title: Crystal forms of torasemide: new insights.
abstract: Crystallization from various organic solvents results in three crystal forms of torasemide: monotropically related mod. I (melting point, 158-161 degrees C) and mod. II (melting point, 155-158 degrees C), as well as a pseudopolymorphic crystal form (form A, channel inclusion compound with 1.9-4.2% water and alcohol). Physicochemical properties were determined by thermoanalysis (hot-stage microscopy, differential scanning calorimetry, thermogravimetry), Fourier transform infra-red and Raman spectroscopy, and X-ray powder diffractometry. The hygroscopicity, relative stability, true density, and heat of solutions were determined, respectively. The dissolution behaviour of mod. I and II was investigated as a function of pH, temperature, and in addition to surfactants. Mod. II is nearly three times more soluble than mod. I (mod. I, 0.34 mmol l(-1); mod. II, 0.93 mmol l(-1) at 20 degrees C, pH 4.90) and proved to be highly kinetically stable. By crystallization from 1-butanol, a new compound was synthesized, which was identified as [[4-[(3-Methylphenyl)amino]-3-pyridinyl]sulfonyl]-carbamic acid, butyl ester (TOBC). The most important properties of this torasemide derivative are given. The present results give a thorough physicochemical characterization of the crystal forms of torasemide. They clearly indicate a mistaken identity of mod. II with crystal form A in formerly published articles.
authors.affiliation: Institute of Pharmacy/Pharmacognosy, University of Innsbruck, Innrain 52, Josef-Moeller-Haus, A-6020 Innsbruck, Austria. judith.rollinger@uibk.ac.at
authors.forename: Judith Maria
authors.initials: JM
authors.lastname: Rollinger
authors.forename: Elisabeth Maria
authors.initials: EM
authors.lastname: Gstrein
authors.forename: Artur
authors.initials: A
authors.lastname: Burger
mesh_terms: D002626:Chemistry, Pharmaceutical; D003460:Crystallization; D004232:Diuretics / Q000737:chemistry; D004355:Drug Stability; D012995:Solubility; D013449:Sulfonamides / Q000737:chemistry*; D000077786:Torsemide
chemical_list: D004232:Diuretics; D013449:Sulfonamides; D000077786:Torsemide