Process for the preparation of 17-desoxy-corticosteroids

Abstract

The present invention provides an improved process for the preparation of 17-desoxy corticosteroid derivatives in a single chemical step by reacting the 17-hydroxy starting material with an excess of Trimethylsilyl Iodide. The present invention is specifically advantageous in preparing 17-desoxy corticosteroid derivatives having one or more halogen groups at positions 2, 6, 7 or 9 of the corticosteroid such as Clocortolone of Desoximetasone.

What is claimed is: 
     
         1 . A process for preparing a compound of Formula I 
       
         
           
           
               
               
           
         
       
       in which R 1  is OH and R 2  is H, or R 1  and R 2  form together a double bond with O, R 3  is H and R 4  is CH 3 , or R 3  is CH 3  and R 4  is H, and wherein at least one of X 1-5  is independently Cl, Br or F, comprising the steps of:
 (a) reacting a compound of the formula II 
 
       
         
           
           
               
               
           
         
       
       in which R 1 -R 4  and X 1-5  are as defined in Formula I with Trimethylsilyl Iodide in a solution comprising an aprotic solvent, wherein the molar ratio between Trimethylsilyl Iodide and the compound of Formula II is between about 2:1 to about 10:1;
 (b) quenching the reaction of step (a); 
 (c) extracting the compound of Formula I from the solution of step (b) using a first organic solvent to yield an organic layer comprising the compound of Formula I; and 
 (d) isolating the compound of Formula I from the organic layer of step (c). 
 
     
     
         2 . The process of  claim 1 , wherein the aprotic solvent of step (a) is methylene chloride or acetonitrile or a combination thereof. 
     
     
         3 . The process of  claim 1 , wherein the compound of formula II is selected from Flumetasone, Dexametasone, Paramethasone, 9-Chloro-6α-fluoro-11,17,21-trihydroxy-16α-methylpregna-1,4-diene-3,20-dione, Halopredone and Alclometasone. 
     
     
         4 . The process of  claim 1 , wherein the molar ratio between Trimethylsilyl Iodide and the compound of Formula II is between about 2:1 to about 6:1. 
     
     
         5 . The process of  claim 1 , wherein the reaction temperature employed in step (a) is in the range from between about −30° C. and about +30° C. 
     
     
         6 . The process of  claim 1 , wherein the compound of Formula I is selected from Diflucortolone, Desoximetasone, Clocortolone, Fluocortolone, 7α-Chloro-11β,21-dihydroxy-16α-methylpregna-1,4-diene-3,20-dione and 2-Bromo-6β,9-difluoro-11,21-dihydroxypregna-1,4-diene-3,20-dione. 
     
     
         7 . The process of  claim 1 , wherein the quenching of step (b) is performed by adding to the reaction solution of step (a) a solution of sodium thiosulfate or bisulfate. 
     
     
         8 . The process of  claim 1 , wherein the first organic solvent of step (c) is selected from ethyl acetate and toluene. 
     
     
         9 . The process of  claim 1 , wherein the isolation of the compound of Formula I in step (d) includes evaporation or filtration. 
     
     
         10 . The process of  claim 1 , wherein the solution of step (a) further comprises between about 0.05% to about 0.5% (v/v) of a polar protic co-solvent. 
     
     
         11 . The process of  claim 10 , wherein the polar protic co-solvent is selected from water and a C 1 -C 4 -alcohol. 
     
     
         12 . The process of  claim 1 , wherein R 1  is OH, R 4  which is CH 3 , X 1  which is C 1  and X 2  which is F. 
     
     
         13 . The process of  claim 1 , wherein R 1  is OH, R 4  which is CH 3  and X 1  which is F. 
     
     
         14 . A method of preparing Clocortolone having the structure of Formula III 
       
         
           
           
               
               
           
         
       
       comprising the steps of
 a) reacting a 17-hydroxy epoxide of Formula IV 
 
       
         
           
           
               
               
           
         
       
       with a stereo-selective fluorinating agent to stereo-selectively form a 17-hydroxy epoxide 6α-fluorinated compound of Formula V 
       
         
           
           
               
               
           
         
       
       wherein R′ and R 2  are OC(O)—Rd, wherein each Rd may be the same or different and is independently selected from (C 1-4 ) alkyl;
 b) hydrolyzing the compound of formula V with an alkaline carbonate in a first organic solvent to form a compound of formula VI; 
 
       
         
           
           
               
               
           
         
         c) opening the epoxide of the compound of formula VI by a reaction with hydrogen chloride to form a compound of formula VII; 
       
       
         
           
           
               
               
           
         
         d) reacting the compound of formula VII with Trimethylsilyl Iodide in the presence of an aprotic solvent, wherein the molar ratio between Trimethylsilyl Iodide and the compound of Formula VII is between about 2:1 to about 10:1, to form a compound of formula III; and 
         e) quenching the reaction of step (d) and isolating the compound of Formula III. 
       
     
     
         15 . The method of  claim 14 , wherein the (C 1-4 ) alkyl is CH 3 . 
     
     
         16 . The method of  claim 14 , wherein the stereo-selective fluorinating agent of step (a) is selected from fluoropyridinium compounds and fluoroquinuclidium compounds. 
     
     
         17 . The method of  claim 16 , wherein the stereo-selective fluorinating agent is selected from the group consisting of 1-fluoropyridinium triflate, 1-fluoropyridinium tetrafluoroborate, and 1-fluoropyridinium pyridine heptafluorodiborate. 
     
     
         18 . The method of  claim 17 , wherein the stereo-selective fluorinating agent is 1-chloromethyl-4-fluoro-1,4-diazoniabicyclol[2.2.2]octane bis-(tetrafluoroborate) (Selectfluor®). 
     
     
         19 . The method of  claim 15 , further comprising generating the 21-ester 17-hydroxy epoxide of Formula IV by (a) reacting a compound having the formula VIII 
       
         
           
           
               
               
           
         
       
       with an acetylating agent in the presence of a weak base and a polar solvent to form the compound of formula IX; 
       
         
           
           
               
               
           
         
       
       and
 (b) reacting the compound of formula IX with isopropenyl acetate to form the compound of Formula X 
 
       
         
           
           
               
               
           
         
       
     
     
         20 . The method of  claim 19 , wherein the acetylating agent is acetic anhydride or acetyl chloride, the weak base is sodium acetate or potassium acetate and the polar solvent is dimethylacetamide or dimethylformamide. 
     
     
         21 . The method of  claim 14 , wherein the reaction of step (a) is conducted in the presence of a solvent selected from the group consisting of acetonitrile and dichloromethane. 
     
     
         22 . The method of  claim 21 , wherein the reaction of step (a) is conducted in the presence of acetonitrile. 
     
     
         23 . The method of  claim 14 , wherein the reaction of step (a) is conducted at room temperature. 
     
     
         24 . The method of  claim 14 , wherein the alkaline carbonate of step (b) is potassium or sodium carbonate. 
     
     
         25 . The method of  claim 14 , wherein the first organic solvent of step (b) is a C 1 -C 3  alcohol. 
     
     
         26 . The method of  claim 14 , wherein the aprotic solvent of step (d) is methylene chloride or acetonitrile or a combination thereof. 
     
     
         27 . The method of  claim 14 , wherein the quenching of step (e) is performed by the addition of a solution of sodium thiosulfate or bisulfate to the reaction of step (d). 
     
     
         28 . The method of  claim 14 , further comprising extracting the compound of Formula III from the reaction of step (e) using a second organic solvent to yield an organic layer comprising the compound of Formula III. 
     
     
         29 . The method of  claim 28 , wherein the second organic solvent is selected from ethyl acetate and toluene. 
     
     
         30 . The method of  claim 14 , wherein the isolation of the compound of Formula III includes evaporation or filtration. 
     
     
         31 . The method of  claim 14 , further comprising reacting the compound of Formula III with Pyvaloyl Chloride in the presence of an organic base and a third organic solvent to form the compound of formula XI 
       
         
           
           
               
               
           
         
       
     
     
         32 . The method of  claim 31 , wherein the organic base is N,N-Dimethylaminopyridine. 
     
     
         33 . The method of  claim 31 , wherein the third organic solvent is methylene chloride.