Relationship between Crystal Polymorphism and Solution Structure of an Imidazopyridine Derivative Developed as a Drug Substance for Osteoporosis

Abstract

An imidazopyridine derivative developed for osteoporosis treatment (a bone proton pump inhibitor, abbreviated BPPI) was crystallized in two kinds of alcohol. Two crystal polymorphs appeared: an unstable B01 form and a stable B02 form. The B01 form was obtained only from an ethanol solution and was never obtained from a methanol solution. The B02 form was obtained from a methanol solution. In order to understand these different behaviors in the appearance of polymorphs from alcohol, the intra- and inter-molecular interactions of BPPI molecules in solution were analyzed by NMR. As a result, the conformation of BPPI molecules and the structure of molecular aggregates in solution were found to resemble those of the polymorphic crystals that appeared in each alcohol. This result suggests that the control of the conformation of solute molecules is important at first to control the appearing polymorph.