title: 1H, 13C and 15N NMR assignments of phenazopyridine derivatives.
abstract: Phenazopyridine hydrochloride (1), a drug in clinical use for many decades, and some derivatives were studied by one- and two-dimensional (1)H, (13)C and (15)N NMR methodology. The assignments, combined with DFT calculations, reveal that the preferred protonation site of the drug is the pyridine ring nitrogen atom. The chemoselective acetylation of phenazopyridine (2) and its influence on the polarization of the azo nitrogen atoms were evidenced by the (15)N NMR spectra. Molecular calculations of the phenazopyridines 2-4 show that the pyridine and phenyl groups are oriented in an antiperiplanar conformation with intramolecular hydrogen bonding between the N-b atom and the C-2 amino group preserving the E-azo stereochemistry.
authors.affiliation: Departamento de Química, Unidad Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, Av. Acueducto s/n, La Laguna Ticomán, México D.F., 07340 Mexico.
authors.forename: Eleuterio
authors.initials: E
authors.lastname: Burgueño-Tapia
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Mora-Pérez
authors.forename: Martha S
authors.initials: MS
authors.lastname: Morales-Ríos
authors.forename: Pedro
authors.initials: P
authors.lastname: Joseph-Nathan
mesh_terms: D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards; D008968:Molecular Conformation; D009587:Nitrogen Isotopes; D010621:Phenazopyridine / Q000032:analysis* / Q000737:chemistry* / Q000592:standards; D011522:Protons; D012016:Reference Values
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D011522:Protons; D010621:Phenazopyridine