Resolution of α-(phenoxy)phenylacetic acid derivatives

1. A process for enantioselectively producing a α-(phenoxy)phenylacetate compound of the formula:

said method comprising:

(a) resolving an enantiomeric mixture of a α-(phenoxy)phenylacetic acid of the formula:

using an enantiomerically enriched chiral amine compound;

to produce an enantiomerically enriched α-(phenoxy)phenylacetic acid, wherein the total amount of enantiomerically enriched chiral amine compound used is less than 0.5 molar equivalents with respect to the α-(phenoxy)phenylacetic acid compound;

(b) producing an enantiomerically enriched activated α-(phenoxy)phenylacetic acid derivative by contacting the enantiomerically enriched α-(phenoxy)phenylacetic acid with a carboxylic acid activating reagent; and

(c) contacting the enantiomerically enriched activated α-(phenoxy)phenyl-acetic acid derivative with a compound of the formula (R 7 −O) w M to produce the α-(phenoxy)phenyl-acetate compound,

wherein

R 1 is alkyl or haloalkyl;

X is halide;

R 7 is heteroalkyl;

M is hydrogen or a metal; and

the subscript w is the oxidation state of M.

2. The method of claim 1 , wherein the α-(phenoxy)phenylacetate compound is (−)-halofenate.

3. The method of claim 1 , wherein said step (a) resolving the enantiomeric mixture of the α-(phenoxy)phenylacetic acid comprises:

(a) producing a crystallization solution mixture comprising a solid enantiomerically enriched acid-base salt of a first enantiomer by contacting the enantiomeric mixture of the α-(phenoxy)phenylacetic acid compound with the enantiomerically enriched chiral amine compound under conditions sufficient to produce the ratio of the amount of first enantiomer to the amount of the second enantiomer in the salt is at least about 3:1, wherein the total amount of enantiomerically enriched chiral amine compound used is less than 0.5 molar euuivalents with respect to the α-(phenoxy)phenylacetic acid compound, and

(b) separating the solid acid-base salt of the first enantiomer from the solution mixture at a temperature where the concentration of an acid-base salt of the second enantiomer of the α-(phenoxy)phenylacetic acid compound is near or below its saturation point.

4. The method of claim 3 , wherein said step (a) of producing the crystallization solution mixture comprising the solid enantiomerically enriched acid-base salt of the first enantiomer comprises:

(i) heating the solution mixture to a temperature above the nucleation temperature of a first enantiomer; and

(ii) subsequently lowering the solution mixture temperature to a temperature at or below the nucleation temperature of the first enantiomer to an enantiomerically enriched α-(phenoxy)phenylacetic acid.

5. The method of claim 3 , wherein said step (b) of separating the solid acid-base salt of the first enantiomer is conducted at a temperature near or above a saturation temperature of an acid-base salt of the second enantiomer.

6. The method of claim 1 further comprising recovering the chiral amine compound by removing the chiral amine compound from the separated solid acid-base salt of the first enantiomer.

7. The method of claim 6 , wherein the enantiomerically enriched chiral amine compound used in producing the acid-base salt of said step (a) comprises the recovered chiral amine compound.

8. The method of claim 1 further comprising racemizing at least a portion of the second enantiomer in the separated solution mixture by contacting the second enantiomer with a base.

9. The method of claim 8 , wherein the enantiomeric mixture of the α-(phenoxy)phenylacetic acid compound used in said step (a) comprises a racemized α-(phenoxy)phenylacetic acid compound.

10. The method of claim 1 , wherein the chiral amine compound is of the formula:

wherein

each of R 2 and R 3 is independently hydrogen or alkyl; or R 2 and R 3 together with atoms to which they are attached to form a heterocyclic ring moiety;

R 4 is hydrogen or alkyl;

each of R 5 and R 6 is independently hydrogen or alkyl, or one of R 5 or R 6 is an amine protecting group; and

Ar is aryl.

11. The method of claim 1 , wherein the α-(phenoxy)phenylacetic acid is an enantiomeric mixture of 4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid, said method comprising:

(a) producing a crystallization solution mixture comprising an enantiomerically enriched acid-base salt of (−)-4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid by contacting the enantiomeric mixture of 4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid with less than 0.5 molar equivalent of an enantiomerically enriched (1R,2R)-2-amino- 1 -(4-nitrophenyl)- 1,3-propanediol in about 4 grams of an alcoholic solvent per gram of (−)-4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid;

(b) separating the enantiomerically enriched acid-base salt from the solution mixture which is enriched with (+)-4-chloro- α-(3-trifluoromethylphenoxy)phenylacetic acid; and

(c) removing (1R,2R)-2-amino- 1 -(4-nitrophenyl)- 1 ,3-propanediol from the acid-base salt to produce enantiomerically enriched (−)-4-chloro-α-(3-trifluoromethyl-phenoxy)phenylacetic acid.

12. The method of claim 11 , wherein the alcoholic solvent is isopropanol.

13. The method of claim 12 , wherein about 0.47 molar equivalent or less of(1R,2R)-2-amino-1-(4-nitrophenyl)-1,3-propanediol is used to form the acid-base salt.

14. The method of claim 13 , wherein said step (a) of producing a solution mixture comprising an enantiomerically enriched acid-base salt of (−)-4-chioro-α-(3-trifluoromethyl-phenoxy)phenylacetic acid comprises heating the solution mixture to a temperature at or above a nucleation temperature of the (−)-acid-base salt.

15. The method of claim 14 , wherein said step (b) of separating the enantiomerically enriched acid-base salt is performed at a temperature near or above a saturation temperature of an acid-base salt of the (+)-enantiomer.

16. The method of claim 12 , wherein the enantiomerically enriched (1R,2R)-2-amino- 1-(4-nitrophenyl)- 1,3-propanediol comprises at least a portion of (1R,2R)-2-amino- 1-(4-nitrophenyl)- 1,3-propanediol that is removed from the acid-base salt of said step (c).

17. The method of claim 12 further comprising racemizing at least a portion of (+)-4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid obtained in said step (b).

18. The method of claim 17 , wherein the enantiomeric mixture of 4-chloro-α-(3 -trifluoromethylphenoxy)phenylacetic acid comprises at least a portion of(+)-4-chloro-α-(3-trifluoromethylphenoxy)phenylacetic acid that is racemized.