Bis[2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium] DL-malate.

Racemic malic acid and trimethoprim [5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine] form a 1:2 salt (monoclinic, P2(1)/c), 2C(14)H(19)N(4)O(3)(+).C(4)H(4)O(5)(2-), in which the malate component is disordered across a centre of inversion. The crystal structure of the salt consists of protonated trimethoprim residues and a malate dianion. The carboxylate group of the malate ion interacts with the trimethoprim cation in a linear fashion through pairs of N-H...O hydrogen bonds to form a cyclic hydrogen-bonded motif. This is similar to the carboxylate-trimethoprim cation interaction observed earlier in the complex of dihydrofolate reductase with trimethoprim. The structure of the salt of trimethoprim with racemic DL-malic acid reported here is the first of its kind. The present study investigates the conformations and the hydrogen-bonding interactions, which are very important for biological functions. The pyrimidine plane makes a dihedral angle of 78.08 (7) degrees with the benzene ring of the trimethoprim cation. The cyclic hydrogen-bonded motif observed in this structure is self-organized, leading to novel types of hydrogen-bonding motifs in supramolecular patterns.