Mometasone furoate revisited, or how did the hydrate get in the bottle?

The redetermined structure of 9α,21-dichloro-11β,17α-dihydroxy-16α-methyl-3,20-dioxopregna-1,4-dien-17-yl furan-2-carboxylate monohydrate, C27H32Cl2O7·H2O, at 100 K has triclinic (P1) symmetry. The structure displays O-H...O hydrogen bonding, which gives rise to infinite sheets extending parallel to the [110] plane. The previously published structure [Chen et al. (2005). J. Pharm. Sci. 94, 2496-2509] was determined at room temperature and no significant anomalous signal was present. Data for the structure presented in this study were collected at low temperature and the absolute configuration could be established based solely on anomalous diffraction. Another point of interest is that the structure determined in this study is that of the monohydrate, even though the crystal was harvested from a bottle of nasal spray that was supposed to contain exclusively crystals of the anhydrous form.