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

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: (2S,6′R)-7-chloro-2′,4,6-trimeth­oxy-6′-methyl-3H,4′H-spiro­[1-benzo­furan-2,1′-cyclo­hex-2-ene]-3,4′-dione}, C17H17ClO6, 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 P212121) and the asymmetric unit contains two mol­ecules.