Method of preparing carboxylic acid functionalized polymers

Abstract

Methods for preparing water soluble, non-peptidic polymers carrying carboxyl functional groups, particularly carboxylic acid functionalized poly(ethylene glycol) (PEG) polymers, are disclosed, as are the products of these methods. In general, an ester reagent R(C═O)OR′, where R′ is a tertiary group and R comprises a functional group X, is reacted with a water soluble, non-peptidic polymer POLY-Y, where Y is a functional group which reacts with X to form a covalent bond, to form a tertiary ester of the polymer, which is then treated with a strong base in aqueous solution, to form a carboxylate salt of the polymer. Typically, this carboxylate salt is then treated with an inorganic acid in aqueous solution, to convert the carboxylate salt to a carboxylic acid, thereby forming a carboxylic acid functionalized polymer.

1 . A method for preparing a water soluble, non-peptidic polymer functionalized with a carboxyl group, the method comprising: 
 i) reacting an ester reagent R(C═O)OR′, where R′ is a tertiary group and R comprises a functional group X, with a water soluble, non-peptidic polymer POLY-Y, where Y is a functional group which reacts with X to form a covalent bond, to form a tertiary ester of the polymer; and    ii) treating the tertiary ester of the polymer with a strong base in aqueous solution, to form a carboxylate salt of the polymer.    
     
     
         2 . The method of  claim 1 , further comprising 
 iii) treating the carboxylate salt of the polymer with an inorganic acid in aqueous solution, to convert the carboxylate salt to a carboxylic acid, thereby forming a carboxylic acid functionalized polymer.    
     
     
         3 . The method of  claim 1 , wherein X is a leaving group and Y is a hydroxyl group.  
     
     
         4 . The method of  claim 1 , wherein said strong base is an alkali metal hydroxide.  
     
     
         5 . The method of  claim 1 , wherein said treating with strong base is effective to produce a reaction pH of about 11 to 13.  
     
     
         6 . The method of  claim 2 , wherein said inorganic acid is an acid that produces non-nucleophilic anions in aqueous solution.  
     
     
         7 . The method of  claim 6 , wherein the acid is selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid.  
     
     
         8 . The method of  claim 1 , wherein the tertiary ester reagent has the structure:  
       
         
           
           
               
               
           
         
       
       wherein: 
 X is a leaving group,  
 each of R 1  and R 2  is independently selected from hydrogen, alkyl, cycloalkyl, alkoxy, aryl, aralkyl, and heterocycle;  
 each of R 3 -R 5  is independently selected from lower alkyl, aryl, aralkyl, and cycloalkyl, where any of R 3 -R 5  may be linked to form a ring or ring system;  
 where any of R 1  to R 5 , excepting hydrogen, may be substituted with a group selected from lower alkyl, lower alkoxy, C 3 -C 6  cycloalkyl, halo, cyano, oxo(keto), nitro, and phenyl; and  
 n is 1 to about 24.  
 
     
     
         9 . The method of  claim 8 , wherein n is 1 to 6.  
     
     
         10 . The method of  claim 9 , wherein n is 1 or 2.  
     
     
         11 . The method of  claim 10 , wherein each of R 1  and R 2  is independently hydrogen or unsubstituted lower alkyl, and each of R 3  to R 5  is independently unsubstituted lower alkyl or phenyl.  
     
     
         12 . The method of  claim 11 , wherein each of R 1  and R 2  is independently hydrogen or methyl, and each of R 3  to R 5  is independently methyl, ethyl, or phenyl.  
     
     
         13 . The method of  claim 12 , wherein each of R 1  and R 2  is H and n is 1.  
     
     
         14 . The method of  claim 13 , wherein the tertiary ester reagent is a t-butyl haloacetate.  
     
     
         15 . The method of  claim 1 , wherein the polymer is selected from the group consisting of poly(alkylene glycols), poly(olefinic alcohol), poly(vinylpyrrolidone), poly(hydroxyalkylmethacrylamide), poly(hydroxyalkylmethacrylate), poly(saccharides), poly(α-hydroxyacetic acid), poly(acrylic acid), poly(vinyl alcohol), polyphosphazene, polyoxazolines, poly(N-acryloylmorpholine), and copolymers or terpolymers thereof.  
     
     
         16 . The method of  claim 15 , wherein the polymer is a poly(ethylene glycol).  
     
     
         17 . The method of  claim 16 , wherein the poly(ethylene glycol) is linear and is terminated at one end with said functional group Y and at the other end with another functional group Y′ or a capping group.  
     
     
         18 . The method of  claim 2 , further comprising converting the carboxylic acid to an activated carboxylic acid derivative.  
     
     
         19 . The method of  claim 18 , wherein said derivative is an activated ester.  
     
     
         20 . The method of  claim 18 , further comprising conjugating said polymer with a biologically active molecule, by reacting said carboxylic acid derivative with a functional group on said molecule.  
     
     
         21 . The method of  claim 20 , wherein the carboxylic acid derivative is an activated ester, and the functional group on said molecule is a nucleophilic group.  
     
     
         22 . The method of  claim 21 , wherein said nucleophilic group is an amino group, a hydroxyl group, or a thiol.  
     
     
         23 . A method for preparing a poly(ethylene glycol) (PEG) functionalized with a carboxyl group, the method comprising: 
 i) reacting a tertiary ester reagent R(C═O)OR′, where R′ is a tertiary alkyl group and R comprises a functional group X, with a polymer PEG-Y, where Y is a functional group which reacts with X to form a covalent bond, to form a PEG tertiary ester; and    ii) treating the PEG tertiary ester with a strong base in aqueous solution, to form a PEG carboxylate salt.    
     
     
         24 . The method of  claim 23 , further comprising 
 iii) treating the PEG carboxylate salt with an inorganic acid in aqueous solution, to convert the carboxylate salt to a carboxylic acid, thereby forming a PEG carboxylic acid.    
     
     
         25 . The method of  claim 23 , wherein X is a leaving group and Y is a hydroxyl group.  
     
     
         26 . The method of  claim 23 , wherein said strong base is an alkali metal hydroxide.  
     
     
         27 . The method of  claim 24 , wherein the acid is selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid.  
     
     
         28 . The method of  claim 23 , wherein the tertiary ester reagent has the structure:  
       
         
           
           
               
               
           
         
       
       wherein: 
 X is a leaving group;  
 each of R 1  and R 2  is independently selected from hydrogen, alkyl, cycloalkyl, alkoxy, aryl, aralkyl, and heterocycle;  
 each of R 3 -R 5  is independently selected from lower alkyl, aryl, aralkyl, and cycloalkyl, where any of R 3 -R 5  may be linked to form a ring or ring system;  
 where any of R 1  to R 5 , excepting hydrogen, may be substituted with a group selected from lower alkyl, lower alkoxy, C3-C6 cycloalkyl, halo, cyano, oxo(keto), nitro, and phenyl; and  
 n is 1 to about 24.  
 
     
     
         29 . The method of  claim 28 , wherein n is 1 to 6.  
     
     
         30 . The method of  claim 29 , wherein n is 1 or 2.  
     
     
         31 . The method of  claim 28 , wherein each of R 1  and R 2  is independently hydrogen or unsubstituted lower alkyl, and each of R 3  to R 5  is independently unsubstituted lower alkyl or phenyl.  
     
     
         32 . The method of  claim 28 , wherein each of R 1  and R 2  is H and n is 1.  
     
     
         33 . The method of  claim 32 , wherein the tertiary ester reagent is a t-butyl haloacetate.  
     
     
         34 . The method of  claim 23 , wherein the poly(ethylene glycol) is linear and is terminated at one end with said functional group Y and at the other end with another functional group Y′ or a capping group.  
     
     
         35 . The method of  claim 23 , wherein the PEG has a molecular weight of about 100 to about 100,000 Da.  
     
     
         36 . The method of  claim 35 , wherein the PEG has a molecular weight of about 300 to about 60,000 Da.  
     
     
         37 . The method of  claim 24 , further comprising converting the PEG-carboxylic acid to an activated carboxylic acid derivative.  
     
     
         38 . The method of  claim 37 , wherein said derivative is an activated ester.  
     
     
         39 . The method of  claim 37 , further comprising conjugating said PEG with a biologically active molecule, by reacting said carboxylic acid derivative with a functional group on said molecule.  
     
     
         40 . An isolated polymer product comprising a carboxylic acid functionalized polymer, made by the method of  claim 2 , 
 wherein the product contains less than 5% by weight of said POLY-Y polymer, with the balance consisting essentially of said carboxylic acid functionalized polymer.    
     
     
         41 . The polymer product of  claim 40 , containing less than 2% by weight of said POLY-Y polymer.  
     
     
         42 . The polymer product of  claim 40 , containing less than 0.5% by weight of said POLY-Y polymer.  
     
     
         43 . The polymer product of  claim 40 , containing substantially no amount of low molecular weight organic acid.  
     
     
         44 . The polymer product of  claim 40 , containing substantially no amount of monomeric organic carboxylic acid.  
     
     
         45 . The polymer product of  claim 40 , containing substantially no amount of trifluoroacetic acid.  
     
     
         46 . The polymer product of  claim 40 , wherein said carboxylic acid functionalized polymer is a PEG carboxylic acid.  
     
     
         47 . The polymer product of  claim 46 , wherein said carboxylic acid functionalized polymer is mPEG-CH 2 —COOH, and said polymer product contains less than 5% by weight of mPEG-OH.  
     
     
         48 . The polymer product of  claim 47 , containing less than 2% by weight of mPEG-OH.  
     
     
         49 . The polymer product of  claim 48 , containing less than 0.5% by weight of mPEG-OH.  
     
     
         50 . The polymer product of  claim 49 , containing substantially no amount of trifluoroacetic acid.  
     
     
         51 . The polymer product of  claim 46 , wherein said carboxylic acid functionalized polymer is HOOC—CH 2 —PEG-CH 2 —COOH, and said product contains less than 5% by weight of HO-PEG-OH.  
     
     
         52 . The polymer product of  claim 51 , containing less than 0.5% by weight of HO-PEG-OH.  
     
     
         53 . The polymer product of  claim 52 , containing substantially no amount of trifluoroacetic acid.  
     
     
         54 . The polymer product of  claim 46 , wherein said carboxylic acid functionalized polymer is a multifunctional branched or multiarm carboxylic acid functionalized PEG represented by PEG-(CH 2 —COOH) x , where x is 3 to 8, and said product contains less than 5% by weight of PEG-(OH) x .  
     
     
         55 . The polymer product of  claim 54 , containing substantially no amount of trifluoroacetic acid.  
     
     
         56 . In a method of preparing a poly(ethylene glycol) (PEG)polymer functionalized with a carboxyl group, by reaction of a tertiary ester reagent R(C═O)OR′, where R′ is a tertiary alkyl group and R comprises a functional group X, with a polymer PEG-Y, where Y is a functional group which reacts with X to form a covalent bond, to form a PEG tertiary ester, 
 an improvement comprising:    treating the PEG tertiary ester with a strong base in aqueous solution, to form a PEG carboxylate salt.    
     
     
         57 . The improvement of  claim 56 , wherein the method further comprises 
 treating the PEG carboxylate salt with an inorganic acid in aqueous solution, to convert the carboxylate salt to a carboxylic acid, thereby forming a PEG carboxylic acid.    
     
     
         58 . The improvement of  claim 56 , wherein said strong base is an alkali metal hydroxide.  
     
     
         59 . The improvement of  claim 56 , wherein said treating with strong base is effective to produce a reaction pH of about 11 to 13.  
     
     
         60 . The improvement of  claim 57 , wherein the acid is selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid.