Anhydrous and hemihydrate crystalline forms of an (

1. Crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate, which exhibits characteristic scattering angles (2θ) at least at 4.04°±0.2°, 6.47°±0.2°, 15.68°±0.2°, 18.91°±0.2° and 22.42°±0.2° in an X-ray powder diffractogram measured using Cu—K α radiation.

2. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , comprising characteristic scattering angles (2θ) at least at 9.46°±0.2°, 10.10°±0.2°, 10.87°±0.2°, 12.88°±0.2°, 19.96°±0.2°, 20.23°±0.2°, 28.07°±0.2° and 28.53°±0.2° in an X-ray powder diffractogram measured using Cu—K α radiation.

3. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , comprising characteristic scattering angles (2θ) at least at 7.97°±0.2°, 9.46°±0.2°, 10.10°±0.2°, 10.87°±0.2°, 12.88°±0.2°, 16.72°±0.2°, 18.16°±0.2°, 19.33°±0.2°, 19.96°±0.2°, 20.23°±0.2°, 20.62°±0.2°, 21.76°±0.2°, 23.55°±0.2°, 24.02°±0.2°, 25.13°±0.2°, 25.61°±0.2°, 26.09°±0.2°, 28.07°±0.2°, 28.53°±0.2°, 29.87°±0.2°, 30.45°±0.2°, 30.74°±0.2°, 31.52°±0.2°, 32.60°±0.2°, 35.94°±0.2° and 36.63°±0.2° in an X-ray powder diffractogram measured using Cu—K α radiation.

4. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , comprising the characteristic scattering angles (2θ) in an X-ray powder diffractogram measured using Cu—K α radiation shown in FIG. 1 .

5. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , comprising from about 2 wt % water to about 3 wt % water.

6. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , which exhibits a first phase transition at a temperature of from about 90° C. to about 110° C., and a second phase transition at a temperature of from about 105° C. to about 125° C. using differential scanning calorimetry at a heating rate of 20 K/min.

7. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 6 , which loses about 2.1% of its total weight in the first phase transition.

8. The crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 , wherein the first phase transition occurs at 100° C., and the second phase transition occurs at 115° C.

9. A pharmaceutical composition comprising the crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate of claim 1 and a pharmaceutically acceptable vehicle.

10. The pharmaceutical composition of claim 9 , wherein the pharmaceutical composition is a sustained release oral dosage formulation.

11. A method of treating a disease or disorder in a patient comprising administering to a patient in need of such treatment a therapeutically effective amount of the pharmaceutical composition of claim 9 , wherein the disease or disorder is selected from spasticity, gastroesophageal reflux disease, emesis, cough, substance addiction and abuse, neuropathic pain and musculoskeletal pain.

12. The method of claim 11 , wherein the pharmaceutical composition is a sustained release oral dosage formulation.

13. A kit comprising the pharmaceutical composition of claim 9 and instructions for administering the pharmaceutical composition to a patient in need thereof for treating a disease or disorder selected from spasticity, gastroesophageal reflux disease, emesis, cough, substance addiction and abuse, neuropathic pain and musculoskeletal pain.

14. A method of making crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid anhydrate, comprising:

a) forming a solution of diastereomers comprising (i) (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid and (ii) (3R)-4-{[(1R)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid;

b) selectively crystallizing the (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid diastereomer as a hemihydrate; and

c) separating the crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate diastereomer from the solution.

15. The method of claim 14 , comprising converting the crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate into crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid anhydrate.

16. The method of claim 14 , wherein the diastereomers are in aqueous solution.

17. The method of claim 14 , wherein the solution comprises solvent in an amount ranging from about 20 v/v % to about 50 v/v % and water in an amount ranging from about 50 v/v % to about 80 v/v %.

18. The method of claim 17 , wherein the solvent is selected from methyl tert-butyl ether, acetonitrile, toluene, chlorobenzene, methylcyclohexane, heptane, methanol, ethanol, diethyl ether, tetrahydrofuran, tert-amyl methyl ether and combinations of the foregoing.

19. The method of claim 15 , wherein the converting comprises drying the crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate.

20. The method of claim 15 , wherein the converting comprises recrystallizing the crystalline (3R)-4-{[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino}-3-(4-chlorophenyl)butanoic acid hemihydrate.