Structural and Thermodynamic Features of Crystal Polymorphs of R-Cinacalcet Hydrochloride

Three polymorphs of the calcimimetic cinacalcet hydrochloride were characterized by a variety of methods including thermal analysis (hot-stage microscopy and differential scanning calorimetry), vibrational spectroscopy (FT-IR and FT-Raman spectroscopy), and X-ray diffractometry (powder and single crystal). The crystal structures of all polymorphs have been determined either from single crystals (form III°) or from powder data (forms I and II). Forms III° and I both exhibit an orthorhombic cell with space group P212121, whereas form II crystallizes in the triclinic space group P1. All three polymorphs show basically the same hydrogen-bond synthon, and the structural differences are associated with conformational changes. In contrast to form III°, form II shows two conformationally different molecules, and in the high temperature form I the phenyl moiety is dynamically disordered. Among the three enantiotropically related polymorphs, form III° (Tfus: 165 °C) is the thermodynamically stable modification belo...