On the influence of using a zwitterionic coformer for cocrystallization: structural focus on naproxen–proline cocrystals

Four original cocrystal structures incorporating a zwitterionic amino acid, prolinium, and a therapeutical agent from profen pharmaceutical family, naproxen, are highlighted and characterized in this study. Powder X-ray diffraction and differential scanning calorimetry permits the observation of the formation of the new structures, obtained by liquid-assisted grinding with methanol. Single-crystal X-ray diffraction gives us a precise outlook of the crystalline network, and allows us to accurately determine the main structural supramolecular synthon: column-like motifs, formed by prolinium entities, around whom the pharmaceutical coformer is organized. From comparison with the CSD, a similar structural pattern emerged in several other structures incorporating prolinium moieties, but not in the case of cocrystals incorporating naproxen and other non-zwitterionic coformers. This result leads us to the conclusion that zwitterionic compounds, such as amino acids, can force a pharmaceutical coformer to structure itself following a known common motif guided only by the zwitterionic entity; a very challenging aspect to take into account when developing new solid forms of therapeutical agents.