Inversion of Population Distribution of Felodipine Conformations at Increased Concentration in Dimethyl Sulfoxide Is a Prerequisite to Crystal Nucleation

Knowledge of the preferred conformations of biologically active compounds is of the utmost importance for a better understanding of the structure-activity relationships underlying their biological activity, as well as their mechanism of action. Moreover, investigating the mechanism of nucleation from a saturated solution can facilitate the discovery and preparation of new polymorphic forms. To search regularities in the crystal nucleation of biologically active compounds (drugs) from a saturated solution, we studied the conformational preference of felodipine in dilute and saturated solution in dimethyl sulfoxide. The inversion of conformation distribution at increased concentration occurs: conformers that dominate in a dilute solution become the least abundant in the saturated one. Conformers that dominate in the saturated solution are of the same type as revealed in crystalline state by X-ray.