Pseudopolymorphism and phase stability in four solid forms of (6R,7R)-7-[2-(5-amino-1,2,4-thiadiazol-3-yl)-(Z)-2-methoxy- iminoacetamid]-3- [(4-carbamoyl-1-quinuclidinio)methyl]-8-oxo-5-thia-1-azabicyclo - [4,2,0]oct-2-ene-2-carboxylate (E1040)

(6R,7R)-7-2-(5-Amino-1,2,4-thiadiazol-3-yl)-(Z)-2-methoxy- iminoacetamid]-3- (4-carbamoyl-1-quinuclidinio)methyl]-8-oxo-5-thia-1-azabicyclo 4,2,0]oct-2-ene-2-carboxylate (1; E1040) was isolated as alpha-(decahydrate), beta-(pentahydrate), and gamma-form (anhydrate) crystals and the X-ray amorphous form. The relationship between the pseudopolymorphic crystal forms of this compound and water content was studied by X-ray diffractometry, coulometric moisture analysis, thermal analysis, and hygroscopic and vacuum-freeze-drying experiments. The phase transition of crystalline 1 clearly indicated the effect of water content on dehydration. During dehydration, hydrated alpha-form (decahydrate) crystals and beta-form (pentahydrate) crystals became anhydrate gamma-form crystals, with the diffraction angle shifting toward shorter spacing accompanied by line broadening. These results indicate conversion of hydrate 1 crystals to the anhydrous form and contraction of the crystal lattice. It was estimated that the decahydrate (alpha-form) crystals contain 8 mol/mol crystal water and 2 mol/mol adhesion water, and that the pentahydrate (beta-form) crystals contain 4 mol/mol crystal water and 1 mol/mol adhesion water. These estimates were made by comparing the data from equilibrium hydration experiments and vacuum-freeze-drying experiments. It thus follows that gamma-form crystals are anhydrate and the X-ray amorphous form exists in either the hydrous or anhydrous form.