The Antifungal Agent 8-Ethyl-5,8-dihydro-5-oxo-2-(1-pyrrolidinyl)pyrido[2,3-d]pyrimidine-6-carboxylic Acid (Piromidic Acid)

The structure of the title compound, C₁₄H₁₆N₄O₃, was determined by single-crystal X-ray methods. The molecule is planar within ±0.15 Å except for the C atoms of pyrrolidine ring and the N-ethyl group, which is displaced by −1.246 (3) Å from the mean plane. There is a significant difference between the two N—C bond lengths in the pyridine ring with the bond N1—C10 to the ring junction being longer by 0.039 (4) Å than N1—C2. The N—C bond lengths in the pyrimidine ring range from 1.306 (4) to 1.373 (3) Å; similar structural features have been reported for pipemedic acid. The N-ethyl group is approximately perpendicular to the plane of the pyrido-pyrimidinone moiety; the C2—N1—C11—C12 torsion angle is −93.2 (3) °. A single intramolecular hydrogen bond is observed between the H atom of the carboxylic group and the O atom of the ketone [O16...H—O15: 2.525 (3) Å, 154 (1) °].

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