Comparing microcrystal electron diffraction (MicroED) and X-ray crystallography as methods for structure determination of Oseltamivir phosphate

Oseltamivir phosphate is a pharmaceutical used in the treatment of influenza viruses. Panče Naumov et al. took two years of dedicated single crystal cultivation and successfully obtained low-quality single crystals through a diffusion method. Cultivation of Oseltamivir phosphate single crystals was proved to be difficult and can extend over several months or more. We employed microcrystalline electron diffraction (MicroED) for direct powder measurements, eliminating the need for lengthy single-crystal cultivation, and the time to obtain the molecular structure of Oseltamivir phosphate was shortened from several months to five hours. Comparative analyses of single crystal (Crystal 1) and MicroED (Crystal 2) results revealed equivalent crystal structures, with minimal differences in hydrogen bond distances, identical powder X-ray diffraction patterns, and negligible variations in Hirshfeld surface analysis. The differential scanning calorimetry (DSC) analysis showcased a higher melting point of Oseltamivir phosphate (206.0 °C) than Oseltamivir (110.7 °C), indicating that Oseltamivir phosphate had high temperature stability, and may result in the selection of Oseltamivir phosphate as a formulation form. The study establishes and verifies a congruence between MicroED detection and traditional single-crystal detection methods and may be applied in the elucidation of compound structures and the surveillance of drug polymorphism.