Investigating differences and similarities between two new abiraterone polymorphs and its hydrochloride salt monohydrate

Abstract Crystal and molecular structures of two polymorphs (forms II and III) of abiraterone are presented. Both crystal modifications crystallize in the monoclinic crystal system P21 with one molecule in the asymmetric unit. Molecules are involved in strong and weak intermolecular hydrogen bonds of O-H⋅⋅⋅N and C-H⋅⋅⋅O types. Differences in crystals packing and intermolecular interactions were demonstrated by the Hirshfeld surface analysis. The spectroscopic studies showed the correlation of O⋅⋅⋅N distances with wavenumbers of OH groups for abiraterone polymorphs. The IR results agree with a density rule for form III suggesting that this form has a lower thermodynamic stability at 0 K. Abiraterone hydrochloride monohydrate is a direct product of abiraterone acetate hydrolysis under acidic conditions. The salt is unstable during crystallization and transforms into abiraterone base. The detailed description of hydrogen bonds and the analysis of main intermolecular contacts to the Hirshfeld surface of the salt measured at 100 K are presented.