Supramolecular hydrogen-bonding patterns of cocrystallized active pharmaceutical ingredient (API) phloroglucinol and N-heterocycles

The active pharmaceutical ingredient phloroglucinol (PHL) has been taken as a drug model to explore the intermolecular interactions which can be established with other molecular entities to build PHL pharmaceutical cocrystals. From a supramolecular perspective, phloroglucinol PHL (1,3,5- trihydroxybenzene,) is a particularly attractive drug since it is rigid, i.e. it does not present torsional flexibility, and has three OH groups that can act as hydrogen-bonding donors and acceptors; from a chemical point of view, it can be classified as a weak acid (pKa value: 8.45). PHL is normally used as an antispasmodic agent. In addition, phloroglucinol and its derivatives exhibit a wide range of effects, such as anti-inflammatory, cytotoxicity, antithrombotic and profibrinolytic activities [1]. The crystal structures of five newly synthesized co-crystals are reported, where PHL is crystallized with N-heterocycles, namely 2-hydroxy-6-methylpyridine (1), 2,4-dimethyl-6-hydroxypyrimidine (2), 4-phenylpyridine (3), 2- hydroxypyridine (4) and 2,3,5,6-tetramethylpyrazine (5). The structural characteristics of these co-crystals, as far as the hydrogen-bonding networks and the crystalline architectures are concerned, are strongly dependent on the chemical features of the coformer molecules, as well as on their size and shape. A detailed analysis of the intermolecular interactions established in all the PHL co-crystals of known structures has allowed the recognition of some regularities in the packing modes that can be useful in the design of new supramolecular adducts forming predictable structural motifs [2]. References [1] Barwell, C. J., et al., (1989). J. Appl.Phycol. 1, 319. [2] Cvetkovski, A., et al., (2016). Acta Cryst. B72