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Sanz del Castillo, Dionisia

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  • Publicación
    Addition reaction of azoles to acetone-d 6: NMR and computational studies
    (Wiley, 2024-05-22) Claramunt Vallespí, Rosa María; Sanz del Castillo, Dionisia; Alkorta, Ibon; Elguero, José
    The reactivity of imidazole, pyrazole, 1,2,4-triazole, 1,2,3-triazole and tetrazole with acetone (propan-2-one) has been studied by 1 H and 13 C NMR using acetone-d 6 as solvent at temperatures ranging from 173 to 300 K at 10 K intervals. Simultaneously, the reaction has been theoretically calculated at the B3LYP/6-311++G(d,p) level and experimental and theoretical results compared. The equilibrium constants between azoles and adducts α,α-dimethyl-azole-methanol were analyzed assuming that the straight part of the plots –R ln Ke vs. 1/T can be used to determine ΔH and ΔS. Calculated and experimental data are related but the theoretical values are proportionally higher. The tautomerism of triazoles and tetrazole has been considered in order to discuss the reactions.
  • Publicación
    Synthesis, structure and NMR study of fluorinated isoxazoles derived from hemi-curcuminoids
    (Elsevier, 2019-03) Nieto Gómez, Carla Isabel; Cornago, María del Pilar; Cabildo, María del Pilar; Sanz del Castillo, Dionisia; Claramunt Vallespí, Rosa María; Elguero, José
    The 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 15N chemical shifts in DMSO-d6 solution and in the solid state. The splitting of some signals observed in Cross-Polarization Magic Angle Spinning (CPMAS) 13C NMR was assigned to 1JCF 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.
  • Publicación
    Determination of the tautomerism of albendazole desmotropes using solution and solid state NMR together with DFT theoretical calculations, both energies and chemical shifts
    (Elsevier, 2022-08-05) Claramunt Vallespí, Rosa María; López García, Concepción; Sanz del Castillo, Dionisia; Elguero, José; Alkorta, Ibon
    This paper reports a structural study of albendazole concerning the desmotropy of its amino and imino tautomers, ABZ-I and ABZ-II, mistakenly called polymorphs. Experimental NMR determination in solution, DMSO-d6, HMPA-d18 and CF3 CO2 H, and in the solid state, CPMAS, together with DFT calculations, energies and NMR chemical shifts, has allowed to understand the complex problem of prototropy combined with rotation about the benzimidazole C2-N exocyclic group that explain the disorder problem of the S-propyl group. The structure of protonated albendazole, ABZH +, has also been studied. The role of the hybrid HF/DFT B3LYP computational method at the B3LYP/6-311++G(d,p) level has been determinant to solve the problems related to the structure of albendazole in the solid state and in solution and the barrier in solution of a phenomenon resulting either from annular tautomerism or from the rotation about the exocyclic C-N bond.