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Synthesis, structure and NMR study of fluorinated isoxazoles derived from hemi-curcuminoids

AuthorsNieto, Carla I.; Cornago, M. P.; Cabildo, M. Pilar; Sanz, Dionisia; Claramunt, Rosa M.; Torralba, M. Carmen; Elguero, José CSIC ORCID
X-ray crystallography
Solid-state NMR
Fluorinated isoxazoles
Issue Date2019
CitationJournal of Fluorine Chemistry 219: 39-49 (2019)
AbstractThe purpose of this work is to prepare a series of isoxazoles bearing phenyl and 4’-hydroxy-styryl substituents at position 3 and 5; besides the phenyl group of the styryl residue bears one or two fluorine substituents. They were prepared to study their structure in the solid state and in solution by X-ray crystallography and solid-state NMR (SSNMR) for the solid state and NMR for the solution. The reaction of hydroxylamine with hemi-curcuminoid β-diketones affords two isomeric isoxazoles we have named series a (3-phenyl) and b (5-phenyl) that have been identified and characterized. Four pairs have been prepared that in three cases bear one or two fluorine atoms. Three X-ray structures have been determined 3a, 3b and 5b; 3a crystallizes without solvent, 3b crystallizes with a water molecule hydrogen-bonded to a phenolic OH, finally 5b crystallizes as a solvate with a methanol molecule hydrogen-bonded to the isoxazole N atom. This hydrogen bond results in larger differences between N chemical shifts in DMSO-d solution and in the solid state. The splitting of some signals observed in Cross-Polarization Magic Angle Spinning (CPMAS) C NMR was assigned to J dipolar couplings. The combined use of crystallography and SSNMR affords a complete characterization of isomeric isoxazoles, in particular the assignment of an isoxazole to a or to b series is not a trivial matter. In this work, we describe methods for the synthesis of isoxazoles bearing fluorine substituents that are promising structures for drug discovery.
Publisher version (URL)http://dx.doi.org/10.1016/j.jfluchem.2018.12.012
Identifiersdoi: 10.1016/j.jfluchem.2018.12.012
issn: 0022-1139
Appears in Collections:(IQM) Artículos
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