Hydrogen-Bonding Patterns in Trimethoprim Nitrate, an Antifolate Drug

In the crystal structure of trimethoprim nitrate [2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium nitrate], C₁₄H₁₉N₄O₃⁺.NO₃^-, the trimethoprim moiety is protonated at N1 atom. The nitrate anion forms a fork-like hydrogen-bonded pattern with the trimethoprim cation which is similar to the carboxylate-trimethoprim cation interaction observed in the trimethoprim cation-dihydrofolate reductase complex. The pyrimidine ring makes a dihedral angle of 93.8 (1)° with the phenyl ring.

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