RESUMO
(-)-Centratherin is a bioactive sesquiterpenoid lactone, whose absolute configuration (AC) was not established, but has been proposed based on those of germacrane precursors. To verify this proposal, the experimental electronic circular dichroism (ECD), electronic dissymmetry factor (EDF), optical rotatory dispersion (ORD), vibrational circular dichroism (VCD), and vibrational dissymmetry factor (VDF) spectra of (-)-centratherin have been analyzed with the corresponding density functional theoretical predictions. These analyses suggest the AC of naturally occurring (-)-centratherin to be (6R,7R,8S,10R,2'Z).
Assuntos
Lactonas/química , Sesquiterpenos/química , Dicroísmo Circular , Lactonas/farmacologia , Modelos Químicos , Estrutura Molecular , Ressonância Magnética Nuclear Biomolecular , Dispersão Óptica Rotatória , Sesquiterpenos/farmacologia , EstereoisomerismoRESUMO
To determine the absolute configuration of 3-ishwarone, the experimental electronic circular dichroism (ECD), electronic dissymmetry factor (EDF), optical rotatory dispersion (ORD), vibrational circular dichroism (VCD), and vibrational dissymmetry factor (VDF) spectra of (+)-3-ishwarone are analyzed with the corresponding density functional theoretical predictions for different diastereomers. ECD and ORD spectra by themselves could not facilitate the determination of the absolute configuration of this molecule. However, the magnitude of the experimental EDF of (+)-3-ishwarone is found to match better with that predicted for the (1R,2S,4S,5R,9R,11R) diastereomer. The analyses of similarity measures between experimental and predicted spectra for VCD and VDF clearly suggested that the absolute configuration of (+)-3-ishwarone is (1R,2S,4S,5R,9R,11R).
Assuntos
Sesquiterpenos/química , Algoritmos , Brasil , Dicroísmo Circular , Estrutura Molecular , Dispersão Óptica Rotatória , Peperomia/química , Componentes Aéreos da Planta/química , EstereoisomerismoRESUMO
3-Ishwarone, (1), a sesquiterpene with a rare ishwarane skeleton, was isolated from Peperomia scandens Ruiz & Pavon (Piperaceae). Its structure was unambiguously determined by 1D- and 2D-NMR and infrared analyses, as well as by comparative theoretical studies which involved calculations of 13C-NMR chemical shifts, using the Density Functional Theory (DFT) with the mPW1PW91 hybrid functional and Pople's 6-31G(d) basis set, and of vibrational frequencies, using the B3LYP hybrid functional and triple ζ Dunning's correlation consistent basis set (cc-pVTZ), of (1) and three of its possible diastereomers, compounds 2-4.
Assuntos
Peperomia/química , Sesquiterpenos/química , Cromatografia Gasosa-Espectrometria de Massas , Espectroscopia de Ressonância Magnética , Estrutura MolecularRESUMO
The reaction of naphthoquinone-oximes (3) and (4) with diazomethane yields directly, in one step, the oxazoles (5) and (6), respectively.
Assuntos
Técnicas de Química Combinatória , Diazometano/química , Naftoquinonas/química , Oxazóis/síntese química , Oximas/química , OxirreduçãoRESUMO
The reaction of naphthoquinone-oximes (3) and (4) with diazomethane yields directly, in one step, the oxazoles (5) and (6), respectively.
A reação das naphthoquinona-oximas (3) e (4) com diazometano fornece diretamente, em uma etapa, os oxazóis (5) e (6), respectivamente.