Structure determination of phase II of the antifungal drug griseofulvin by powder X‐ray diffraction

摘要

Two new crystalline polymorphs of the widely used antifungal drug griseofulvin (phases II and III), which originate from the crystallization of the melt, have been detected recently. The crystal structure of phase II of griseofulvin {systematic name: (2 S ,6′ R )‐7‐chloro‐2′,4,6‐trimethoxy‐6′‐methyl‐3 H ,4′ H ‐spiro[1‐benzofuran‐2,1′‐cyclohex‐2‐ene]‐3,4′‐dione}, C 17 H 17 ClO 6 , has been solved by powder X‐ray diffraction (PXRD). The PXRD pattern of this new phase was recorded at room temperature using synchrotron radiation. The starting structural model was generated by a Monte Carlo simulated annealing method. The final structure was obtained through Rietveld refinement with soft restraints for interatomic bond lengths and angles, except for the aromatic ring, where a rigid‐body constraint was applied. The symmetry is orthorhombic (space group P 2 1 2 1 2 1 ) and the asymmetric unit contains two molecules.