Phase identification and discovery of hidden crystal forms in a polycrystalline pharmaceutical sample using high-throughput 3D electron diffraction

3D electron diffraction (3D ED), also known as MicroED, has shown great potential in crystal structure determination in materials, small organic molecules, and macromolecules. In this work, a high-throughput 3D ED method has been implemented to identify six phases in an active pharmaceutical ingredient, griseofulvin (GSF). Batch data collection under low-dose conditions using the widely available commercial software EPU-D (Thermo Fisher Scientific) was combined with semi-automated data processing and clustering to collect and process over 100 datasets over three days. Accurate unit cell parameters obtained from 3D ED data allowed identification of GSF Forms III, I, GSF-and PEG IC-I, as well as three additional phases undetected in powder X-ray diffraction data, namely GSF II, GSF-V and a new phase GSF-PEG IC-II. Their structures were directly determined by 3D ED. Through structure analysis, we discovered polymorphism within inclusion complexes built from the same clinical drug-polymer combination. These results demonstrate the ability of the high-throughput method to accurately reveal the phase information of complex, beam-sensitive crystallisation products, which is significant for drug design where crystal form screening is crucial for the overall efficacy of the drug product.