Methods for synthesizing and purifying aminoalkyl tetracycline compounds

Abstract

Methods for the synthesis and purification of 9-amino alkyl tetracycline compounds are described.

1 . A method of purifying an alkylaminomethyl minocycline compound, comprising:
 a) injecting a low pH aqueous solution of said alkylaminomethyl minocycline compound into a liquid chromatography device in a polar organic solvent gradient, and combining the product fractions;   b) adjusting the pH of said product fractions to 4.0-4.5;   c) washing said product fractions with a first non-polar organic solvent to form a first organic layer and a first aqueous layer, and discarding said first organic layer;   d) adjusting the pH of said first aqueous layer to 7.5-8.5; and   e) washing said first aqueous layer with a second non-polar organic solvent to form a second organic layer and a second aqueous layer, and discarding said second aqueous layer,   such that said alkylaminomethyl minocycline compound is purified.   
   
   
       2 . The method of  claim 1 , wherein said low pH aqueous solution has a pH of 2-3. 
   
   
       3 . The method of  claim 1 , wherein said low pH aqueous solution comprises methyl sulfonic acid. 
   
   
       4 . The method of  claim 1 , wherein said polar organic solvent is acetonitrile. 
   
   
       5 . The method of  claim 1 , wherein said pH in step b) or d) is adjusted with a base. 
   
   
       6 . The method of  claim 5 , wherein said base is selected from the group consisting of metal hydroxide, metal carbonate, metal bicarbonate, ammonia, organic primary amine, organic secondary amine and organic tertiary amine 
   
   
       7 . The method of  claim 6 , and wherein said metal is selected from the group consisting of lithium, sodium, potassium, calcium, magnesium and aluminum. 
   
   
       8 . The method of  claim 6 , wherein said base is sodium hydroxide or ammonia. 
   
   
       9 . The method of  claim 1 , wherein said first non-polar organic solvent is methylene chloride. 
   
   
       10 . The method of  claim 1 , wherein said first organic layer comprises by-products, hydrophobic impurities and oxidative degradents of said alkylaminomethyl minocycline compound. 
   
   
       11 . The method of  claim 1 , wherein said second non-polar organic solvent is methylene chloride. 
   
   
       12 . The method of  claim 1 , wherein said second aqueous layer comprises by-products and β epimer of said alkylaminomethyl minocycline compound. 
   
   
       13 . The method of  claim 1 , wherein an antioxidant is added. 
   
   
       14 . The method of  claim 13 , wherein said antioxidant is ammonium sulfite, sodium sulfite, bisulfite or meta bisulfite. 
   
   
       15 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound is: 
     
       
         
         
             
             
         
       
       wherein R A  is alkyl, and R B  is hydrogen or alkyl. 
     
   
   
       16 . The method of  claim 15 , wherein R B  is hydrogen. 
   
   
       17 . The method of  claim 16 , wherein R A  is alkyl. 
   
   
       18 . The method of  claim 17 , wherein said alkyl is (CH 3 ) 3 CCH 2 —. 
   
   
       19 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound is: 
     
       
         
         
             
             
         
       
     
   
   
       20 . The method of  claim 1 , wherein hydrophobic impurities and oxidative degradents are removed from said alkylaminomethyl minocycline compound. 
   
   
       21 . The method of  claim 1 , wherein by-products and β-C-4 epimer are removed from said alkylaminomethyl minocycline compound. 
   
   
       22 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound is essentially free of hydrophobic impurities and oxidative degradents. 
   
   
       23 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound is essentially free of by-products, β-C-4 epimer, hydrophobic impurities and oxidative degradents. 
   
   
       24 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound comprises at least 50% α-C-4 epimer. 
   
   
       25 . The method of  claim 24 , wherein said alkylaminomethyl minocycline compound comprises at least 95% α-C-4 epimer. 
   
   
       26 . The method of  claim 25 , wherein said alkylaminomethyl minocycline compound comprises at least 99.9% α-C-4 epimer. 
   
   
       27 . The method of  claim 1 , wherein said alkylaminomethyl minocycline compound comprises less than 7% β-C-4 epimer. 
   
   
       28 . The method of  claim 27 , wherein said alkylaminomethyl minocycline compound comprises less than 3% β-C-4 epimer. 
   
   
       29 . A pharmaceutical composition comprising alkylaminomethyl minocycline compound purified by the method of  claim 1  and a pharmaceutically acceptable carrier.