Hydrogen-bonded supramolecular ribbons in the antifolate drug pyrimethamine
Abstract
In the crystal structure of pyrimethamine [2,4-diamino-5-(p-chlorophenyl)-6-ethylpyrimidine], C12H13ClN4, the asymmetric unit contains two crystallographically independent pyrimethamine molecules (A and B), differing in their conformations. The dihedral angle between the pyrimidine and the substituted phenyl plane is 74.4 (1)° in molecule A and 82.4 (1)° in molecule B. Molecule A is linked with molecule B through a pair of N—H⋯N hydrogen bonds on one side and through another pair of N—H⋯N hydrogen bonds on the other side. Thus, there is a supramolecular ribbon, consisting of A and B molecules arranged in an alternating manner. Two such ribbons are connected centrosymmetrically through a pair of N—H⋯Cl bonds. These ABAB pairs and BABA interconnections lead to a supramolecular sheet-like structure.