Abstract:
9-dihydro-13-acetylbaccatin III, one of the chemicals obtained from  Taxus canadensis  is used to produce, inter alia, 10-decetylbaccatin III, a useful intermediate for the preparation of paclitaxel and analogues thereof The 9-dihydro-13-acetylbaccatin III is converted into the 10-deacetylbaccatin III by a simple three step process involving (a) replacement of the C-7 hydroxyl group of the 9-dihydro compound with a protecting group, (b) the oxidizing of the C-7 protected compound to produce a C-9 keytone, and (c) the deprotecting of the C-9 keytone to produce 10-deacetylbaccatin III

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a method of converting 9-dihydro-13-acetylbaccatin III to 10-deacetylbaccatin III.  
           [0003]    2. Discussion of the Prior Art  
           [0004]    Many taxanes, e.g. paclitaxel and docetaxol are being aggressively studied and tested for use as cancer treating agents. As described in many publications such as Canadian Patent Application No. 2,188,190, published Apr. 18, 1998 in the name of Zamir et al, which is incorporated herein by reference, the taxanes are active in various tumor systems. Taxanes are substances occurring naturally in yew trees such as  Taxus canadensis,  which is common in Eastern Canada and the United States. One of the chemicals extracted from the needles of  Taxus canadensis  is 9-dihydro-13-acetylbaccatin III, which is used to produce, inter alia, 10-deacetylbaccatin III—a useful intermediate for the preparation of paclitaxel and analogues thereof.  
           [0005]    Various methods of converting 9-dihydro-13-acetylbaccatin III into 10-deacetylbaccatin III have been proposed (see, for example the above mentioned CA 2,188,190) However, it has been found that such methods result in poor yields of finished product Thus, a need still exists for an efficient method for converting 9-dihydro-13 acetylbaccatin III to 10-deacetylbaccatin III (DAB III)  
         GENERAL DESCRIPTION OF THE INVENTION  
         [0006]    The object of the present invention is to meet the above defined need by providing a relatively efficient method of converting 9-dihydro-13-acetylbaccatin III to DAB III.  
           [0007]    Accordingly, the invention relates to a method of converting 9-dihydro-13-acetylbaccatin III into 10-deacetylbaccatin III comprising the steps of  
           [0008]    (a) protecting the C-7 group of 9-dihydro-13-acetylbaccatin III by replacing the C-7 hydroxyl group with a protecting group;  
           [0009]    (b) oxidizing the C-9 hydroxyl group in the resulting product to produce a C-9 ketone; and  
           [0010]    (c) deprotecting the C-9 ketone to form 10-deacetylbaccatin III.  
         DESCRIPTION OF THE PREFERRED EMBODIMENT  
       General Procedure  
         [0011]    The first step in the method of the present invention involves the dissolving of 9-dihydro-13-acetylbaccatin III in dry solvent such as CH 2 Cl 2 , CHCl 3 , THF, Et 2 O or Bz. A dry base, e.g. pyridine, TEA or NaHCO 3  and/or a catalytic amount of p-N,N-dimethylaminopyridine (DMAP) is added to the solution, followed by 1-6 equivalents of a protecting reagent (TMSCl, TESCl or Ac 2 O) at a temperature of between room temperature and −78° C. The mixture is stirred continuously for 0.5-6 hours before being quenched by the addition of water. The mixture is poured into ethyl acetate and washed sequentially with dilute acid, water and brine, and dried over magnesium sulfate. The solution is evaporated under vacuum to give a crude solid (7-OH protected-9-baccatin III up to 91% yield)  
           [0012]    A 3,5-disubstituted pyrazole such as 3,5-dimethyl-pyrazole is added to a suspension of metal oxide, e.g. chromium trioxide (2-20 equivalents) in a solvent. Suitable solvents include CH 2 Cl 2 , CHCl 3 , THF, Et 2 O and Bz. The mixture is stirred at room temperature for at least 15 minutes, A 7-OH protected 9-dihydro-13-acetylbaccatin III in the same solvent is added to the solution in one portion, and the mixture is stirred for 0.5 hour to one week to produce a C-9 ketone in up to 90% yield  
           [0013]    The C-9 ketone is dissolved in a suitable organic solvent such as an alcohol, an ether, CH 2 Cl 2  or CHCl 3 , with or without water, and reacted with an acid, a base, or a strong nucleophile, such as a bicarbonate, a carbonate, ammonia, an amine, a hydrazine, a hydroxide, a hydroperoxide or an alkyllithium. The reaction mixture thus produced is stirred at a controlled temperature (0° C. to solvent reflux). The reaction is monitored by thin-layer chromatography until it has progressed satisfactorily, Routine liquid extraction is performed followed by solvent evaporation to produce crude 10-deacetylbaccatin III in up to 85% yield  
           [0014]    The reaction scheme for the above described general procedure is as follows  
                         
 
           [0015]    In accordance with a preferred embodiment of the invention, R in the above formula is an acetyl group. The reaction scheme for the preferred embodiment is as follows  
                         
 
       
    
    
     EXAMPLES  
     Selective Protection of 7-hydroxyl Group of 9-dihydro-13-acetylbaccatin III  
       [0016]    [0016]                           
         [0017]    Several experiments were carried out using a variety of reagents to produce 7-OH protected-9-baccatin III with different protecting groups in the 7-position. The results of the experiments are listed in Tables 1 and 2 (for the sake of simplicity, all tables are found at the end of this description).  
         [0018]    Additional experiments were conducted in which R in the above formulae was an acetyl group.  
                         
 
         [0019]    In the method of producing 9-dihydro-7,13-diacetylbaccatin III, 9-dihydro-13-acetylbaccatin III (0 1 mmole) was dissolved in 2.5 mL of dry methylene chloride and cooled to −23° C. using a slurry of CCl 4  and liquid nitrogen. 0.6 mmole of dry pyridine and a catalytic amount of DMAP (5% in mole) were added to the mixture foilowed by 0.3 mmole of acetic anhydride. The mixture was stirred for 1 5 h and then the reaction was quenched by the addition of 5.0 mL of water. The mixture was poured into 25 mL of ethyl acetate and washed sequentially with 15 mL of 1% HCl, 15 mL water and mL brine, and dried over MgSC 4 . The solution was evaporated under vacuum and gave a crude solid (95% yield, 91% 9-dihydro-7,13-diacetylbaccatin III). The details and results of similar experiments are listed in Table 2.  
       Oxidation of the Protected 9-dihydro-13 acetylbaccatin III  
       [0020]    [0020]                           
         [0021]    Details of experiments using a variety of reagents and conditions are listed in Table 3  
         [0022]    Subsequent oxidation experiments (which are listed as Examples 45 to 49 in Table 4) were conducted using 9-dihydro-7,13-diacetylbaccatin III as the starting material.  
                         
 
         [0023]    In one experiment, 3 3 mmole of 3,5-dimethylpyrazole (DMP) was added to a suspension of 3.0 mmole of chromium trioxide (CrO 3 ) in CH 2 Cl 2 , and the mixture was stirred for 15 minutes. 0.15 mmole of 9-dihydro-7,13-diacetylbacctin III in the same solvent was added to the resulting DMP/CrO 3  solution, and the fixture thus produced was stirred for two days The mixture was filtered through silicia gel and evaporated to yield a solid product.  
         [0024]    Details of the experiments (Examples 45 to 49) are found in Table 4.  
       Deprotecting  
       [0025]    [0025]                           
         [0026]    Several experiments were conducted using various reagents and conditions. Details of the experiments are listed in Examples 50 to 75 in Tables 5 and 6.  
         [0027]    Additional experiments were carried out using 7,13-diacetylbaccatin III as the starting material to produce the desired product, DAB-III. In a specific reaction of this type, a solution of 4.5 mg (0.00675 mmole) of 7,13-diacetylbaccatin III in 0.08 mL of 95% ethanol was cooled to 7° C. 0 08 mL of hydrazine hydrate was added to the solution, which was then kept at 7° C. for 141 5 hours. The resulting mixture was diluted with ethyl acetate, and then washed sequentially with saturated aqueous ammonium chloride, water and brine. The organic layer was dried over MgSO 4 , filtered and evaporated in vacuo to yield 4.2 mg of crude product. NMR spectroscopy revealed that the product consisted mainly of 10-deacetylbaccatin III plus trace amounts of by-products. The conditions and results of the hydrazine-based hydrolysis experiments are listed in Examples 76 to 112 in Table 6.  
         [0028]    From the foregoing, and in particular from the specific examples, it is readily apparent that the preferred method of converting 9-dihydro-13-acetylbaccatin III into 10-deacetylbaccatin III involves the steps of:  
         [0029]    (a) protecting the C-7 position of the 9-dihydro-13-acetylbaccatin III with an acetyl group using acetic anydride in the presence of a base and DMAP to produce 9-dihydro-7,13-diacetylbaccatin III,  
         [0030]    (b) oxidizing the 9-dihydro-7,13-diacetylbaccatin III using CrO 3 /DMP to produce 7,13-diacetylbaccatin III, (the choice of oxidant here is important to success), and  
         [0031]    (c) replacing the C-7,C-10 and C-13 OAc groups in the 7,13-diacetylbaccatin III with OH groups using hydrazine hydrate.  
                                             TABLE 1                       Example       Reagents and Conditions   Yield                                1   R = TES   TES-Cl (7.5 eq), pyr, CH 2 Cl 2 , RT, 24 h   43%       2   R = TES   TES-Cl (5 eq), TEA, CH 2 Cl 2 , RT, 2.5 H       3   R = TES   TES-Cl (3 eq), pyr, CH 2 Cl 2 , RT, 24 h       4   R = TES   TES-Cl (5 eq), TEA, CH 2 Cl 2 , −89° C., 4 h   &gt;90%       5   R = TES   TES-Cl (5 eq), TEA, CH 2 Cl 2 , −89° C., 2.5 h   &gt;95%       6   R = TES   TES-Cl (5 eq), TEA, CH 2 Cl 2 , −89° C., 2 h   &gt;97%       7   R = Ac   Ac 2 O (10 eq), TEA, DMAP, CH 2 Cl 2 , −89° C., 5 h   &gt;51%       8   R = CBz   Cl-CBz (4 eq), TEA, CH 2 Cl 2 , RT, 20 h   a       9   R = CO 2 Me   MeOCOCl (2 eq), DMAP, TEA, CH 2 Cl 2 , RT, 24 h   b       10   R = CO 2 Me   MeOCOCl (5 eq), TMP, CH 2 Cl 2 , RT, 24 h   c       11   R = CO 2 CF 3     (CF 3 CO) 2 O (5 eq), Pyr, RT, 24 h   d       12   R = Ac   Ac 2 O (5 eq), Pyr, DMAP, CH 2 Cl 2 , 0° C., 6 h   &gt;50%       13   R = CO 2 CCl 3     CCl 3 COCl (2 eq), TEA, CH 2 Cl 2 , 0° C., 24 h   e                                                          
 
         [0032]    [0032]                                                                                     TABLE 2                           9-DHB   Ac 2 O   Solvents       Temperature   Reaction   Yield   7-Acetyl       Example   (mmole)   (mmole)   (ml)   DMAP   (° C.)   Time   (%)   (%)                                14   0.25   0.375   Pyr (5)   Yes   0-RT   20   5   76       15   0.1   0.3   Pyr (2.5)   Yes   0   1:20′   &gt;95   78-82       16   0.1   0.3   Pyr (2.5)   Yes   RT   1:20′   &gt;95   55-69       17   0.1   0.4   TEA (2), THF (1)   Yes   0   2   &gt;95   42-62       18   0.1   0.3   Pyr (2.5)   Yes   0   53′   &gt;90   71-83       19   0.1   0.3   Pyr (2.5), THF (1)   Yes   −23   3   &gt;92   84-92       20   0.1   0.3   Pyr (1), DCM (2)   Yes   −23   1.5   &gt;97   85-89       21   0.1   0.3   Pyr (1), DCM (2)   Yes   −43   1.5   &gt;93   65-95       22   0.1   0.3   Pyr (6 eq), DCM (2.5)   Yes   −23   1.5   &gt;95   67-94       23   0.1   0.3   TEA (6 eq), DCM (2.5)   Yes   −23   1.5   &gt;98   79                    
         [0033]    [0033]                                             TABLE 3                       Example       Reagents and Conditions   Yield                                24   R = TES   CrO 3 —Pyr 2 (12 eq), CH 2 Cl 2 , RT   a       25   R = TES   DMSO (4.8 eq), (COCl) 2  (2.2 eq), TEA (5 eq), CH 2 Cl 2     a       26   R = TES   DMSO (4.8 eq), (COCl) 2  (2.2 eq), TEA (5 eq), CH 2 Cl 2     a       27   R = TES   DMSO (9.6 eq), (COCl) 2  (4.4 eq), TEA(10 eq), CH 2 Cl 2     a       28   R = TES   DMSO (2.2 eq), (COCl) 2  (2.2 eq), TEA (5 eq), CH 2 Cl 2     a       29   R = TES   DMSO (2.4 eq), (COCl) 2  (2.2 eq), TEA (5 eq), CH 2 Cl 2     a       30   R = TES   DMSO (9.6 eq), (COCl) 2  (4.4 eq), TEA (10 eq), CH 2 Cl 2     a       31   R = TES   DMSO (9.6 eq), (COCl) 2  (4.4 eq), TEA (10eq), CH 2 Cl 2     a       32   R = TES   DMSO (5 eq), (COCl) 2  (5.5 eq), TEA (6 eq), CH 2 Cl 2     a       33   R = TES   DMSO (5.5 eq), (COCl) 2  (5 eq), TEA (6 eq), CH 2 Cl 2     a       34   R = TES   NaClO 2 , NaH 2 PO 4 , t-BuOH, 2-Methyl-2-butene   b       35   R = TES   Al(OPr-i) 3 , Acetone, C 6 F 5 OH   b       36   R = TES   CrO 3  (6 eq), 3,5-DMP (6.3 eq), CH 2 Cl 2     b       37   R = TES   Br 2 , HMPA, CH 2 Cl 2     b       38   R = TES   Ca(OCl) 2 , HOAc   b       39   R = Ac   CrO 3  (10 eq), 3,5-DMP (12 eq), CH 2 Cl 2     85%       40   R = Ac   DMSO (12 eq), (COCl) 2  (10 eq), TEA (20 eq), CH 2 Cl 2     b       41   R = Ac   CrO 3 —Pyr 2  (6 eq), CH 2 Cl 2 , RT, 2 days   b       42   R = TES   CrO 3  (10 eq), 1H-Tetrazole (10.2 eq), CH 2 Cl 2     a       43   R = TES   CrO 3  (10 eq), 2-(1H)-Pyridone (10.2 eq), CH 2 Cl 2     b       44   R = Ac   MnO 2  (20 eq), CH 2 Cl 2 , RT, 2 days   b                                    
         [0034]    [0034]                                             TABLE 4                               Weight of           Example   Reagents and Conditions   SM (mg)   Yield %                                45   CrO 3  (20 eq), DMP (22 eq), CH 2 Cl 2 , RT, 2 days   43.2    80-90 (a)       46   CrO 3  (2.7 eq), DMP (2.7 eq), CH 2 Cl 2 , RT, 3 days   20.4   80-90(a)       47   CrO 3  (10 eq), DMP (11 eq) CH 2 Cl 2 , RT, 7 days   250.0   68(b, c)       48   CrO 3  (20 eq), DMP (22 eq), CH 2 Cl 2 , RT, 5 eq CrO 3 -   100.9   80-90(a)           DMP complex added after 1 hr of rxn, 2 days       49   CrO 3  (3 eq), DMP (3 eq), CH 2 Cl 2 , RT, 3 eq CrO 3 -DMP   103.2   80-90(a)           complex added after 23 hrs of rxn, 26 hrs                                                    
         [0035]    [0035]                                             TABLE 5                       Example       Reagents and Conditions   Notes                                50   R = Ac   CH 3 Li (15 eq), THF, −89° C., ca 2 h   a       51   R = Ac   H 2 NNH 2 , H 2 O, 95%EtOH, 13 h   (4) and (5)(b)       52   R = Ac   H 2 NNH 2 , H 2 O, 95%EtOH, 20 h   (4) and (5)(b)       53   R = Ac   n-BuLi (6 eq), THF, −89° C., ca 2 h   (6)(c)       54   R = Ac   H 2 NNH 2 , MeOH, H 2 O, 3 days   (4) and(5)(b)       55   R = Ac   NH 3 , H 2 O, MeOH, H 2 O, 4 days   Decomposed       56   R = Ac   NHMe 2 , MeOH, 1 day   Decomposed       57   R = Ac   NMe 3 , MeOH, H 2 O, 20 h   Decomposed       58   R = Ac   NaHCO 3 , MeOH, 3 days at RT, 3.5 h at 50° C.   Decomposed       59   R = Ac   NHEt 2 , MeOH, H 2 O, ca 20 h   Decomposed       60   R = Ac   H 2 NNHCOPh, MeOH, 2 days at RT, ca 5 h at 50° C.   No reaction       61   R = Ac   DMAP, MeOH, ca 2 days at 50° C.   No reaction       62   R = Ac   NaHCO 3 , H 2 O 2 , THF, 3 days at RT   No reaction       63   R = Ac   H 2 NNH 2 , MeOH, ca 26 h   Complicated       64   R = Ac   n-BuLi (6 eq), THF, −89° C., ca 0.5 h   (6)(c)       65   R = Ac   n-BuLi (6 eq), THF, −40 to −45° C., ca 1 h   (6)(c)       66   R = Ac   n-BuLi (6 eq), CH 2 Cl 2 , −40 to −45° C., ca 5 h   Complicated       67   R = Ac   LiOh, H 2 O 2 , THF, 20 h at RT   (5)(d)       68   R = Ac   sec-BuLi (20 eq), THF, −40 to −45° C., at 0.5, 1 day at rt   No reaction       69   R = Ac   n-BuLi (3 eq), THF, −40 to −45° C., ca 5 h   Complicated       70   R = Ac   n-BuOLi (10 eq), THF, −40 to −45° C., ca 6 h   Complicated       71   R = Ac   H 2 NNH 2 , MeOH, ca 26 h at 50-55° C.   Decomposed       72   R = Ac   LiOH, H 2 O 2 , THF, 20 h at RT   (5)(d)       73   R = Ac   H 2 NNH 2 , THF, ca 26 h at RT   Decomposed       74   R = Ac   H 2 NNH 2 , 95%EtOH, 50-55° C., 24 h   Decomposed       75   R = Ac   n-BuLi (6 eq), THF, −40 to −50° C., ca 0.5 h   (5)(d)                                                    
         [0036]    [0036]                                                     TABLE 6                           Amount of   Reagents                   7.13-DABIII   and               Example   (mg)   Solvent   Conditions   Products (Yield)                                76   9.1   HMH,   room temperature,   a(66.4%)               95% EtOH   25.5 hours   b(27.0%)                       plus 1 by-product       77   1.9 of a   HMH,   room temperature,   starting material               95% EtOH   71 hours       78   15.1   HMH,   room temperature,   a(53.0%)               95% EtOH   72.5 hours   b(18.0%)                       plus 1 by-product       79   2.4   HMH,   45-50° C.,   a(50.0%)               95% EtOH   23.5 hours   b(49.4%)                       plus 1 by-product       80   10.8   DIBAL,   −78° C. -room   b(42.5%)               dry THF   temperature,   c(20.2%)                   22 hours   plus 1 by-product       81   5.8   HMH   room temperature   6.5 mg of crude a               dry THF   30 hours   starting material       82   6.1   Anhydrous   room temperature   7.1 mg of crude a               hydrazine,   30 hours   starting material               dry THF       83   7.0   HMH   room temperature   b(42.0%)               0.75 eq. DMAP,   50 hours   plus 2 by-products               95% EtOH       84   25.0   HMH   room temperature   a(37.0%)               0.5 eq. DMAP   48.5 hours   b(34.9%)               95% EtOH       plus 1 by-product       85   20.6   HMH   40° C., 22 hours   decomposition               0.5 eq. DMAP               95% EtOH       86   19.9   HMH   room temperature   a(17.8%)               0.75 eq. DMAP   69 hours   b(26.6%)               95% EtOH       plus 2 by-products 1,2         87   20.6   HMH   room temperature   a(11.7%)               2.5 eq. DMAP   22 hours   b(22.1%)               95% EtOH       plus 3 by-products 2         88   5.8   HMH   0-−4° C.   7.4 mg crude               2.5 eq. DMAP   334 hours   a(major)               95% EtOH       b(minor)       89   5.8   HMH   room temperature   a(33.5%)               2.5 eq. DMAP   73 hours   b(65.8%)               95% EtOH       plus 1 by-product 2         90   6.4   HMH   room temperature   a(62.5%)               2.5 eq, DMAP   75 hours   b(38.5%)               95% EtOH       plus 1 by-product 2         91   4.7 of b   HMH   room temperature   3.9 mg of crude               2.5 eq. DMAP   187 hours   starting material               95% EtOH       plus 3 other                       products 1,2         92   6.9   HMH   room temperature   a(36.4%)               5 eq. Pyridine   70 hours   b(57.0%)               95% EtOH       plus 1 by-product 2         93   5.7   HMH   7° C., 335 hours   7.6 mg of crude               2.5 eq. DMAP       a(minor)               95% EtOH       b(major)                       plus 2 by-products 1,2         94   3.7   HMH   room temperature   3.5 mg of crude               2.5 eq. Imidazole   70 hours   a(minor)               95% EtOH       b(major)                       plus 2 by-products 1,2         95   3.6   HMH   room temperature   3.6 mg of crude               2.5 eq.   70 hours   a(very minor)               Diisopropylamine       b(major)               95% EtOH       plus 2 by-products 1,2         96   3.3   HMH   room temperature   4.2 mg of crude               2.5 eq collidine   71 hours   starting material               95% EtOH       (very minor)                       a(major)                       b(minor)                       plus 2 by-products 1,2         97   3.5   HMH   room temperature   3.7 mg of crude               2.5 eq TEA   71 hours   starting material               95% EtOH       (very minor)                       a(major)                       b(minor)                       plus 2 by-products                       (major) 1,2         98   3.3   HMH   room temperature   3.9 mg of crude               2.5 eq.   71.5 hours   starting               N-methylmorpholine       material (minor)               95% EtOH       a(major)                       b(major)                       plus 2 by-products 1,2         99   3.8   HMH   room temperature   4.3 mg of crude               2.5 eq   72 hours   starting               3-Quinuclidinol       material (major)               95% EtOH       a(major)                       b(minor)                       plus 1 by-product 1         100   2.7   HMH   room temperature   2.7 mg of crude               2.5 eq. Imidazole   23.5 hours   a(minor)               95% EtOH       b(major)                       plus 1 by-product                       (major) 2         101   2.7   HMH   room temperature   3.7 mg of crude               2.5 eq.   23 hours   a(minor)               Diisopropylamine       b(major)               95% EtOH       plus 2 by-products                       (major) 2         102   3.7   HMH   room temperature   4.1 mg of crude               2.5 eq   25 hours   a(minor)               Diisopropylamine       b(major)               acetonitrile       plus 3 by-products 1,2         103   3.4   HMH   room temperature   3.6 mg of crude               2.5 eq.   25 hours   a(minor)               Diisopropylamine       b(major)               DMG       plus 3 by-products 1,2         104   3.7   HMH   room temperature   4.8 mg of crude               2.5 eq.   25.5 hours   a(minor)               Diisopropylamine       b(major)               DMSO       plus 3 by-products 1,2         105   3.6   HMH   room temperature   5.0 mg of crude               2.5 eq   25.5 hours   a(minor)               Diisopropylamine       b(major)               HMPA       plus 3 by-products 1,2         106   4.5   HMH   room temperature   4.8 mg of crude b               2.5 eq   197 hours   plus 3 by-products               Diisopropylamine               MEOH       107   3.6   HMH   room temperature   4.2 mg of crude b               2.5 eq   197 hours   plus 3 by-products               Diisopropylamine               iso-Butanol       108   4.5   HMH   7° C., 141.5 hours   4.2 mg of crude               2.5 eq DMAP       virtually no a               95% EtOH       b(major)                       plus 2 by-products                       (minor)       109   5.0   HMH   7° C., 141.5 hours   5.4 mg of crude               2.5 eq.       virtually no a               Imidazole       b(major)               95% EtOH       plus 2 by-products                       (minor)       110   4.7   HMH   7° C., 142 hours   4.2 mg of crude               2.5 eq       virtually no a               Diisopropylamine       b(major)               95% EtOH       plus 2 by-products                       (minor)       111   4.5   HMH   4° C., 42 hours   a               2.5 eq. DMAP       b               95% EtOH       112   4.7   HMH   4° C., 42 hours   a               2.5 eq.       b               Imidazole               95% EtOH