Effects of Solvent on Polymorph Formation and Nucleation of Prasugrel Hydrochloride

Abstract

Three intrinsic properties of solvent were used to evaluate the effects of solvent on polymorph formation of prasugrel hydrochloride. In situ Raman spectroscopy, FTIR, and powder X-ray diffraction were used to characterize two solvent-free polymorphs and five solvates of prasugrel hydrochloride, the two of which were reported for the first time. Reactive crystallization in 24 different pure solvents was studied at 313.15 K. It was found that polymorph formation of prasugrel hydrochloride directly depends on the solvents used in the experiments. Form I was obtained in solvents with low values of hydrogen bond donor ability (HBD), while form II was obtained in solvents with high values of HBD. The thermodynamic and kinetic reasons for the solvent effects were explained by using the solubility data and the nucleation experiments. The solubilities of forms I and II were experimentally determined by a gravimetric method, and an equation based on the linear free energy approach for predicting solubility was applied to correlate the solubility of form II. It was found that the values of HBD of the solvents also affect the solubility of prasugrel hydrochloride. From desolvation experiments of the five solvates in seven pure solvents at 293.15 and 313.15 K, it was found that the polymorphs of prasugrel hydrochloride obtained after desolvation are closely related to the solvents. The heterogeneous nucleation of form I during the solvent-mediated polymorphic transformation was also studied at 313.15 K, and it was found that the solute–solvent interactions will also affect the nucleation rate of form I. A hypothesis was then proposed that prasugrel hydrochloride form I is prone to crystallize when van der Waals force dominates the interaction between the solute and the solvent molecules, while prasugrel hydrochloride form II is prone to nucleate and grow when hydrogen bonding dominates the interaction between the solute and the solvent molecules.