Abstract:
A method for preparing a pharmaceutical compound by way of magnetic carbon nanocapsules is disclosed. The method comprises steps of: (a) providing a magnetic carbon nanocapsule with C—(COOH) 2  group, and Pt cations, to form a complex; (b) collecting the complex from the magnetic carbon nanocapsule; and (c) removing the Pt cations on the complex.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for preparing pharmaceutical compounds, particularly a method for preparing pharmaceutical compounds by magnetic carbon nanocapsules.  
         [0003]     2. Description of Related Art  
         [0004]     A carbon nanocapsule is a polyhedron composed of a enclosed multilayer graphite structure, whose diameter ranges from 1 to 100 nm but is usually 30-40 nm. It is able to be stuffed with magnetic metal inside (a carbon nanocapsule stuffed with magnetic metal is referred to as M@CNC hereafter). As to the graphite layer on the shell of a carbon nanocapsule, the central parts are exclusively six-member rings, the corners are composed of five-member rings, and every carbon atom is sp 2 ; the enclosed multilayer graphite structure endows effective protection of the internal metal particles against oxidization and aggregation, allowing magnetism of internal nano metal to be preserved stably. Besides, the surface of the graphite layer shell of the carbon nanocapsule can be chemically modified, making it disperse in a solvent easily, ready to use, and have stronger affinity.  
         [0005]     Platinum anticancer drug Cisplatin is widely used to fight against cancer, but because the required material, PtCl4, is very expensive, the manufacture costs of Cisplatin-series anticancer drugs have been high, and the price depends on the yield of the method used for preparation. For methods of prior arts, cis-form and trans-form compounds usually coexist in the products, making it uneasy to purify desired trans-form compounds used to prepare drugs, which often leads to low yields. To avoid formation of cis-form compounds, the prior arts usually need extra steps of preparation in order to raise the proportion of trans-compounds.  
         [0006]     There are various ways to prepare cisplatin-series anticancer drugs and the analogs thereof. The yields are usually 28-70% with current techniques. The following formulas exemplifies methods of synthesis known in the art:  
                         
 
         [0007]     Yields of Cisplatin synthesized by the above procedures are low because of the occurrence of cis-form compounds, which are capped at 70%. Thus, to improve yields in order to lower the costs of drug manufacturing, developing a novel and cheap method of preparation is necessary.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention employs carbon nanocapsules filled with magnetic metal as the carriers of synthesis of Cisplatin, which are stereo-selective and characterized by the ability to be recycled magnetically.  
         [0009]     The present invention relies on the principles that magnetic carbon nanocapsules can be recycled and controlled magnetically, and that [C(—COOH) 2 ] group pairs on their surfaces are easy to be modified and chelate easily with platinum, to make them the carriers for synthesis of Cisplatin. Cisplatin is a commonly used agent in chemotherapy. The present inventions developed novel synthesis steps and improved the yield of Cisplatin preparation.  
         [0010]     The present invention is a method for preparation of pharmaceutical compounds using magnetic carbon nanocapsules, comprising steps of: (a) providing platinum cations and carbon nanocapsules having C—(COOH) 2  groups to form a complex; (b) collecting the complexes from the magnetic carbon nanocapsule; and (c) removing the platinum ion on the complex.  
         [0011]     The platinum ion of step (a) of the present invention is quadridentate, which forms bonds with the [C(—COOH) 2 ] groups on the carbon nanocapsule on one side and with two chloride ions on the other side (Fe@CNC—[C(COO—) 2 PtCl 2 ] n ). In step (b), collection of complexes can be performed by any method known in the art Preferably, the collection is done by magnetism, gravity forces, or centrifugal forces. The method of the present invention can further comprise a step (b1), which follows step (b), proceeding with aminization on collected complexes. By way of the aminization, NH 2  replaces chloride ions of the complexes. In step (c), it is preferred to remove platinum on the complexes through hydrolysis. Meanwhile, to fully utilize costly platinum, a step (d) recovering the platinum on the complexes is preferably taken.  
         [0012]     The assembly of the magnetic carbon nanocapsule suitable to the method of the present invention can be an outer shell having enclosed multilayer graphite structure and magnetic metals comprised inside thereof, thereby forming a polyhedral carbon cluster. Magnetic metal comprised in the magnetic carbon nanocapsule can be Fe, Co, Ni or the alloy thereof. Preferably, the diameter of the magnetic carbon nanocapsule is in a range of 3-100 nm. More preferably, the diameter of the magnetic carbon nanocapsule is in a range of 30-40 nm. By using the method of the present invention, the Cisplatin-series drugs (including cisplatin and dehydrate cisplatin) can be prepared.  
         [0013]     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is the flow chart of the method of the present invention;  
         [0015]      FIG. 2  is the diagram showing the reverse titration curve of quantifying the number of —COOH functional groups, and the number of —COOH measured=(66-37.375)*1 m/10.5mg=123 mmole/g;  
         [0016]      FIG. 3  is the H-NMR spectrum of the product of Example 1, which shows the product is Cis-Pt(NH 2 ) 2 (OH) 2 ;  
         [0017]      FIG. 4  is the FTIR diagram of the product of Example 1, which shows: a is standard cisplatin (provided by Phytohealth Co. ltd), b is monohydrate cisplatin obtained from hydrolysis of standard cisplatin, and c is the product Fe@CNC—[C(COOEt) 2 ]n in Example 1; comparing characteristics on FTIR diagram, it is known that the product is Cis-Pt(NH 2 ) 2 (OH) 2 ;  
         [0018]      FIG. 5  shows measuring Pt contents in the product of Example 1 by a TGA test (a), and the data shows the variations of the intermediate products in different stages (Fig b illustrates the content in each step); and  
         [0019]      FIG. 6  is HPLC analysis, and HPLC diagrams of standard cisplatin and the synthesized product of equal concentrations are compared; the retention time of the product of Example 2 is equal to standard cisplatin, and purity is also fairly equal. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     The techniques to synthesize cisplatin-series drugs disclosed in the present invention employ [C(—COOH) 2 ] group pairs on the magnetic carbon nanocapsules (M@CNC) to form coordinate bonding with platinum cations and form stable complex intermediates. The M@CNC—[C(COO—) 2 PtCl 2 ] complexes are possible to be reused by magnetic recycling, so as to avoid loss of expensive platinum and improve usage of platinum.  
       EXAMPLES  
       [0021]     First, a —COOH pair on the magnetic carbon capsule is modified and the —COOH group pair are sure to form a stable cis-form complex intermediate with PtCl4; the Fe@CNC—[C(COO—) 2  PtCl 2 ] n  complex is possibly to be reused by magnetic recycling to avoid loss of expensive platinum, so as to improve the usage of platinum. Subsequently, Cl on the Fe@CNC—[C(COO—) 2  PtCl 2 ] n  complex is replaced with NH 2 , resulting in a Fe@CNC—[C(COO—) 2 Pt(NH 3 ) 2 ] 2 ] n  complex. Finally, platinum is removed by hydrolysis and Pt(NH 2 )Cl 2  is obtained.  
         [0022]     Fe@CNC carrier can be recycled and reused, and Pt(NH 2 )Cl 2  products are ensured to be cis-form due to the steric effect of a [C(—COOH) 2 ] group pair thereon.  
       Example 1  
       [0023]     Experimental procedures are shown in  FIG. 1 ( a )-( g ), and each step is explained in details as follows:  
         [0000]     Step 1. Modification of Functional Groups on the Surface of the Carbon Nanocapsule  
         [0024]     0.5 g of carbon nanocapsules (as shown in  FIG. 1 ( a )) and the carbon nanocapsule having the shape illustrated in  FIG. 2  are added with 1 g of diethyl bromomalonate, and 12.5 g of 1,8-Diazabicyclo[5.4.0]undec-7-ene. Toluene (15 ml) was used as a solvent. Then the product Fe@CNC—[C(COOEt) 2 ] n  was dried.  
         [0025]     The dried product Fe@CNC—[C(COOEt) 2 ] n  was put into diluted hydrochloric acid and is refluxed for 4 hours. Then carbon nanocapsules containing [C(—COOH) 2 ] group pairs as shown in  FIG. 1 ( b ) were obtained.  
         [0026]     The obtained product was reverse titrated by 1 mN NaOH and identified. After titration and the identification, the number of the functional group —COOH was identified about 123 mmol/g.  
         [0000]     Step 2. Forming Cis-Form Complexes of Platinum and Carbon Nanocapsules  
         [0027]     The 2-valence Pt salts are then chelated with [C(—COOH) 2 ] group pairs to form stable cis-form complexes. The detailed experiment procedures are illustrated as follows:  
         [0028]     0.5 g of Fe@CNC—[C(COOEt) 2 ] n  was (see  FIG. 1 ( b )) dispersed and dissolved in 1 ml of dichloromethane solvent; and then 500 mg of PtCl 4  was added. The mixture was substantially stirred and dissolved, and the reaction was carried on for 24 hours. A small portion of the product was drawn out and checked the contents of Pt by TGA experiment, which is 10%.  
         [0000]     Step 3. Aminization  
         [0029]     The Cl on the product Fe@CNC—[C(COO—) 2 PtCl 2 ] n  obtained in step 2 is replaced in the present step, and Fe@CNC—[C(COO—) 2 Pt(NH 3 ) 2 ] 2 ] n  complexes will be obtained. The detailed experiment procedures are illustrated as follows:  
         [0030]     The Fe@CNC—[C(COO—) 2 PtCl 2 ] n  obtained in step 2 was taken (see  FIG. 1 ( c )) and subjected to reaction with NH 3  at a proportion of 1 ml NH 3  to 1 mg carbon nanocapsules. The lower the temperature, the more fully the reaction proceeds. Temperature is the key determinant of reaction rate in this regard. After drying, Fe@CNC—[C(COO—) 2 Pt(NH 3 ) 2 ] 2 ] n  complexes were obtained. (see  FIG. 1 ( d )).  
         [0000]     Step 4. Hydrolysis  
         [0031]     After Fe@CNC—[C(COO—) 2 Pt(NH 3 ) 2 ] 2 ] n  complexes intermediates obtained in step 3 are isolated by centrifugation, platinum in the product is removed by hydrolysis(as shown in  FIG. 1 ( e )). The detailed experiment procedures are illustrated as follows:  
         [0032]     0.01N of NaOH was used as a catalyst of hydrolysis, resulting in the product Cis-Pt(NH 2 ) 2 (OH) 2 . The products are identified by qualitative analysis such as NMR ( FIG. 3 ) and FTIR ( FIG. 4 ). Compared with the diagrams of prior arts, the product was surely Cis-Pt(NH 2 ) 2 (OH) 2  (as shown in  FIG. 1 ( g )).  
         [0033]     The product was subsequently subjected to quantitative analysis. From the results of TGA and HPLC experiments, the yield was about 86 % (See  FIG. 5  and Table 1).  
                                                     TABLE 1                                       UV                   Flow   detection       No.   column   Mobile phase   rate (ml/         )   (nm)                                1.   LichroCAR   Ammonium   0.5   90       2.   TC18   sulphate 0.8 g/2 L   2   209       3.           0.5   209       4.   YMC   Ammonium   2   209           ODS-M80   sulphate 0.8 g/3 L       5.   VERCOPAK   ethyl acetate/   0.5   209       6.   NUCLEOSIL   methanol/   0.5   310               DMF/water       7.       Ammonium   0.5   209               sulphate 0.8 g/2 L       8.       ethyl acetate/   0.5   310               methanol/               DMF/water       9.       Ammonium   0.5   310               sulphate 0.8 g/2 L                  
 
       Example 2  
       [0034]     The Fe@CNC—[C(COO—) 2 Pt(NH 3 ) 2]   2 ] n  complex intermediates obtained in step 3 of Example 1 were dispersed in 0.01N HCl solution and then refluxed at high temperature for 6 hours. A plain yellow solution and black nanocapsules were obtained after separation of solid and liquid phased by magnetic-field absorption. Water of the yellow solution was dried out by decompression, and the resultant dried yellow powder was Cis-Pt(NH 2 ) 2 (Cl) 2 . The product was subjected to HPLC quantitative analysis ( FIG. 6 ), and the yield was 80%. The solids of black carbon nanocapsules were Fe@CNC—[C(COOH) 2 ] n,  which were recyclable and reusable.(As shown in  FIG. 1 ( f )).  
         [0035]     The method of the present invention using magnetic carbon nanocapsules to prepare Cisplatin mainly employs magnetic nanocapsules as carriers. The design not only makes PtCl 4  material recyclable and reusable, but endows steric-selective functions that make product exclusively cis-form. Thus, the synthesis procedures are simpler than those known in the art, and the yield of Cisplatin can reach up to 80 mol %.  
         [0036]     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.