Crystal engineering of the composition of pharmaceutical phases. 3. Primary amide supramolecular heterosynthons and their role in the design of pharmaceutical co-crystals

Abstract

Abstract A Cambridge Structural Database study of supramolecular synthons involving primary amides reveals that 84% form amide-amide dimers, whereas 14% form catemers in the absence of other competing hydrogen bond donors and/or acceptors. However in the presence of chemically different but complementary functional groups, e.g. , carboxylic acids or aromatic nitrogen moieties, primary amides tend to form supramolecular heterosynthons. Supramolecular heterosynthons represent an opportunity for design of multi-component crystals (co-crystals) in which one molecule contains a primary amide and a second molecule (the co-crystal former) contains the functional group that is complementary to the primary amide. The results of the CSD analysis facilitated the selection of components for seven new primary amide co-crystals: A . Isonicotinamide/2-hydroxybenzoic acid (1:1); B. Nicotinäamide/3-hydroxybenzoic acid (1:1); C. Pyrazinamide/2,5-dihydroxybenzoic acid (1:1); D. Carbamazepine (CBZ)/4,4′-bipyridine (2:1); E. CBZ/4-aminobenzoic acid (2:1); F. CBZ/4-aminobenzoic acid/H 2 O (2:1:1); G. CBZ/2,6-pyridinedicarboxylic acid (1:1). The molecular recognition events involving the amide moieties are discussed in the context of our experimental results and their implications for crystal engineering of pharmaceutical co-crystals.