Polymorph Determination for the gp IIb/IIIa Antagonist, Roxifiban, Using a Combination of Electron Diffraction and Synchrotron X-ray Powder Diffraction Techniques

Unit cell parameters of two polymorphs of roxifiban have been determined by a combination of transmission electron microscopy (TEM) single-crystal and synchrotron X-ray powder diffraction techniques. While it was difficult to differentiate the two forms by their standard X-ray diffraction patterns, the high-resolution synchrotron patterns clearly showed striking differences. Unit cells for the two forms required the use of cell parameters derived from TEM diffraction patterns. The two unit cells are, not surprisingly, very similar except for a doubling of one of the axes for form II. The combined use of TEM and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large unit cell) polymorphs.