Bis[2,4-diamino-5-(3,4,5-trimethoxy-benz-yl)pyrimidin-1-ium] dl-malate

<!?tpct=1pt>Racemic malic acid and trimethoprim [5-(3,4,5-trimethoxy- benz-yl)pyrimidine-2,4-diamine] form a 1:2 salt (monoclinic, P21/c), 2Cl 4H19N4O3+·C4H4O52-, 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 carboxyl-ate 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 carboxyl-ate-trimethoprim cation inter-action observed earlier in the complex of dihydro-folate 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 inter-actions, which are very important for biological functions. The pyrimidine plane makes a dihedral angle of 78.08 (7)° 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 supra-molecular patterns. © 2009 International Union of Crystallography.