High-Throughput Encapsulated Nanodroplet Screening for Accelerated Co-Crystal Discovery

Co-crystals are composed of two or more chemically inequivalent molecular species, excluding solvents, generally in a stoichiometric ratio. Co-crystals are particularly important in pharmaceutical development, where a suitable co-crystal can significantly improve the physiochemical and pharmacokinetic properties of an active pharmaceutical ingredient. However, co-crystal discovery remains both practically challenging and resource intensive, requiring the extensive searching of complex experimental space. Herein, we demonstrate a high-throughput (HTP) nanoscale co-crystallisation method for the rapid screening of large areas of co-crystallisation space with minimal sample requirements, based on Encapsulated Nanodroplet Crystallisation (ENaCt). HTP co-crystallisation screening by ENaCt allowed rapid access to all 18 possible binary co-crystal combinations of 3 small molecules and 6 co-formers, through the use of 3,456 individual experiments exploring solvent, encapsulating oil and stoichiometry, resulting in 10 novel binary co-crystal structures by single crystal X-ray diffraction (SCXRD). ENaCt co-crystallisation is also shown to be a powerful method for higher-order co-crystal (HOC) discovery, through its ability to efficiently address highly complex experimental landscapes. HTP ENaCt co-crystallisation screening of molecule/co-former/co-former and molecule/co-former/co-former/co-former combinations gave ready access to both ternary and quaternary HOCs, each containing three or four different molecular species respectively. In total, 12,288 individual ENaCt experiments are presented resulting in 50 co-crystal structures by SCXRD, including 17 novel binary co-crystals, 7 novel ternary co-crystals and 2 novel quaternary co-crystals. ENaCt co-crystallisation is thus demonstrated to be a highly impactful and efficient tool in the search for small molecule co-crystals, through the employment of parallelised HTP nanoscale experimental workflows.