Abstract: (‒)-Encecanescin (1) has been isolated from the leaves of Eupatorium aschembornianum. Two conformers are present in the crystal structure as a result of molecular disorder. The structure of 1 was established by 1H- and 13C-NMR spectroscopy in CDCl3 solution using 2D NMR techniques (gHSQC, gHMBC and NOESY). A Monte Carlo random search using molecular mechanics followed by the geometry optimization of each minimum energy structure using density functional theory (DFT) calculations at the B3LYP/6–31G* level and a Boltzmann analysis of the total energies generated accurate molecular models describing the conformational behavior of 1. The three most stable conformers 2–4 of compound 1 were reoptimized at the B3LYP/6-311++G(d,p) level of theory using CHCl3 as a solvent. Correlations between the experimental 1H- and 13C-NMR chemical shifts (δexp) have been found, and the GIAO/B3LYP/6-311++G(d,p) calculated magnetic isotropic shielding tensors (σcalc) for conformers 2 and 3, δexp = a + b σcalc, are reported. A good linear relationship between the experimental and calculated NMR data has been obtained for protons and carbon atoms.
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Reyes-Trejo, B.; Guerra-Ramírez, D.; Zuleta-Prada, H.; Santillán, R.; Sánchez-Mendoza, M.E.; Arrieta, J.; Reyes, L. Molecular Disorder in (‒)-Encecanescin. Molecules 2014, 19, 4695-4707.
Reyes-Trejo B, Guerra-Ramírez D, Zuleta-Prada H, Santillán R, Sánchez-Mendoza ME, Arrieta J, Reyes L. Molecular Disorder in (‒)-Encecanescin. Molecules. 2014; 19(4):4695-4707.
Reyes-Trejo, Benito; Guerra-Ramírez, Diana; Zuleta-Prada, Holber; Santillán, Rosa; Sánchez-Mendoza, María E.; Arrieta, Jesús; Reyes, Lino. 2014. "Molecular Disorder in (‒)-Encecanescin." Molecules 19, no. 4: 4695-4707.