Conformational evaluation and detailed ¹H and ¹³C NMR assignments of eremophilanolides

Abstract

Extensive application of 1D and 2D NMR methodology, combined with molecular modeling, allowed the complete 1H and 13C NMR assignments of eremophilanolides from Senecio toluccanus. Comparison of the experimental 1H, 1H coupling constant values with those generated employing a generalized Karplus-type relationship, using dihedral angles extracted from MMX and DFT calculations, revealed that the epoxidized eremophilanolides 1 and 2 show conformational rigidity at room temperature, whereas molecules 3-6, containing an isolated double bond, are conformationally mobile.

High Diversity of Ligularia dictyoneura in Chemical Composition and DNA Sequence

“…6). From sample 9 (type 3), furanoeremophilane (12) H-NMR data of 15 were identical with those of 6b-acetoxy-1,10-epoxyfuranoeremophilane reported by Bohlmann et al [28] and by Burgueno-Tapia et al [29]. Bohlmann and co-workers initially assigned the configuration of the epoxide to be 1a,10a, but they later revised the configuration to be 1b,10b [30].…”

“…The 1 H-NMR data of 15 were clearly different from those of 6b-acetoxy1a,10a-epoxyfuranoeremophilane (20) reported by Kitagawa et al [32]. The structure of 1a,10a-epoxide reported by Burgueno-Tapia et al [29] should be revised to 1b,10b-epoxide, because their assignment was presumably based on the initial report of Bohlmann et al [28]. (Tables 2 and 3).…”

Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: Comparison of experimental and calculated circular dichroism spectra

“…[48][49][50][51] To assign the absolute configuration of compounds 1-10, the experimental CD curves (Figs. 1, 3, 5, 7, and 9) were compared with those simulated on the basis of calculated rotational strengths, (Figs.…”

Chemical and Pharmacological Research on Plants from the Genus Senecio

“…The 1 H-NMR spectra of 324 -328 showed the presence of cacalol derivatives with an O-atom function at C(2) and C (14), while the phenolic OH group was esterified with propionic acid. The configuration of the O-atom function at C(2) followed from the couplings of HÀC (2). Although the relative position of the ester groups at C(2) and C(14) in 326 could not be established with certainty, the observed chemical shifts favor the proposed structure [89].…”

“…-The genus Senecio, which belongs to the tribe Senecioneae, is the largest and most complex genus in the family of the Asteraceae (Compositae) and includes more than 1500 species with a worldwide distribution [1] that have been extensively investigated for their secondary metabolites. Pyrrolizidine alkaloids (PAs), eremophilanolides, and cacalolides are particularly characteristic for species of this genus [2]. Some Senecio species have a negative impact in many agricultural countries, because these plants are responsible for more deaths to livestock than any other poisonous plant.…”