removed from the chamber.  
           [0030]    In both the non-reactive and reactive crystallization processes, each of the solutions may be introduced separately into the chamber where the stator and rotor are present. Altenatively, the solutions may be mixed prior to introducing the solutions into the chamber.  
           [0031]    The step of introducing the solutions into the chamber includes the step of regulating the flow of each of the solutions into the chamber. Conventional flow regulation mechanisms such as metering pumps, valves and the like may be used for this purpose.  
           [0032]    The temperature of one or both of the solutions may be adjusted prior to their introduction into the chamber. This may be achieved by any conventional temperature adjusting equipment, such as a heater or a cooling bath associated with the solution source.  
           [0033]    The process may also include the step of introducing seed crystals into the chamber. The seed crystals may be placed into the chamber prior to the introduction of the solutions or seed crystals may be added to one of the solutions prior to its introduction into the chamber. These seed crystals must be insoluble in the individual solvents and in the solvent mixture.  
           [0034]    The seed crystals are preferably introduced to the chamber on a continuous basis. This may be achieved by continuously re-circulating a portion of the contents of the chamber, such as by connecting the chamber outlet and the chamber inlet. Alternatively, a continuous supply of fresh crystals may be introduced into the chamber.  
           [0035]    The process may include the additional step of mixing the product after it is removed from the chamber. The temperature of one or both of the solutions may be adjusted prior to introduction into the chamber.  
           [0036]    In accordance with another aspect of the present invention, apparatus is provided for crystallization of a chemical material from a first solution and a second solution. The apparatus includes a first source of the first solution and a second source of the second solution. A chamber having a stator and a rotor is provided. Inlet means, connected to the chamber and to each of the first and second sources, receives the first and second solutions. Means are provided for rotating the rotor relative to the stator to form a crystallized product. Outlet means in the chamber permit removal of the crystallized product from the chamber.  
           [0037]    The first solution may include the material to be crystallized dissolved in a solvent. The second solution may include an anti-solvent.  
           [0038]    Alternatively, the first solution may include a solvent and a first reactive intermediate. The second solution may include a solvent and a second reactive intermediate. The mixing force is applied under conditions of temperature and pressure that permit reaction of the first and second reactive intermediates to form a product of limited solubility in the solvent mixture.  
           [0039]    In accordance with another aspect of the present invention, apparatus for crystallization of a chemical material from non-reactive constituents such as a solution containing the material to be crystallized dissolved in a solvent and an anti-solvent solution is provided. The apparatus includes a first source of the material-containing solution and a second source of an anti-solvent solution. A chamber including a stator and a rotor is provided, as are means for rotating the rotor relative to the stator. Inlet means, connected to the chamber and to each of the first and second sources receives the material containing solution and the anti-solvent solution. An outlet is provided in the chamber through which the crystallized product is removed.  
           [0040]    In accordance with another aspect of the present invention, apparatus is provided for crystallization of chemical material from reactive constituents such as a first solution comprising a solvent and a first reactive intermediate and a second solution comprising a solvent and a second reactive intermediate. The apparatus includes a first source of the first solution and a second source of the second solution. A chamber including a stator and a rotor is provided. Inlet means, connected to the chamber and to each of the first and second sources, receives the first and second solutions. Means are provided for rotating the rotor to combine the first and second solutions in the chamber under conditions of temperature and pressure that permit the first and second reactive intermediates to produce a product of limited solubility in the solvent mixture. Outlet means are also provided for removing the crystallized product from the chamber.  
           [0041]    Whether non-reactive or reactive constituents are being combined, the inlet means of the apparatus includes first and second conduits connected to the first and the second sources, respectively. Each of the conduits has an end portion that terminates in the chamber. In this way, the solutions can be introduced separately into the chamber.  
           [0042]    In one preferred embodiment, one of the conduits is located within the other conduit. In another preferred embodiment, the conduits include parallel end sections adjacent the chamber.  
           [0043]    The inlet means may include a mixing conduit. The mixing conduit is located between the sources and the chamber.  
           [0044]    The apparatus may also include first means for pumping the first solution from the first source to the chamber, through the inlet means. It may also include second means for pumping the second solution from the second source to the chamber, through the inlet means.  
           [0045]    The rotor defines a recess. The first solution and the second solution are received within the rotor recess. The outlet means is preferably located outside the stator.  
           [0046]    The apparatus further includes means for adjusting the temperature of the first solution. It may also include means for adjusting the temperature of the second solution.  
           [0047]    The apparatus may further include means for recirculating a portion of the contents of the chamber. A re-circulation conduit connecting the outlet means and the inlet means may be provided for this purpose.  
           [0048]    The apparatus further includes means for mixing the product after it is removed from the chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0049]    To these and such other objects which may hereinafter appear, the present invention relates to a crystallization process using homogenization, as described in detail in the following specification and recited in the annexed claims, taken together with the accompanying drawings, wherein like numerals refer to like parts and in which:  
         [0050]    [0050]FIG. 1 is a schematic drawing of the apparatus utilized to perform the process of the present invention;  
         [0051]    [0051]FIG. 2 is a cross-sectional view of the chamber with the stator and rotor;  
         [0052]    [0052]FIG. 3 is a cross-sectional view taken along line  3 - 3  of FIG. 2;  
         [0053]    [0053]FIG. 4 is a cross-sectional view of a first preferred embodiment of the homogenization apparatus;  
         [0054]    [0054]FIG. 5 is a cross-sectional view of a second preferred embodiment of the homogenization apparatus;  
         [0055]    [0055]FIG. 6 is a cross-sectional view of a third preferred embodiment of the homogenization apparatus; and  
         [0056]    [0056]FIG. 7 is a cross-sectional view of a fourth preferred embodiment of the homogenization apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]    As illustrated in FIG. 1, the process of the present invention is used for crystallization of a chemical material, preferably an organic compound. It involves the use of two pumps and three vessels, in addition to the homogenization apparatus. The homogenization apparatus includes a chamber with a stator and a rotor. One vessel holds a first solution and functions as a source of that solution. The other vessel holds a second solution and functions as a source of that solution. The third vessel is used to collect the crystallized product, after it is removed from the homogenization apparatus. Pumps are used to control the feed rate of the first solution and of the second solution, respectively, to the homogenization chamber.  
         [0058]    For simplicity, the apparatus is disclosed as it would be used to crystallize a material utilizing two constituents. However, it should be understood that additional constituents and sources of those additional constituents could be used, if the process so required.  
         [0059]    The process is preferably performed continuously. The first solution is continuously mixed with the second solution by the rapid rotation of the rotor within the chamber. Shear, mixing and crystallization take place simultaneously in the chamber. Through the regulation of the flow rates of the solutions, as well as regulation of the agitation speed of the rotor, a high degree of control can be exercised over the particle size of the resulting crystals.  
         [0060]    The first solution is situated in a first vessel, generally designated A. For non-reactive crystallization, the first solution may be a supersaturated solution of the material to be crystallized in a solvent. This solution may, for example, be 4-(5-chloro-2-hydroxyphenyl)-3-(2-hydroxyethyl)-6-(trifluoromethyl)-2(1H)-Quinolinone dissolved in ethanol. The second solution is situated in a second vessel, generally designated B. That solution is an anti-solvent, for example, water.  
         [0061]    When used in reactive crystallization to form, for example, pharmaceutical salts, the first solution may be a solution containing a first reactive intermediate, for example, a reagent such as a base. The second solution may be a solution containing a second reactive intermediate, for example, a second reagent such as an acid.  
         [0062]    For example, the first solution could be the free base 1-(3′-aminobenzisoxazol 5′yl)-trifluoronmethyl-5-[[4-[2′-dimethylaminomethyl)imidazol-1′-yl]-2-fluorophenyl]aminocarbgonyl]pyrazole dissolved in ethanol at 70 deg. C. The acid HCl, dissolved in isopropyl alcohol at 65 deg. C, could be the second solution. The solutions are introduced into the homogenization chamber and combined by rapid rotation of the rotor. The salt 1-(3′-aminobenzisoxazol-5′-yl)-3 trifluoromethyl-5-[[4-[(2′-dimethylaminomethyly)imidazol-1′yl]-2-fluorophenyl]aminocarbonyl]pyrazole.HCl is formed.  
         [0063]    The solvents used to form the first and second solutions may be the same or different solvents. The solubility of the solvents differ based upon the polarity of the compounds. Additives such as surfactant or excipients may be included in the solutions. The parameters of the product may be changed depending upon the type of solvent.  
         [0064]    As seen in the drawings, a first solution from vessel A is fed to the homogenization apparatus, generally designed C, by a first pump  10  through a supply conduit  11 . The second solution from vessel B is fed to apparatus C by a second pump  12 , through a supply conduit  13 .  
         [0065]    The material is crystallized in the chamber of apparatus C. The resulting crystal slurry is then discharged through conduit  15  into a collection vessel, generally designated D.  
         [0066]    A control unit, generally designated E, is connected to pumps  10 ,  12  and to the motor (not shown) which drives the rotor  28  (FIGS. 2 and 3) in apparatus C. Control Unit E controls the speed of pumps  10 ,  12  and thus the flow rates of the solutions into apparatus C. It also controls the rotation speed of the rotor within apparatus C.  
         [0067]    A mixer, generally designated F, is provided to mix the product in vessel D. Mixer F is also controlled by unit E.  
         [0068]    Further, temperature control units, generally designated G and H, are provided. Units G and H control the temperature of the first solution and of the second solution, respectively, and may take the form of heaters, cooling baths or any other conventional temperature adjusting equipment.  
         [0069]    [0069]FIGS. 2 and 3 illustrate the crystallization chamber of apparatus C in greater detail. The chamber is defined by a cylindrical wall  14 , and side walls  16  and  18 . Within wall  14  is situated a stator, generally designated  20 , formed by a plurality of spaced stationary blades  22  which extend from and are fixedly mounted on the interior surface of side wall  18 .  
         [0070]    Side wall  18  has a centrally located chamber inlet port  24 . The solutions are received into the chamber through port  24  from an inlet conduit  34 , which in turn is connected to supply conduits  11  and  13 .  
         [0071]    Side wall  16  also has a central opening  25 . The drive shaft  26  for rotor  28  extends through opening  25 . Rotor  28  is formed of a plurality of spaced blades  30  which define a recess aligned with port  24 .  
         [0072]    Wall  14  has a chamber outlet port  32  located outside the stator blades  22 . After processing, the crystallized product and the solvent mixture are removed from the chamber through port  32 , which leads to conduit  15 .  
         [0073]    [0073]FIGS. 4, 5,  6  and  7  illustrate four different preferred embodiments of a homogenization apparatus which can be used to perform the process of the present invention. In each apparatus, a chamber defined by walls  14 ,  16  and  18  with a stator  20  formed of spaced stationary blades  22 , a rotor  28  formed of spaced rotor blades  30 , and inlet and outlet ports  24  and  32 , are present. The main difference between the first three preferred embodiments is the structure of the input conduit. The fourth preferred embodiment involves a re-circulation system.  
         [0074]    In the embodiment of FIG. 4, inlet conduit  34  includes an internal tube  36  connected to receive the first solution from vessel A, through supply conduit  11 . Tube  36  extends into inlet port  24  of the chamber. The second solution is received from vessel B, through supply conduit  13 , into the portion of inlet conduit  34  that surrounds tube  36 . Accordingly, the solutions are introduced separately into the chamber. Crystallization, mixing and shear occur almost simultaneously within the chamber.  
         [0075]    In the preferred embodiment of FIG. 5, an internal tube  38  is provided. Tube  38  is connected to vessel A by supply conduit  11  to receive the first solution. However, tube  38  does not extend into inlet port  24  like tube  36  of FIG. 4, but instead terminates some distance from the inlet port. Accordingly, in this embodiment, mixing of the solutions occurs within inlet conduit  34 , prior to introduction of the solutions into the chamber. The length of tube  38  can be altered to change the point where mixing takes place.  
         [0076]    In the embodiment of FIG. 6, two separate inlet tubes  36  and  40  are present within tube  34 . Tubes  36  and  40  are connected to conduits  11  and  13 , respectively. The tubes have parallel end sections. The end sections of both tubes extend into port  24  such that the solutions are introduced separately into the chamber, as in the embodiment of FIG. 4.  
         [0077]    Although the apparatus has been described for use in combining two solutions, in some instances, more than two solutions may be involved. In those situations, additional supply vessels, supply conduits and inlet conduits can be incorporated into the apparatus.  
         [0078]    A wide range of rotor speeds can be used depending on the system of interest. The crystal size distribution of the product may vary with the rotor speed. Further, mixing of the product after it is removed from the chamber, by mixer F (shown in FIG. 1), may effect crystal size distribution by yielding smaller crystals.  
         [0079]    The flow ratio of the solutions also effects crystal size distribution. Exemplary flow rates of 34.8 ml/min for the first solution and from 34.3 to 140.8 ml/min for the second solution have been used. Other flow rates may be selected according to the system components and reacting conditions.  
         [0080]    The homogenization apparatus C can be obtained by modifying a commercially available ULTRA-TURRAX UTL 25 Inline dispenser, available from IKA Works, Inc. of 2635 North Chase Parkway SE, Wilmington, N.C. 28405. The conventional dispenser is modified for use in the process of the present invention by utilizing a custom designed T-shaped two port input conduit connected to the chamber inlet port, as illustrated in FIGS. 4, 5 and  6 .  
         [0081]    For some applications, it may be desirable to alter the temperature of one or both of the solutions prior to introduction into the chamber. For example, heating the first solution by a heater G and chilling the second solution using a cooling bath H may enhance supersaturation during the crystallization process.  
         [0082]    It has also been found that adding seed crystals to the mixture of solutions may alter the crystalline form of the product. This can be accomplished by filling the chamber with seed crystals prior to beginning the process or continuously adding fresh seed crystals to one of the solutions.  
         [0083]    It has been observed that if the seed crystals are present in the chamber prior to running, this seed material is gradually discharged from the chamber with the product, and is mostly washed away during longer runs. To overcome this problem, a modified apparatus, illustrated in FIG. 7, was developed.  
         [0084]    The preferred embodiment of FIG. 7 is essentially the same as that of FIG. 4, with the addition of a recycle conduit  42  connecting outlet conduit  15 , at a point beyond outlet port  32 , and second solution supply conduit  13 , at a point before it connects to conduit  34 . Recycle conduit  42  serves to continually re-circulate a portion of the contents of the chamber, thereby providing seed material to the chamber on a continuous basis.  
         [0085]    It should now be appreciated that the present invention relates to a crystallization process using homogenization that produces a pure crystallized compound with molecules having small, uniform particle size, high surface area and short dissolution time, which require no post-production milling. The stator/rotor structure within the chamber permits crystallization, mixing and shear to occur almost simultaneously. Problems of alignment of high velocity fluid jet streams and solution ratio control are entirely eliminated.  
         [0086]    Although only a limited number of preferred embodiments of the present invention have been disclosed for purposes of illustration, it is obvious that many modifications and variations could be made thereto. It is intended to cover all of these modifications and variations which fall within the scope of the present invention, as set forth in the following claims: