Abstract:
Provided are an L-proline complex of a sodium-glucose cotransporter 2 inhibitor, and a monohydrate and a crystal of the L-proline complex. Specifically, provided are 1,6-dehydrated-1—C{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose L-proline (a compound of formula (I)), a monohydrate and a type A crystal thereof, and a preparation method therefor. The obtained type A crystal of the compound of formula (I) has good chemical stability and crystal stability, and the crystallization solvent used has low toxicity and low residue, so the type A crystal can be better used in clinical treatment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Section 371 of International Application No. PCT/CN2015/089128, filed Sep. 8, 2015, which was published in the Chinese language on Apr. 7, 2016, under International Publication No. WO 2016/050134 A1 and the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose L-proline complex, a monohydrate and a crystal form A thereof. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the socio-economic development and the improvement of material living standards, the number of diabetics on a global scale is increasing rapidly. Diabetes is usually divided into two types, such as type I and type II, in which more than 90% of diabetes is type II. Many types of diabetes drugs are already commercially available, but so far no drug has been able to single-handedly keep the blood glucose levels of patients with type II diabetes within the target range for a long time. In recent years, more and more approaches for the treatment of type II diabetes are provided due to the in-depth study of the pathogenesis of diabetes. The discovery of sodium-glucose cotransporter 2 (SGLT-2) inhibitors provides another new idea for the treatment of diabetes. The mechanism of action of SGLT-2 inhibitors is to selectively inhibit the activity of SGLT-2, thereby reducing blood glucose. SGLT-2 is selected as a target spot, on one hand because of its absolute reabsorption of glucose, and on the other hand because it is only expressed in the kidney. The current study also finds that the mechanism of action of SGLT-2 does not depend on the dysfunction of β cells or the degree of insulin resistance, and its effect is not decreased with function failure of β-cell or severe insulin resistance. Therefore, it is reasonable to believe that the use of SGLT-2 inhibitors in the current treatment of type II diabetes has a promising future. 
         [0004]    WO2012019496 discloses a SGLT-2 inhibitor having the following formula, whose chemical name is 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0005]    However, it is impractical to directly use 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose as a pharmaceutically active ingredient due to its poor development form resulting from the lower melting point (83° C.) and hygroscopic properties. Therefore, it is important to develop a stable form of the compound. 
         [0006]    The crystal structure of the pharmaceutically active ingredient often affects the chemical stability of the drug. Different crystallization conditions and storage conditions may lead to changes in the crystal structure of the compound, and sometimes may be accompanied with the production of other crystal forms. In general, an amorphous drug product does not have a regular crystal structure, and often has other defects, such as poor product stability, smaller particle size, difficult filtration, easy agglomeration, and poor liquidity. Thus, it is necessary to improve the various properties of the above product. There is a need to identify a new crystal form with high purity and good chemical stability. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides an L-proline complex of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose represented by formula (I): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0008]    The complex of formula (I) can be prepared by co-crystallization of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose with L-proline. The invention provides a preparation method of the complex of formula (I), comprising a step of co-crystallizing 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose with L-proline, wherein the molar ratio of L-proline to 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose added for co-crystallization is less than to 2:1, preferably from 2:1 to 0.1:1, more preferably from 1.5:1 to 0.5:1, and most preferably from 1.5:1 to 1:1 or from 1.2:1 to 0.8:1. 
         [0009]    In comparison to 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl} -5—C-(hydroxymethyl)-β-L-idopyranose, the complex of formula (I) has a higher melting point and improved stability. 
         [0010]    In another aspect, the invention provides a monohydrate of the complex of formula (I) and crystal form A thereof. 
         [0011]    A series of crystal products of the complex of formula (I) obtained under various crystallization conditions were subjected to X-ray diffraction and differential scanning calorimetry (DSC) measurement. It was found that a stable crystal form of the complex of formula (I), which is referred to as crystal form A, can be obtained under the normal crystallization condition. The DSC spectrum of crystal form A according to the present application shows a melting endothermic peak at about 109.51° C. The X-ray powder diffraction spectrum of crystal form A, which is obtained by using Cu-Ka radiation and represented by 2θ angle and interplanar distance (d value), is shown in  FIG. 1  in which there are characteristic peaks at 5.50 (16.07), 7.82 (11.30), 8.64 (10.22), 10.33 (8.55), 12.18 (7.26), 12.49 (7.08), 14.47 (6.11), 15.51 (5.71), 15.89 (5.57), 17.28 (5.13), 18.89 (4.70), 19.39 (4.58), 20.40 (4.35), 22.85 (3.89), 23.89 (3.72), 25.93 (3.43), 27.66 (3.22), 28.97 (3.08) and 31.16 (2.87). 
         [0012]    The invention further provides a preparation method of crystal form A of a monohydrate of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose L-proline, comprising the following steps of: 
         [0013]    (1) dissolving 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose and L-proline in a solvent, then cooling the reaction solution to precipitate a crystal, wherein the solvent is selected from the group consisting of an organic solvent and a mixed solvent of an organic solvent and water; the organic solvent is one or more selected from the group consisting of alcohols, ketones, esters, ethers, hydrocarbons and nitriles having 6 or less carbon atoms; and 
         [0014]    (2) filtering the crystal, then washing and drying it; 
         [0015]    preferably, wherein the molar ratio of L-proline and 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose added in step (1) is less than to 2:1, preferably from 2:1 to 0.1:1, more preferably from 1.5:1 to 0.5:1, and most preferably from 1.5:1 to 1:1 or from 1.2:1 to 0.8:1. 
         [0016]    In a preferred embodiment of the invention, the organic solvent is selected from of the group consisting of alcohols, ketones, and esters having 3 or less carbon atoms; or a mixed solvent of one or more of the above solvents and halogenated hydrocarbons having 3 or less carbon atoms. More preferably, the organic solvent is selected from methanol, ethanol, and isopropanol; or methanol/water, ethanol/water, isopropanol/water or ethanol/n-hexane. 
         [0017]    Most preferably, the single solvent is ethanol. 
         [0018]    In one preferred embodiment of the invention, the mixed solvent is a mixed solvent of ethanol/water, and the ratio of the two is not particularly limited. In a preferred embodiment of the present invention, the volume ratio of ethanol/water is 19:1. 
         [0019]    The recrystallization method is not particularly limited and can be carried out by a conventional recrystallization process. For example, the raw material i.e., the complex of formula (I) can be dissolved in an organic solvent under heating, and then the solution is cooled slowly to precipitate a crystal. After the completion of crystallization, the resulting product is filtered and dried to obtain the desired crystal. In particular, the crystal obtained by filtration is usually vacuum-dried under reduced pressure at about 20 to 60° C., preferably at room temperature, to remove the recrystallization solvent. 
         [0020]    The crystal form of the obtained complex of formula (I) was determined by differential scanning calorimetry (DSC) and X-ray diffraction spectrum. Meanwhile, the residual solvent of the obtained crystal was also determined. 
         [0021]    Crystal form A of the complex of formula (I) prepared according to the method of the invention does not contain or contains only a relatively low content of residual solvent, which meets the requirement of the national pharmacopoeia concerning the limitation of the residual solvent of drug products. Thus, the crystal of the invention is suitable for use as a pharmaceutically active ingredient. 
         [0022]    It has been shown that the stability of crystal form A of the complex of formula (I) prepared by the invention is significantly better than that of the amorphous sample under the conditions of high temperature and high humidity. Moreover, crystal form A has good stability under the conditions of grinding, pressure and heating, which meets the production, transportation and storage requirements of drug products. The preparation process of crystal form A is stable, repeatable and contolled, and is suitable for industrial production. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows the X-ray powder diffraction spectrum of crystal form A of the complex of formula (I); 
           [0024]      FIG. 2  shows the DSC spectrum of crystal form A of the complex of formula (I); 
           [0025]      FIG. 3  shows the X-ray powder diffraction spectrum of the amorphous solid of the complex of formula (I); 
           [0026]      FIG. 4  shows the DSC spectrum of the amorphous solid of the complex of formula (I); 
           [0027]      FIG. 5  shows the DSC spectrum of the solid prepared in Example 15 with 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose/L-proline ratio of 1:2; 
           [0028]      FIG. 6  shows the Thermo Gravimetric Analyzer (TGA) spectrum of the solid prepared in Example 15 with 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose/L-proline ratio of 1:2; 
           [0029]      FIG. 7  shows the DSC spectrum of the solid prepared in Example 16 with 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose/L-proline ratio of 1:2; and 
           [0030]      FIG. 8  shows the TGA spectrum of the solid prepared in Example 16 with 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose/L-proline ratio of 1:2. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The following examples serve to illustrate the invention in more detail, but the examples of the invention are only intended to describe the technical solution of the invention, and should not be considered as limiting the spirit and the scope of the invention. 
         [0032]    Test instruments used in the experiments 
         [0033]    1. DSC spectrum 
         [0034]    Instrument type: Mettler Toledo DSC 1 Stare e  System 
         [0035]    Purging gas: Nitrogen 
         [0036]    Heating rate: 10.0° C./min 
         [0037]    Temperature range: 40-200° C. 
         [0038]    2. X-ray diffraction spectrum 
         [0039]    Instrument type: Bruker D8 Focus X-ray powder diffractometer 
         [0040]    Rays: monochromatic Cu-Ka rays (λ=1.5406 Å) 
         [0041]    Scanning mode: θ/20, Scanning range: 2-40° 
         [0042]    Voltage: 40 KV Electric Current: 40 mA 
       EXAMPLE 1 
       [0043]    1.0 g (2.2 mmol) of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose (prepared according to the method disclosed in WO2012019496) was dissolved in 7.20 g of ethanol with stirring. 0.2786 g of L-proline (2.42 mmol, 1.1 eq) was added into the solution at room temperature. The mixture was stirred and heated to reflux for 10 minutes until the reaction solution became clear, then filtered while it was hot. The filtrate was cooled to room temperature with stirring. A large amount of white solid was precipitated. The mixture was left overnight, then filtered and dried to obtain 1.14 g of the complex of formula (I) as a white solid in 88% yield. The X-ray diffraction spectrum of this crystal sample is shown in  FIG. 1  in which there are characteristic peaks at 5.50 (16.07), 7.82 (11.30), 8.64 (10.22), 10.33 (8.55), 12.18 (7.26), 12.49 (7.08), 14.47 (6.11), 15.51 (5.71), 15.89 (5.57), 17.28 (5.13), 18.89 (4.70), 19.39 (4.58), 20.40 (4.35), 22.85 (3.89), 23.89 (3.72), 25.93 (3.43), 27.66 (3.22), 28.97 (3.08) and 31.16 (2.87). The DSC spectrum of this crystal sample is shown in  FIG. 2 , which has a melting endothermic peak at 109.5° C. This crystal form was defined as crystal form A. 
       EXAMPLE 2 
       [0044]    1.0 g (2.2 mmol) of 1,6-anhydro-1—C-{4—chloro—3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose (prepared according to the method disclosed in WO2012019496) was dissolved in 8 mL of methanol/water (V:V=1:1) with stirring. Then, 0.38 g of L-proline (3.3 mmol, 1.5 eq) was added into the solution at room temperature. The mixture was stirred and heated to reflux for 10 minutes until the reaction solution became clear, then filtered while it was hot. The filtrate was cooled to room temperature with stirring. A large amount of white solid was precipitated. The mixture was left overnight, then filtered and dried to obtain 1.08 g of the complex of formula (I) as a white solid in 83.1% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 3 
       [0045]    1.0 g (2.2 mmol) of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose (prepared according to the method disclosed in WO2012019496) was dissolved in 10 mL of isopropanol/water (V:V=1:1) with stirring. Then, 0.25 g of L-proline (2.2 mmol, 1.0 eq) was added into the solution at room temperature. The mixture was stirred and heated to reflux for 10 minutes until the reaction solution became clear, then filtered while it was hot. The filtrate was cooled to room temperature with stirring. A large amount of white solid was precipitated. The mixture was left overnight, then filtered and dried to obtain 1.10 g of the complex of formula (I) as a white solid in 84.6% yield. The X-ray diffraction spectrum of this crystal sample is shown in  FIG. 1 . The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 4 
       [0046]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 250 ml one-necked flask and dissolved in 160 ml of water under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 336 mg of an off white solid in 33.6% yield. The X-ray diffraction spectrum of this solid sample is shown in  FIG. 3  in which there are no characteristic peaks of a crystal. The DSC spectrum of this solid sample is shown in  FIG. 4 , which has no melting absorption peak below 200° C. The product was thus identified as an amorphous solid. 
       EXAMPLE 5 
       [0047]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of ethanol under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 728 mg of a white solid in 72.8% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 6 
       [0048]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of methanol under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 643 mg of a white solid in 64.3% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 7 
       [0049]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of 50% methanol under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 602 mg of a white solid in 60.2% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 8 
       [0050]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of isopropanol under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 740 mg of a white solid in 74.0% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 9 
       [0051]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of 50% ethanol under heating. The solution was refluxed for 10 min, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 595 mg of a white solid in 59.5% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 10 
       [0052]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 2 ml of 95% ethanol under heating. The solution was refluxed for 10 min, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 813 mg of a white solid in 81.3% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 11 
       [0053]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 25 ml one-necked flask and dissolved in 3 ml of ethanol/n-hexane (V:V=3:1) under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 804 mg of a white solid in 80.4% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 12 
       [0054]    1.0 g (1.7 mmol) of the complex of formula (I) (prepared according to Example 1) was added to a 250 ml one-necked flask and dissolved in 94 ml of 10% ethanol under heating. The solution was refluxed for 10 minutes, then cooled and left to stand for precipitation. The resulting precipitate was collected by filtration and dried to obtain 338 mg of a white solid in 33.8% yield. The product was identified as crystal form A after studying and comparing the X-ray diffraction and DSC spectra. 
       EXAMPLE 13 
       [0055]    Crystal form A prepared in Example 1 and the amorphous sample prepared in Example 4 were spread flat in the air to test their stability under the conditions of lighting (4500 Lux), heating (40° C., 60° C.), and high humidity (RH 75%, RH 90%). Sampling times of 5 days and 10 days were studied, and the purity as detected by HPLC is shown in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Comparison of stability of crystal form A and amorphous sample of the complex of formula (I) 
               
             
          
           
               
                 Batch number 
                 Time (Day) 
                 Lighting 
                 40° C. 
                 60° C. 
                 RH 75% 
                 RH 90% 
               
               
                   
               
             
          
           
               
                 Crystal form A 
                 0 
                 99.76% 
                 99.76% 
                 99.76% 
                 99.76% 
                 99.76% 
               
               
                 S1052110422 
                 5 
                 99.76% 
                 99.76% 
                 99.74% 
                 99.75% 
                 99.76% 
               
               
                   
                 10 
                 99.76% 
                 99.75% 
                 99.74% 
                 99.74% 
                 99.75% 
               
               
                 Amorphous 
                 0 
                 99.68% 
                 99.68% 
                 99.68% 
                 99.68% 
                 99.68% 
               
               
                 20140411 
                 5 
                 99.60% 
                 99.65% 
                 99.67% 
                 99.66% 
                 99.66% 
               
               
                   
                 10 
                 99.55% 
                 99.62% 
                 99.56% 
                 99.65% 
                 99.64% 
               
               
                   
               
             
          
         
       
     
         [0056]    After crystal form A and the amorphous sample were spread flat in the air to test the stability under the conditions of lighting, high temperature, high humidity, the results of the stability study showed that high humidity does not have much effect on the two examples, but under the conditions of lighting and high temperature, the stability of crystal form A is significantly better than that of the amorphous sample. 
       EXAMPLE 14 
       [0057]    Crystal form A of the complex of formula (I) prepared according to the method of Example 1 was grinded, heated and pressed. The results showed that the crystal form was stable and the detailed experimental data are shown in Table 2 below. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Stability study of crystal form A of the complex of formula (I) 
               
             
          
           
               
                   
                 Treatment 
                   
                 Crystal 
                   
               
               
                 Batch number 
                 process 
                 Experiment procedure 
                 form 
                 DSC peak 
               
               
                   
               
               
                 Experiment 14.1 
                 Grinding 
                 1.0 g of crystal form A of the 
                 crystal 
                 DSC peak 
               
               
                 20140415G 
                 treatment 
                 complex of formula (I) was grinded 
                 form A 
                 110.46° C. 
               
               
                   
                 for 10 min 
                 for 10 min in a mortar under nitrogen 
               
               
                   
                   
                 atmosphere. 
               
               
                 Experiment 14.2 
                 Heating 
                 1.0 g of crystal form A of the 
                 crystal 
                 DSC peak 
               
               
                 20140415H 
                 treatment at 
                 complex of formula (I) was spread 
                 form A 
                 110.64° C. 
               
               
                   
                 60° C. for 3 
                 flat and heated at 60° C. for 3 hours 
               
               
                   
                 hours 
               
               
                 Experiment 14.3 
                 Pressing 
                 Crystal form A of the complex of 
                 crystal 
                 DSC peak 
               
               
                 20140415P 
                 treatment 
                 formula (I) was pressed to a slice 
                 form A 
                 110.29° C. 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 15 
       [0058]    According to the same method disclosed in Example 15 of CN104031098A, 0.23 g (2 mmol) of L-proline was dissolved in 1.2 mL of 90% ethanol/water, the solution was heated to a low boil, then a solution of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose (0.5 mmol) in 4 mL of ethanol was added. Acetone was slowly added to 10% of the total volume, the resulting solution was cooled to −20° C. for 2 hours, and a solid was formed during this time. The mixture was left for 2 days at room temperature. The container was centrifuged, and the supernatant was removed. 
         [0059]    The remaining solid was washed with n-hexane and dried under vacuum to obtain a white solid. HPLC analysis showed that the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline is about 0.46 in the white crystalline solid. DSC and TGA spectra of the resulting solid were shown in  FIG. 5  and  FIG. 6 , respectively. The DSC spectrum showed that the resulting solid had three endothermic peaks at 60.78° C., 69.79° C. and 105.90° C., which suggested that this substance might be unstable and that it was possible to produce degradation at lower temperatures, thereby leading to the loss of proline from the co-crystal. The TGA spectrum showed that the weight loss of proline in the solid is 30.58% (the theoretical value is 33.4% when the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline is 1:2). The analysis of the HPLC, DSC, and TGA results indicated that the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline in the resulting solid product is 1:2, and the stability of the resulting product was poor. 
       EXAMPLE 16 
       [0060]    According to the same method disclosed in Example 15 of CN104031098A, 0.23 g (2 mmol) of L-proline was dissolved in 1.2mL of 90% ethanol/water, the solution was heated to a low boil, and then a solution of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose (0.5 mmol) in 4 mL of ethanol was added. Acetone was slowly added to 5% of the total volume, the resulting solution was cooled to −20° C. for 3 hours, and a solid was formed during this time. The mixture was left for 1.5 days at room temperature. The container was centrifuged, and the supernatant was removed. The remaining solid was washed with n-hexane and dried under vacuum to obtain a white solid. HPLC analysis showed that the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline was about 0.54 in the white crystalline solid. The DSC and TGA spectra of the resulting solid are shown in  FIG. 7  and  FIG. 8 , respectively. The DSC spectrum showed that the resulting solid had three endothermic peaks at 59.55° C., 72.24° C. and 105.49° C., which suggested that this substance might be unstable and that it was possible to produce degradation at lower temperatures, thereby leading to the loss of proline from the co-crystal. The TGA spectrum showed that the weight loss of proline in the solid was 32.82% (the theoretical value is 33.4% when the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline is 1:2). The analysis of the HPLC, DSC, and TGA results indicated that the molar ratio of 1,6-anhydro-1—C—{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5—C-(hydroxymethyl)-β-L-idopyranose to L- proline in the resulting solid product was 1:2, and the stability of the resulting product was poor.