title: Tautomeric ratio and prototropic equilibrium constants of tenoxicam, a 1H and 13C NMR theoretical and experimental study.
abstract: The determination of the micro-equilibrium prototropic constants is often a tough task when the tautomeric ratio favors one of the species or when the chemical exchange is not slow enough to allow the quantitative detection of the tautomeric species. There are just few experimental methods available to reveal the constants of the tautomeric micro-equilibriums; its applicability depends on the nature of the tautomeric system. A combination of experimental and quantum chemistry calculated (1)H and (13)C NMR chemical shifts is presented here to estimate the population of the species participating in the tautomeric equilibriums of the tenoxicam, an important anti-inflammatory drug. A multivariate fitting of a fraction-mol-weighted contribution model, for the NMR chemical shifts of the species in solution, was used to find the populations of the tautomers of tenoxicam. To consider and evaluate the effect of the solvent polarity on the tautomers' populations, experimental determinations were carried out in DMSO-d(6), in an equimolar DMSO-H(2)O mixture of deuterated solvents and in D(2)O. Additionally, by employing HYPNMR, it has been possible to refine the acid-base macroscopic constants of tenoxicam.
authors: Laboratorio de Fisicoquímica Analítica, Unidad de Investigación Multidisciplinaria, FES Cuautitlán, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, Estado de México, 54714, México.
authors: Marco
authors: M
authors: Franco-Pérez
authors: Rosario
authors: R
authors: Moya-Hernández
authors: Alberto
authors: A
authors: Rojas-Hernández
authors: Atilano
authors: A
authors: Gutiérrez
authors: Rodolfo
authors: R
authors: Gómez-Balderas
mesh_terms: D002247:Carbon Isotopes / Q000737:chemistry; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D010894:Piroxicam / Q000031:analogs & derivatives* / Q000737:chemistry; D011789:Quantum Theory; D014867:Water / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D014867:Water; D010894:Piroxicam; D006859:Hydrogen; D004121:Dimethyl Sulfoxide; C032801:tenoxicam