Patent ID: 8609865

Claim:
A method of preparing a crystalline zwitterion of 5-({[2-amino-3-(4-carbamoyl-2,6-dimethyl-phenyl)-propionyl]-[1-(4-phenyl-1H-imidazol-2-yl)-ethyl]-amino}-methyl)-2-methoxy-benzoic acid comprising the steps of: combining a strong ionizable acid with 5-({[2-tert-butoxycarbonylamino-3-(4-carbamoyl-2,6-dimethyl-phenyl)-propionyl]-[1-(4-phenyl-1 H-imidazol-2-yl)-ethyl]-amino}-methyl)-2-methoxy-benzoic acid to prepare a salt of 5-({[2-amino-3-(4-carbamoyl-2,6-dimethyl-phenyl)-propionyl]-[1-(4-phenyl-1 H-imidazol-2-yl)-ethyl]-amino}-methyl)-2-methoxy-benzoic acid; washing said salt of 5-({[2-amino-3-(4-carbamoyl-2,6-dimethyl-phenyl)-propionyl]-[1-(4-phenyl-1H-imidazol-2-yl)-ethyl]-amino }-methyl)-2-methoxy-benzoic acid with an inorganic base to obtain the zwitterion of 5-({[2-amino-3-(4-carbamoyl-2,6-dimethyl-phenyl)-propionyl]-[1-(4-phenyl-1H-imidazol-2-yl)-ethyl]-amino}-methyl)-2-methoxy-benzoic acid; and crystallizing the zwitterion wherein the crystallizing comprises storing the zwitterion at a relative humidity of between about 0 to about 40% or at greater than about 60%.