DIVERSE MODES OF SOLVENT INCLUSION IN CRYSTALLINE PSEUDOPOLYMORPHS OFTHE ANTHELMINTIC DRUG NICLOSAMIDE

Single crystal X-ray structures of solvated forms of the anthelmintic drug Niclosamide reveal distinctly different modes of inclusion for di fferent solvents. These modes are, respectively, cavity occupation by water molecules in 1:1 niclosamide.H2O, channel occupation by tetrahyd rofuran molecules in 1:1 niclosamide.THF, and intercalation by tetraet hylene glycol molecules in 2:1 niclosamide.TEG. In all three compounds the host drug molecule adopts the same, nearly planar conformation, w hich is maintained by an intramolecular N-H ... O hydrogen bond. Host- guest recognition invariably involves hydrogen bonding between the dru g hydroxyl group and an oxygen acceptor atom of the solvent molecule. The observed modes of solvent inclusion can be reconciled with the beh aviour of the crystals on heating.