Simvastatin: structure solution of two new low-temperature phases from synchrotron powder diffraction and ss-NMR

Simvastatin is a substance used for the treatment of hypercholesterolemia. In addition to the already known room temperature structure of simvastatin (ejka et al. in Acta Cryst C59:o428, 2003) two new low-temperature polymorphs were found by X-ray powder diffraction with the phase transition at 261 and 223 K (later confirmed by DSC to be 272 and 232 K). The main differences among three polymorphs consist in the side-chains conformation only and the phase changes are fully reversible. The structures of the polymorphs were studied by the powder diffraction based on synchrotron radiation as well as by solid-state NMR spectroscopy.