Alogliptin and its benzoate salt

The crystal structure of the free base of the anti­diabetic drug alogliptin [systematic name: 2-({6-[(3R)-3-amino­piperidin-1-yl]-3-methyl-2,4-dioxo-1,2,3,4-tetra­hydro­pyrimidin-1-yl}methyl)benzo­nitrile], C₁₈H₂₁N₅O₂, displays a two-dimensional N—H...O hydrogen-bonded network. It contains two independent mol­ecules, which have the same conformation but differ in their hydrogen-bond connectivity. In the crystal structure of the benzoate salt (systematic name: (3R)-1-{3-[(2-cyano­phenyl)methyl]-1-methyl-2,6-dioxo-1,2,3,6-tetra­hydropyrimidin-4-yl}piperidin-3-aminium benzoate), C₁₈H₂₂N₅O₂⁺·C₇H₅O₂⁻, the NH₃⁺ group of the cation is engaged in three inter­molecular N—H...O hydrogen bonds to yield a hydrogen-bonded layer structure. The benzoate salt and the free base differ fundamentally in the conformations of their alogliptin moieties.