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Twigs of Nectandra barbellata were extracted using a solution of the ionic liquid 1-butyl-3-methylimidazolium bromide (BMImBr) in H2O, assisted by microwave (MAE). After successive chromatographic steps, one sesquiterpene, costic acid, and three new related lactones, (R)-3(7)-Z-3-hexadec-21-enylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (1), (R)-3(7)-Z-3-hexadecylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (2), and (R)-3(7)-Z-3-docosylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (3), were isolated. After structural elucidation using IR, UV, HRESIMS, NMR, ECD, and VCD, compounds 1-3 were tested against trypomastigote forms of Trypanosoma cruzi. The mechanism of action of bioactive isolated compounds was studied using different fluorescent-based approaches to investigate alterations of the plasma membrane, permeability/electric potential (ΔΨp), reactive oxygen species levels, mitochondria (electric membrane potential, ΔΨm/ATP levels), Ca2+ levels, and pH of the acidocalcisomes. In addition, in silico studies predicted no resemblance to pan assay interference compounds (PAINS).

Five new neocassane-like diterpenes (1-5) were isolated from the roots of Eragrostis plana. Their structures were elucidated by spectroscopic data, and the absolute configurations of the representative compounds neocassa-12(17),15-dien-3-one (2) and neocassa-12(13),15-diene-3,14-dione (5) were assigned by vibrational circular dichroism. The phytotoxic activity of compounds 3, 4, and 5 was evaluated against the germination and growth of Ipomoea grandifolia and Euphorbia heterophylla. Compound 4 exhibited the most potent activity for growth variables, resulting in the smallest radicle length of I. grandifolia and in the smallest aerial part length of E. heterophylla. Compound 5 reduced the germination speed index more effectively than the herbicide glyphosate (Roundup).

Gaudichaudianic acid, a prenylated chromene isolated from Piper gaudichaudianum, has been described as a potent trypanocidal compound against the Y-strain of Trypanosoma cruzi. We herein describe its isolation as a racemic mixture followed by enantiomeric resolution using chiral HPLC and determination of the absolute configuration of the enantiomers as (+)-S and (-)-R by means of a combination of electronic and vibrational circular dichroism using density functional theory calculations. Investigation of the EtOAc extract of the roots, stems, and leaves from both adult specimens and seedlings of P. gaudichaudianum revealed that gaudichaudianic acid is biosynthesized as a racemic mixture from the seedling stage onward. Moreover, gaudichaudianic acid was found exclusively in the roots of seedlings, while it is present in all organs of the adult plant. Trypanocidal assays indicated that the (+)-enantiomer was more active than its antipode. Interestingly, mixtures of enantiomers showed a synergistic effect, with the racemic mixture being the most active.

Six novel monoterpene chromane esters were isolated from the aerial parts of Peperomia obtusifolia (Piperaceae) using chiral chromatography. This is the first time that chiral chromane esters of this kind, ones with a tethered chiral terpene, have been isolated in nature. Due to their structural features, it is not currently possible to assess directly their absolute stereochemistry using any of the standard classical approaches, such as X-ray crystallography, NMR, optical rotation, or electronic circular dichroism (ECD). Herein we report the absolute configuration of these molecules, involving four chiral centers, using vibrational circular dichroism (VCD) and density functional theory (DFT) (B3LYP/6-31G*) calculations. This work further reinforces the capability of VCD to determine unambiguously the absolute configuration of structurally complex molecules in solution, without crystallization or derivatization, and demonstrates the sensitivity of VCD to specify the absolute configuration for just one among a number of chiral centers. We also demonstrate the sufficiency of using the so-called inexpensive basis set 6-31G* compared to the triple-ζ basis set TZVP for absolute configuration analysis of larger molecules using VCD. Overall, this work extends our knowledge of secondary metabolites in plants and provides a straightforward way to determine the absolute configuration of complex natural products involving a chiral parent moiety combined with a chiral terpene adduct.