The compound (E)-.alpha.-[2-n-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methyl ene-2-thiophenepropionic acid monomethanesulfonate is known by the name "eprosartan" and is the subject of U.S. Pat. No. 5,185,351 (the '351 patent), issued Feb. 9, 1993. This patent discloses in Example 41 a process for making the anhydrous form of (E)-.alpha.-[2-n-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methyl ene-2-thiophenepropionic acid monomethanesulfonate. Additionally, the '351 patent discloses conventional techniques for formulating (E)-.alpha.-[2-n-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methyl ene-2-thiophenepropionic acid monomethanesulfonate and Example; 108-111 specifically detail the preparation of certain formulations. This compound is claimed to have utility in blocking angiotensin II receptors and to be useful in the treatment of hypertension, congestive heart failure and renal failure.
It has been found that the monohydrate of (E)-.alpha.-[2-n-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methyl ene-2-thiophenepropionic acid monomethanesulfonate is formed during the vacuum drying of the dihydrated form of this compound or when the anhydrate of (E)-.alpha.-[2-n-butyl-1-[(4-carboxy-phenyl)methyl]-1H-imidazol-5-yl]methy lene-2-thiophenepropionic acid monomethanesulfonate is granulated with water, stored at 50.degree. C. overnight and vacuum dried overnight at ambient temperature.