Polymorphism of dehydrocholic acid: Crystal structure of the b-phase and guest-mediated solid phase conversion

Dehydrocholic acid may be obtained in two polymorphic forms: α and β. The complete characterization and the crystal structure of the β-phase (obtained by unconventional powder diffraction methods) are described and discussed. Conversion of the α-form into the thermodynamically more stable β-polymorph may be obtained through a room temperature solvent-mediated process. On the other hand, transformation of the β-form into the α-form is realized through two distinct pathways: via a temperature-mediated process or as a guest-mediated solid state conversion, without the intervention of an amorphous state. R-(+)-Methyl p-tolyl sulfoxide is the guest of choice for this unusual β-to-α transformation.